JP2009261456A - X-ray ct device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT device which does not cost much, simplifies an X-ray detection structure, and obtains two or more kinds of reconfiguration images different in X-ray energy at the same cross section position. <P>SOLUTION: The X-ray CT device 1 is provided with: an X-ray radiator 3c for radiating X-ray to an examinee M; an X-ray detector 3e in which a plurality of scintillators for emitting fluorescence by incidence of the X-ray are arranged in a grid shape, which has a scintillator block where two different kinds of scintillator columns different in X-ray energy characteristic are arranged in four rows or more by turns, and detects X-ray transmitting the examinee M; a data collection part 3f for collecting X-rays detected by the X-ray detector 3e as X-ray transmission data; and an image reconfiguration part which sorts X-ray transmission data into two kinds or more energy data different in X-ray energy and reconfigures two kinds or more tomographic images differing in X-ray energy by matching positions in the body axis direction of the examinee. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus.

  An X-ray CT apparatus (X-ray computed tomography apparatus) irradiates a subject such as a patient with an X-ray by an X-ray irradiation apparatus, and detects and detects an X-ray dose transmitted through the object by an X-ray detection apparatus. The apparatus collects X-ray transmission data based on the X-ray dose and performs a reconstruction process on the acquired X-ray transmission data to acquire a cross-sectional image (slice image) of the subject. In this X-ray CT apparatus, for example, a conventional scan for performing imaging while fixing a bed on which a subject sleeps, a helical scan for performing imaging while moving the bed, and the like are performed.

In such an X-ray CT apparatus, an X-ray CT apparatus capable of dual energy measurement that realizes an improvement in density resolution by performing X-ray energy separation has been developed. The X-ray CT apparatus capable of measuring dual energy includes an X-ray CT apparatus having two sets of X-ray irradiation apparatuses and an X-ray detection apparatus, and an X-ray of a two-layer scintillator in which two scintillators having different X-ray energy characteristics are stacked. X-ray CT apparatus provided with a detection apparatus, X-ray CT apparatus provided with an X-ray detection apparatus of a two-row scintillator in which two scintillators having different X-ray energy characteristics are arranged in the body axis direction of the subject (for example, see Patent Document 1) Has been proposed.
JP-A-6-296607

  However, in the X-ray CT apparatus provided with the above-described two sets of X-ray irradiation apparatus and X-ray detection apparatus, two sets of units of the X-ray irradiation apparatus and the X-ray detection apparatus are required, which increases the cost. Further, in the X-ray CT apparatus using the above-described two-layer scintillator, the structure of the X-ray detection apparatus is complicated, and mass production or the like when the scintillators are arranged in multiple rows becomes difficult. In addition, in the X-ray CT apparatus using the above-described two-row scintillator, when two types of reconstructed images having different X-ray energies are obtained by performing a conventional scan, the cross-sectional positions (slice positions) of the two types of reconstructed images ) Differ, it is not possible to obtain two types of reconstructed images at the same cross-sectional position.

  The present invention has been made in view of the above, and an object of the present invention is to realize cost reduction and simplification of the X-ray detection structure, and two or more types of reconstructed images having different X-ray energies. An X-ray CT apparatus that can be obtained at the same cross-sectional position is provided.

  A feature of the invention described in claim 1 is that in the X-ray CT apparatus, an X-ray irradiation apparatus that irradiates the subject with X-rays and a plurality of scintillators that emit fluorescence upon incidence of X-rays are arranged in a lattice pattern. X-ray detection device for detecting X-rays transmitted through the subject, and having a scintillator block in which two or more types of scintillator rows having different X-ray energy characteristics are alternately arranged, and detected by the X-ray detection device A data collection unit that collects X-rays as X-ray transmission data, and the X-ray transmission data are separated into two or more types of energy data having different X-ray energies, and two or more types of cross-sectional images having different X-ray energies are obtained. And an image reconstruction unit that reconstructs the body axis in the same position.

  According to the present invention, it is possible to realize cost reduction and simplification of the X-ray detection structure, and further, X-ray CT capable of obtaining two or more types of reconstructed images having different X-ray energies at the same cross-sectional position. An apparatus can be provided.

