JP2003305034A - Multi-row detector type tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-row detector type tomographic apparatus reducing the streak artifact caused by discontinuity at the phase direction edge of data without increasing the error of defined inclined cross sections and radiation source locus. <P>SOLUTION: A reconstruction arithmetic unit 21 is provided with a generating means 21a. The generating means 21a uses data in a wide range in a phase direction to reduce an error at the edge of a phase data range, defines a plurality of inclined cross sections having different angles of inclination and interpolatively combines a plurality of inclined cross-section images having the different angles of inclination to generate one inclined tomographic image. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-row detector type tomography apparatus having a plurality of radiation detector rows in the orbiting axis direction.

[0002]

2. Description of the Related Art A single-row detector type X-ray computed tomography apparatus using a single-row detector (third generation system, hereinafter,
In SDCT), initially, an X-ray is radiated from an X-ray source that orbits the subject while the bed is fixed, and fan beam imaging data (projection data) is obtained by 360-degree circular scanning at a slice position of the subject. Then, the subject is moved along the orbiting axis to collect projection data in the same manner, and projection data of a plurality of slices is collected by repeating this. These data are discrete every 360 degrees, and a tomographic image is created based on the projection data of 360 degrees which is different for each slice. On the other hand, with the advent of slip rings, spiral scanning is possible,
It has become possible to acquire continuous data in the direction of the orbit, and it is now possible to take multiple arbitrary cross-sections at once. This spiral scanning is usually realized by the X-ray source and the X-ray detector facing the X-ray detector orbiting around the subject in a circular orbit, and the subject moving in the orbiting axis direction. This made it possible to shoot a wide area at once, and the shooting time was dramatically reduced.

However, the data obtained by spiral scanning is not continuous 360 ° circular orbit data,
If the image reconstruction (two-dimensional Radon inverse transformation) for circular orbit that was performed so far is used as it is, the image quality will be deteriorated. Therefore, interpolation is used to interpolate the spiral orbit data into a circular orbit. A weighted spiral correction reconstruction method for reconstructing orbital data has come to be used. Figure 3 (a)
Shows the movement locus 24 of the X-ray source during the circular orbit scan, and FIG. 3B shows the movement locus 25 of the X-ray source during the spiral orbit scan.
Indicates. When the image is taken on the circular movement locus 24 as shown in FIG. 3A, the image at the X-ray source position can be accurately reproduced by performing the filter-corrected two-dimensional back projection.
When the image is taken on the spiral movement trajectory 25 as shown in FIG. 3B, due to the discontinuity of the data in the z direction at the imaging end position, only the filter-corrected two-dimensional backprojection causes a streak-like shape at that position. Creates artifacts. Therefore, data interpolation is used for the data obtained on the spiral movement locus 25 as shown in FIG. 3B to correct the circular trajectory data as shown in FIG. Perform dimensional backprojection. By using interpolation in this way, an image with reduced discontinuity can be obtained. The degree of artifact in this case is determined by the degree of discontinuity in the X-ray source trajectory, that is, the degree of artifact changes depending on the moving speed of the subject. Normally used S
In the DCT, a spiral pitch (ratio of the moving speed of the object to the thickness of the X-ray beam at the orbital axis position) is generally used up to about 2.

By the way, in recent years, a multi-row detector type X-ray computed tomography apparatus (hereinafter referred to as MDCT) in which a plurality of detector rows are arranged in the orbiting axis direction has appeared. This MDC
In T, by arranging a plurality of detector element rows narrower in the direction of the orbiting axis than in SDCT to form a wider detector,
By covering a wide range of imaging areas at once and moving the subject at a faster speed than SDCT, the imaging time can be shortened, artifacts due to movements such as breathing can be reduced, and resolution in the orbital axis direction can be improved. Became possible. That is, as shown in FIG. 4 (b), a plurality of narrower single-row detectors are arranged in the orbiting axis direction to realize a detector wider than the single-row detector shown in FIG. 4 (a) as a whole. ing. As can be seen from FIG. 5, which shows the collimation thickness of the X-ray beam per row (hereinafter referred to as the detector collimation thickness), the multi-row detector of FIG. The detector collimation thickness of the X-ray beam per column is smaller than that of the detector, and a wider range can be imaged at one time as a whole.
The spatial resolution of the tomographic image thus obtained in the orbiting axis direction largely depends on the detector collimation thickness of the X-ray beam per column, and the thinner the detector collimation thickness, the higher the axial resolution.

