AU2007200872A1 - Doppler Ultrasound - Google Patents

Description

P001 Section 29 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Doppler Ultrasound The following statement is a full description of this invention, including the best method of performing it known to us: DOPPLER

ULTRASOUND

TECH-NICAL

FIELD

00 The invention relates generally to medical monitoring and N- diagnostic procedures and devices, and more particularly to a Doppler ultrasound method and apparatus for monitoring blood flow.

BACKGROUND OF THE nNENTION Doppler ultrasound has been used to measure blood flow velocity for many years. The well-known Doppler shift phenomenon provides that ultrasonic signals reflected from moving targets will have a shift in frequency directly proportional to the target velocity component parallel to the direction of the ultrasound beam. The frequency shift is the same for any object moving at a given velocity, whereas the amplitude of the detected signal is a funiction of the acoustic reflectivity of the moving object reflecting the ultrasound. Pulse Doppler ultrasound systems commonly produce a spectrogram. of the detected return signal frequency velocity) as a function of time in a particular sample volume, with the spectrogram. being used by a physician to determine blood flow characteristics of a patient Some Doppler ultrasound systems also have the capability to detect and characterize emboli flowing in the bloodstream. An example Doppler ultrasound system with embolus detection capability is described in U.S. Patent No. 5,348,015, entitled "Method And Apparatus For Ultrasonically Detecting, Counting, and/or Characterizing Emboli," issued September 20, 1994, to Moehring et al., the disclosure of which is incorporated herein by reference.

Such ultrasound systems are advantageously used both for diagnostic *exams (to determine the presence and significance of vascular disease or dysfunction) and during surgical interventions (to indicate surgical manipulations that produce emboli or alter/interrupt blood flow).

Typically, a user of ultrasound equipment finds it rather difficult to properly orient arnd position an ultrasound transducer or probe on the patient, as well as to select a depth along the ultrasound beam corresponding to the desired location where blood flow is to be monitored. This is particularly true in ultrasound ci applications such as transcranial Doppler imaging (TOD). The blood vessels 00 most commonly observed with TCD are the middle, anterior, and posterior cerebral arteries, and the vertebral and basilar arteries. The Doppler transducer must be positioned so the ultrasound beam passes through the skull via the temporal windows for the cerebral arteries, and via the foramen magnum for the vertebral and basilar arteries. The user of the ultrasound equipment may find it difficult to locate these particular windows or to properly orient the ultrasound probe once the particular window is found.

A complicating factor in locating the ultrasound window is determination of the proper depth at which the desired blood flow is located. Commonly, the user does not know if he is looking in the correct direction at the wrong depth, the wrong direction at the right depth, or whether the ultrasound wiindow is too poor for appreciating blood flow at all. Proper location and orientation of the Doppler ultrasound probe, and the proper setting of depth parameters, is typically by trial and error. Not only does this make the use of Doppler ultrasound equipment quite inconvenient and difficult, it also creates a risk that the desired sample volume may not be properly located, with the corresponding diagnosis then being untenable or potentially improper.

SUMMARY OF THE INVENTION In a first aspect of the present invention, th ere is provided a Doppler ultrasound system for providing blood flow information of a subject the system including: an ultrasound transducer from which ultrasound signals are emitted into the subject along an ultrasound beam axis; an ultrasound receiver detecting echo signals resulting from the ultrasound signals emitted into the subject (1 an analog-to-digital converter (ADC) circuit coupled to the ultrasound Sreceiver to quantize the echo signals received by the ultrasound receiver into digital sample values; Cl a digital signal processor coupled to the ADC circuit for processing the digital sample values to calculate blood flow velocity data and detected Doppler signal power data as functions of time for a plurality of locations along the 0 0 ultrasound beam axis; O a graphical display; and a display controller coupled to the digital signal processor and the graphical display for controlling the graphical display to display blood flow velocity data and detected Doppler signal power data as a graphical image representative of blood flow detected along the ultrasound beam axis as a function of time, the graphical image having a color at each of the locations along the ultrasound beam axis for which data is displayed based on the blood flow velocity data and the color having a color property that varies based on the detected Doppler signal power data.

In a second aspect of the present invention, there is provided a data processing engine for a Doppler ultrasound system having an ultrasound transducer from which ultrasound signals are emitted into the subject along an ultrasound beam axis, an ultrasound receiver detecting echo signals resulting from the ultrasound signals emitted into the subject, and a color graphical display, the data processing engine including: an analog-to-digital converter (ADC) circuit coupled to the ultrasound receiver to quantize the echo signals received by the ultrasound receiver into digital sample values, the digital sample values stored as sample vectors; a digital signal processor coupled to the ADC circuit for processing the digital sample vectors to calculate blood flow data and detected Doppler signal power data as functions of time for a plurality of locations along the ultrasound beam axis; and a display controller coupled to the digital signal processor and the graphical display for controlling the graphical display to display the blood flow data and the detected Doppler signal power data as a graphical image representative of the blood flow detected along the ultrasound beam axis as a Cl function of time, the graphical image having a color at each of the locations for which data is displayed based on the blood flow data and the color having a color property that varies based on the detected Doppler signal power data.

c-i In a third aspect of the present invention, there is provided a method for providing blood flow information of a subject to which the Doppler ultrasound system emitting pulsed ultrasound signals along an ultrasound beam axis and 00 detecting echo signals resulting therefrom, is applied, the method including the steps of for each -pulse of ultrasound, quantizing the detected echo signals to generate a plurality of digital sample values representative of the echo signals; processing digital sample values of the pulses of ultrasound to calculate data representative of blood flow information as a function of time including detected Doppler signal power data for a plurality of locations along the ultrasound beam axis; and displaying the data representative of the blood flow information for the plurality of locations along the ultrasound beam axis as a function of time, the blood flow information displayed as having an associated color at each of the plurality of locations, the associated color having a color property that varies based on the detected Doppler signal power data.

In a fourth aspect of the present invention, there is provided a method for providing blood flow information of a subject to which a Doppler ultrasound system emitting ultrasound signals along an ultrasound beam axis and detecting echo signals resuling therefrom is applied, the method including the steps of: q uantizing the detected echo signals to generate a plurality of digital sample values representative of the echo signals; generating quadrature vectors from the plurality of digital sample values; processing the quadrature vectors to calculate blood flow data and detected Doppler signal power data as functions of time for a plurality of locations along the ultrasound beam axis; and displaying the blood flow data and the detected Doppler signal power data as a graphical image representative of blood flow detected along the ultrasound beam axis as a function of time, the detected blood flow displayed as having a color at each of the locations for which data is displayed based on the blood flow CI data and the color having a color property based on the detected Doppler signal power data.

In fifth aspect of the present invention, there is provided a computerc-i readable medium having computer executable instructions for controlling digital processing circuitry in a Doppler ultrasound system to process detected ultrasound echo signals and provide blood flow information, by: 00 controlling an analog-to-digital converter (ADC) circuit to quantize the detected ultrasound echo signals to generate a plurality of digital sample values representative of the ultrasound echo signal; generating quadrature vectors from the plurality of digital sample values; processing the quadrature vectors to calculate blood flow data as a function of time including detected Doppler signal power data for a plurality of locations along the ultrasound beam axis; and processing the blood flow data for display as a function of time for the plurality of locations along the ultrasound beam axis, the blood flow data displayed as having an associated color at each of the plurality of locations indicative of blood flow velocity and the associated color having a color property based on the detected Doppler signal power data.