  An embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an X-ray CT apparatus (X-ray computed tomography apparatus) 1 according to an embodiment of the present invention includes a bed 2 on which a subject M such as a patient is placed, and the bed 2. An imaging unit 3 that performs an imaging operation for imaging a medical image of the subject M and a control device 4 that controls driving of the imaging unit 3 are provided. The X-ray CT apparatus 1 is an apparatus for tomographic imaging of a subject M on a bed 2 by an imaging unit 3.

  The bed 2 includes a top 2a on which the subject M is placed, and a top drive 2b that supports the top 2a and moves it horizontally and vertically. The couch 2 moves the couchtop 2a by the couchtop drive unit 2b and positions the subject M on the couchtop 2a at a predetermined position.

  The imaging unit 3 includes a rotating frame 3a that is rotatably provided in the housing, a rotation driving unit 3b that rotates the rotating frame 3a, an X-ray irradiation device 3c that is provided on the rotating frame 3a and that emits X-rays, A high voltage generator 3d for supplying a high voltage to the X-ray irradiation device 3c, an X-ray detection device 3e for detecting X-rays irradiated by the X-ray irradiation device 3c, and the X-ray detection device 3e detected And a data collection unit 3f that collects X-rays as X-ray transmission data.

  The rotating frame 3a is formed in an annular shape, for example. An X-ray irradiation device 3c, an X-ray detection device 3e, and the like are fixed to the rotary frame 3a. As a result, the X-ray irradiation device 3c and the X-ray detection device 3e sandwich the subject M on the bed 2 and place the subject on the bed 2 in a plane perpendicular to the body axis direction of the subject M on the bed 2. Rotate around the specimen M (around the body axis of the subject M). The top plate 2a of the bed 2 is inserted into the frame of the rotating frame 3a.

  The rotation drive part 3b is provided in the housing. The rotation driving unit 3b performs rotation driving of the rotating frame 3a according to control by the control device 4. For example, the rotation drive unit 3b rotates the rotation frame 3a at a predetermined rotation speed in one direction based on the control signal transmitted from the control device 4. In addition, the rotation frame 3a and the rotation drive unit 3b function as a rotation mechanism.

  The X-ray irradiation apparatus 3 c includes an X-ray tube 11 that emits X-rays and a diaphragm unit 12 that restricts the X-rays emitted from the X-ray tube 11. The X-ray irradiation device 3c emits X-rays by the X-ray tube 11, narrows the X-rays by the diaphragm 12, and forms a fan beam having a cone angle with respect to the subject M on the bed 2, for example, X-rays having a cone shape or a pyramid shape are irradiated.

  The high voltage generator 3d is provided in the rotary frame 3a. The high voltage generator 3d is a device that generates a high voltage to be supplied to the X-ray irradiation device 3c, boosts and rectifies the voltage supplied from the control device 4, and supplies the voltage to the X-ray irradiation device 3c. . The control device 4 controls various conditions such as the waveform of the voltage applied to the high voltage generator 3d, that is, the amplitude and the pulse width, in order to cause the X-ray irradiation device 3c to generate desired X-rays.

  The X-ray detection device 3e is arranged to face the X-ray irradiation device 3c. The X-ray detection device 3e converts X-rays transmitted through the subject M on the bed 2 into optical information, converts the optical information into electrical signals, and transmits the electrical signals to the data collection unit 3f.

  The data collection unit 3f is provided in the X-ray detection device 3e. The data collection unit 3 f collects the electrical signals transmitted from the X-ray detection device 3 e as X-ray transmission data and transmits the X-ray transmission data to the control device 4.

  The control device 4 is an image that performs image processing including a control unit 4a that controls driving of each unit, preprocessing using X-ray transmission data as projection data, and image reconstruction processing that performs image reconstruction on the projection data. A processing unit 4b, a storage unit 4c for storing various data such as medical images and various programs, an operation unit 4d for receiving an input operation by an operator, a display unit 4e for displaying an image, and the like are provided. These parts 4a to 4e are electrically connected by a bus line 4f.

