JPH1189827A - X-ray computerized tomograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray computerized tomograph equipped with a detector system for removing the trouble of scattered beams at low cost. SOLUTION: This apparatus is provided with a channel direction collimator 11 for preventing scattered beams in channel direction from making incident to a two-dimensional detection element array 10 and a slice direction collimator 12 for preventing scattered beams in slice direction from making incident to the same detection element array, the channel direction collimator 11 is constituted by providing plural collimator boards 12 extended along with the slice direction at the close intervals of arrangement in the channel direction, and the slice direction collimator 13 is constituted by providing plural collimator boards 14 extended along with the channel direction at the thinness intervals of arrangement in the slice direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray computed tomography apparatus (hereinafter referred to as "X-ray CT") for photographing, for example, a tomographic plane of a subject, and more particularly, to a rotation axis of a system. The present invention relates to an X-ray CT having a detector system having a spread in a direction (direction of a central axis for rotating a focal position, simply, direction of a thickness of a tomographic plane).

[0002]

2. Description of the Related Art A conventional X-ray CT irradiates a part of a subject with a thin X-ray beam (called a fan beam), performs image reconstruction processing based on the transmission data, and irradiates the fan beam. To obtain a tomographic image at the specified position. FIG.
FIG. 4 is a diagram showing a detector system provided in a conventional X-ray CT. In general, the subject arranged between the X-ray tube and the detector system is often a human body, and is arranged such that the center axis of rotation is substantially horizontal. In the drawings, the rotation center axis is shown in a vertical direction (vertical direction in the drawing) for convenience.

FIG. 34 shows a system generally called the third generation, in which a focal point (X-ray tube) and a detector system are arranged to face each other with a rotation center axis therebetween, and these are integrated. To collect imaging data of an imaging region while rotating around the subject. Although not shown here, the fourth generation system in which the detector system is arranged on the circumference and collects projection data while rotating only the focal point (X-ray tube) also has a circumferential detector system. Research and development of next-generation systems, such as a fifth-generation system in which an X-ray focus is rotated around a subject by scanning an electron beam, are also underway. These systems are common in that they use thin fan beams, and are collectively referred to as fan beam systems.

[0004] In addition, a dual slice (Du) in which a conventional detector is partially overlapped in two rows in a slice thickness direction is provided.
al-slice) has also been put to practical use. However, this system merely doubles the slice thickness over the prior art and is still included in the fan beam system.

[0005] The detection principle of the detector system is as follows: a gas detector which collects electric charges of a gas ionized by X-rays (mainly Xe gas is used) to obtain a signal, and X-rays incident on a scintillator A solid-state detector (Solid-State-Detector) that converts the scintillator light generated when it is used into an electrical signal using an optical sensor (mainly a photodiode)
or: SSD), but recently, an efficient SSD is becoming the mainstream, and in this specification, the description will be made assuming that the detector system includes the SSD.

[0006] As described above, the detecting element is composed of the scintillator and the photodiode. X-rays transmitted through the subject are converted into light by the scintillator. Generally, the scintillator has a wide directivity in the X-ray incident direction, and has sensitivity to X-rays incident from various directions. The projection data in the principle of the reconstruction of the X-ray CT means data of X-rays (referred to as “direct rays”) transmitted straight from the X-ray focal point to the detector. For this reason, the X-rays scattered in the subject and changed in direction (referred to as “scattered rays”) are factors that degrade the quality of the final X-ray CT image. Therefore, in a detector system using a scintillator having a wide directivity as a detection element, it is necessary to limit the X-rays incident on the scintillator to only direct rays and remove scattered rays.

As a method of removing scattered radiation, a scattered radiation removal collimator (or scattered radiation removal grid) for physically removing scattered radiation is disposed in front of the scintillator, or a detector (scattering device) for measuring only scattered radiation. A method has been put into practical use in which a scattered ray is mathematically removed (scattered ray correction) using data from the detector. However, recently, the collimator method has been mainly used because it is necessary to reduce the time required for data processing in order to improve the throughput.

FIG. 35 is a view for explaining removal of scattered radiation by a collimator. When a collimator is not provided as shown in FIG. 35 (a), both direct rays and scattered rays emitted from the focal point and transmitted through the subject enter the scintillator. On the other hand, when a collimator is provided as shown in FIG. 35 (b), scattered rays among transmitted X-rays are blocked by the collimator plate, and only direct rays enter the scintillator.