In a sixth aspect of the present invention, there is provided a Doppler ultrasound system for processing ultrasound signals along an ultrasound beam axis and for displaying information to a user concerning blood flow, including: an ultrasound transducer operable to detect ultrasound signals and responsively produce corresponding electical signals; a graphical display device; and signal processing circuitry coupled to the transducer and operable to receive the electric signals and determine blood flow characteristics corresponding wit the detected ultrasound signals, the signal processing circuitry further coupled to the graphical display device and operable to process the detected ultrasound signals and provide data to the graphical display to display blood flow information along a time domain for a plurality of locations along the ultrasound beam axis a depiction of detected blood flow having intensity varying as a function of detected Doppler ultrasound amplitude.

3c ci In a seventh aspect of the present invention, there is provided a method in a Doppler ultrasound system for providing information to a user conceming blood l flow, including the steps of: Sdisplaying blood flow information as a function of time for a plurality of locations along an ultrasound beam axis at which blood flow is detected; and N varying display intensity as a function of detected Doppler ultrasound r00 amplitude and detected blood flow velocity at each ofhe locations.

00 amplitude and detected blood flow velocity at each of the locations.

(N

rO BRIEF DESCRIPTON OF THE DRAWINGS C~1 Figure 1 is a graphical diagram depicting a first Doppler ultrasound system display mode in accordance with an embodiment of the invention.

Figure 2 is a graphical diagram depicting velocity and signal power 00 0 5 parameters used in preparation of the display mode of Figure 1.

Figure 3 is a graphical diagram depicting velocity and signal power parameters used in preparation of an alternative embodiment of the display mode N of Figure 1.

Figure 4 shows the alternative embodiment of the display mode of Figure 1 in color.

Figure 5 is a graphical diagram depicting the display mode of Figure 4 and its use to identify the pulmonary artery.

Figure 6 is a graphical diagram depicting a second Doppler ultrasound system display mode in accordance with an embodiment of the invention.

Figure 7 shows two views of the display mode of Figure 6 in color.

Figure 8 is the graphical diagram of the display mode shown in Figure 1, further depicting and distinguishing embolic signals from artifact signals.

Figure 9 is a functional block diagram depicting a Doppler ultrasound system in accordance with an embodiment of the invention.

Figures 10 and 11I are functional block diagrams depicting particular details of pulse Doppler signal processing circuitry included in the Doppler ultrasound system of Figure 9.

Figures 12-16 are process flow charts depicting particular operations performed by the pulse Doppler signal processing circuitry of Figures and 11.

DETAILED DESCRIPTION OF THE INVENTION The following describes a novel method and apparatus for providing Doppler ultrasound information to a user, such as in connection with measuring blood velocities to detect hemodynanhically significant deviations 00 0 5 from normal values, and to assess blood flow for the occurrence of microembolic CI signals. Certain details are set forth to provide a sufficient understanding of the invention. However, it will be clear to one skilled in the art that the invention CI may be practiced without these particular details. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the invention.

Figure 1 is a graphical diagram depicting a first display mode of Doppler ultrasound information in accordance with an embodiment of the invention. I this first display mode, referred to as an Aiming mode 100, two distinct ultrasound displays are provided to the user. A depth-mode display 102 15 depicts, with color, blood flow away from and towards the ultrasound probe at various depths along the ultrasound beam axis (vertical axis) as a function of time (horizontal axis).

The depth-mode display 102 includes colored regions 104 and 106.

Region 104 is generally colored red and depicts blood flow having a velocity component directed towards the probe and in a specific depth range. Region 106 is generally colored blue and depicts blood flow having a velocity component away from the probe and in a specific depth range. The red and blue regions are not of uniform color, with the intensity of red varying as a function of the detected intensity of the return Doppler ultrasound signal. Those skilled in the art will understand that such a display is similar to the conventional color Mmode display, in which variation in red and blue coloration is associated with variation in detected blood flow velocities. However, such M-mode displays have not been used concurrently with a spectrogram and with the specific application of locating blood flow as an input to the spectrogramn, from which diagnostic decisions are made.

The Aiming mode 100 also includes a displayed spectrogram. 108, with Figure 1 depicting a velocity envelope showing the characteristic systolicdiastolic pattern. Like the depth-mode display 102, the spectrogramn 108 includes data points (not shown) within the velocity envelope that are colored in varying intensity as a function of the detected intensity of the return ultrasound signal.

The particular sample volume for which the spectrogram 108 applies is at a depth indicated in the depth-mode display 102 by a depth indicator or pointer 109. In N this way, a user of the ultrasound system can conveniently see and select particular depths at which to measure the spectrogramn 108. The depth-mode display 102 readily and conveniently provides the information concerning the range of appropriate depths at which a meaningflul spectrogramn may be obtained.

As described above, the color intensity of regions 104 and 106 preferably vary as a function of the detected intensity of the return ultrasound signal. Referring to Figure 2, a graphical diagram depicts how such color intensity is determined. In order to avoid display of spurious information, signals that may be intense but low velocity (such as due to tissue motion) are ignored and not displayed in the depth-mode display 102 of Figure 1. This is referred to as clutter filtering and is depicted in Figure 2 as the threshold magnitude clutter cutoff limits for positive and negative velocities. Similarly, low power signals associated with noise are also ignored and not displayed in the depth-mode display 102 of Figure 1. The user can determine the upper power limit for the color intensity mapping by selecting a power range value. Signals above a maximum power are then ignored-another clutter filtering which is especially helpful when monitoring blood flow in the cardiac environment. Those skilled in the art will appreciate that other filtering techniques may be employed to improve the depth-mode display image, including delta modulator or other suitably adapted filtering techniques.

While the currently preferred embodiment of the depth-mode display 102 employs color intensity mapping as a fliniction of signal intensity, and further colored red or blue according to flow directions towards or away from the probe, those skilled in the art will appreciate that color intensity as a function of detected velocity may be employed instead. In such case, and as shown in Figure 3, color intensity varies from the clutter cutoff magnitude to a 00 maimumvelocity magnitude, corresponding with one-half the pulse repetition frequency (PRF). Detected signals having a power below the noise threshold or above the selected upper power limit are ignored. Figure 4 is a color figure that shows the Aiming mode display 100 in which the color intensity of the regions 104 and 106 vary as a function of detected velocity. Both the depth-mode display 102 and the spectrogramn 108 are displayed relative to the same time axis, and the depth-mode display shows variation both in spatial extent and in color intensity with the same periodicity as the heart beat Those skilled in the art will also appreciate that instead of varying color intensity, solely as a function of signal amplitude or solely as a function of velocity, one could advantageously vary color intensity as a function of both signal amplitude and velocity.

The particularly depicted depth-mode display 102 shown in Figure I shows a simplified display of a single, well-defined red region 104 and a single, well-defined blue region 106. Those skilled in the art will appreciate that the number and characteristics of colored regions will vary depending on ultrasound probe placement and orientation. Indeed, a catalogue of characteristic depth-mode displays can be provided to assist the user in determining whether a particularly desired blood vessel has, in fact, been located. Once the user finds the characteristic depth-mode display for the desired blood vessel, the user can then conveniently determine the depth at which to measure the spectrogram, 108.

The Aiming mode 100 enables the user to quickly position the ultrasound probe, such as adjacent to an ultrasound window through the skull so that intracranial blood flow can be detected. Use of colorized representation of signal amplitude is particularly advantageous for this purpose, since a strong signal is indicative of good probe location and orientation. The use of colorized representation of flow velocity may not be as advantageous, except where blood flow velocities vary significantly over blood vessel cross-section. However, when attempting to monitor blood flow near appreciably moving tissue cardiac motion above clutter cutoff velocity), colorized representation of flow velocities may be preferred.

