CA1121500A - Ultrasonic scanner - Google Patents
Ultrasonic scannerInfo
- Publication number
- CA1121500A CA1121500A CA000311265A CA311265A CA1121500A CA 1121500 A CA1121500 A CA 1121500A CA 000311265 A CA000311265 A CA 000311265A CA 311265 A CA311265 A CA 311265A CA 1121500 A CA1121500 A CA 1121500A
- Authority
- CA
- Canada
- Prior art keywords
- scanner
- ultrasonic waves
- reflector means
- housing
- reflector
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/18—Methods or devices for transmitting, conducting or directing sound
- G10K11/26—Sound-focusing or directing, e.g. scanning
- G10K11/35—Sound-focusing or directing, e.g. scanning using mechanical steering of transducers or their beams
- G10K11/352—Sound-focusing or directing, e.g. scanning using mechanical steering of transducers or their beams by moving the transducer
- G10K11/355—Arcuate movement
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/18—Methods or devices for transmitting, conducting or directing sound
- G10K11/26—Sound-focusing or directing, e.g. scanning
- G10K11/28—Sound-focusing or directing, e.g. scanning using reflection, e.g. parabolic reflectors
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Ultra Sonic Daignosis Equipment (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An ultrasonic scanner for producing a sector scan in an object to be examined in which one or more ultrasonic transducers traverse an arcuate path with respect to a reflector which is positioned to receive the ultrasonic waves scanning the surface of the reflector from each of the transducers and coverge such waves at a point a preselected distance in front of the reflector.
In general, the ultrasonic waves are converged at a point outside the scanner and inside the object to produce a sector scan in the object having its center at the convergence point, In one embodi-ment of the scanner the reflector only partially reflects the ultrasonic waves and an additional stationary transducer is pro-vided which is positioned to produce ultrasonic waves which radiate through the reflector and coincide with one of the lines of the sector scan, thus permitting simultaneous M-mode or pulse Doppler echo information to be obtained in perfect registration with the sector scan lines. Attenuation, absorbtion and anti-reflection means are provided to suppress echo artifacts.
An ultrasonic scanner for producing a sector scan in an object to be examined in which one or more ultrasonic transducers traverse an arcuate path with respect to a reflector which is positioned to receive the ultrasonic waves scanning the surface of the reflector from each of the transducers and coverge such waves at a point a preselected distance in front of the reflector.
In general, the ultrasonic waves are converged at a point outside the scanner and inside the object to produce a sector scan in the object having its center at the convergence point, In one embodi-ment of the scanner the reflector only partially reflects the ultrasonic waves and an additional stationary transducer is pro-vided which is positioned to produce ultrasonic waves which radiate through the reflector and coincide with one of the lines of the sector scan, thus permitting simultaneous M-mode or pulse Doppler echo information to be obtained in perfect registration with the sector scan lines. Attenuation, absorbtion and anti-reflection means are provided to suppress echo artifacts.
Description
BACK~ROUND OF T~E INVENTION
Field of the Invention . _ .
The invëntion relates to the field of ultrasonic scanners-and,.in particular, to ultrasonic scanners for producing sector scans in an o~ject to be scanned.
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Field of the Invention . _ .
The invëntion relates to the field of ultrasonic scanners-and,.in particular, to ultrasonic scanners for producing sector scans in an o~ject to be scanned.
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2 Dynamic cross-sectional echography (DCE) is a com-
3 monly used technique for producing sequential two-dimensional
4 images of cross-sectional slices of the human anatomy by means
5~ of ultrasound radiation at a frame rate sufficiently high to
6 enable dynamic visualization of moving organs. Apparatus
7 utilizing DCE are generally called DCE scanners and transmit 81 and receive short, ultrasonic pulses in the form of narrow 9 beams or lines. The reflected signal strength as a func~ion 10 of time, which is converted to a position using a nominal 11 sound speed, is displayed on a cathode ray tube, or other 12 suitable device, in a manner somewhat analogous to radar or 13 sonar displays. While DCE can be used to produce images of 14 any object, it is frequently used for visualization of the 15 heart and main heart vessels.
16 Existing DCE scanners can be classified according 17 to the geometry of their field of view (linear or sector 18 scanning), according to the means used for scanning that 19 field of view (mechanical or electronic scanning), and 20 according to whether the transducer scans the patien~ or 21 object through an intervening water bath or by direct contact 22 with the surface of the object as, for example, the skin of 23 a patient using an appropriate contact gel or oil. Linear 24 scanners produce a scan of the anatomy consisting of a set 25 of nominally parallel scan lines, displaced with respect to 26 one another by a line spacing roughly comparable to the 27 effective width of each line, as determined primarily by the 28 transducers used in the apparatus. The cross-section imaged 29 by such scanners is theréfore approximately rectangular in 32 / 2.
1~2~
1 shape, its width being determined by the line _pccing and 21 total number of lines, while its depth is determined by the 3~ lesser of the useful penetration depth of the ultrasound 4 radiation into the body and the unambigous range of the device.
5! Linear scanners are generally used where there is a relatively 6~ extended region on the body surface from which access to the 7l parts of interest of the anatomy is possible, as in the abdo-81 minal organs. Sector scanners produce a scan of the anatomy 9~ consisting of a fan of diverging lines spaced angularly from one another but intersecting (nominally) at a point. The 11 angular spacing being even or uneven depending upon the 12 apparatus and roughly comparable to the effective angular 13 width of each line. The cross-section imaged by such scanners 14 i~ therefore approximately wedge or pie-shaped, i.e., it is approximately a circular sector, the total angular width of 16 the sector~ or sector scan angle, being determined by the 17 angular line spacing and total number of lines, and the sector 18 radius being determined by the lesser of the useful penetra-19 tion depth of the ultrasound radiation into the body and the unabiguous range of the device. Sector scans are generally 21 used where the anatomical window or region on the body surface 22 from which access to the anatomical part of interest is 23 relatively small, as in the adult heart, the brain and the eye in particular.
A large amount of work has gone into the develop-26 ment of DCE sector scanners. Existing direct contact sector 27 scanners include both phased array and mechanical scanners.
29 In phased array scanners such as those exemplified in articles by M~ G. Maginness et a~, "State-of-the-art in Two-dimensional 32 /~' l 3.
llZ3L5~}0 1l Ultrasonic Tranducer Array Technology", Medical Physics, Vol.
2 3, No. 5, Sept./Oct. 1976, Von Ramm et al, "Cardio-Vascular 3 Diagnosis in the Real Time Ultrasound Imaging", Acoustical 41 Holography, Vol. 6, 1975, and J. Kisslo et al, "Dynamic Cardiac 51 Imaging Using a Phased-Array Transducer System", published by 6~ Duke University, Durham, North Carolina, a large (16-60 element) 7 linear array of small transducers is used, with a variable time
16 Existing DCE scanners can be classified according 17 to the geometry of their field of view (linear or sector 18 scanning), according to the means used for scanning that 19 field of view (mechanical or electronic scanning), and 20 according to whether the transducer scans the patien~ or 21 object through an intervening water bath or by direct contact 22 with the surface of the object as, for example, the skin of 23 a patient using an appropriate contact gel or oil. Linear 24 scanners produce a scan of the anatomy consisting of a set 25 of nominally parallel scan lines, displaced with respect to 26 one another by a line spacing roughly comparable to the 27 effective width of each line, as determined primarily by the 28 transducers used in the apparatus. The cross-section imaged 29 by such scanners is theréfore approximately rectangular in 32 / 2.
1~2~
1 shape, its width being determined by the line _pccing and 21 total number of lines, while its depth is determined by the 3~ lesser of the useful penetration depth of the ultrasound 4 radiation into the body and the unambigous range of the device.
5! Linear scanners are generally used where there is a relatively 6~ extended region on the body surface from which access to the 7l parts of interest of the anatomy is possible, as in the abdo-81 minal organs. Sector scanners produce a scan of the anatomy 9~ consisting of a fan of diverging lines spaced angularly from one another but intersecting (nominally) at a point. The 11 angular spacing being even or uneven depending upon the 12 apparatus and roughly comparable to the effective angular 13 width of each line. The cross-section imaged by such scanners 14 i~ therefore approximately wedge or pie-shaped, i.e., it is approximately a circular sector, the total angular width of 16 the sector~ or sector scan angle, being determined by the 17 angular line spacing and total number of lines, and the sector 18 radius being determined by the lesser of the useful penetra-19 tion depth of the ultrasound radiation into the body and the unabiguous range of the device. Sector scans are generally 21 used where the anatomical window or region on the body surface 22 from which access to the anatomical part of interest is 23 relatively small, as in the adult heart, the brain and the eye in particular.
A large amount of work has gone into the develop-26 ment of DCE sector scanners. Existing direct contact sector 27 scanners include both phased array and mechanical scanners.
29 In phased array scanners such as those exemplified in articles by M~ G. Maginness et a~, "State-of-the-art in Two-dimensional 32 /~' l 3.
llZ3L5~}0 1l Ultrasonic Tranducer Array Technology", Medical Physics, Vol.
2 3, No. 5, Sept./Oct. 1976, Von Ramm et al, "Cardio-Vascular 3 Diagnosis in the Real Time Ultrasound Imaging", Acoustical 41 Holography, Vol. 6, 1975, and J. Kisslo et al, "Dynamic Cardiac 51 Imaging Using a Phased-Array Transducer System", published by 6~ Duke University, Durham, North Carolina, a large (16-60 element) 7 linear array of small transducers is used, with a variable time
8 (phase) delay inserted between elements of the array both in
9 the transmission and reception of the ultrasound signal, result-ing in a transmitted beam and a receiving beam or sensitivity 11 pattern whose direction is determined by the magnitude of the 12 inter-element time delay. In sector scanning using phased 13 array scanners, such scanning is achieved without any mechanical 14 motion of the transducer array which remains in stationary con-tact with, for example, the patient's skin. Such phased array 16 scanners have, however, several severe practical limitations.