  The control unit 4a controls driving of each unit such as the top plate driving unit 2b, the rotation driving unit 3b, and the high voltage generating unit 3d. In addition, the control unit 4a also performs display control for displaying the medical image in the storage unit 4c on the display unit 4e.

  The image processing unit 4b performs image processing including preprocessing and image reconstruction processing on the X-ray transmission data transmitted from the data collection unit 3f, and additionally stores the medical image in the storage unit 4c. For example, an array processor or the like is used as the image processing unit 4b.

  The storage unit 4c is a storage device that stores various programs, various data, and the like, and in particular, is a storage device that stores captured medical images as various data. For example, a ROM, a RAM, a flash memory, and a hard disk are used as the storage unit 4c. The medical image data may be stored in an image server or the like connected to the control device 4 via a network.

  The operation unit 4d is an input unit that is input by an operator. For example, a keyboard or a mouse is used as the operation unit 4d. The operator performs an input operation on the operation unit 4d, performs various settings, performs imaging by the imaging unit 3, and selects a desired medical image from a plurality of reconstructed medical images. Display.

  The display unit 4e is a display device that displays various images such as medical images and operation screens of the subject. As the display unit 4e, for example, a liquid crystal display, a CRT (CRT) display, or the like is used.

  Next, the X-ray detection device 3e will be described in detail.

  As shown in FIG. 2, the X-ray detection device 3 e includes a scintillator block 21 for detecting X-rays emitted from the focal spot S of the X-ray irradiation device 3 c and a plurality of photoelectric elements joined to the scintillator block 21. And a conversion element 22. In the scintillator block 21, a plurality of scintillators 21a and 21b that emit fluorescence when X-rays are incident are arranged in a lattice pattern. In other words, this X-ray detection device 3e is a multi-slice array in which scintillator rows in which scintillators 21a and 21b as X-ray detection elements are arranged along the channel direction A1 are arranged in a plurality of rows along the column direction (slice direction) A2. X-ray detection apparatus. The channel direction A1 is a direction orthogonal to the body axis direction of the subject M, and the column direction A2 is the body axis direction of the subject M. In addition, as each photoelectric conversion element 22, a photodiode etc. are used, for example.

  As shown in FIG. 3, the scintillator block 21 includes scintillators 21a and 21b arranged in a lattice pattern as scintillator segments. A reflector for preventing crosstalk is provided between the scintillators 21a and 21b. In this scintillator block 21, two or more types of scintillator columns having different X-ray energy characteristics are alternately arranged in the column direction A2 in four or more columns (for example, 16 columns or 64 columns). The two types of scintillator rows are a row in which scintillators 21a are arranged in the channel direction A1, for example, about 800 to 1300, and a scintillator 21b is arranged in the channel direction A1 in the same number as the scintillators 21a. The scintillator 21a is a low energy scintillator having sensitivity on the low energy side, and the scintillator 21b is a high energy scintillator having sensitivity on the high energy side.

The X-ray energy sensitivity characteristic difference between the scintillators 21a and 21b is caused by the material type of the scintillators 21a and 21b, as shown in FIG. As the scintillator 21a for low energy, for example, a scintillator (density about ^{3 to 5} g / cm ³ ) such as NaI, CsI or CaF is used, and as the scintillator 21b for high energy, for example, a scintillator such as GOS (density about 7 g) / Cm ³ ).

  In the present embodiment, the X-ray energy sensitivity characteristic difference is generated depending on the material type of the scintillators 21a and 21b. However, the present invention is not limited to this. For example, as shown in FIG. 5, the scintillators 21a and 2b The X-ray energy sensitivity characteristic difference may be caused by the presence or absence of the filter F with respect to the surface (X-ray incident surface), and the thicknesses of the scintillators 21a and 21b (X-ray An X-ray energy sensitivity characteristic difference may be caused by a difference in thickness in the incident direction.