Referring to Figure 5, use of the Aiming mode 100 is shown in connection with identifying a particular blood vessel, such as the pulmonary artery or femoral vein. In this case, a colorized representation of flow velocity is 0 advantageously used in the depth-mode display 102, because of the high variation in blood flow velocities in these particular blood vessels. By observing the temporal variation in the depth-mode display 102, and the corresponding spectrogramn 108, a user can identify optimal location of the pulmonary artery as follows: the depth-mode display of the pulmonary artery will be blue with the same periodicity as the heart beat; (2)the blue region will typically reside between 4 and 9 cm depth; along the time axis, the blue signal will be relatively intense in the middle of systole, corresponding to peak velocity, and the signal will have the largest vertical extent in the depth-mode display, indicating that the user has positioned the probe such that the longest section of the pulmonary artery is aligned coincident with the ultrasound beam during systole. The user can then adjust other parameters, such as gate depth for the displayed spectrogram 108 and clutter filter parameters.

The Aiming mode 100 also indicates to the user where to set the depth of the pulse Doppler sample gate so that the spectrogramn 108 will process Doppler shifts from desired blood flow signals. It is the spectrogram 108 that is of primary clinical interest, allowing the user to observe and measure parameters associated with a particular blood flow and providing information that might suggest hemodynaniically significant deviations in that blood flow. Along with the depth-mode display 102 and the correspondingly selected spectrogram 108, the information displayed to a user also typically includes well-known numerical parameters associated with the spectrogram, such as mean peak systolic velocity, mean end diastolic velocity, pulsatility index, and the relative change in mean peak systolic velocity over time. Those skilled in the art will appreciate that other parameters and displays may also be provided, including data provided by N other monitoring devices, such as EKG- or EEG-related information.

The Aiming mode display 100 of Figure 1 is particularly useful in 00 positioning and orienting the Doppler ultrasound probe, and in first selecting a depth at which to measure the spectrogram 108. Following probe location and CI orientation and range gate selection, the user will typically prefer to have an 0 information display emphasizing the clinically valuable spectrogrm 108.

N Referring to Figure 6, a second display mode is shown that is referred to as a Spectral mode 1 10. In this mode, the spectrogram 108 occupies a larger display area. instead of the full depth-mode display 102, a compressed depth-mode di splay 112 is provided. This compressed depth-mode display 112, on a shortened time scale, provides infornation concerning the depth of the sample volume at which the spectrogram 108 is taken, and the status of the blood flow in that sample volume, towards or away from the probe Thus, the user is continually informed concerning the desired sample volume depth and associated blood flow. This allows for quick understanding and compensation for any changes in the location of the desired sample volume relative to the blood flow, such as due to probe motion. This also allows a user of the ultrasound system to fine tune the sample volume depth even while focusing primary attention on the clinically important spectrogram 108.

Figure 7 shows two different views of the Spectral mode 110 in color. In one view, the selected depth indicated by the pointer 109 in the compressed depth-mode display 112 is not a location at which blood flows, and consequently no there are no blood flow signals in the displayed spectrogram, 108. In the other view, the selected depth indicated by the pointer 109 does coincide with blood flow, and a corresponding spectrogram 108 is displayed. in the particular embodiment shown in Figure 7, the color intensity of the region 104 varies as a function of detected velocity, and shows a characteristic color variation that may be associated with variation in blood velocity across blood Svessel cross-section, a variation with depth in the alignment of the detected blood Sflow relative to the ultrasound beam axis, or both.

Those skilled in the art will appreciate the important advantages 0- provided by the diagnostic information displays shown in Figures 1,4, 6, and 7.

While the displayed spectrogram 108 is not itself new, today's pulse Doppler ultrasound systems that do not have B-mode capability lack a means for successfully and reliably locating and orienting an ultrasound probe and determining an appropriate sample volume depth at which to detect the blood flow of interest. Also, while colorized representation of blood flow directions and speeds or signal amplitude is well known in the art, such as in color M-mode displays, such displays have not been used for the purpose of aiming ultrasound probes or in selecting particular sample volume depths for concurrent spectrogram analysis.

Referring to Figure 8, the simultaneous presentation of the depthmode display 102 and spectrogram 108 can also provide important information for detecting embolic signals and differentiating such signals from non-embolic artifacts. Figure 8 depicts three events: A, B, and C. In event A, the depthmode display 102 shows a particularly high intensity signal having a non-vertical slope-4.e., a high-intensity signal that occurs at different depths at different times. In event A, the signal exists only within the boundary of one of the colored blood flow regions 104 and 106. In the spectrogram 108, a particularly high intensity signal is seen to have different velocities, bounded by the maximum flow velocity, within a short temporal region within the heartbeat cycle. Event A is strong evidence of an embolus passing through a blood flow region near the selected sample volume.

Event B is another likely candidate for an embolus. In this case, the high-intensity signal seen in the depth-mode display 102 is non-vertical, but does not appear exclusively within a range of depths where blood is flowing.

While this signal is strong enough and/or has a long enough back scatter to appear outside the blood flow margin in the depth-mode display 102, the spectrogram display 108 still shows the characteristic high intensity tansient signal associated with an embolus. Event B is also evidence of an embolus, but likely an embolus different in nature from that associated with event A S Although the particular signal characteristics of various emboli have not yet been fully explored in the depth-mode display, the distinction between events A and B is likely that of different embolus types. For example, event A may be associated with a particulate embolus, whereas event B may be associated with a gaseous embolus, with the different acoustic properties of a gas bubble causing the particularly long back scatter signal and the appearance of occurrence outside the demonstrated blood flow margins.

Event C is an artifact, whether associated with probe motion or some other non-embolic event. Event C appears as a vertical line in the depthmode display 102, meaning that a high-intensity signal was detected at all depth locations at precisely the same time-a characteristic associated with probe motion or other artifact. Similarly, the high-intensity signal displayed in the spectrogram display 108 is a vertical line indicating a high-intensity signal detected for a wide range of velocities (including both positive and negative velocities and velocities in excess of the maximum blood flow velocities) at precisely the same time. Event C then is readily characterized as an artifact signal, and not embolic in nature.

Those skilled in the art will appreciate that the simultaneous display of the depth-mode display 102 and the spectrogram 108 provides not only convenient means for locating the desired sample volume, but also provides a particularly useful technique for distinguishing embolic signals from artifact signals, and perhaps even for characterizing different embolic signals. Such embolic detection and characterization is easily observed by the operator, but can also be automatically performed and recorded by the ultrasound apparatus.

Automatic embolus detection is provided by observing activity in two or more sample gates within the blood flow at the same time. The system discriminates between two different detection hypotheses: If the signal is embolic, then it will present itself in multiple Ssample gates over a succession of different times.

00 If the signal is a probe motion artifact, then it will present Sitself in multiple sample gates simultaneously.

O 5 These two hypotheses are mutually exclusive, and events that are declared C embolic are done so after passing the "Basic Identification Criteria of Doppler Microembolic Signals" (see, for example, Stroke, voL 26, p. 1123, 1995) and verifying that successive detection (by time-series analysis or other suitable technique) of the embolic signal in different sample gates is done at different points in time, and that the time delay is consistent with the direction of blood flow. The differentiation of embolic from artifact signals can be further confirmed by also observing activity at one or more sample gates outside the blood flow.