17 One such limitation resides in the relative complexity of the 18 multi-element transducer array and especially of the transmit/
19 receive electronics necessary to achieve electronic beam steering, resulting in a relatively high cost of phased array 21 scanners. In addition, the ultrasonic beam quality in phased 22 array scanners, in terms of lateral resolution and side lobe 23 levels and the possible occurance of grating lobes, is poor 24 compared to that of single transducer scanners, particularly for beam direction angles greater than 30 degrees away from 26 the normal to the transducer, limiting its useful scanning 27 angles to about 60 degrees even though the beam might be 28 steered beyond that limit. Another significant limitation 29 of existing phased array scanners and all direct contact 33o ///
3Z ! 4.
llZ15C~0 11 scanners is that the scanned section is centered at the center 2~ of the transducer face, essentially at the skin or surface of 31~ the object and therefore outside of the patient or object, so 4 that in certain applications close-in structures are not well resolved, while in other applications anatomical structures 6~ can limit the field of view of the scanner. This is particu-7 larly the case in adult cardiac scanning, where the ult{asonic 8 access window to the heart is generally in the second to fifth 9 ~ intercostal spaces, just to the left of the sternum. In that case, the ribs will tend to limit the scanner field of view, 11 particularly in obese adult patients where the ribs are close 12 to the patient's skin, so that ~he transducer window cannot 13 readily be pressed into the intercostal space. It would be 14 necessary, in order to avoid the rib interference problem, to have the center of the sector scan replaced somewhat inside 16 the patient, in or near the space between the interfering ribs~
17 Limitations of the scanning sector angle to values significant-18 ly below 90 degrees due to rib interference or beam steering 19 limitations or both, can prevent, in many cases, visualization of the entire long dimension of the heart and can seriously 21 affect the diagnostic value of DCE in cardiac examinations as 22 well as in other examinations.
23 A further limitation of present phased array scanners 24 is that they can only be dynamically focused in range in one 25 ¦ lateral dimension, namely in the plane of scanning. Two-26¦ dimensional focusing would require a two~dimensional matrix 27 ~ or array of phased transducer elements and is beyond the 2~1 present commercial state of the art.
29 1 -.
3~ 5.
l~Z15UO
,1 Another class of sector scanners are mechanical in 2~ nature and can be divided into two classes, oscillating trans-3~ ducer scanners and rotating transducer scanners. An oscillating 41 transducer scanner is exemplified by the scanner described by J. Griffith et al, "A Sector Scanner for Real Time Two-Dimen-6 sional Echocardiography", Circulation, Volume XLIX, June, 1974, 7 in which a single transducer is oscillated about an axis nomi-8~ nally lying in the front plane and passing through the center 9 of the transducer with an appropriate angle sensor being used to monitor the angular position of the transducer at any time.
11 Contact with the patient is maintained by the use of a gel, and 12 in operation the patient's tissues must conform to the movement 13 of the transducer which is essentially rigid. While the oscil-14 lating transducer scanner described by Griffith is of the direct contact variety, oscillating transducer scanners can also be of 16 the non direct or water bath variety as described by A. Ashberg, 17 "Ultrasonic Cinematography ~f the Living Heart", Ultrasonics, 18 April, 1967, in which the internal struc~ures of the human heart 19 have been investigated by using the ultrasound pulse-echo method and an ultrasound optical mirror system immersed in a water tank 21 having one wall consisting of a thin rubber membrane pressed 22 against the chest wall of the patient through which ultrasonic 223 energy can easily penetrate. These mechanical sector scanners also suffer from a number of limitations and drawbacks which limit their use. Both of the above described mechanical sector 26 scanners s~ffer the same rib interference limitation as the 28 phased array scanners. In addition, the direct contact mechan-29 ical sector scanners are limited in their useful scanning angle by the problems of the ~oving contact and physical angulation ///
~2 I ~
6.
1 of the tr~nsducer away from the skin, in most cases to values of 30 to 45 degrees. A limitation cor~mon to both of the mechanical sector scanners described i5 that their angular rate of sweep is not uniform, since the transducer or mirror system must reverse direction at the end of each sweep in each direction, so that the line density is greatest at the edges of the sector, where it is usually least desirable, and is lowest at the center of the sector, i.e., the cerlter of the region of interest. Concomitant with this limitation is the fact that the alternate direction of sweep means that an area at the end of a sweep is interrogated twice in a very short interval, as the scan crosses it in opposite direc-tions, and is not interrogated again until nearly the duration of t~o frames. In addition~ only the mid-point of the scan is inter-rogated at a constant frame rate. Another disadvantage of the direct contact of the oscillating transducer scanner described by Griffith arises from the physical transducer motion itself and includes patient discomfort, vibration of the transducer in the operator's hand, and mechanical ~ear of the tranducers moving parts which are subjected to significant forces.
A further limitation of direct contact scanners, includ~
ing phased array scanners, arises from near field non-uniformities in the so-called Fresnel zone of the transducer or array. As is well known, the acousitc pressure field for an unfocused trans-ducer exhibits large scale oscillations, including a series of peaks and nulls, within a distance D=r /~ from the face of the transducer, where r is the effectlve radius of the transducer, or ~rra~, ~n~ e ~ nc~ giv~ w~h~ a ~t~nc~
D, which is referred to herein as the "near" Fresnel zone. is Z
characterized by particularly large fluctions in amplitude ~oth 3~ laterally and in range, target positions and strengths will be 1 falsely displayed as a sector scan is carried out in that region.
For typical transducer radium to wavelength ratio of 10, and typical wavelengths of 0~7mm, the length D oE the near Fresna~
region, extends 3.5 centimeters in front of the transducer, and this will frequently include portions of the body which are of diagnostic interest.
Another type of mechanical sector scanner is the rotat-ional scannlr described by Barber et al. "Duplex Scanner II: For Simultaneous Imaging of Artery Tissuesand Flow", IEEE, 1974 Ultra-sonics Symposium Proceedings, and by Daigle et al, "A DuplexScanning System for Pediatxic Cardiology", Proceedings 1st Meeting of ~orld Federation for Ultrasound in Medicine and Biology~ 1976, which uses a set of transducers mounted on a rotor coupled to the patient through a water column which is separated from the skin surface by a thin silastic or ru~ber membrane. ~hile the rotating transducer water bath scanner described by Barber~ called the "Duplex Echo-l)oppler Scanner" permits a stationary contact ~ith the patient and provides a uniform beam spacing or line density as well as uniform sampling, it is severely limited in its appli-cation to adult cardiac scanning by the fact that the center oraxis of the sector .scan is removed or offset from the skin surface by a distance equal to the sum of the rotating radius and the length of the water column, resulting in a severe rih interference problem, The device of Barber et al, is primarily intended for use in pediatric cardiology where rib interference is not serious.
A further limitation of all present mechanical scanners i5 that they cannot provide a s~multaneous M mode or Doppler scan of any selected line of the scanned sector at l~Z15(~0 1 rates adequate for measurements of heart valve and heart wall 2 ~ motions. While any line of the sector scan of a mechanical 3 ¦ scanner can be sampled at the frame rate of the sector scan 4 itself, typically 20 to 45 frames per second and displayed on an M-mode type display, this rate is too slow since a minimum 6 of 300 frames per second is necessary in order to resolve 7 rapid motions, such as the motion of the mitral valve of the 8 heart, with existing M-mode single beam echocardlographic 9 probes operating at frame rates in excess of l000 frames per second. In addition, even if such rates could be attained by 11 a mechanical scanner, the unambiguous range, or useful pene-12 tration, corresponding to a frame rate of 300 or more frames 13 per second of the 80 to l00 lines typically forming a sector 14 scan would be less than two centimeters, and therefore totally useless. One attempt to provide a Doppler scan in a mechanical 1~ scanner is shown in the rotational scanner described by Barber 17 in which an auxiliary transducer operated in the pulsed Doppler 18 mode is provided which permits obtaining information about 19 velocities of blood flow and movement of cardiac structures essentially simultaneously (within less than a millisecond~
21 with the echoamplitude information. However, the Doppler scan 22 in the device described by Barber is not centered around the 23 same point as the echo scan, since the transducer is mounted 24 off to the side of the echo scanning head. Thus, the point of entry of the Doppler beam and the corresponding interrogated 26 volume are different than the point of entry of the echo 27 sounding beam and its corresponding interrogated volume, 23 creating problems both of access and of interpretation as the 29 same line as one of the~sector lines is not simultaneously ///
~2 //
~. ~
11~15~0 1 sampled.
2¦ The image producing capabilities of current ultra-3 ~ sonic scanners are further limited by the existence of "echo"
4 ~ artifacts which degrade the quality of and complicate the interpretation of the reflected signals from ~he object being 6~ visualized. Such echo artifacts are caused by ultrasound en-7~ ergy being received by a detector which energy is not directly 8 reflected from the body or target under examination. In a 9 system utilizing mirrors and membranes, such as described by ~sberg, a portion of the echo artifacts are caused by partial 11 reflection of acoustic pulses along the path of the desired 12 or "target" echoes by the membranes and the mirrors before 13 they reach the body or target under examination. Another 14 portion of the echo artifacts are caused by partial reflection of acoustic pulses from the membranes and mirrors not along 16 the return path of the target echoes but along other paths 17 resulting in reflections from numerous internal surfaces which 18 eventually inpinge upon the detector. A further portion of the 2 echo artifacts results from stray acoustic radiation that is 2 not intercepted by the membranes or mirrors but merely re-22 flects around the scanner with some of it reaching the detector 2 and producing false echoes.
23 Accordingly, it is a general object of the present 4 invention to provide an improved ultrasonic sector scanner.
It is another object of the present invention to 26 provide a sector which has a sector scan center of focus which 27 can be located in front of the scanner so as to minimi~e inter-28 f~rence problems.