  In FIG. 5, the scintillator 21a without the filter F is a low energy scintillator, and the scintillator 21b with the filter F is a high energy scintillator. For example, a metal film or ceramic is used as the filter F. In FIG. 6, the thin scintillator 21 a is a low energy scintillator and the thick scintillator 21 b is a high energy scintillator compared to each other.

  Next, the image processing unit 4b will be described in detail.

  As shown in FIG. 7, the image processing unit 4 b includes an image reconstruction unit 23 that performs image reconstruction on X-ray transmission data. The image reconstruction unit 23 includes a low energy processing unit 23a, a high energy processing unit 23b, and a total energy processing unit 23c. The image reconstruction unit 23 separates X-ray transmission data into three types (two or more types) of energy data, that is, low energy data, high energy data, and total energy data, and a low energy processing unit 23a, a high energy processing unit Three types (two or more types) of reconstructed images having different X-ray energies are acquired by 23b and the total energy processing unit 23c.

  The low energy processing unit 23a generates a low energy reconstructed image using the low energy data. The high energy processing unit 23b generates a high energy reconstructed image using the high energy data. The total energy data generates a reconstructed image of the total energy using the low energy data and the high energy data.

  Here, a conventional scan in which imaging is performed with the top plate 2a of the bed 2 fixed, and a helical scan in which imaging is performed while moving the top plate 2a of the bed 2 are performed. In the case of performing conventional scanning, image reconstruction is performed. The unit 23 acquires three types of reconstructed images having different X-ray energies by matching the center of gravity position (the position of the subject M in the body axis direction).

  For example, as shown in FIG. 8, for each desired cross-sectional position (slice position) S1, three types of reconstructed images corresponding to the desired cross-sectional position S1, that is, a low-energy reconstructed image and a high-energy reconstructed image. And a full energy reconstruction image is generated. Since these three types of reconstructed images are sequentially obtained for every two columns of the scintillator block 21, when the width of each scintillator 21a, 21b in the body axis direction is, for example, 0.5 mm, dual energy measurement by conventional scanning is performed. If it carries out, the column direction resolution will be 1.0 mm.

  In the low energy reconstruction image, 75% of the low energy data by the low energy scintillator 21a closest to the desired cross-sectional position S1 is used, and the low energy data by the low energy scintillator 21a closest to the desired cross-sectional position S1 is low. 25% energy data is used. This ratio is the ratio of the separation distance between the center of the desired cross-sectional position S1 and the nearest low-energy scintillator 21a to the separation distance between the desired cross-sectional position S1 and the center of the next low-energy scintillator 21a (FIG. 8). It is set based on the inverse ratio of 1: 3).

  Similarly, in the high-energy reconstruction image, 75% of high-energy data from the high-energy scintillator 21b closest to the desired cross-sectional position S1 is used, and the high-energy scintillator next closest to the desired cross-sectional position S1. High energy data from 21a is used 25%. This ratio is an inverse ratio of the ratio of the distance between the center of the desired cross-sectional position S1 and the nearest high-energy scintillator 21b and the distance between the center of the desired cross-sectional position S1 and the center of the next high-energy scintillator 21b. It is set based on.

  Further, in the reconstructed image of all energy, 50% of the low energy data by the low energy scintillator 21a closest to the desired sectional position S1 is used, and by the high energy scintillator 21b closest to the desired sectional position S1. High energy data is used 50%. This ratio is an inverse ratio of the ratio of the separation distance between the center of the desired cross-sectional position S1 and the nearest low energy scintillator 21a and the separation distance between the center of the desired cross-sectional position S1 and the nearest high-energy scintillator 21b. Is set based on. In this way, three types of reconstructed images, that is, a low energy reconstructed image, a high energy reconstructed image, and a total energy reconstructed image are obtained at the same cross-sectional position S1.

  On the other hand, also in the case of performing the helical scan, the image reconstruction unit 23 has three types of reconstruction images having different X-ray energies at the same cross-sectional position S1, that is, a low energy reconstruction image, a high energy reconstruction image, and all Obtain a reconstructed image of energy.