Figure 9 is a functional block diagram that depicts an ultrasound system 150 in accordance with an embodiment of the invention. The ultrasound system 150 produces the various display modes described above in connection with Figures 1-8 on an integrated flat panel display 152 or other desired display format via a display interface connector 154. The signal processing core of the Doppler ultrasound system 150 is a master pulse Doppler circuit 156 and a slave pulse Doppler circuit 158. The Doppler probes 160 are coupled with other system components by a probe switching circuit 162. The probe switching circuit 162 provides both presence-detect functionality and the ability to distinguish between various probes, such as by detecting encoding resistors used in probe cables or by other conventional probe-type detection. By providing both the master and slave pulse Doppler circuits 156 and 158, two separate ultrasound probes 160 may be employed, thereby providing unilateral or bilateral ultrasound sensing capability (such as bilateral transcranial measurement of blood velocity in the basal arteries of the brain). The master and slave pulse Doppler circuits 156 and 158 receive the ultrasound signals detected by the respective probes 160 and perform signal and data processing operations, as will c-i be described in detail below. Data is then transmitted to a general purpose host 00 computer 164 that provides data storage and display. A suitable host computer 0 5 164 is a 200 MHz Pentium processor-based system having display, keyboard, internal hard disk, and external storage controllers, although any of a variety of suitably adapted computer systems may be employed.

The ultrasound system 150 also provides Doppler audio output signals via audio speakers 166, as well as via audio lines 168 for storage or for output via an alternative medium. The ultrasound system 150 also includes a microphone 170 for receipt of audible information input by the user. This information can then be output for external storage or playback via a voice line 172. The user interfaces with the ultrasound system 150 primarily via a keyboard or other remote input control unit 174 coupled with the host computer 164.

Figures 10 and 11I depict particular details of the master and slave pulse Doppler circuits 156 and 158. To the extent Figures 10 and 11 depict similar circuit structures and interconnections, these will be described once with identical reference numbers used in both Figures. Figure 10 also depicts details concerning the input and output of audio information to and from the ultrasound system 150 via the microphone 170, the speakers 166, and the audio output lines 168 172, the operations of which are controlled by the master pulse Doppler circuit 156.

At the transducer input/output stage, each of the pulse Doppler circuits 156 and 158 includes a transmit/receive switch circuit 175 operating under control of a timing and control circuit 176 (with the particular timing of operations being controlled by the timing and control circuit 176 of the master pulse Doppler circuit 156). The timing and control circuit 176 also controls operation of a transmit circuit 178 that provides the output drive signal causing the Doppler probes 160 (see Figure 9) to emit ultrasound. The timing and 14 control circuit 176 also controls an analog-to-digital converter circuit 180 coupled to the transmit/receive switch 175 by a receiver circuit 182. The function and operation of circuits 175-182 are well known to those skilled in the 0- art and need not be described further.

The primary signal processing functions of the pulse Doppler circuits 156 and 158 are performed by four digital signal processors PI-P4. P1 is Sat the front end and receives digitized transducer data from the receiver 182 via the analog-to-digital converter circuit 180 and a data buffer circuit or FIFO 186.

P4 is at the back end and performs higher level tasks such as final display preparation. A suitable digital signal processor for P1 is a Texas Instruments TMS320LC549 integer processor, and suitable digital signal processors for P2- P4 are Texas Instruments TMS320C31 floating point processors, although other digital signal processing circuits may be employed to perform substantially the same functions in accordance with the invention.

Received ultrasound signals are first processed by the digital signal processor P1 and then passed through the signal processing pipeline of the digital signal processors P2, P3, and P4. As described in detail below, the digital signal processor P1 constructs quadrature vectors from the received digital data, performs filtering operations, and outputs Doppler shift signals associated with 64 different range gate positions. The digital signal processor P2 performs clutter cancellation at all gate depths. The digital signal processor P3 performs a variety of calculations, including autocorrelation, phase, and power calculations.

P3 also provides preparation of the quadrature data for stereo audio output The digital signal processor P4 performs most of the calculations associated with the spectrogram display, including computation of the spectrogram envelope, systole detection, and also prepares final calculations associated with preparation of the Aiming display.

Each of the digital signal processors P -P4 is coupled with the host computer 164 (see Figure 9) via a host bus 187 and control data buffer circuitry, such as corresponding FIFOs 188(1) 188(4). This buffer circuitry allows initialization and program loading Of the digital signal processors PlI-P4, as well as other operational communicationls between the digital signal processors PlI-P4 and the host computer. Each of the digital signal processors P2-P4 is coupled 00 with an associated high-speed memory or SRAM 190(2) 190(4), which function S 5 as program and data memories for the associated signal processors. In the particularly depicted signal processing chain of Figure 10 or 11, the digital signal procssorP1 has sufficient internal mnemory, and no external program and data memory need be provided. Transmission of data from one digital signal processor to the next is provided by intervening data buffer or FIFO, circuitry 192(2) 192(4). The ultrasound data processed by the digital signal processor P4 is provided to the host computer 164 via data buffer circuitry such as a dual port SRAM 194.

Referring to Figure 10, the digital signal processor P4 of the master pulse Doppler circuit 156 also processes audio input via the microphone 170, as well as controlling provision of the audio output signals to the speakers 166 and audio output lines 168, 172. P4 controls the audio output signals by controlling operations of an audio control circuit 196, which receives audio signals from both the master and the slave pulse Doppler circuits 156 and 158.

Referrng to process flow charts shown in Figures 12-16, a detailed description will now be provided of the operations performed by of each of the digital signal processors Pl-P4 included in both the master and slave pulse Doppler circuits 156 and 158. Particular detailed calculations and numerical infornation are provided to disclose a current embodiment of the invention, but those skilled in the art will appreciate that these details are exemplary and need not be included in other embodiments of the invention.

Referring to Figure 12, the operations of digital signal processor P1I are as follows: 1. DIGITIZATION OF RAW DATA. Read a series of N 14-bit values from the input AID. The values are converted at 4X the Doppler o 16 I q L carrier frequency (8MHz), and commence synchronously with the start of (the transmit burst. N=1000 if the Doppler pulse repetition frequency (PRF) is 8kHz, 1280 if the Doppler PRF is 6.25kHz, and 1600 if the rDoppler PRF is 00 2. QUADRATURE VECTOR CONSTRUCTION. Construct two vectors Swith N/4 points each according to the following rules: and N Br and Bi are the digitally demodulated quadrature Doppler values for a series of N/4 different gate depths. The subtractions here remove DC bias from the data.

3. LOW-PASS FILTER COEFFICIENTS. Br and Bi contain frequencies up to carrier/4, and need to be further filtered to remove noise outside the bandwidth of the Doppler transmit burst. The coefficients for accomplishing this low-pass filtering are determined by a creating, with standard digital filter design software such as MATLAB, an order 21 lowpass FIR filter. The normalized cutoff of this filter is where T is the time duration of the transmit burst, and fs is the sample rate of the data in Br and Bi (2MHz). Call this filter C(l:21). The coefficients of this filter will vary as the transmit burst length is changed by the user, and a bank of several different sets of filter coefficients is accordingly stored to memory.

4. INDEX ARRAYS. Data from 64 range gate positions are to be processed and passed onto P2. For ease of graphical display, these range gate positions are selected to be 1mm apart. However, the quadrature vectors Br and Bi do not contain elements that are spaced 1mm apart-they are .385mm apart. Therefore, indices into the Br and Bi arrays are used that correspond to values falling closest to multiples of 1mm, as a means to decimating Br and Bi to 1mm sampling increments. This is done by having a prestored array of indices, Dl(l:64), corresponding to depths 29:92mm for 8kHz PRF, and indices D2(1:64) and D3(1:64) with corresponding or deeper depth ranges for 6.25kHz and 5kHz PRFs.