17 One such limitation resides in the relative complexity of the 18 multi-element transducer array and especially of the transmit/
19 receive electronics necessary to achieve electronic beam steering, resulting in a relatively high cost of phased array 21 scanners. In addition, the ultrasonic beam quality in phased 22 array scanners, in terms of lateral resolution and side lobe 23 levels and the possible occurance of grating lobes, is poor 24 compared to that of single transducer scanners, particularly for beam direction angles greater than 30 degrees away from 26 the normal to the transducer, limiting its useful scanning 27 angles to about 60 degrees even though the beam might be 28 steered beyond that limit. Another significant limitation 29 of existing phased array scanners and all direct contact 33o ///
3Z ! 4.
llZ15C~0 11 scanners is that the scanned section is centered at the center 2~ of the transducer face, essentially at the skin or surface of 31~ the object and therefore outside of the patient or object, so 4 that in certain applications close-in structures are not well resolved, while in other applications anatomical structures 6~ can limit the field of view of the scanner. This is particu-7 larly the case in adult cardiac scanning, where the ult{asonic 8 access window to the heart is generally in the second to fifth 9 ~ intercostal spaces, just to the left of the sternum. In that case, the ribs will tend to limit the scanner field of view, 11 particularly in obese adult patients where the ribs are close 12 to the patient's skin, so that ~he transducer window cannot 13 readily be pressed into the intercostal space. It would be 14 necessary, in order to avoid the rib interference problem, to have the center of the sector scan replaced somewhat inside 16 the patient, in or near the space between the interfering ribs~
17 Limitations of the scanning sector angle to values significant-18 ly below 90 degrees due to rib interference or beam steering 19 limitations or both, can prevent, in many cases, visualization of the entire long dimension of the heart and can seriously 21 affect the diagnostic value of DCE in cardiac examinations as 22 well as in other examinations.
23 A further limitation of present phased array scanners 24 is that they can only be dynamically focused in range in one 25 ¦ lateral dimension, namely in the plane of scanning. Two-26¦ dimensional focusing would require a two~dimensional matrix 27 ~ or array of phased transducer elements and is beyond the 2~1 present commercial state of the art.
29 1 -.
3~ 5.
l~Z15UO
,1 Another class of sector scanners are mechanical in 2~ nature and can be divided into two classes, oscillating trans-3~ ducer scanners and rotating transducer scanners. An oscillating 41 transducer scanner is exemplified by the scanner described by J. Griffith et al, "A Sector Scanner for Real Time Two-Dimen-6 sional Echocardiography", Circulation, Volume XLIX, June, 1974, 7 in which a single transducer is oscillated about an axis nomi-8~ nally lying in the front plane and passing through the center 9 of the transducer with an appropriate angle sensor being used to monitor the angular position of the transducer at any time.
11 Contact with the patient is maintained by the use of a gel, and 12 in operation the patient's tissues must conform to the movement 13 of the transducer which is essentially rigid. While the oscil-14 lating transducer scanner described by Griffith is of the direct contact variety, oscillating transducer scanners can also be of 16 the non direct or water bath variety as described by A. Ashberg, 17 "Ultrasonic Cinematography ~f the Living Heart", Ultrasonics, 18 April, 1967, in which the internal struc~ures of the human heart 19 have been investigated by using the ultrasound pulse-echo method and an ultrasound optical mirror system immersed in a water tank 21 having one wall consisting of a thin rubber membrane pressed 22 against the chest wall of the patient through which ultrasonic 223 energy can easily penetrate. These mechanical sector scanners also suffer from a number of limitations and drawbacks which limit their use. Both of the above described mechanical sector 26 scanners s~ffer the same rib interference limitation as the 28 phased array scanners. In addition, the direct contact mechan-29 ical sector scanners are limited in their useful scanning angle by the problems of the ~oving contact and physical angulation ///
~2 I ~
6.
1 of the tr~nsducer away from the skin, in most cases to values of 30 to 45 degrees. A limitation cor~mon to both of the mechanical sector scanners described i5 that their angular rate of sweep is not uniform, since the transducer or mirror system must reverse direction at the end of each sweep in each direction, so that the line density is greatest at the edges of the sector, where it is usually least desirable, and is lowest at the center of the sector, i.e., the cerlter of the region of interest. Concomitant with this limitation is the fact that the alternate direction of sweep means that an area at the end of a sweep is interrogated twice in a very short interval, as the scan crosses it in opposite direc-tions, and is not interrogated again until nearly the duration of t~o frames. In addition~ only the mid-point of the scan is inter-rogated at a constant frame rate. Another disadvantage of the direct contact of the oscillating transducer scanner described by Griffith arises from the physical transducer motion itself and includes patient discomfort, vibration of the transducer in the operator's hand, and mechanical ~ear of the tranducers moving parts which are subjected to significant forces.
A further limitation of direct contact scanners, includ~
ing phased array scanners, arises from near field non-uniformities in the so-called Fresnel zone of the transducer or array. As is well known, the acousitc pressure field for an unfocused trans-ducer exhibits large scale oscillations, including a series of peaks and nulls, within a distance D=r /~ from the face of the transducer, where r is the effectlve radius of the transducer, or ~rra~, ~n~ e ~ nc~ giv~ w~h~ a ~t~nc~
D, which is referred to herein as the "near" Fresnel zone. is Z
characterized by particularly large fluctions in amplitude ~oth 3~ laterally and in range, target positions and strengths will be 1 falsely displayed as a sector scan is carried out in that region.
For typical transducer radium to wavelength ratio of 10, and typical wavelengths of 0~7mm, the length D oE the near Fresna~
region, extends 3.5 centimeters in front of the transducer, and this will frequently include portions of the body which are of diagnostic interest.
Another type of mechanical sector scanner is the rotat-ional scannlr described by Barber et al. "Duplex Scanner II: For Simultaneous Imaging of Artery Tissuesand Flow", IEEE, 1974 Ultra-sonics Symposium Proceedings, and by Daigle et al, "A DuplexScanning System for Pediatxic Cardiology", Proceedings 1st Meeting of ~orld Federation for Ultrasound in Medicine and Biology~ 1976, which uses a set of transducers mounted on a rotor coupled to the patient through a water column which is separated from the skin surface by a thin silastic or ru~ber membrane. ~hile the rotating transducer water bath scanner described by Barber~ called the "Duplex Echo-l)oppler Scanner" permits a stationary contact ~ith the patient and provides a uniform beam spacing or line density as well as uniform sampling, it is severely limited in its appli-cation to adult cardiac scanning by the fact that the center oraxis of the sector .scan is removed or offset from the skin surface by a distance equal to the sum of the rotating radius and the length of the water column, resulting in a severe rih interference problem, The device of Barber et al, is primarily intended for use in pediatric cardiology where rib interference is not serious.
A further limitation of all present mechanical scanners i5 that they cannot provide a s~multaneous M mode or Doppler scan of any selected line of the scanned sector at l~Z15(~0 1 rates adequate for measurements of heart valve and heart wall 2 ~ motions. While any line of the sector scan of a mechanical 3 ¦ scanner can be sampled at the frame rate of the sector scan 4 itself, typically 20 to 45 frames per second and displayed on an M-mode type display, this rate is too slow since a minimum 6 of 300 frames per second is necessary in order to resolve 7 rapid motions, such as the motion of the mitral valve of the 8 heart, with existing M-mode single beam echocardlographic 9 probes operating at frame rates in excess of l000 frames per second. In addition, even if such rates could be attained by 11 a mechanical scanner, the unambiguous range, or useful pene-12 tration, corresponding to a frame rate of 300 or more frames 13 per second of the 80 to l00 lines typically forming a sector 14 scan would be less than two centimeters, and therefore totally useless. One attempt to provide a Doppler scan in a mechanical 1~ scanner is shown in the rotational scanner described by Barber 17 in which an auxiliary transducer operated in the pulsed Doppler 18 mode is provided which permits obtaining information about 19 velocities of blood flow and movement of cardiac structures essentially simultaneously (within less than a millisecond~
21 with the echoamplitude information. However, the Doppler scan 22 in the device described by Barber is not centered around the 23 same point as the echo scan, since the transducer is mounted 24 off to the side of the echo scanning head. Thus, the point of entry of the Doppler beam and the corresponding interrogated 26 volume are different than the point of entry of the echo 27 sounding beam and its corresponding interrogated volume, 23 creating problems both of access and of interpretation as the 29 same line as one of the~sector lines is not simultaneously ///
~2 //
~. ~
11~15~0 1 sampled.
2¦ The image producing capabilities of current ultra-3 ~ sonic scanners are further limited by the existence of "echo"
4 ~ artifacts which degrade the quality of and complicate the interpretation of the reflected signals from ~he object being 6~ visualized. Such echo artifacts are caused by ultrasound en-7~ ergy being received by a detector which energy is not directly 8 reflected from the body or target under examination. In a 9 system utilizing mirrors and membranes, such as described by ~sberg, a portion of the echo artifacts are caused by partial 11 reflection of acoustic pulses along the path of the desired 12 or "target" echoes by the membranes and the mirrors before 13 they reach the body or target under examination. Another 14 portion of the echo artifacts are caused by partial reflection of acoustic pulses from the membranes and mirrors not along 16 the return path of the target echoes but along other paths 17 resulting in reflections from numerous internal surfaces which 18 eventually inpinge upon the detector. A further portion of the 2 echo artifacts results from stray acoustic radiation that is 2 not intercepted by the membranes or mirrors but merely re-22 flects around the scanner with some of it reaching the detector 2 and producing false echoes.
23 Accordingly, it is a general object of the present 4 invention to provide an improved ultrasonic sector scanner.
It is another object of the present invention to 26 provide a sector which has a sector scan center of focus which 27 can be located in front of the scanner so as to minimi~e inter-28 f~rence problems.
10.
, ~ .
SUO
1, It is a further object of the present invention to 2 provide a sector scanner having a large effective sector scan 31¦ angle.
4~ It is another object of the present invention to 51 provide a sector scanner which has a stationary contact with 6~ the object being scanned and is free of vibration problems.
71~ It is still another object of the present invention 811 to provide a sector scanner which has uniform line density and 91 sampling rate at all angles, a high frame rate, and high 101~ quality radiating and receiving beam patterns.
, ~ .
SUO
1, It is a further object of the present invention to 2 provide a sector scanner having a large effective sector scan 31¦ angle.
4~ It is another object of the present invention to 51 provide a sector scanner which has a stationary contact with 6~ the object being scanned and is free of vibration problems.
71~ It is still another object of the present invention 811 to provide a sector scanner which has uniform line density and 91 sampling rate at all angles, a high frame rate, and high 101~ quality radiating and receiving beam patterns.