  Here, the relationship between the position (tube position) of the X-ray irradiation device 3c and the body axis direction at the time of the helical scan will be described by taking four rows of scintillator blocks 21 (when the number of scintillator rows is 4) as an example. To do. 9 to 11, a reconstructed image is created using data in an arbitrary cross section of the region R1 indicated by a square frame. In FIG. 9 to FIG. 11, the solid line is the locus of the high energy scintillator array (scintillator 21 b array), and the dotted line is the locus of the low energy scintillator array (scintillator 21 a array).

  Data is interpolated where data is missing when creating a reconstructed image. For example, when creating a high-energy recombined image, use only odd-numbered columns, or when creating a low-energy re-synthesized image, use only even-numbered column reconstruction. By performing the above, it is possible to obtain a column direction resolution comparable to that of a normal helical scan (helical scan in which dual energy measurement is not performed). For example, data of an arbitrary angle at the cross-sectional position S1 to be reconstructed is obtained by interpolation using data of different cross-sectional positions on the same path.

  As shown in FIG. 9, in the first helical scan, reconstruction is performed using only the data in the odd-numbered columns (first and third columns) and even-numbered columns (second and fourth columns). In this case, since the number of data used to create one reconstructed image is half that of a normal helical scan, there is a concern that the image quality will deteriorate. Note that the helical pitch (movement pitch of the subject M) in the first helical scan is 5.

  Therefore, the second helical scan shown in FIG. 10 and the second helical scan shown in FIG. 11 are used. According to these scans, the moving pitch of the couchtop 2a of the bed 2, that is, the helical pitch (moving pitch of the subject M) can be reduced, and the number of data in an arbitrary cross section can be increased, thereby improving the image quality. Can be made.

  As shown in FIG. 10, in the second helical scan, the helical pitch is changed from 5 to 2.5 to ½. Thus, when the movement pitch of the couchtop 2a of the bed 2 (movement pitch of the subject M) decreases, the number of data in an arbitrary cross section increases, so that the image quality can be improved. However, in this case, odd-numbered columns or even-numbered columns pass along a relatively close locus. This means that data density occurs for each position (tube position) of the X-ray irradiation device 3c.

  As shown in FIG. 11, in the third helical scan, the helical pitch (movement pitch of the subject M) is set to an odd number equal to or less than the number of acquisition rows, that is, the helical pitch is set to 3 in the case of 4-row acquisition. As a result, in addition to the improvement in image quality, the trajectory of both the even and odd columns comes to the same position, so that the data density is smaller than in the case of FIG. 10, and the deterioration of the image quality can be further prevented. .

  In the above-described helical scan, the helical pitch is described by taking 4-row collection as an example, but it is considered that there is an optimum helical pitch in each of 16-row and 64-row collection, etc. It is preferable to use an odd number less than the number of columns. Among them, the smaller the value of the pitch, the more the data of tooth missing due to collecting every other row can be supplemented. In addition, if a helical pitch of 1/2 or less of the total number of rows is used, all Can supplement the missing tooth data.

  Therefore, the trajectory for each column of the scintillator block 21 is overlapped by making the moving pitch of the top plate 2a of the bed 2 an odd number less than 1/2 of the total number of columns (an odd number of 32 or less if 64 columns are collected). Thus, it is possible to obtain data equivalent to a normal helical scan in each of the odd and even columns. Based on the moving pitch of the top plate 2a set in this way, the control unit 4a controls the bed 2, the rotation drive unit 3b, and the like to perform a helical scan. For example, when the helical pitch is set to 1 in the above-described four-row acquisition, the trajectories of both the even and odd rows overlap over the entire imaging range, and the data density is further reduced compared to the case of FIG. Therefore, it is possible to further prevent image quality degradation.