Since this MDCT has a plurality of sets of inclination angles in different orbital axis directions for each detection row (the dimension of projection data has increased), the image reconstruction method is diversified and improved for high-speed MDCT operation. The two-dimensional backprojection method that considers the X-ray beam tilt (cone angle), including the weighted spiral correction reconstruction method that is the two-dimensional backprojection method
R (Advanced Single Slice R)
(ebinning) or Fe considering the X-ray beam tilt as a reconstruction algorithm when higher accuracy is required.
Various methods such as a three-dimensional reconstruction method represented by the ldkamp method and the Wang method have been proposed.

[0006]

However, the MDC
In the image reconstruction algorithm in T, in the weighted spiral correction reconstruction method, the inclination of the X-ray beam in the orbiting axis direction is ignored, so that the allowable upper limit of the moving speed (throughput) of the object in the orbiting axis direction is high and the calculation is performed. However, as the detector width in the orbiting axis direction becomes wider, that is, the inclination angle of the X-ray beam in the orbiting axis direction becomes larger, the difference between the reconstructed cross section and the X-ray beam path becomes larger. The quality of the captured image is reduced. On the other hand, in the three-dimensional reconstruction method, more accurate reconstruction can be realized by considering the inclination angle of the X-ray beam in the orbiting axis direction, but on the other hand, the allowable moving speed upper limit (throughput) of the object in the orbiting axis direction is allowed.
Is low, the amount of calculation is large, and it takes more time to create a tomographic image. Also, in ASSR, the data phase range to be used is determined, an inclined section that approximates the X-ray source locus is defined for this data phase range, and reconstruction is performed by using the data closest to this inclined section. is doing.
In ASSR, when the data phase range to be used is narrowed, a strong streak-like artifact is generated due to the discontinuity at the end in the phase direction of the data, and therefore, data generally wider than the 180-degree phase range must be used. However, if the used data phase range is widened, the discontinuity at the end of the projection data in the phase direction is reduced, but the error between the defined tilted cross section and the X-ray source locus is increased and the X-ray beam tilt angle is large, That is, when the spiral pitch is high, a larger distortion occurs.

An object of the present invention is to provide a multi-row detector type tomography apparatus which reduces streak artifacts due to discontinuity at the end in the phase direction of data without increasing the error between the defined inclined section and the radiation source trajectory. To provide.

[0008]

In order to achieve the above object, the present invention has a radiation source and a radiation multi-row detector facing the radiation source, and the radiation source is provided relative to an object. While moving around the object, the object is moved relatively parallel to the orbiting axis and the radiation transmitted through the object is detected using the radiation multi-row detector, and the detected projection data is reconstructed. A multi-row detector type tomographic apparatus for generating a tomographic image is characterized in that it is provided with generation means for interpolating from a plurality of tilted cross-sectional images approximate to a spiral to generate a tilted one-plane tomographic image. .

Since the multi-row detector type tomography apparatus according to the present invention is provided with the generating means for interpolating a plurality of tilted cross-sectional images approximate to a spiral to generate a tilted one-plane tomographic image, the defined tilted cross-section is obtained. It is possible to reduce streak artifacts due to discontinuity at the end of the phase direction of the data without increasing the error between the radiation source locus and the radiation source trajectory, and to obtain a high-quality image with reduced distortion without using complicated calculations. It can be created at high speed.