11 It is a further object of the present invention to
12 provide a sector scanner which can provide a simultaneous
13 M-mode or pulsed Doppler scan of any selected line of the
14 sector scan at a high frame rate comparable to conventional M-mode frame rates or pulsed Doppler systems.
16 It is another object of the present invention to 17 provide a sector scanner which is free of echo artifacts.
18 It is a further object of the present invention to 19 provide a sector scanner in which no part of the body of diagnostic interest lies in the~Fresnel zone of large varia-21 tions of acoustic intensity.
_ _ .
24 An ultrasonic scanner for producing a sector scan in an object to be examined is provided in which one or more 26 ultrasonic transducers traverse an arcuate path with respect 27 to a reflector which is positioned to receive the ultrasonic 229 waves scanning the surface of the reflector from each of the ///
11 .
l~Z1500 1 transducers and converge such waves at a point a preselected 2¦1 distance in front of the reflector. In general the ultrasonic 3¦ waves are converged at a point outside the scanner and inside 4~ the object to produce a sector scan in the object having its 51 center at the convergence point. In one embodiment of the 61 scanner, the reflector only partially reflects the ultrasonic 7 waves and an additional stationary transducer is provided which 8 is positioned to produce ultrasonic waves which radiate through 9 ¦ the reflector and coincide with one of the lines of the sector 10~ scan, thus permitting simultaneous M-mode or pulse Doppler echo 11 information to be obtained in perfect registration with the 12 sector scan lines~ Attenuation, absorbtion and anti-reflection 13 means are provided to suppress echo artifacts.
14 The novel features which are believed to be charac-teristic of the invention, both as to its organization and its 16 method of operation, together with further objects and advan-17 tages thereof, will be better understood from the following 18 description in connection with the accompanying drawings in 19 which a presently preferred embodiment of the invention is il-lustrated by way of example. It is to be expressly understood, 21 however, that the drawings are for purposes of illustration and 22 description only and are not intended as a definition of the 23 limits of the invention.
25 BRIEF DESCRIPTION OF T~lE DRAWINGS
26 FIGURE 1 is a perspective view of a preferred 27 embodiment of the present invention illustrating the sector 8 scan produced within the object to be examined;
29 , 32 "//
12.
llZi500 1~ FIGURE 2 is a cross-sectional view of the present 2 invention taken along the line 2-2 of FIGURE l;
3 FIGURE 3 is a cross-sectional view of the present 4 invention taken along the lines 3-3 of FIGURE 2;
FIGURE 4 is a perspective view of the present 6 invention illustrating the reflection and convergence of the 7 ultrasonic waves produced by the present invention;
8 FIGURE 5 and FIGURE 6 are cross-sectional views of 9 alternative embodiments of the face portion of the present invention taken along the line 2-2 of FIGURE l; and 11 FIGURE 7 illustrates a partial reflector utilized 12l in the present invention.
~31 Referring now to FIGURE l, a preferred embodiment 16 of the present invention is illustrated. The ultrasonic scanner 17 lO is shown having a membrane 12 which is placed in contact with 18 the surface 14 of the object to be examined, such as the heart 19 region of the human body. The lower or face portion 16 of the scanner lO houses the moving ultrasonic transducers and the 21 reflector while the upper portion 18 of the scanner lO houses 22 the electronics of the scanner lO. A motor 20 is provided on 23 top of the scanner lO to drive the transducers and a cable 22 24 provides the electrical power for the various elements of the scanner lO. As is shown in FIGURE l, the ultrasonic waves 24 6 produced by the scanner lO converge at a point 26 outside of 27 the scanner lO, between the ribs 28 of the chest of a patient, 28 and then diverge to produce the ultrasonic waves 30 which per-29 form a sector scan of t~e heart region. The ultrasonic waves 32 / 13.
1~2~.S~I~
1~ 30 are reflected by the various portions of the heart region 2 and are received by the generating transducers and processed 3 in accordance with the pulse-echo method described in the prior 4 art literature referenced herein.
In FIGURES 2 and 3 a set of ultrasonic transducers 6 32a-e are shown affixed to ring 34 which is supported by shaft 7 36. The shaft 36 is supported by bearings 38 and 40 coupled 8 to the lower portion 16 and the upper portion 18, respectively, 9 of the scanner 10 and is driven by the motor 20 controlled through leads 42. The ring 34 rotates within aperature 44 11 formed by the lower or face portion 16 and a dividing plate 46 12 and is immersed in a liquid 48 which is contained by seal 50 13 and membrane 12, plate 46 being opaque to ultrasonic waves and 14 having an aperature 52 therein to allow ultrasonic waves pro-duced by the transducers 32a-e and reflected off the mirror 54 16 coupled to the plate 46 to pass through the aperature 52 in 17 the plate 46 and the membrane 12. As stated previously, part 18 of the energy of the ultrasonic waves is reflected by portions 19 of the heart region and returns along the same path to the ultrasonic transducers 32a-e and is detected and displayed as 21 in conventional pulse echo instruments.
22 The transducers 32a-e are coupled to leads 56a-e 23 ¦ which pass through the ring 34 into the hollow center of the 24 shaft 36 and are coupled to slip rings 58, 60 mounted on disc 62 coupled to the shaft 36 and positioned above the transducers 26 32a-e. The slip rings 58, 60 are cut through at the midpoints 27 between the transducers 32a-e so that the brushes 64, 66 coupled 28¦ to leads 68 perform a commutating action upon rotation of the s~;ft 36 and ehe disc 62 to ruccessively energize the trant-32 / 14.
1 ducers 32a-e and to transmit information received by the trans-ducers 32a-e to the processing e~uipment. An optical tachometer 70 coupled to leads 72 is affixed to the upper portion 18 and provides an angular reference pulse train of about 500 pulses per shaft revolution in addition to an index pulse once per revolution which is used in conjunctlon with the pulse train to indicate the angular position of the shaft 36, and hence the position of the transducers 32a-e, at all times, and is also used to servo control the speed of the motor with the pulse rate applied to the transducers 32a-e to produce the ultrasonic wa~es.
As illustrated in FIGURES 3 and 4, the transducers 32a-e are located on the ring 34 at 72 degree intervals and are sequentially energized in the vicin~ty of the reflector 54 to produce a series of waves or pulses 74~ Due to the constrained circular path of the transducers 32a-e, the ultrasonlc waves 74 are directed radially toward the center line of the shaft 36 and scan across the surface of the reflector 54 which is mounted at an angle of 45 degrees with respect to the axis of the shaft 36.
Because reflector 54 is located closer to the actuated transducer 32a-e than the radial distance between said transducer and the axis o~ shaft 36, the ultrasonic waves 74 impinging on the surface of the reflector 54 are reflected through the aperture 52, the fluid 48 and the membrane 12, The emerging ultraso~ic waves 24 pass through the surface 14, converge at the point 26 and form a sector scan comprised of waves 30 centered at the intersection of the transducer axis with the shaft axis as projected by the reflector 54 outside the scanner 10 ~hile sector scans can be produced us;`ng only one transducer, higher frame rates are achieved by the use of multiple transducers, as described above.
The plane of the sector is parallel to the axis of the shaft . ?
~lS~ .
1 unless the shaft axis is tilted with respect to the surface of 2~l the object bein~ examined and the fluid 48 has a velocity of 3 propagation of sound therein different from the velocity of 4 propagation within the objectl in which case the actual angle of the plane is defined by Snell's law, sin ~ / sin ~j = Cl/C~
6 where a, is the angle of incidence, ~ the angle of refraction, 7 Cj the velocity of propagation of sound in the incidence 8 medium and C~ the velocity of propagation of sound in the 9 incidence medium and Ct the velocity of propogation of sound in the refracting medium.
11 The maximum usable sector angle is limited to those 12 angles for which the reflector 54 intercepts substantially all 13 of the ultrasonic beams. Since the distance between the shaft 14 axis and the mirror determines the distance of point 26 from the scanner lO, and since it is desirable for certain applica-16 tions, such as cardiography, to maintain the point 26, i.e., 17 the effective or projected axis of rotation, within the object, 18 the reflector 54 must be placed sufficiently far from the 19 shaft axis to ensure that the point 26 is within the object.
For a hand held device of modest size, however, the maximum 21 scan sector angle is then limited by the mechanical interfer-22 ence of the reflector 54 with the path of the transducers 23 32a-e as the reflector 54 moves farther from the shaft axis 24 toward the transducers. This limitation can be overcome by using for the fluid 48 a fluid such as an emulsion of toluene 26 in 40% ethanol amine, 60% chloroform, which has a slower 27 ¦ velocity of propagation therein than in the object and thus 28 ¦ results, by Snell's law, in a larger scan sector angle in the 29 object. As is described more fully hereinafter, the fluid 48 should also have a specific impedance substantially equal to ~ 16.
1121SO(:~
1 the specific impedance of the object being scanned since 2l! multiple reflection artifacts result when a sufficiently large 3 echo results at the interface 14 due to an impedance mismatch.
4 It has been found that fluids with specific impedances of 5 ~ between 1.65 and 1.75 when used in conjunction with a thin 6~ latex membrane 12 yield acceptable results and can provide a 7~ sector angle of 90 degrees in a human object with a sector 8 angle of 70 degrees within the scanner 10. While the thin 9 I elastic membrane enables uneven body contours to be accommo-dated and the scanner to be tilted to look behind interfering 12 structures, a rigid membrane can be used for industrial appli catlons .
13 As shown in FIGURES 5 and 6, in order to minimize 14 echo artifacts on reflections from the membrane 12, a flexible membrane may be used, as stated above, made of a material such 16 as latex, together with a window section cut out large enough 17 to accommodate the entire sector scan at the plane of the skin 18 or contact surface 14, with a very thin (eg. 25~thick) film 19 12' of a material such as polyethylene covering the window section. Such a film 12' because it is much less than a wave-21 length in thickness and has a characteristic impedance not 22 very different than that of the materials on either side of it, 23 will be essentially totally transparent to the ultrasonic 24 radiationO If it is desired to use a more rigid membrane 12, made for example of polyethylene, quarter-wave anti-reflection 26 ~atching layers 80, 82 composed of low density polyethylene, 27 as shown in FIGURE 6, can be used on both surfaces of the 28 membrane 12 to match to the fluid 48 and to the skin or contact Z9 surface 14.