LOW-PASS FILTER AND DECIMATION OF QUADRATURE

DATA.

The Br and Bi arrays are low-pass filtered and decimated to 64 gates by the following rules (note is the 32 bit accumulated integer dot product of vectors a and b): 8kHz PRF: Erj)

C,

Ei(j)

C,

6.25kHz PRF: ErO) C, Ei(j)

C,

PRF:

Erj)

C,

Ei(j)

C,

Bi( D1(j0)+-10:10) and j=1:64.

Br( D20)+(-10:10))> Bi( D20)+(-10: 10) and j=1:64.

Br( D3 Bi( D30)+(-10:10) and j=1:64.

6. PASS RESULTS TO P2. Er and Ei, 128 values altogether, comprise the Doppler shift data for 1 pulse repetition period, over a set of 64 different sample gates spaced approximately Imm apart. These arrays are passed to P2 with each new transmit burst.

Referring to Figure 13, the operations of digital signal processor P2 are as follows: 1. ACCUMULATE INPUT DATA. Collect a buffer of M Er and Ei vectors from P1 over a period of 8ms, into floating point matrices Fr and Fi. At the PRFs of [8,6.25,5]kHz, the matrices Fr and Fi will each contain respectively M=[64,50,40] vectors. The jth Er and Ei vectors at their respective destinations are denoted by Fr(l:64j) and Fi(1:64j) (these are column vectors). The kth gate depth across the M collected vectors is indexed by Fr(k, I:M) and Fi(k, 1:M) (these are row vectors).

2. PRESERVATION OF RAW DATA AT "CHOSEN" GATE DEPTH.

N

Reserve in separate buffer the raw data at the user-chosen gate depth, k, at which the Doppler spectrogram is processed. This row vector data, Gr(l:M)=Fr(k,l:M) and Gi(1:M)=Fi(k,I:M), is passed forward to P3 and 00 O 5 eventually to the host for recording purposes.

S3. CLUTTER CANCELLATION. Apply a fourth order clutter cancellation Sfilter to each row of Ft and Fi. Hr(l:64,1:M) and Hi(l:64,1:M) are the destination matrices of the filtered Fr(l:64,1:M) and Fi(l:64,1:M) data.

Application of this filter with continuity requires maintaining state variables and some previous Fr and Fi values. The coefficients of the clutter filter will vary depending on the user choice of [Low Boost, 100Hz, 200Hz, 300Hz, and High Boost]. These coefficients are available by table lookup in processor RAM, given the user choice from the above options.

4. PASS RESULTS TO P3.

Gr, Gi, Hr and Hi are passed to P3 for further processing.

Referring to Figure 14, the operations of digital signal processor P3 are as follows: 1. ACCUMULATE INPUT DATA. Receive Gr, Gi, Hr and Hi from P2.

2. COMPUTE AUTOCORRELATION. Compute the first lag of the autocorrelation of the data at each gate over time. Use all M values at each gate in this calculation. This will generate an array of 64 complex values, one for each gate. For the kth gate depth, let P=Hr(k, :M)+jHi(k, Then the first lag autocorrelation for this depth is AC(k) (Note that in a dot product of complex values, the second vector is conjugated. Also note that this and all dot products in P2, P3, or P4 are floating point calculations.) In this manner, construct the complex vector AC(1:64).

3. COMPUTE PHASE FOR EACH AC VALUE. For each autocorrelation value, us a four quadrant arctangent lookup to determine the phase of the complex value. Specifically, ANGLE(k) arctan( imag( AC(k) real( AC(k) The ANGLE(k) value is proportional to the mean flow 00 0 5 velocity at the gate depth k.

S4. If embolus characterization distinguishing a particle from a bubble) O capability is enabled, the method routes to a subroutine described below C in connection with Figure 16.

COMPUTE POWER. Compute the signal power. Use all M values at each gate in this calculation. This will generate an array of 64 real values, one for each gate. For the kth gate depth, again let P=Hr(k,l:M)+jHi(k,l:M). Then the power for this depth is POWER(k) (note that in a dot product of complex values, the second vector is conjugated). In this manner, construct the real vector POWER(1:64).

6. LOG COMPRESS POWER. Convert POWER to Decibels: POWERd(1:64) 10*log I 0(POWER(1:64)).

7. COMPUTE POWER TRACES FOR EMBOLUS DETECTION. For each of four preset gate depths (one being the user selected depth and the other three being correspondingly calculated), compute power from a 60 point moving window at M different positions of the window. Note that some history of the data at the specific gate depths will be required to maintain this calculation without interruption from new data spilling in every 8ms.

Specifically, for gate n, POWER_TRACEn(i) <Hr(ni-59:i) jHi(n,i- 59:i), Hr(n,i-59:i) jHi(n,i-59:i)>. Note 3 power traces are taken from the region including the sample volume placed inside blood flow, while the fourth power trace is taken from a sample volume well outside the blood flow.

8. COMPLEX BANDPASS FILTER FOR USE IN AUDIO OUTPUT PREPARATION. The min and max frequencies resulting from user specified spectral unwrapping of the spectrogram are used to determine a

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complex bandpass filter for making the audio output sound congruent with what is shown on the spectrogram display. For example, if the unwrapping occurs at [-1,7]kHz, then the audio complex bandpass filter has edges at -1kHz and +7kHz. A bank of several sets of complex Sbandpass filter coefficients, corresponding to different unwrap ranges, is generated offline and placed in memory. Each coefficient set corresponds N to one of the unwrapping selections the user can make. Let the operative set of filter coefficients be called UWa(l:O) and UWb(l:O), where O is the filter order plus one.

9. AUDIO OUTPUT PREPARATION: RESAMPLE. At the gate depth selected by the user, k, the Doppler shift signals are to be played out the audio speakers. Before doing so, some prepping of the audio signals is important to match the user-selected spectral unwrapping. Resample the audio signal Hr(k, and Hi(k, to twice the PRF by multiplexing the respective arrays with zeros: Qr(k,1:2M)={Hr(k,l), 0, Hr(k,2), 0, Hr(k,3), 0, Hr(k,M), 0} and Qi(k,l:2M)={Hi(k,l), 0, Hi(k,2), 0, Hi(k,3), 0, Hi(k,M), 0}.

AUDIO OUTPUT PREPARATION: COMPLEX BANDPASS. Apply a complex bandpass filter to Qr+jQi in order to remove the extra images introduced by multiplexing the data with zeros: R(n) where Q(k) Qr(k)+jQi(k).

11. AUDIO OUTPUT PREPARATION: HILBERT TRANSFORM. The audio data in the sequence R(n) is in quadrature format and needs to be converted into stereo left and right for playing to the operator. This is done with a Hilbert transform, and a 95 point transform, H(l:95), is used in this work-the coefficients can be obtained with formulas in the literature or standard signal processing software such as MATLAB. The 0 21

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C application of the Hilbert transform to a data sequence is done as an FIR Sfilter. Construction of stereo separated signals RL and RR from R(n) is done according to [RL Hilbert(Rr) Delay(Ri), RR Hilbert(Rr) E- Delay(Ri)] where Delay is a (Nh+l)/2 step delay of the imaginary O 5 component of R, and Nh is the size of the Hilbert filter S12. Pass Gr, Gi, ANGLE, POWERd, POWER_TRACE1, POWER_TRACE2, SPOWER TRACE3, POWER_TRACE4, Rr, Ri, RL and RR to P4 for C further processing.