In order to achieve the above object, the present invention described in claim 2 is characterized in that, in the object described in claim 1, the plurality of tilted sectional images have different tilted angles in a phase direction. To do.

The multi-row detector type tomography apparatus according to the present invention is provided with generating means for interpolating from the plurality of tilted cross-section images approximate to a spiral to generate a tilted one-plane tomography image, and to provide a plurality of tilted cross-sections. Since a plurality of tilted cross-sectional images each having a different tilt angle in the phase direction were used as images,
The tilted screen image can be more specifically approximated to a spiral, and streak artifacts due to the discontinuity at the end in the phase direction of the data can be obtained without increasing the error between the defined tilted section and the radiation source trajectory. The image quality can be reduced and high-quality images with reduced distortion can be created at high speed without using complicated calculations.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a perspective view showing the appearance of a multi-row detector tomography apparatus according to an embodiment of the present invention. The multi-row detector type tomography apparatus is composed of a scanner 1 used for imaging, a bed 2 for moving an object to be examined, a mouse, a keyboard, etc., and moving speed information and a reconstructed position of the bed 2. The input device 3 for inputting the measurement reconstruction parameters, the arithmetic device 5 for processing the data obtained from the multi-row radiation detectors 4, the display device 6 for displaying the reconstructed image, and the like. ing.

FIG. 1 is a block diagram of the above-mentioned multi-row detector type tomography apparatus. Here, the multi-row detector type tomography apparatus uses a rotate-rotate method (third generation) as its scan method, and is mainly composed of a scanner 1 and an operation unit 7. The scanner 1 includes an X-ray generator 8, a high voltage switching unit 9, and a high voltage generator 1.
0, an X-ray controller 11 and the like, a bed 2 on which the subject 17 is mounted, a radiation detector 4 facing the radiation source with the subject 17 sandwiched between the radiation source and the subject 17. Limiting means configured by a collimator 12 and a collimator control device 13 arranged to limit the radiation, a driving device 14 and a scanner control device 15 for rotating the scanner 1 located on the outer periphery of the subject 17 in the circumferential direction, and a radiation detector. The preamplifier 16 that converts the radiation detected in 4 into a current, amplifies it, and inputs it as a projection data signal into the arithmetic unit 5
And a central controller 18 for controlling them.

From the input device 3 in the operation unit 7, photographing conditions, that is, bed moving speed, tube current, tube voltage, slice position, and reconstruction conditions (reconstruction high-quality mode, reconstruction high-speed mode, reconstruction interval, reconstruction FOV). , Image size, etc.), a control signal necessary for imaging is sent from the central controller 18 to the X-ray controller 11, the bed controller 19, and the scanner controller 15 based on the instruction, and the imaging start signal is received. The shooting starts. When the imaging is started, the X-ray controller 11 sends a control signal to the high voltage generator 10, and the high voltage is applied to the X-ray generator 8 via the high-voltage switching unit 9. From this X-ray generator 8, Radiation such as X-rays is applied to the subject 17.

At the same time, a control signal is sent from the scanner control device 15 to the drive device 14, and the X-ray generator 8, the radiation detector 4, the preamplifier 16 and the like rotate around the outer periphery of the subject 17 in the circumferential direction. On the other hand, the bed 2 on which the subject 17 is placed by the bed control device 19 is stationary during the circular orbit scan, and moves in parallel in the circumferential axis direction of the X-ray generator 8 or the like during the spiral orbit scan. At this time, the moving speed of the couch 2 that moves in parallel is measured by the couch movement measuring device 20 and input to the computing device 5. Radiation emitted from the X-ray generation device 8 has its irradiation area limited by a limiting means such as a collimator 12, is absorbed or attenuated by each tissue in the subject 17, and is detected by the radiation detector 4. The radiation detected by the radiation detector 4 is converted into a current, amplified by the preamplifier 16 and input to the arithmetic unit 5 as a projection data signal. The projection data signal input to the arithmetic unit 5 is
Reconstruction processing is performed by the reconstruction arithmetic unit 21 in the arithmetic unit 5,
The reconstructed image processed by the image processing device 22 is stored in the storage device 23.
And a CT image is displayed on the display device 6.