///
17.
11 In order to reduce the magnitude of those echoes 21l which result at least partly from reflection or scattering from 3 supporting structures within the scanner 10, the transducer ring 4 34, the portion support 55 of the reflector 54, the plate 46, 5~ and the inside surface of the face portion 16, can be made of 6l or covered with a layer 84 of an acoustically highly absorbing 7~ material, which has a characteristic impedance Z~ closely 8 matching the characteristic impedance ZL of the liquid 48, 9 and which may additionally be clad with a quarter-wave anti-reflection matching layer 86, approximately .2mm ~hick and 11 with a characteristic impedance ZM ~ (Z~ ZL ) 12 Since only echo artifacts (but no target echoes) 13 impinge on those internal support structures, the attenuation 14 of the materials may be chosen as high as i5 feasible without any deleterious effects on the signal strength. A suitable 16 material choice in this case is low-density polyethylene, 17 preferably loaded with carbon, or carbon loaded natural rubber.
18 The material chosen for a matching layer will depend on the 19 liquid selected, and may be composed of a low density polyethylene or an unloaded natural rubber to match a loaded 21 natural rubber wall to castor oil used as the fluid 48.
22 To further reduce echo artifacts, the fluid 48 can be 23 chosen to be a sound attenuating liquid, such as castor oil, 24 salt solutions such as solutions of hydrated manganese chloride in water, or emulsions such as emulsions of toluene in water 26 which can be made highly attenuating, as described in an arti-~7 cle by J. R. Allegra and S. A. Hawley, Journal Acoustical 28 Society of America, Vol. 151, 1972. While the provision of 29 a sound attenuating liq~id alone has been found quite effective, ///
~2 //
1~.
1 there are, however, limits on the values of attenuation coef-2 ficient which are acceptable for the liquid 48, because the 3 target echoes must also travel in the liquid 48, and excessive 4 attenuation of those signals must be avoided to maintain a 51 useful signal-to-noise ratio and dynamic range based on signal-6 to~noise ratio. For example, in order to meet the requirements 7 of having the entire scanned sector or field of view beyond the' 8 Fresnel zone ~ of the transducers 32, where d is the trans-9 ducer diameter and ~ is the acoustic wave-length, and achieving a large sector scan angle, within a scanner of minimum external 11 dimensions, the radius of a scanner used in cardiac scanning 12 should be between about 2.5 cm and 3.5 cm, and the corresponding 13 acoustic path length R within the scanner head will be between 14 2 and 3 cm, with a typical value of 2.5 cm. Pulses leading to target echoes at a range R travel a distance 2R in the liquid 16 48 and a distance 2R~ = 2R-2R~ in the body or external medium 17 examined. Multiple echo artifacts appearing at range R travel 18 a distance 2R (or nearly 2R for echo artifacts arising from 19 subcutaneous layers) within the liquid 48. Thus, if the atten-uation coefficient of the liquid 48 isC~ , measured in db/cm, 21 and the average attenuation coefficient of the examined tissue 22 isG~, then the target echoes from range R will suffer an 23 attenuation A=2R~ ~L+ 2Re~T on 2R~+ 2RC (~L -~r ) whereas 24 multiple echo artifacts will suffer an attenuation (due to the liquid) of about 2R~. Clearly, the larger ~ compared toC~r , 26 the greater the attenuation of the multiple echoes with respect 27 to the signal echoes, but also the greater the absolute atten-28 uation of the signal echoes. l'he excess attenuation 2R~ c~, 29 of the signal means a dégradation of the system signal-to-noise 19 .
1 ratio, for a given transducer input power, efficiency, sensi-2 tivity, and preamplifier noise figure. If attenuation in the 3 liquids 48 is used as the sole means of attenuating the basic 4 echo artifacts, and a liquid is chosen that will provide 40 db of attenuation for the multiple echoes at range 2R~(i.e.
6 the first spurious echoes from the membrane 12), then for a 7 typical value R =~2.5cm,~ = 4db/cm. The excess attenuation 8 of the target echoes will be 20db, providing a net reduction 9 of the echo artifacts of 20 db.
In conjunction with an attenuating liquid therefore 11 a layer of a highly absorbing or attenuating solid material 88 12 may be placed in the primary acoustic path, either on the 13 mirror 54 itself, or immediately adjacent to the transducer 32 14 or membrane 12. Since it is desirable to provide a scanner 10 which is as small in diameter as is practicable, a suitable 16 absorbing material such as carbon loaded rubber, with an at-17 tenuation coefficient as hïgh as 25 db/cm can be utilized, 18 with a layer 2mm thick resulting in a two-way attenuation of 19 lOdb. Since the layer 88 should be located so as to intercept (and therefore attenuate) all or nearly all artifactual echoes, 21 and since very close matching of the liquid to the attenuating 22 layer is required to avoid having their interface act as a new 23 source of echo artifacts, location on the transducer 32 is 24 preferred.
In addition to the use of an attenuating layer 88 26 or liquid 48, it has been found desirable to make the reflector 27 54 only partially reflecting and of highly acoustically absor-28 ¦ bing material so that the portion of the ultrasonic energy 29 which is not reflected ~y the reflector will be absorbed and 32 20.
11 ~9 ~ 0 0 1I not contribute to echo artifacts. The partial reflecivity of 2 the reflector 54 may be achieved by use of a reflector material 3~ with a suitable impedance mismatch with the liquid 48. Since, 4l however, this approach can lead to reflectivity which is de pendent on the sector scan angle, and requires compensation of 6 the transducer receiver gain (or transmitted power, or both) 7l as a function of scan angle to lead to a uniform display 8 signal strength for a given target echo strength, a suitable 9 ~ partial reflector 54' may be employed, as is shown in FIGURE 7, which is comprised of a non-reflecting or weakly reflecting 11 material 90, such as rubber, with narrow, closely spaced (less 12 than a half wave-length) strips 92 of a highly reflecting metal 13 such as tungsten. The use of such a partial reflector 54', 14 attenuating layers 84 and 88, an attenuating liquid 48, and antireflection layers 82 and 86 has resulted in the reduction 16 of echo artifacts, compared to the target echoes and at a 17 range R~ in the examined body of about 3cm or greater, of 18 20db, sufficient for artifact-free or substantially artifact-19 free operation of the scanner of the present invention in medical diagnostic applications.
21 Since, in order to achieve the echo artifact sup-22 pression as described above, the target echoes have also 23 been attenuated by approximately 20db, it is desirable to use 24 highly efficient transducers 32, and in particular transducers with a relatively high Q-factor. This is, however, contrary 26 to current practice in which pulse excited low efficiency, low 27 (mechanical and electrical) Q transducers are used in order to 28 achieve extremely high range resolution. Since, however, the 29 very short wideband pulses used in the present art scanners 21.
1 become stretched and distorted as they travel through tissues, 2 particularly muscle, because such tissues have a large fre-3 quency dependent attenuation, the higher frequency components 4 are resultingly preferentially attenuated, with a resultant effective stretching of the pulse. It has thus, been found 6 that the use of a higher Q transducer with a longer, narrower 7 bandwith pulse results in less distortion and pulse stretching, 8 with the effective lengths significantly greater than those 9 of the low Q, low efficiency transducers.
In FIGURE 6 an alternative embodiment of the present 11 invention is shown in which an auxiliary stationary transducer 12 94 is provided which is positioned in line with one of the 13 ultrasonic waves 24 and behind the partial reflector 54'. The 14 partial reflector 54' has a solid backing 96 with an attenua-tion similar to the liquid 48 which is coupled to an additional 16 highly absorbing block 98 used to thoroughly dampen the energy 17 which passes through the partial reflector 54. The backing 18 96 may be composed, for example, of room temperature vul-19 canized silicone rubber and the block 98 may be composed also of rubber. The tr~nsducer 94 is coupled by bracket lO0 to 21 block 98 which i5 coupled to plate 46. Leads 102 are pro-22 vided to energize transducer 94 and to transmit information 23 received by transducer 94 to the processing eguipment. The 24 ultrasonic waves produced by transducer 94 radiate through the partial reflector 54' in coincidence with one of the lines 26 of the sector scan, thus permitting simultaneous M-mode or 27 pulse Doppler echo information to be obtained in perfect 28 registration with the sector scan lines.
///
32 22.
50~
1I Having described the invention, it is obvious that 21 numerous modifications and departures may be made by those 3 skilled in the art; thus the invention is to be construed as 4 limited only to the spirit and scope of the appended claims.
What is claimed is:
3~ :.
16 It is another object of the present invention to 17 provide a sector scanner which is free of echo artifacts.
18 It is a further object of the present invention to 19 provide a sector scanner in which no part of the body of diagnostic interest lies in the~Fresnel zone of large varia-21 tions of acoustic intensity.
_ _ .
24 An ultrasonic scanner for producing a sector scan in an object to be examined is provided in which one or more 26 ultrasonic transducers traverse an arcuate path with respect 27 to a reflector which is positioned to receive the ultrasonic 229 waves scanning the surface of the reflector from each of the ///
11 .
l~Z1500 1 transducers and converge such waves at a point a preselected 2¦1 distance in front of the reflector. In general the ultrasonic 3¦ waves are converged at a point outside the scanner and inside 4~ the object to produce a sector scan in the object having its 51 center at the convergence point. In one embodiment of the 61 scanner, the reflector only partially reflects the ultrasonic 7 waves and an additional stationary transducer is provided which 8 is positioned to produce ultrasonic waves which radiate through 9 ¦ the reflector and coincide with one of the lines of the sector 10~ scan, thus permitting simultaneous M-mode or pulse Doppler echo 11 information to be obtained in perfect registration with the 12 sector scan lines~ Attenuation, absorbtion and anti-reflection 13 means are provided to suppress echo artifacts.
14 The novel features which are believed to be charac-teristic of the invention, both as to its organization and its 16 method of operation, together with further objects and advan-17 tages thereof, will be better understood from the following 18 description in connection with the accompanying drawings in 19 which a presently preferred embodiment of the invention is il-lustrated by way of example. It is to be expressly understood, 21 however, that the drawings are for purposes of illustration and 22 description only and are not intended as a definition of the 23 limits of the invention.