Referring to Figure 15, the operations of digital signal processor P4 are as follows: 1. ACCUMULATE INPUT DATA. Receive Gr, Gi, ANGLE, POWERd, POWER_TRACE1, POWER_TRACE2, POWER_TRACE3, POWERTRACE4, Rr, Ri, RL and RR from P3.

2. CALCULATE SPECTROGRAM. Compute power spectrum via the following steps: a) Concatenate new points in the Rr+jRi sequence with old points such that there are 128 points altogether, b) Multiply the 128 point sequence against a 128 point Hanning window, c) Calculate P, the FFT of the 128 point sequence, d) Calculate Pd 10*loglO(P), and e) FFTSHIFT the Pd sequence such that DC is at its center.

3. ENVELOPE. Compute the maximum frequency follower or "envelope" function, which indicates the upper edge of the flow signals in the spectrogram. This is an integer between 0 and 63, and is indexed by FFT calculation-i.e., for every spectral line calculation there is one value of E. Those skilled in the art will know of a variety of algorithms for making this calculation.

4. SYSTOLE DETECTION. Based on the maximum frequency follower, detect the start of systole. When the systolic start has been determined, set SYSTOLEFLAG=TRUE. Also calculate the end diastolic velocity r-- N 22 value, VEND, the peak systolic velocity value, VPEAK, and the mean Svelocity, VMEAN.

AIMING DISPLAY PREPARATION. Prepare the Aiming display via the following steps: a) Subtract the value of the "aim noise" parameter set by 00 the user from the POWERd array: POWERd2=POWERd-aim_noise, b) l multiply POWERd2 by a factor which is 64 (the number of color shades) Sdivided by the value of the "aim range" parameter set by the user- C' POWERd3=POWERd2*64/aim_range, c) clip the resulting power data at 0 on the low end and 63 on the high end-the values now correspond to entries in a 64-value red or blue color table, and place results in array POWERd4, and d) multiply each of the power values by 1, 0 or -1, depending respectively on whether the associated ANGLE value is greater than the "filter cutoff parameter", less in absolute value than the filter cutoff parameter, or less than the negative of the filter cutoff parameter.

This results in 64 values (one per gate depth) in the range of This modified aiming array, POWERd5, is ready to display after sending to the host computer.

6. SPECTROGRAM DISPLAY PREPARATION. Prepare the spectrogram display via the following steps: a) Subtract the user-selected noise floor parameter from the array Pd-Pd2=Pd-spectral_noise, b) Rescale the spectral data to contain 256 colors across the user-specified dynamic range-Pd3=Pd2*256/spectral_range, c) truncate/clip the data to be integer valued from 0 to 255-Pd4=min(255,floor(Pd3)), d) truncate the data to 8 bits-Pd5=8 bit tuncate(Pd4).

7. AUDIO OUTPUT. Send the arrays RR and RL, the right and left speaker audio outputs, to the speakers via port writes.

8. INPUT MICROPHONE. Sample M values into vector MIC from the input microphone port (M is of transmit pulse repetitions within an 8ms period).

9. EMBOLUS DETECTION: BACKGROUND POWER IN POWER c N TRACES. For each of the four power traces, POWER_TRACE1..POWER_TRACE4, corresponding to the four preset gate depths, compute a background power level. Recall that 00 POWERTRACEn contains M values, where M is of transmit pulse N repetitions within an 8ms period). The background power value is 0 obtained by a delta-follower for each trace, and is denoted by 81, 82, 83, (C and d 84.

81new=81old+A, where A=sign(81old-mean(POWER_TRACE1)) 0. dB.

82new=82old+A, where A=sign(82old-mean(POWER_TRACE2)) 0.ldB.

63new=63old+A, where A=sign(83old-mean(POWER_TRACE3)) 0.ldB.

54new=84old+A, where A=sign(B4old-mean(POWER_TRACE4)) 0.1dB.

This update in the background values is done once every M power values, or every 8ms.

EMBOLUS DETECTION: PARABOLIC FIT. Apply a parabolic fit algorithm to the power trace each gate and determine if an event is occurring during the 8ms period. This fit must be applied to successive data windows spaced apart by at most 1ms. If the parabolic fit is concave down, and has a peak that exceeds the background power for the gate depth by 6 dB (an arbitrary threshold), then an event is detected.

11. EMBOLUS DETECTION: TIME DETERMINATION. For any singlegate events, compute the exact time of the event by analyzing the power trace between the -6dB points on either side of the peak power of the event. Record event results and times so that current events may be compared to past ones.

12. EMBOLUS DETECTION: HIGH LEVEL CALCULATION. If the following conditions are true, then set DETECTION=TRUE: a) at least two adjacent of three gates in vicinity of blood flow show events within a 40ms time window, b) the gate outside the blood flow shows no detection, and c) the timing of events shows progression in the direction of blood flow the embolus is not swimming upstream).

S13. Pass Gr, Gi, POWERdS, Pd5, SYSTOLE_FLAG, VEND, VMEAN, VPEAK, MIC and DETECTION to host for further processing.

SReferring to Figure 16, the embolus characterization subroutine CIl operations of digital signal processor P3 are as follows: 4A. CALCULATE MATRIX ELEMENT MAGNITUDES of Hr jHi: Hmag(1:64,1:M) 10*logl0(Hr.^2 Hi^.2).

4B. CALCULATE REFERENCE BACKGROUND POWER LEVEL Pb.

Hmean sum( sum(Hmag(l:64,1:M) IF PbOLD>Hmean THEN Pb=PbOLD-0.1dB, ELSE Pb=PbOLD+0.1dB. (This is a delta follower of the background power level).

4C. DETERMINATION OF R1 and R2, constants to be used in characterization. Tl--transmit burst length in microseconds. T2=pulse repetition period, in microseconds. We know a priori that elements of Hk(l:64) are attached to 1mm increments in depth. Then Rl=axial resolution in mm=c*T1/2, where c=1.54mm/microsecond, and R2=2*R1.

For example, a 20 cycle transmit burst at 2MHz carrier frequency has R1=7.2mm, where R2=14.4mm.

4D. DETECT EMBOLUS SIGNATURE by examining each column of Hmag(1:64,1:M) and determining longest contiguous segment of data such that each element in the contiguous segment is greater than Pb+XdB More specifically, let Hk(1:64)=Hmag(l:64,k). Locate longest sequence within Hk, demarcated by starting and ending indices Hk(il:i2), such that Hk(i)>Pb+X if il<-i<-i2. The length of this sequence is then determined by fitting the first three points of Hk(il:i2) with a parabola, and finding the left most point on the abscissa, zl, where the parabola crosses the ordinate of Pb. If the parabola does not intersect the line y=Pb, then zl=il. Similarly, the last three points of Hk(ilU2) are N fitted with a parabola and z2 is located. If the parabola does not intersect the line y=Pb, then z2i2U. The length of Hlk(il:i2) is z2-zl. IF z2-zl<Rl, then no embolus; is present If Rl<,z2-zl<R2, then a particulate is present 00 0 5 If z2-zl>R2, then a bubble is present Nl 4E. Pass this information along to P4. If P4 agrees that an embolus is being 0 detected, then attach the characterization information.

Those skilled in the art will appreciate that the invention may be accomplished with circuits other than those particularly depicted and described in connection with Figures 9-11. These figures represent just one of many possible implementations of a Doppler ultrasound system in accordance with the invention. Likewise, the invention may be accomplished using process steps other than those particularly depicted and described in connection with Figure 12-16.