FIG. 6 is a perspective view for explaining a spiral correction method in a spiral trajectory scan by the above-mentioned multi-row detector type tomography apparatus. Normally, in the weighted spiral correction reconstruction method, the spiral trajectory 27 of the X-ray source in the spiral trajectory scan is interpolated and reconstructed into the circular trajectory 28 perpendicular to the moving direction, but in the spiral correction described here, It is approximated and interpolated to the inclined elliptical locus 29 inclined in the moving direction to reconstruct.

FIG. 7 is a characteristic diagram of a locus for explaining a method for acquiring a reconstructed image, where the horizontal axis represents the imaging phase direction and the vertical axis represents the imaging z direction. FIG. 7A shows the spiral locus 27, and shows that the z position increases or decreases with a change in the phase direction. Further, FIG. 7B is a diagram showing an inclined elliptical locus 29 drawn by the intersection of the inclined cross section approximated to the spiral locus and the cylindrical surface on which the X-ray source circulates. The axial section having no tilt angle defined by the weighted spiral correction reconstruction corresponds to the β axis of the horizontal axis in FIG. 7A.

FIG. 8 is a view in which the inclination angle of the inclined section to be reconstructed with respect to the spiral locus 27 is changed. As can be seen from the figure, an error occurs in the z direction between the reconstruction cross section and the X-ray beam trajectory. In order to reduce this error, the integrated value in the phase direction of the Z-direction error between the reconstructed inclined section locus and the spiral locus in the phase data range to be used is minimum, and the Z-direction error (maximum value) in each phase is smaller. In this case, the inclined cross section becomes an inclined cross section that approximates a spiral locus. here,
It can be seen from FIGS. 7 and 8 that the inclination angle of the inclined cross section that approximates the spiral locus changes according to the phase data size used. For example, in a narrower data range near the phase of β = 0, the inclined cross-section locus and the tangential spiral locus almost coincide.
However, when using a wider data range, for example, −
When π / 2 ≦ β ≦ π / 2 is used, as shown in (a), if the inclined section is determined so that the tangential direction of the inclined section locus and the spiral locus coincide with each other, the error is close to the phase of β = 0. Although small, a large z-direction error occurs in the vicinity of the phase of β = ± π / 2, compared with the vicinity of β = 0. Here, when the tilt angle is determined to be small as shown in (b), the z-direction error is dispersed in each phase and the error is reduced as a whole, and z = ± π / 2
The large z-direction error at is reduced. Further, when the inclination angle is determined so as to coincide with the spiral locus at the β = ± π / 2 position as shown in (c), the discontinuity of the inclined cross section is reduced, but the z-direction error is totally reduced in each phase. growing.

As described above, the tilt angle of the tilted section that approximates the spiral locus changes depending on the phase data size used. Further, the error between the spiral locus and the reconstructed inclined section can be reduced as a whole, using a narrower range of data, but the discontinuity at the end of the data becomes a problem. On the other hand, if the data range end is corrected by using a wider range of data and the data range end is corrected, the distortion due to the Z direction error at the data range end is reduced, but the path between the inclined section and the spiral locus is reduced. The error increases.

Therefore, the reconstruction arithmetic unit 21 shown in FIG.
Is provided with a generation means 21a, which uses a wide range of data in the phase direction in order to reduce the error at the end of the phase data range, and defines a plurality of inclined cross sections having different inclination angles. A plurality of tilted sectional images having different tilt angles are interpolated and combined to create a tilted one-plane tomographic image.