25 BRIEF DESCRIPTION OF T~lE DRAWINGS
26 FIGURE 1 is a perspective view of a preferred 27 embodiment of the present invention illustrating the sector 8 scan produced within the object to be examined;
29 , 32 "//
12.
llZi500 1~ FIGURE 2 is a cross-sectional view of the present 2 invention taken along the line 2-2 of FIGURE l;
3 FIGURE 3 is a cross-sectional view of the present 4 invention taken along the lines 3-3 of FIGURE 2;
FIGURE 4 is a perspective view of the present 6 invention illustrating the reflection and convergence of the 7 ultrasonic waves produced by the present invention;
8 FIGURE 5 and FIGURE 6 are cross-sectional views of 9 alternative embodiments of the face portion of the present invention taken along the line 2-2 of FIGURE l; and 11 FIGURE 7 illustrates a partial reflector utilized 12l in the present invention.
~31 Referring now to FIGURE l, a preferred embodiment 16 of the present invention is illustrated. The ultrasonic scanner 17 lO is shown having a membrane 12 which is placed in contact with 18 the surface 14 of the object to be examined, such as the heart 19 region of the human body. The lower or face portion 16 of the scanner lO houses the moving ultrasonic transducers and the 21 reflector while the upper portion 18 of the scanner lO houses 22 the electronics of the scanner lO. A motor 20 is provided on 23 top of the scanner lO to drive the transducers and a cable 22 24 provides the electrical power for the various elements of the scanner lO. As is shown in FIGURE l, the ultrasonic waves 24 6 produced by the scanner lO converge at a point 26 outside of 27 the scanner lO, between the ribs 28 of the chest of a patient, 28 and then diverge to produce the ultrasonic waves 30 which per-29 form a sector scan of t~e heart region. The ultrasonic waves 32 / 13.
1~2~.S~I~
1~ 30 are reflected by the various portions of the heart region 2 and are received by the generating transducers and processed 3 in accordance with the pulse-echo method described in the prior 4 art literature referenced herein.
In FIGURES 2 and 3 a set of ultrasonic transducers 6 32a-e are shown affixed to ring 34 which is supported by shaft 7 36. The shaft 36 is supported by bearings 38 and 40 coupled 8 to the lower portion 16 and the upper portion 18, respectively, 9 of the scanner 10 and is driven by the motor 20 controlled through leads 42. The ring 34 rotates within aperature 44 11 formed by the lower or face portion 16 and a dividing plate 46 12 and is immersed in a liquid 48 which is contained by seal 50 13 and membrane 12, plate 46 being opaque to ultrasonic waves and 14 having an aperature 52 therein to allow ultrasonic waves pro-duced by the transducers 32a-e and reflected off the mirror 54 16 coupled to the plate 46 to pass through the aperature 52 in 17 the plate 46 and the membrane 12. As stated previously, part 18 of the energy of the ultrasonic waves is reflected by portions 19 of the heart region and returns along the same path to the ultrasonic transducers 32a-e and is detected and displayed as 21 in conventional pulse echo instruments.
22 The transducers 32a-e are coupled to leads 56a-e 23 ¦ which pass through the ring 34 into the hollow center of the 24 shaft 36 and are coupled to slip rings 58, 60 mounted on disc 62 coupled to the shaft 36 and positioned above the transducers 26 32a-e. The slip rings 58, 60 are cut through at the midpoints 27 between the transducers 32a-e so that the brushes 64, 66 coupled 28¦ to leads 68 perform a commutating action upon rotation of the s~;ft 36 and ehe disc 62 to ruccessively energize the trant-32 / 14.
1 ducers 32a-e and to transmit information received by the trans-ducers 32a-e to the processing e~uipment. An optical tachometer 70 coupled to leads 72 is affixed to the upper portion 18 and provides an angular reference pulse train of about 500 pulses per shaft revolution in addition to an index pulse once per revolution which is used in conjunctlon with the pulse train to indicate the angular position of the shaft 36, and hence the position of the transducers 32a-e, at all times, and is also used to servo control the speed of the motor with the pulse rate applied to the transducers 32a-e to produce the ultrasonic wa~es.
As illustrated in FIGURES 3 and 4, the transducers 32a-e are located on the ring 34 at 72 degree intervals and are sequentially energized in the vicin~ty of the reflector 54 to produce a series of waves or pulses 74~ Due to the constrained circular path of the transducers 32a-e, the ultrasonlc waves 74 are directed radially toward the center line of the shaft 36 and scan across the surface of the reflector 54 which is mounted at an angle of 45 degrees with respect to the axis of the shaft 36.
Because reflector 54 is located closer to the actuated transducer 32a-e than the radial distance between said transducer and the axis o~ shaft 36, the ultrasonic waves 74 impinging on the surface of the reflector 54 are reflected through the aperture 52, the fluid 48 and the membrane 12, The emerging ultraso~ic waves 24 pass through the surface 14, converge at the point 26 and form a sector scan comprised of waves 30 centered at the intersection of the transducer axis with the shaft axis as projected by the reflector 54 outside the scanner 10 ~hile sector scans can be produced us;`ng only one transducer, higher frame rates are achieved by the use of multiple transducers, as described above.
The plane of the sector is parallel to the axis of the shaft . ?
~lS~ .
1 unless the shaft axis is tilted with respect to the surface of 2~l the object bein~ examined and the fluid 48 has a velocity of 3 propagation of sound therein different from the velocity of 4 propagation within the objectl in which case the actual angle of the plane is defined by Snell's law, sin ~ / sin ~j = Cl/C~
6 where a, is the angle of incidence, ~ the angle of refraction, 7 Cj the velocity of propagation of sound in the incidence 8 medium and C~ the velocity of propagation of sound in the 9 incidence medium and Ct the velocity of propogation of sound in the refracting medium.
11 The maximum usable sector angle is limited to those 12 angles for which the reflector 54 intercepts substantially all 13 of the ultrasonic beams. Since the distance between the shaft 14 axis and the mirror determines the distance of point 26 from the scanner lO, and since it is desirable for certain applica-16 tions, such as cardiography, to maintain the point 26, i.e., 17 the effective or projected axis of rotation, within the object, 18 the reflector 54 must be placed sufficiently far from the 19 shaft axis to ensure that the point 26 is within the object.
For a hand held device of modest size, however, the maximum 21 scan sector angle is then limited by the mechanical interfer-22 ence of the reflector 54 with the path of the transducers 23 32a-e as the reflector 54 moves farther from the shaft axis 24 toward the transducers. This limitation can be overcome by using for the fluid 48 a fluid such as an emulsion of toluene 26 in 40% ethanol amine, 60% chloroform, which has a slower 27 ¦ velocity of propagation therein than in the object and thus 28 ¦ results, by Snell's law, in a larger scan sector angle in the 29 object. As is described more fully hereinafter, the fluid 48 should also have a specific impedance substantially equal to ~ 16.
1121SO(:~
1 the specific impedance of the object being scanned since 2l! multiple reflection artifacts result when a sufficiently large 3 echo results at the interface 14 due to an impedance mismatch.
4 It has been found that fluids with specific impedances of 5 ~ between 1.65 and 1.75 when used in conjunction with a thin 6~ latex membrane 12 yield acceptable results and can provide a 7~ sector angle of 90 degrees in a human object with a sector 8 angle of 70 degrees within the scanner 10. While the thin 9 I elastic membrane enables uneven body contours to be accommo-dated and the scanner to be tilted to look behind interfering 12 structures, a rigid membrane can be used for industrial appli catlons .
13 As shown in FIGURES 5 and 6, in order to minimize 14 echo artifacts on reflections from the membrane 12, a flexible membrane may be used, as stated above, made of a material such 16 as latex, together with a window section cut out large enough 17 to accommodate the entire sector scan at the plane of the skin 18 or contact surface 14, with a very thin (eg. 25~thick) film 19 12' of a material such as polyethylene covering the window section. Such a film 12' because it is much less than a wave-21 length in thickness and has a characteristic impedance not 22 very different than that of the materials on either side of it, 23 will be essentially totally transparent to the ultrasonic 24 radiationO If it is desired to use a more rigid membrane 12, made for example of polyethylene, quarter-wave anti-reflection 26 ~atching layers 80, 82 composed of low density polyethylene, 27 as shown in FIGURE 6, can be used on both surfaces of the 28 membrane 12 to match to the fluid 48 and to the skin or contact Z9 surface 14.
///
17.
11 In order to reduce the magnitude of those echoes 21l which result at least partly from reflection or scattering from 3 supporting structures within the scanner 10, the transducer ring 4 34, the portion support 55 of the reflector 54, the plate 46, 5~ and the inside surface of the face portion 16, can be made of 6l or covered with a layer 84 of an acoustically highly absorbing 7~ material, which has a characteristic impedance Z~ closely 8 matching the characteristic impedance ZL of the liquid 48, 9 and which may additionally be clad with a quarter-wave anti-reflection matching layer 86, approximately .2mm ~hick and 11 with a characteristic impedance ZM ~ (Z~ ZL ) 12 Since only echo artifacts (but no target echoes) 13 impinge on those internal support structures, the attenuation 14 of the materials may be chosen as high as i5 feasible without any deleterious effects on the signal strength. A suitable 16 material choice in this case is low-density polyethylene, 17 preferably loaded with carbon, or carbon loaded natural rubber.
18 The material chosen for a matching layer will depend on the 19 liquid selected, and may be composed of a low density polyethylene or an unloaded natural rubber to match a loaded 21 natural rubber wall to castor oil used as the fluid 48.
22 To further reduce echo artifacts, the fluid 48 can be 23 chosen to be a sound attenuating liquid, such as castor oil, 24 salt solutions such as solutions of hydrated manganese chloride in water, or emulsions such as emulsions of toluene in water 26 which can be made highly attenuating, as described in an arti-~7 cle by J. R. Allegra and S. A. Hawley, Journal Acoustical 28 Society of America, Vol. 151, 1972. While the provision of 29 a sound attenuating liq~id alone has been found quite effective, ///
~2 //
1~.