FIG. 36 is a diagram showing a configuration of an SSD using a collimator method. A channel direction collimator 93 is arranged on the front surface (focal side) of the detection element array 92. The channel direction collimator 93 is configured such that collimator plates 94 arranged in the channel direction are supported by a support member 95. FIG.
In FIG. 6, the detection element array 92 is connected to the collimator 9
3, the collimator 93 and the detection element array 92 are actually arranged close to each other. In the conventional fan beam system, since the shape of the fan beam is wide in the channel direction and narrow in the slice thickness direction, the incident direction of the scattered radiation is almost limited to the channel direction. Directional collimator).

Since the conventional X-ray CT system described above uses a fan beam, there is a problem that the imaging region in the slice thickness direction is narrow. Therefore, helical scanning has been put into practical use and is becoming popular as a method for solving this problem. However, since helical scanning also uses a fan beam, it is not a fundamental solution, and there is a limit that the resolution in the slice direction depends on the thickness of the fan beam.

In order to enlarge the photographing area, the fan beam may have a cone beam shape by increasing the slice thickness. In this case, it is necessary to configure the two-dimensional detector system by arranging the detecting elements also in the slice direction in order to improve the resolution by enlarging the detector system in the slice direction.

FIG. 37 is a diagram showing an arrangement of a detector system in cone beam X-ray CT. In FIG.
00 indicates a two-dimensional detector system.

Here, in the cone beam X-ray CT detector system, since the cone beam X-ray is used, the X-ray beam becomes thick in the slice direction. For this reason, not only scattered radiation incident on the scintillator in the channel direction but also scattered radiation in the slice direction cannot be ignored. Therefore, scattered radiation removal measures are required.

In the scattered radiation correction by the fan beam X-ray CT, a scattered radiation detector is arranged at a position where direct rays do not enter, and a fan beam (direct rays are incident) based on the scattered dose measured by the detector. Is estimated, and the scattered dose is estimated and subtracted.

On the other hand, in the case of the cone beam X-ray CT, the distance from the position of the scattered radiation detector to the center of the cone beam to be estimated (the center in the slice thickness direction) increases, and the fan beam X-ray CT It is expected that the same correction accuracy as that described above will not be obtained. For this reason, it is difficult to realize a method of mathematically removing scattered radiation (scattered radiation correction) in cone beam X-ray CT. In addition to the X-ray CT, as a scattered radiation distribution measuring method for an X-ray diagnostic apparatus using a cone beam, Japanese Patent No. 1631264 (application: Apr. 1984)
On March 3, registration: December 26, 1991). According to this method, scattered radiation data is calculated based on the transmitted X-ray data of the subject when the X-ray shielding unit is used and when it is not used, and an X-ray image of only direct rays is obtained by subtracting the scattered radiation data from the original image. ing.

Meanwhile, a method of removing scattered radiation by a collimator in cone-beam X-ray CT is disclosed in Japanese Patent Application No. Hei 8-162003 (application: June 21, 1996). And so on. FIG. 38 is a diagram for explaining removal of scattered radiation in the slice direction by the collimator in the slice direction. As shown in FIG. 38 (a), when no collimator is provided, a direct line emitted from the focal point F and transmitted through the subject,
And scattered radiation both enter the scintillator. Also,
As shown in FIG. 38B, when a collimator is provided, scattered rays among transmitted X-rays are blocked by the collimator plate 101, and only direct rays enter the scintillator.

Further, as shown in FIGS. 39, 40 and 41, there are also known examples of various collimator configurations in which the shape (curved surface or plane) of the collimator plate differs depending on the shape (cylinder or plane) of the detector. ing.

FIG. 42 is a view of the two-dimensional detection element array viewed from the front (X-ray focal point side). FIG. 43 is a view showing a cross section of the detector when viewed from the side. In FIG. 43, X-rays are emitted from the left side of the paper toward the detector. Here, FIG. 44 is a graph showing the X-ray intensity when the subject is actually photographed. In the graph, a region surrounded by a dotted line indicates scattered radiation removed by the collimator, and a region indicated by hatching indicates a component detected by the scintillator, that is, a direct line.

[0019]

Here, various scattered radiation corrections in various X-ray CTs as described above have the following problems.

First, the scattered radiation correction used in the conventional fan beam X-ray CT has a problem that it is difficult to cope with a cone beam due to insufficient accuracy.