9 (a), 9 (b) and 9 (c) show a plurality of inclined sections used in the above-mentioned generating means 21a, that is, different inclined angles using the same phase range for the same spiral locus. It is a characteristic view which shows inclined cross section 30a, 30b, 30c. By using such wide data, discontinuity can be corrected by overlapping data at the end of the phase data, and by using data having different tilt angles, the error of the spiral trajectory and the X-ray beam path can be reduced. The influence can be reduced.

Generating means 21 provided in the reconstruction arithmetic unit 21
For a, for example, 180 ° phase data (data size used for half reconstruction), which is narrower in the phase direction is used, a plurality of tilted cross-section images with a small error between the tilted cross-section and the spiral locus are created, and the error It is also possible to combine a plurality of tilted cross-sectional images with a small number to create a tilted one-plane tomographic image.

FIGS. 10A, 10B and 10C are characteristic diagrams showing inclined sections 31a, 31b and 31c using different phase ranges for the same spiral locus. In this way, by using narrow data as the plurality of inclined cross sections used in the above-mentioned generating means 21a, it is possible to reduce the influence of the error of the spiral trajectory and the X-ray beam path, and by using the data of different phases, 11 (a) to 11 (c)
As shown in FIG. 11, the phase in which the influence of discontinuity appears at the end of the phase data changes, and by combining a plurality of these, the artifact intensity can be reduced as shown in FIG. 11D.

FIG. 12 is a flow chart showing a concrete processing operation of the above-mentioned reconstruction arithmetic unit 21. First,
In step S1, measurement parameters such as imaging conditions and reconstruction conditions are set using the input device 3 for creating a reconstructed cross section, and based on these, the central controller 18 performs a spiral trajectory scan in step S2. Next, step S
In step 3, a plurality of projection data for creating different tilted sections from different phase data or a plurality of projection data for creating tilted sections having the same phase but different tilt angles are created. Here, when combining in the reconstructed images, the generation means 21a reconstructs the projection data obtained in step S4 to obtain a plurality of different reconstructed inclined sectional images, and in step S5 from the plurality of reconstructed inclined sectional images. One reconstruction tomographic image is generated by interpolation in consideration of the tilt angle.

FIG. 13 is a flow chart showing another processing operation by the reconstruction arithmetic unit 21. First, in step S1, measurement parameters, that is, imaging conditions, reconstruction conditions, etc., are set using the input device 3 for creating a reconstructed cross section, and based on this, a spiral trajectory scan is performed in step S2. Next, in step S3, projection data for creating different tilted sections from different phase data or a plurality of projection data for creating tilted sections having the same phase but different tilt angles are created. Here, in order to combine the data in the projection data, the generation means 21a has the step S6.
As shown in FIG. 4, interpolation processing is performed on the projection data to create one piece of modified projection data, and in step S7, the acquired modified projection data is reconstructed to obtain a reconstructed tomographic image of an inclined plane. I am trying to get it.

As described above, a plurality of tilted cross-sectional images having different tilt angles are combined so as to generate a tilted one-plane tomographic image, whereby problems in the ASSR can be improved. For example, the error due to the X-ray beam path on the reconstruction plane is reduced by creating and combining tilted cross-sectional images that are arranged at the same position on at least the central axis of rotation and have different tilt angles from wider projection data in the view directions of substantially the same phase. can do. Further, by combining data in the same position on the rotation center axis and in a narrower phase range having different phases, discontinuous distortion occurring at the data end in the phase direction increases the error between the reconstruction surface and the X-ray beam path. Can be corrected without In the former case, by using the data at the same position, it is possible to suppress the deterioration of the body axis resolution, and by using wider projection data (data with redundancy) in the view direction, the discontinuity that occurs at the end of the range of phase data By combining the images having different tilt angles, it is possible to reduce the artifacts caused by the error between the reconstruction plane and the X-ray beam path. In the latter case, the error between the reconstruction plane and the X-ray beam path is reduced by using the data in the narrower phase range, and the error occurring at the end of the phase data range is caused by using the plurality of data having different phases. Continuity can be corrected.