1 there are, however, limits on the values of attenuation coef-2 ficient which are acceptable for the liquid 48, because the 3 target echoes must also travel in the liquid 48, and excessive 4 attenuation of those signals must be avoided to maintain a 51 useful signal-to-noise ratio and dynamic range based on signal-6 to~noise ratio. For example, in order to meet the requirements 7 of having the entire scanned sector or field of view beyond the' 8 Fresnel zone ~ of the transducers 32, where d is the trans-9 ducer diameter and ~ is the acoustic wave-length, and achieving a large sector scan angle, within a scanner of minimum external 11 dimensions, the radius of a scanner used in cardiac scanning 12 should be between about 2.5 cm and 3.5 cm, and the corresponding 13 acoustic path length R within the scanner head will be between 14 2 and 3 cm, with a typical value of 2.5 cm. Pulses leading to target echoes at a range R travel a distance 2R in the liquid 16 48 and a distance 2R~ = 2R-2R~ in the body or external medium 17 examined. Multiple echo artifacts appearing at range R travel 18 a distance 2R (or nearly 2R for echo artifacts arising from 19 subcutaneous layers) within the liquid 48. Thus, if the atten-uation coefficient of the liquid 48 isC~ , measured in db/cm, 21 and the average attenuation coefficient of the examined tissue 22 isG~, then the target echoes from range R will suffer an 23 attenuation A=2R~ ~L+ 2Re~T on 2R~+ 2RC (~L -~r ) whereas 24 multiple echo artifacts will suffer an attenuation (due to the liquid) of about 2R~. Clearly, the larger ~ compared toC~r , 26 the greater the attenuation of the multiple echoes with respect 27 to the signal echoes, but also the greater the absolute atten-28 uation of the signal echoes. l'he excess attenuation 2R~ c~, 29 of the signal means a dégradation of the system signal-to-noise 19 .
1 ratio, for a given transducer input power, efficiency, sensi-2 tivity, and preamplifier noise figure. If attenuation in the 3 liquids 48 is used as the sole means of attenuating the basic 4 echo artifacts, and a liquid is chosen that will provide 40 db of attenuation for the multiple echoes at range 2R~(i.e.
6 the first spurious echoes from the membrane 12), then for a 7 typical value R =~2.5cm,~ = 4db/cm. The excess attenuation 8 of the target echoes will be 20db, providing a net reduction 9 of the echo artifacts of 20 db.
In conjunction with an attenuating liquid therefore 11 a layer of a highly absorbing or attenuating solid material 88 12 may be placed in the primary acoustic path, either on the 13 mirror 54 itself, or immediately adjacent to the transducer 32 14 or membrane 12. Since it is desirable to provide a scanner 10 which is as small in diameter as is practicable, a suitable 16 absorbing material such as carbon loaded rubber, with an at-17 tenuation coefficient as hïgh as 25 db/cm can be utilized, 18 with a layer 2mm thick resulting in a two-way attenuation of 19 lOdb. Since the layer 88 should be located so as to intercept (and therefore attenuate) all or nearly all artifactual echoes, 21 and since very close matching of the liquid to the attenuating 22 layer is required to avoid having their interface act as a new 23 source of echo artifacts, location on the transducer 32 is 24 preferred.
In addition to the use of an attenuating layer 88 26 or liquid 48, it has been found desirable to make the reflector 27 54 only partially reflecting and of highly acoustically absor-28 ¦ bing material so that the portion of the ultrasonic energy 29 which is not reflected ~y the reflector will be absorbed and 32 20.
11 ~9 ~ 0 0 1I not contribute to echo artifacts. The partial reflecivity of 2 the reflector 54 may be achieved by use of a reflector material 3~ with a suitable impedance mismatch with the liquid 48. Since, 4l however, this approach can lead to reflectivity which is de pendent on the sector scan angle, and requires compensation of 6 the transducer receiver gain (or transmitted power, or both) 7l as a function of scan angle to lead to a uniform display 8 signal strength for a given target echo strength, a suitable 9 ~ partial reflector 54' may be employed, as is shown in FIGURE 7, which is comprised of a non-reflecting or weakly reflecting 11 material 90, such as rubber, with narrow, closely spaced (less 12 than a half wave-length) strips 92 of a highly reflecting metal 13 such as tungsten. The use of such a partial reflector 54', 14 attenuating layers 84 and 88, an attenuating liquid 48, and antireflection layers 82 and 86 has resulted in the reduction 16 of echo artifacts, compared to the target echoes and at a 17 range R~ in the examined body of about 3cm or greater, of 18 20db, sufficient for artifact-free or substantially artifact-19 free operation of the scanner of the present invention in medical diagnostic applications.
21 Since, in order to achieve the echo artifact sup-22 pression as described above, the target echoes have also 23 been attenuated by approximately 20db, it is desirable to use 24 highly efficient transducers 32, and in particular transducers with a relatively high Q-factor. This is, however, contrary 26 to current practice in which pulse excited low efficiency, low 27 (mechanical and electrical) Q transducers are used in order to 28 achieve extremely high range resolution. Since, however, the 29 very short wideband pulses used in the present art scanners 21.
1 become stretched and distorted as they travel through tissues, 2 particularly muscle, because such tissues have a large fre-3 quency dependent attenuation, the higher frequency components 4 are resultingly preferentially attenuated, with a resultant effective stretching of the pulse. It has thus, been found 6 that the use of a higher Q transducer with a longer, narrower 7 bandwith pulse results in less distortion and pulse stretching, 8 with the effective lengths significantly greater than those 9 of the low Q, low efficiency transducers.
In FIGURE 6 an alternative embodiment of the present 11 invention is shown in which an auxiliary stationary transducer 12 94 is provided which is positioned in line with one of the 13 ultrasonic waves 24 and behind the partial reflector 54'. The 14 partial reflector 54' has a solid backing 96 with an attenua-tion similar to the liquid 48 which is coupled to an additional 16 highly absorbing block 98 used to thoroughly dampen the energy 17 which passes through the partial reflector 54. The backing 18 96 may be composed, for example, of room temperature vul-19 canized silicone rubber and the block 98 may be composed also of rubber. The tr~nsducer 94 is coupled by bracket lO0 to 21 block 98 which i5 coupled to plate 46. Leads 102 are pro-22 vided to energize transducer 94 and to transmit information 23 received by transducer 94 to the processing eguipment. The 24 ultrasonic waves produced by transducer 94 radiate through the partial reflector 54' in coincidence with one of the lines 26 of the sector scan, thus permitting simultaneous M-mode or 27 pulse Doppler echo information to be obtained in perfect 28 registration with the sector scan lines.
///
32 22.
50~
1I Having described the invention, it is obvious that 21 numerous modifications and departures may be made by those 3 skilled in the art; thus the invention is to be construed as 4 limited only to the spirit and scope of the appended claims.
What is claimed is:
3~ :.
Claims (60)
1. An ultrasonic scanner comprising:
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means; and means for causing said transducer means to traverse an arcuate path with respect to said reflector means, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means.
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means; and means for causing said transducer means to traverse an arcuate path with respect to said reflector means, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means.
2. The scanner of Claim 1 wherein said transducer means are positioned on a circular ring mounted on the inside of said reflector means, said ultrasonic waves being directed radially inward.
3. The scanner of Claim 2 wherein said reflector means is disposed on the inside of said housing and angularly positioned to reflect ultrasonic waves from said transducer means and to converge said waves at a point outside of said housing.
4. The scanner of Claim 2 wherein said preselected distance is determined by the distance between said reflector means and the center of said circular ring.
24.
24.
5. The scanner of Claim 1 further comprising means for determining the angular position of said transducer means.
6. The scanner of Claim 1 further comprising means for conducting said ultrasonic waves reflected from said re-flector means.
7. The scanner of Claim 6 wherein said reflector means and said transducer means are positioned with respect to one another to cause said ultrasonic waves to converge at a point outside of said conducting means.
8. The scanner of Claim 6 wherein said conducting means comprises a fluid having a specific impedance substan-tially equal to the impedance of an object being scanned by said scanner.
9. The scanner of Claim 8 wherein said fluid has an acoustic propagation velocity therein substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object.
10. An ultrasonic scanner comprising:
a housing having a face portion;
a circular ring mounted in the vicinity of the face portion of said housing;
a plurality of ultrasonic transducers 25.
mounted on said ring and facing inwardly toward the center of said ring;
driving means coupled to said ring to rotate said ring about an axis positioned in said housing;
reflector means angularly mounted on the face of said housing to intercept and reflect ultra-sonic waves produced by said transducers, said reflector means causing said ultrasonic waves to converge at a point located a preselected distance in front of the face of said housing;
commutator means coupled to said trans-ducer to sequentially supply electrical power to said transducers;
means coupled to said driving means for determining the angular position of said trans-ducers; and means coupled to the face of said housing to conduct said ultrasonic waves to the object being scanned by said scanner.
a housing having a face portion;
a circular ring mounted in the vicinity of the face portion of said housing;
a plurality of ultrasonic transducers 25.
mounted on said ring and facing inwardly toward the center of said ring;
driving means coupled to said ring to rotate said ring about an axis positioned in said housing;
reflector means angularly mounted on the face of said housing to intercept and reflect ultra-sonic waves produced by said transducers, said reflector means causing said ultrasonic waves to converge at a point located a preselected distance in front of the face of said housing;
commutator means coupled to said trans-ducer to sequentially supply electrical power to said transducers;
means coupled to said driving means for determining the angular position of said trans-ducers; and means coupled to the face of said housing to conduct said ultrasonic waves to the object being scanned by said scanner.
11. An ultrasonic scanner comprising:
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means movably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
26.
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and attenuating means for substantially eli-minating echo artifacts in said scanner.
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means movably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
26.
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and attenuating means for substantially eli-minating echo artifacts in said scanner.
12. The scanner of Claim 11 wherein said attenu-ating means is a fluid having a preselected coefficient of attenuation, said fluid being contained by said housing and providing the transmission medium for said ultrasonic waves.
13. The scanner of Claim 11 wherein said attenuating means comprises a layer of absorbing material, said material being disposed on preselected surfaces of said scanner.
14. The scanner of Claim 13 wherein said absorbing material is placed on the surface of said transducers.
15. The scanner of Claim 13 wherein said absorbing material is placed on the surface of said reflector means.
16. The scanner of Claim 11 wherein said housing includes a membrane adapted to transmit said ultrasonic waves to an object to be scanned.