Those skilled in the art will also understand that each of the circuits whose functions and interconnections are described in connection with Figures 9-11 is of a type known in the art. Therefore, one skilled in the art will be readily able to adapt such circuits in the described combination to practice the invention. Particular details of these circuits are not critical to the invention, and a detailed description of the internal circuit operation need not be provided, Similarly, each one of the process steps described in connection with Figures 12- 16 will be understood by those skilled in the art, and may itself be a sequence of operations that need not be described in detail in order for one skilled in the art to practice the invention.

It will be appreciated that, although specific embodiments of the invention have been described for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. For example, a user interface in accordance with the present invention may be provided by means other thm a video display, such as a printer or other visual 26

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N, display device. Those skilled in the art will also appreciate that many of the advantages associated with these circuits and processes described above may l be provided by other circuit configurations and processes. Accordingly, the invention is not limited by the particular disclosure above, but instead the scope of the invention is determined by the following claims.

Cl Comprises/comprising and grammatical variations thereof when used in 00 this specification are to be taken to specify the presence of stated features, 0integers, steps or components or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims (37)

1. A Doppler ultrasound system, including: an ultrasound transducer from which ultrasound signals are emitted into the subject along an ultrasound beam axis; an ultrasound receiver detecting echo signals resulting from the ultrasound oO 00 O signals emitted into the subject; an analog-to-digital converter (ADC) circuit coupled to the ultrasound Sreceiver to quantize the echo signals received by the ultrasound receiver into S 10 digital sample values; and a processor coupled to the ADC circuit for processing the digital sample values to calculate blood flow velocity data as functions of time for a plurality of locations along the ultrasound beam axis, the processor further operable to generate data from the blood flow velocity data that is representative of blood flow velocity detected along the ultrasound beam axis as a function of time and having a component associated with blood flow velocity at each of the locations along the ultrasound beam axis for which data is generated.

2. The system of claim 1 wherein the processor includes a processor calculating detected Doppler signal power data as a function of time for a plurality of locations along the ultrasound beam axis and the processor is further operable to generate data that varies the blood flow velocity component based on the detected Doppler signal power data.

3. The system of claim 1 wherein the processor includes: first processing circuitry for processing the digital sample values to calculate data representative of quadrature vectors, each quadrature vector having a first vector component and a second vector component; digital filter circuitry coupled to the first processing circuitry for processing the data representative of the quadrature vectors to provide filtered quadrature vector data, the filtered quadrature vector data representative of the quadrature vectors having noise from outside a bandwidth of interest removed; Sclutter removal circuitry coupled to the digital filter circuitry for processing the filtered quadrature vector data to provide clutter cancelled vector data, the Sclutter cancelled vector data representative of the filtered quadrature vector data having contribution from stationary reflectors removed; and second processing circuitry coupled to the clutter removal circuitry for N processing the clutter cancelled vector data to provide the blood flow velocity data o- as a function of time for the plurality of locations along the ultrasound beam axis. 00 c 4. The system of claim 3 wherein the second processing circuitry coupled to the clutter removal circuitry further processes the clutter cancelled vector data to C provide detected Doppler signal power data as a function of time for the plurality of locations along the ultrasound beam axis. The system of claim 4 wherein the first and second vector components includes a real vector component and an imaginary vector component, respectively.

6. The system of claim 1 wherein a first blood flow velocity component is representative of blood flow in a first direction, and a second blood flow velocity component is representative of blood flow in a second direction.

7. The system of claim 1 wherein the processor coupled to the ADC is further operable to generate data indicating blood flow velocities as a function of time for a selected location along the ultrasound beam axis.

8. A data processing engine for a Doppler ultrasound system having an ultrasound transducer from which ultrasound signals are emitted into the subject along an ultrasound beam axis and an ultrasound receiver detecting echo signals resulting from the ultrasound signals emitted into the subject, the data processing engine including: an analog-to-digital converter (ADC) circuit coupled to the ultrasound receiver to quantize the echo signals received by the ultrasound receiver into digital sample values, the digital sample values stored as sample vectors; and Sa processor coupled to the ADC circuit for processing the digital sample vectors to calculate blood flow data as a function of time for a plurality of locations along the ultrasound beam axis, the processor further operable to generate data from the blood flow data that is representative of the blood flow velocity detected along the ultrasound beam axis as a function of time and has a component associated with blood flow velocity at each of the locations for which data is 0 generated.

9. The data processing engine of claim 8 wherein the processor includes a processor for processing the digital sample vectors to calculate detected Doppler N signal power data as a function of time for a plurality of locations along the ultrasound beam axis, and further operable to generate data to vary the component based on the detected Doppler signal power data. The data processing engine of claim 8 wherein processing the digital sample vectors by the digital signal processor to calculate blood flow data includes calculating a mean blood flow velocity for the plurality of locations along the ultrasound beam axis and the display controller generates data to display a color at each of the locations for which data is displayed that is representative of the direction of blood flow.

11. The data processing engine of claim 8 wherein the digital signal processor includes: first processing circuitry for processing the sample vectors to calculate data representative of quadrature vectors; digital filter circuitry coupled to the first processing circuitry for processing the data representative of the quadrature vectors to provide filtered quadrature vector data, the filtered quadrature vector data representative of the quadrature vectors having noise from outside a bandwidth of interest removed; clutter removal circuitry coupled to the digital filter circuitry for processing the filtered quadrature vector data to provide clutter cancelled vector data, the clutter cancelled vector data representative of the filtered quadrature vector data having contribution from stationary reflectors removed; and V second processing circuitry coupled to the clutter removal circuitry for processing the clutter cancelled vector data to provide the blood flow velocity data.

12. The system of claim 3 wherein the second processing circuitry coupled to the clutter removal circuitry further processes the clutter cancelled vector data to r- provide detected Doppler signal power data as a function of time for the plurality 00 Sof locations along the ultrasound beam axis.

13. The data processing engine of claim 12 wherein the first processing (circuitry includes processing circuitry for calculating data representative of quadrature vectors, each quadrature vector having a first vector component and a second vector component.

14. The data processing engine of claim 13 wherein the first and second vector components includes a real vector component and an imaginary vector component. The data processing engine of claim 8 wherein the processor further generates data indicating blood flow velocities as a function of time for a selected location along the ultrasound beam axis.

16. In a Doppler ultrasound system emitting pulsed ultrasound signals along an ultrasound beam axis and detecting echo signals resulting therefrom, a method for generating blood flow information of a subject to which the Doppler ultrasound system is applied, the method including: for each pulse of ultrasound, quantizing the detected echo signals to generate a plurality of digital sample values representative of the echo signals; and processing digital sample values of the pulses of ultrasound to calculate data representative of blood flow information that is representative of blood flow velocity detected along the ultrasound beam axis as a function of time and having a component associated with blood flow velocity at each of the plurality of locations along the ultrasound beam axis.

17. The method of claim 16, further including generating detected Doppler signal power data for a plurality of locations along the ultrasound beam axis and Sgenerating data that is representative of varying the component based on the detected Doppler signal power data.

18. The method of claim 16, further including calculating filter coefficients based on the rate at which the detected echo signals are quantized and wherein 00oO processing the digital sample values includes: N generating a quadrature vector from the plurality of digital sample values of each pulse of ultrasound; processing each quadrature vector using the filter coefficients to calculate filtered quadrature vector data representative of the quadrature vector having noise from outside a bandwidth of interest removed; and calculating from a plurality of quadrature vectors clutter cancelled vector data representative of the filtered quadrature vectors having contribution from stationary reflectors removed from the filtered quadrature vectors; and

19. The method of claim 18, further including calculating detected Doppler signal power for the plurality of locations along an ultrasound beam axis from the clutter cancelled vector data. The method of claim 18 wherein quantizing includes quantizing the detected echo signals at four times the frequency of the emitted ultrasound signals.