In the above-described embodiment, the multi-row detector type tomography apparatus using X-rays has been described, but the present invention is not limited to this and uses gamma rays, neutron rays, positrons, electromagnetic energy and light. It can also be applied to a conventional tomography apparatus. Further, the scanning method is not limited to any one of the first generation, the second generation, the third generation, and the fourth generation, and a multi-tube CT device equipped with a plurality of X-ray sources or a doughnut-type tube can be used. It can also be used for CT devices. The radiation detectors are also located on the cylindrical surface centering on the radiation source, flat detectors, detectors located on a spherical surface centering on the radiation source, and on the cylindrical surface centering on the orbiting axis. It is possible to apply it to any radiation detector such as a radiation detector.

[0028]

As described above, according to the multi-row detector type tomography apparatus of the present invention, the error in the defined tilted section and the radiation source locus is not increased, and the data is detected at the end in the phase direction of the data. Streak artifacts due to discontinuity can be reduced, and high-quality images with reduced distortion can be created at high speed without using complicated calculations.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a multi-row detector type tomography apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the multi-row detector tomography apparatus shown in FIG.

FIG. 3 is a perspective view showing different trajectory scans.

FIG. 4 is a side view showing different radiation detectors.

5 is a side view showing the collimation thickness of an X-ray beam per column in the radiation detector shown in FIG.

6 is a perspective view showing spiral correction in a spiral trajectory scan by the multi-row detector tomography apparatus shown in FIG.

FIG. 7 is a characteristic diagram showing an inclined elliptical locus drawn by an intersection of an inclined cross section approximated to a spiral locus and a cylindrical surface around which an X-ray source circulates.

FIG. 8 is a characteristic diagram in which an inclination angle of an inclined cross section reconstructed with respect to a spiral locus is changed.

9 is a characteristic diagram showing tilted cross sections with different tilt angles using the same phase range used in the reconstruction arithmetic unit of the multi-row detector tomography apparatus shown in FIG.

10 is a characteristic diagram showing tilted cross sections of different tilt angles using different phase ranges used in the reconstruction arithmetic unit of the multi-row detector tomography apparatus shown in FIG.

11 is a plan view showing a combination of a plurality of inclined cross sections performed by the reconstruction arithmetic unit of the multi-row detector tomography apparatus shown in FIG.

FIG. 12 is a flowchart showing a process of interpolating from a plurality of tilt images to generate a one-plane image by the multi-row detector tomography apparatus shown in FIG.

13 is a flow chart showing another process of generating a one-plane image by interpolating from a plurality of tilt images by the multi-row detector tomography apparatus shown in FIG.

[Explanation of symbols]

1 scanner 3 input devices 5 arithmetic unit 21 Reconstruction arithmetic unit 21a Generating means 22 Image processing device 29 inclined elliptical locus 30a to 30c inclined cross section 31a-31c inclined cross section

Continued front page    F-term (reference) 2G088 EE01 FF02 GG09 JJ37                 4C093 AA22 BA10 CA13 EA02 EB18                       EB22 FC30 FD07 FD12 FE12                       FE14 FF36 FF45                 5B047 AA17 AB02 BA02 BB10 BC11                       BC14 DC20                 5B057 AA09 BA03 CA12 CB12 CD12                       CE02 CH01 DA16

Claims (2)

[Claims] 1. A radiation source and a radiation multi-row detector facing the radiation source, wherein the radiation source is rotated relative to the object while the object is relatively rotated with respect to an axis of rotation. In a multi-row detector type tomography apparatus for detecting radiation that has moved in parallel and transmitted through an object using the radiation multi-row detector, and reconstructs the detected projection data to generate a tomographic image A multi-row detector type tomography apparatus comprising: a generating unit that interpolates a plurality of tilted cross-sectional images approximate to a spiral to generate a tilted one-plane tomographic image. 2. The multi-row detector type tomography apparatus according to claim 1, wherein the plurality of tilted cross-sectional images have different tilt angles in a phase direction.