27.
27.
17. The scanner of Claim 16 wherein a portion of said membrane comprises a thin film window substantially transparent to said ultrasonic waves.
18. The scanner of Claim 16 wherein said membrane has a layer of absorbing material thereon.
19. The scanner of Claim 16 wherein said membrane is comprised of a rigid material and has one or more quarter-wave anti-reflecting layers thereon.
20. The scanner of Claim 13 wherein said atten-uating means comprises a quarterwave anti-reflecting layer, said layer being disposed on said layer of absorbing material.
21. The scanner of Claim 11 wherein said reflector means is adapted to partially reflect said ultrasonic waves.
22. The scanner of Claim 21 wherein said partial reflector means has backing means coupled thereto and said attenuating means is an attenuating fluid, said backing means having an attenuation coefficient substantially equal to the attenuation coefficient of said attenuating fluid.
23. The scanner of Claim 21 wherein said backing means has an absorbing block coupled thereto for absorbing the ultrasonic waves passing through said partial reflector means.
28.
28.
24. The scanner of Claim 21 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
25. The scanner of Claim 11 wherein said trans-ducers have a high Q-factor for producing a long narrow band width pulse.
26. An ultrasonic scanner comprising:
a housing;
partial reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflec-tor means, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and stationary transducer means positioned to direct ultrasonic waves through said partial reflector means along a path substantially coincident with said reflected ultrasonic waves.
a housing;
partial reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflec-tor means, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and stationary transducer means positioned to direct ultrasonic waves through said partial reflector means along a path substantially coincident with said reflected ultrasonic waves.
27. The scanner of Claim 26 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
29.
29.
28. An ultrasonic scanner comprising:
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said ref-lector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and fluid disposed within said housing for conducting said ultrasonic waves reflected from said reflector means, said fluid having an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object, 29. An ultrasonic scanner comprising:
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said ref-lector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and fluid disposed within said housing for conducting said ultrasonic waves reflected from said reflector means, said fluid having an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object, 29. An ultrasonic scanner comprising:
a housing;
reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said
Claim 29 continued .....
reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a layer of absorbing material disposed on preselected surfaces of said scanner and a quarter-wave anti-reflecting layer disposed on said layer of absorbing material.
reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a layer of absorbing material disposed on preselected surfaces of said scanner and a quarter-wave anti-reflecting layer disposed on said layer of absorbing material.
30. An ultrasonic scanner comprising:
a housing;
partial reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said reflector means angled with respect to said ultrasonic waves, whereby said ultra-sonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and stationary transducer means positioned to direct ultrasonic waves through said partial reflector means along a path substantially coincident with said reflected ultrasonic waves.
a housing;
partial reflector means positioned within said housing;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said reflector means angled with respect to said ultrasonic waves, whereby said ultra-sonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and stationary transducer means positioned to direct ultrasonic waves through said partial reflector means along a path substantially coincident with said reflected ultrasonic waves.
31. The scanner of claim 30 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
32. The scanner of claim 28 wherein said reflector means is adapted to partially reflect said ultrasonic waves.
33. The scanner of claim 32 wherein said partial reflector means has an absorbing block coupled thereto for absorbing the ultrasonic waves passing through said partial reflector means.
34. The scanner of claim 32 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
35. The scanner of claim 28 further comprising attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a layer of absorbing material disposed on preselected surfaces of said scanner and a quarter-wave anti-reflecting layer disposed on said layer of absorbing material.
36. The scanner of claim 28 further comprising a membrane adapted to transmit said ultrasonic waves to an object to be scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
37. The scanner of claim 29 further comprising fluid dis-posed within said housing for conducting said ultrasonic waves reflected from said reflector means, said fluid having an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object.
38. The scanner of claim 29 wherein said reflector means is adapted to partially reflect said ultrasonic waves.
39. The scanner of claim 38 wherein said partial reflector means has an absorbing block coupled thereto for absorbing the ultrasonic waves passing through said partial reflector means.
40. The scanner of claim 38 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
41. The scanner of claim 29 further comprising a membrane adapted to transmit said ultrasonic waves to an object to be scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
42. The scanner of claim 30 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
43. The scanner of claim 30 further comprising fluid dis-posed within said housing for conducting said ultrasonic waves reflected from said reflector means, said fluid having an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object.
44. The scanner of claim 30 further comprising attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a layer of absorbing material disposed on preselected surfaces of said scanner and a quarter-wave anti-reflecting layer disposed on said layer of absorbing material.
45. The scanner of claim 30 further comprising a membrane adapted to transmit said ultrasonic waves to an object to be
45. The scanner of claim 30 further comprising a membrane adapted to transmit said ultrasonic waves to an object to be
Claim 45 continued .....
scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
46. An ultrasonic scanner comprising:
a housing;
reflector means positioned within said housing; one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path,and said reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and a membrane adapted to transmit said ultrasonic waves to an object to be scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
a housing;
reflector means positioned within said housing; one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path,and said reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said reflector means and are reflected to converge at a point a preselected distance in front of said reflector means; and a membrane adapted to transmit said ultrasonic waves to an object to be scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
47. The scanner of claim 46 wherein said reflector means is adapted to partially reflect said ultrasonic waves.
48. The scanner of claim 47 wherein said partial reflector means has an absorbing block coupled therto for absorbing the ultrasonic waves passing through said partial reflector means.
49. The scanner of claim 47 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
50. The scanner of claim 46 further comprising attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a layer of absorbing material disposed on preselected surfaces of said scanner and a quarter-wave anti-reflecting layer disposed on said layer of absorbing material.
51. The scanner of claim 46 further comprising fluid dis-posed within said housing for conducting said ultrasonic waves reflected from said reflector means, said fluid having an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object.
52. An ultrasonic scanner comprising;
a housing;
partial reflector means positioned within said housing, said partial reflector means having a backing means coupled thereto, one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said partial reflector means and are partially reflected to converge at a point a preselected distance in front of said reflector means; and
52. An ultrasonic scanner comprising;
a housing;
partial reflector means positioned within said housing, said partial reflector means having a backing means coupled thereto, one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means;
means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said partial reflector means and are partially reflected to converge at a point a preselected distance in front of said reflector means; and
Claim 52 continued .....
attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a fluid having an attenuation coefficient substantially equal to the attenuation coefficient of said backing means.
attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a fluid having an attenuation coefficient substantially equal to the attenuation coefficient of said backing means.
53. The scanner of claim 52 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
54. The scanner of claim 52 wherein said fluid has an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object.
55. The scanner of claim 52 further comprising a membrane adapted to transmit said ultrasonic waves to an object to be scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
56. An ultrasonic scanner comprising:
a housing;
partial reflector means positioned within said housing, said partial reflector means having a reflectivity substantially less than that of a perfect reflector;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means; and means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said
56. An ultrasonic scanner comprising:
a housing;
partial reflector means positioned within said housing, said partial reflector means having a reflectivity substantially less than that of a perfect reflector;
one or more ultrasonic transducer means moveably mounted within said housing and positioned to direct ultrasonic waves toward and across the surface of said reflector means; and means for causing said transducer means to traverse an arcuate path with respect to said reflector means, said reflector means positioned closer to said transducer means than the radial distance defined by said arcuate path, and said
Claim 56 continued .....
reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said partial reflector means and are partially reflected to converge at a point a a preselected distance in front of said reflector means.
reflector means angled with respect to said ultrasonic waves, whereby said ultrasonic waves scan across said partial reflector means and are partially reflected to converge at a point a a preselected distance in front of said reflector means.
57. The scanner of claim 56 further comprising fluid dis-posed within said housing for conducting said ultrasonic waves reflected from said reflector means, said fluid having an acoustic propagation velocity substantially less than the acoustic propagation velocity of an object being scanned by said scanner, whereby a larger scan sector angle is obtained in said object.
58. The scanner of claim 56 further comprising attenuating means for substantially eliminating echo artifacts in said scanner, said attenuating means comprising a layer of absorbing material disposed on preselected surfaces of said scanner and a quarter-wave anti-reflecting layer disposed on said layer of absorbing material.
59. The scanner of claim 56 further comprising a membrane adapted to transmit said ultrasonic waves to an object to be scanned, said membrane comprised of a rigid material and having one or more quarter-wave anti-reflecting layers thereon.
60. The scanner of claim 56 wherein said partial reflector means comprises a layer of non-reflecting material having a plurality of closely spaced metallic strips thereon.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/833,244 US4143554A (en) | 1977-03-14 | 1977-09-14 | Ultrasonic scanner |
| US833,244 | 1986-02-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121500A true CA1121500A (en) | 1982-04-06 |
Family
ID=25263854
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000311265A Expired CA1121500A (en) | 1977-09-14 | 1978-09-13 | Ultrasonic scanner |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5538180A (en) |
| CA (1) | CA1121500A (en) |
| DE (1) | DE2839881B2 (en) |
| GB (1) | GB2010484B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5745832A (en) * | 1980-08-30 | 1982-03-16 | Aloka Co Ltd | Ultrasonic probe for endoscope |
| CA1189936A (en) * | 1981-01-15 | 1985-07-02 | Norman S. Neidell | Navigational systems using phase encoded angular coordinates |
| JPS57192547A (en) * | 1981-05-21 | 1982-11-26 | Olympus Optical Co | Ultrasonic diagnostic apparatus for body cavity |
| GB8317247D0 (en) * | 1983-06-24 | 1983-07-27 | Atomic Energy Authority Uk | Ultrasonic scanning probe |
-
1978
- 1978-09-07 GB GB7835865A patent/GB2010484B/en not_active Expired
- 1978-09-13 CA CA000311265A patent/CA1121500A/en not_active Expired
- 1978-09-13 DE DE19782839881 patent/DE2839881B2/en not_active Ceased
- 1978-09-14 JP JP11322078A patent/JPS5538180A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB2010484A (en) | 1979-06-27 |
| DE2839881A1 (en) | 1979-03-29 |
| GB2010484B (en) | 1982-03-24 |
| JPS5538180A (en) | 1980-03-17 |
| DE2839881B2 (en) | 1980-06-12 |
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