  As described above, according to the embodiment of the present invention, the scintillator block 21 in which two or more types of scintillator columns having different X-ray energy characteristics are alternately arranged is provided, and the X-ray transmission data has different X-ray energy. By classifying into three types of energy data and reconstructing three types of cross-sectional images with different X-ray energies by matching the positions of the subject M in the body axis direction, the X-ray irradiation device 3c and the X-ray detection device 3e Dual energy measurement can be performed with a single unit, and the structure of the scintillator block 21 can be simplified. Therefore, the cost can be reduced and the X-ray detection structure can be simplified. it can. In addition, since the position of the subject M in the body axis direction is matched in the three types of cross-sectional images, three types of reconstructed images can be obtained at the same cross-sectional position. In particular, in terms of hardware, dual energy measurement can be realized by changing only the scintillator block 21 with respect to a conventional X-ray detection apparatus.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, in the above-described embodiment, the two types of scintillator rows are alternately arranged in the column direction A2. However, the present invention is not limited to this, and the two types of scintillator rows are alternately arranged in the channel direction A1. Alternatively, two types of scintillator rows may be alternately arranged in both the channel direction A1 and the row direction A2. This makes it possible to perform various dual energy measurements.

  Further, in the above-described embodiment, X-ray transmission data is classified into three types of energy data, and three types of cross-sectional images having different X-ray energies are reconstructed. The X-ray transmission data may be classified into two types of energy data, and two types of cross-sectional images having different X-ray energies may be reconstructed.

  Moreover, in the above-mentioned embodiment, although various materials are mentioned, those materials are illustrations and are not limited. In addition, although various numerical values are listed, these numerical values are examples and are not limited.

1 is a schematic diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention. It is a perspective view which shows schematic structure of the X-ray detection apparatus with which the X-ray CT apparatus shown in FIG. It is a top view which expands and shows a part of scintillator block of the X-ray detection apparatus shown in FIG. It is explanatory drawing for demonstrating the 1st structure of the scintillator for low energy, and the scintillator for high energy. It is explanatory drawing for demonstrating the 2nd structure of the scintillator for low energy, and the scintillator for high energy. It is explanatory drawing for demonstrating the 3rd structure of the scintillator for low energy, and the scintillator for high energy. It is a block diagram which shows schematic structure of the image process part of the control apparatus with which the X-ray CT apparatus shown in FIG. 1 is provided. It is explanatory drawing for demonstrating the image reconstruction by a conventional scan. It is explanatory drawing for demonstrating the image reconstruction by a 1st helical scan. It is explanatory drawing for demonstrating the image reconstruction by a 2nd helical scan. It is explanatory drawing for demonstrating the image reconstruction by a 3rd helical scan.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 2 Bed 3c X-ray irradiation apparatus 3e X-ray detection apparatus 3f Data collection part 4a Control part 21 Scintillator block 21a Scintillator 21b Scintillator 23 Image reconstruction part M Subject

Claims (5)

An X-ray irradiation apparatus for irradiating the subject with X-rays;
A plurality of scintillators that emit fluorescence upon incidence of the X-rays are arranged in a lattice pattern, and have a scintillator block in which two or more types of scintillator columns having different X-ray energy characteristics are alternately arranged and pass through the subject. An X-ray detection device for detecting X-rays,
A data collection unit for collecting the X-rays detected by the X-ray detection device as X-ray transmission data;
The X-ray transmission data is divided into two or more types of energy data having different X-ray energies, and two or more types of cross-sectional images having different X-ray energies are reconstructed by matching the positions in the body axis direction of the subject. A component,
An X-ray CT apparatus comprising: A bed for moving the subject in the body axis direction of the subject;
A rotation mechanism for rotating the X-ray irradiation apparatus and the X-ray detection apparatus with the subject on the bed in between;
A control unit configured to set a movement pitch of the subject so that trajectories for each row of the scintillator blocks overlap, and to perform a helical scan by controlling the bed and the rotation mechanism;
The X-ray CT apparatus according to claim 1, further comprising:   The X-ray CT apparatus according to claim 1, wherein the two types of scintillator rows are alternately arranged in the body axis direction.   The X-ray CT apparatus according to claim 1, wherein the two types of scintillator arrays are alternately arranged in a direction orthogonal to the body axis direction.   3. The X-ray CT apparatus according to claim 1, wherein the two types of scintillator arrays are alternately arranged in both directions of the body axis direction and a direction orthogonal to the body axis direction.

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