21. The method of claim 20 wherein generating quadrature vectors from the plurality of digital sample values of each pulse of ultrasound includes: dividing the sample values into sets of four values, each set having first, second, third and fourth values; and for each set, subtracting the third from the first values to generate a real vector component of the quadrature vector and subtracting the fourth from the second values to generate an imaginary vector component of the quadrature vector.

22. The method of claim 16 wherein processing the digital sample values to N calculate data representative of blood flow information further includes calculating Smean blood flow velocity data as a function of time for locations along the ultrasound beam axis.

23. The method of claim 22 wherein generating data to display the blood flow information for the plurality of locations along the ultrasound beam axis includes 00oo generating data corresponding to blood flow detected as having a blood flow N' velocity exceeding a velocity threshold.

24. The method of claim 23 wherein the velocity threshold is user programmable. The method of claim 16 wherein generating data to display the blood flow information for the plurality of locations along the ultrasound beam axis includes generating data to display color regions corresponding with the locations at which blood flow is detected having a detected Doppler signal power exceeding a power threshold.

26. The method of claim 25 wherein the power threshold is user programmable.

27. The method of claim 16, further including generating data to representing spectral graphical information indicating blood flow velocities at the selected one of the displayed locations. 26. The method of claim 16, further including generating data to display locations along the ultrasound beam axis at which blood flow is not detected.

29. In a Doppler ultrasound system emitting ultrasound signals along an ultrasound beam axis and detecting echo signals resulting therefrom, a method for providing blood flow information of a subject to which the Doppler ultrasound system is applied, the method including: Squantizing the detected echo signals to generate a plurality of digital sample values representative of the echo signals; generating quadrature vectors from the plurality of digital sample values; processing the quadrature vectors to calculate blood flow data as a function of time for a plurality of locations along the ultrasound beam axis; and generating data from the blood flow data that is representative of blood oOC flow detected along the ultrasound beam axis as a function of time, the data having a component associated with blood flow velocity at each of the locations Sfor which data is generated. C 30. The method of claim 29, further including processing the quadrature vectors to calculate detected Doppler signal power data as a function of time for the plurality of locations along the ultrasound beam axis, and generating data from the detected Doppler signal power data representative of varying the blood flow velocity component based on the detected Doppler signal power data.

31. The method of claim 29 wherein quantizing includes quantizing the detected echo signals at four times the frequency of the emitted ultrasound signals.

32. The method of claim 31 wherein generating quadrature vectors from the plurality of digital sample values includes: dividing the sample values into sets of four values, each set having first, second, third and fourth values; and for each set, subtracting the third from the first values to generate a real vector component of the quadrature vector and subtracting the fourth from the second values to generate an imaginary vector component of the quadrature vector.

33. The method of claim 29, further including calculating filter coefficients based on the rate at which the detected echo signals are quantized, and wherein processing the quadrature vectors to calculate blood flow data includes: Sprocessing each quadrature vector using the filter coefficients to calculate filtered quadrature vector data representative of the quadrature vector having noise from outside a bandwidth of interest removed; calculating from the data for a plurality of quadrature vectors clutter cancelled vector data representative of the filtered quadrature vectors having Scontribution from stationary reflectors removed from the filtered quadrature oC- vectors; and 00

34. The method of claim 33, further including calculating detected Doppler signal power for each of the first plurality of locations along an ultrasound beam Saxis from the clutter cancelled vector data. The method of claim 29, further including processing the quadrature vectors to calculate a mean velocity for each of the plurality of locations along the ultrasound beam axis.

36. The method of claim 29, further including generating data representing spectral graphical information indicating blood flow velocities at the selected one of the displayed locations.

37. A computer-readable medium having computer executable instructions for controlling digital processing circuitry in a Doppler ultrasound system to process detected ultrasound echo signals and provide blood flow information, by: controlling an analog-to-digital converter (ADC) circuit to quantize the detected ultrasound echo signals to generate a plurality of digital sample values representative of the ultrasound echo signal; generating quadrature vectors from the plurality of digital sample values; processing the quadrature vectors to calculate blood flow data as a function of time for a plurality of locations along the ultrasound beam axis; and processing the blood flow data to generate data that is representative of blood flow velocity as a function of time detected for the plurality of locations along the ultrasound beam axis, the blood flow data having a component at each of the plurality of locations indicative of blood flow velocity.

38. The computer readable medium of claim 37 wherein the computer executable instructions for processing the blood flow data includes processing the quadrature vectors to calculate detected Doppler signal power data for the plurality of locations along the ultrasound beam axis and processing the blood flow data to generate data representing varying the component based on the detected Doppler signal power data. 00oO

39. The computer readable medium of claim 37 wherein the computer executable instructions for controlling the ADC circuit includes computer executable instructions for controlling the ADC circuit to quantize the detected N echo signals at four times the frequency of the emitted ultrasound signals. The computer readable medium of claim 39 wherein the computer executable instructions for generating quadrature vectors from the plurality of digital sample values includes computer executable instructions for: dividing the sample values into sets of four values, each set having first, second, third and fourth values; and for each set, subtracting the third from the first values to generate a real vector component of the quadrature vector and subtracting the fourth from the second values to generate an imaginary vector component of the quadrature vector.

41. The computer readable medium of claim 37, further including computer executable instructions for calculating filter coefficients based on the rate at which the detected echo signals are quantized, and wherein the computer executable instructions for processing the quadrature vectors to calculate blood flow data includes computer executable instructions for. processing the quadrature vectors using the filter coefficients to calculate filtered quadrature vector data representative of the quadrature vectors having noise from outside a bandwidth of interest removed; and calculating clutter cancelled vector data representative of the filtered quadrature vector data having contribution from stationary reflectors removed from the filtered quadrature vector data.

42. The computer readable medium of claim 41, further including computer executable instructions for calculating the detected Doppler signal power as a J function of time for the plurality of locations along an ultrasound beam axis from the clutter cancelled vector data.

43. The computer readable medium of claim 37, further including computer executable instructions for processing the quadrature vectors to calculate a mean 00 velocity for the plurality of locations along the ultrasound beam axis.

44. The computer readable medium of claim 37, further including computer C executable instructions for processing the blood flow data to display spectral graphical information indicating blood flow velocities at the selected one of the displayed locations. The computer readable medium of claim 37, further including computer executable instructions for processing the blood flow data to display locations along the ultrasound beam axis at which blood flow is not detected.

46. The computer readable medium of claim 37 wherein the computer executable instructions for processing the blood flow data for display includes computer executable instructions for processing the blood flow data to generate data representative of blood flow in a first direction and generate data representative of blood flow in a second direction.

47. The computer readable medium of claim 37 wherein the computer executable instructions for processing the blood flow data for display includes computer executable instructions for processing the blood flow data to generate data corresponding with the locations at which blood flow having a blood flow velocity exceeding a velocity threshold.

48. The computer readable medium of claim 37 wherein the computer executable instructions for processing the blood flow data for display includes computer executable instructions for processing the blood flow data to generate 37 O O data corresponding with the locations at which blood flow is detected having (N e detected Doppler signal power exceeding a power threshold. WATERMARK PATENT TRADE MARK ATTORNEYS 00