Next, in consideration of applying a scattered radiation distribution measuring method for an X-ray diagnostic apparatus (Japanese Patent No. 1631264) to X-ray CT, a case where X-ray shielding means is used for each angle is used. However, there is a problem that the transmitted X-ray data of the subject is required, which is not practical from the viewpoint of imaging time.

When a collimator for removing scattered radiation is used, for example, assuming that detection elements having a pitch of 1 mm are arranged in a two-dimensional detector having a width of several tens cm in the slice thickness direction, for example, several hundreds It becomes necessary to arrange the collimator plates with high precision, and there is a problem that the cost is high even if it is technically possible.

The present invention has been made in view of such circumstances, and has as its object to provide an X-ray computed tomography apparatus having a detector system for removing the adverse effects of scattered radiation at low cost.

[0024]

In order to solve the above problems and achieve the object, an X-ray computed tomography apparatus of the present invention is configured as follows.

(1) The X-ray computed tomography apparatus of the present invention irradiates a subject with X-rays, and transmits a transmitted X-ray transmitted through the subject using a two-dimensional detector element array. X-ray computed tomography apparatus, wherein the two-dimensional detector system comprises: a channel direction collimator for preventing a channel direction scattered ray from being incident on the two-dimensional detection element array; and a slice direction scattered ray. And a slice-direction collimator for preventing the light from being incident on the two-dimensional detection element array. The channel-direction collimator has a plurality of collimator plates extending along the slice direction, which are arranged closely in the channel direction. A plurality of collimator plates, wherein the slice direction collimator extends along the channel direction. Characterized in that the arrangement interval to the slice direction, which are arranged such that the crude.

With this configuration, (2) the X-ray computed tomography apparatus of the present invention is the apparatus described in (1) above, and is output from the two-dimensional detection element array. The apparatus further includes a correction unit for estimating a scattered dose included in the scan data and correcting the scan data based on the scattered radiation amount. The scattered radiation removal rate is stored for each, and at the time of actual scanning, the direct ray component distribution is estimated based on the output value from the detection element having the slice direction collimator, and the detection element not having the slice direction collimator. Estimate the component distribution of the sum of the straight line and the scattered ray based on the output value from the, from the component distribution of the sum of the straight line and the scattered ray estimated by this, Estimate the distribution of only the scattered radiation by subtracting the previously estimated straight line component distribution, multiply the distribution of only the scattered radiation estimated by this, the scattered radiation removal rate, for each of the elements The method is characterized in that an incident scattered dose is estimated and subtracted from the scan data.

(3) An X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (1), wherein
Estimating the scattered dose included in the scan data output from the two-dimensional detection element array, further comprising a correction means for correcting the scan data based on the scattered dose, the correction means, the correction means had been measured in advance before scanning A scattered radiation removal rate for each element of the two-dimensional detection element array is stored, and at the time of actual scanning, a direct ray component distribution is estimated based on an output value from a detection element having the slice direction collimator. By subtracting the previously estimated direct ray component from the output value from the detection element having no direction collimator, the value of only the scattered ray of the detection element is estimated, and based on the value of only the scattered ray of the detection element. Thus, the distribution of only the entire scattered radiation is estimated, and the distribution of only the entire scattered radiation is multiplied by the removal rate of the scattered radiation, whereby the light is incident on each element. Scattered dose estimates, and wherein the subtracting from the scan data.

(4) An X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (1), wherein
Estimating the scattered dose included in the scan data output from the two-dimensional detection element array, further comprising a correction means for correcting the scan data based on the scattered dose, the correction means, the correction means had been measured in advance before scanning Storing a scattered radiation removal rate for each element of the two-dimensional detection element array, estimating a component distribution of a sum of straight lines and scattered rays based on an output value from a detection element having no slice direction collimator; By subtracting the output value from the detection element having the slice direction collimator from the component distribution of the sum of the previously estimated straight line and scattered ray, the value of only the scattered ray of the detection element is estimated, and only the scattered ray is estimated. From the value of, the distribution of only the entire scattered radiation is estimated, and
The apparatus is characterized in that a scattered dose incident on each of the elements is estimated by multiplying the scattered radiation removal rate, and is subtracted from the scan data.

(5) The X-ray computed tomography apparatus according to the present invention is the apparatus according to any one of the above (2), (3) and (4), and the X-ray computed tomography apparatus has an approximation in the distribution estimation by the correction means. The method is characterized by one of a curve approximation and a straight line approximation, or a combination of both.

(6) The X-ray computed tomography apparatus according to the present invention is the apparatus according to any one of the above (2), (3) and (4), and the distribution is estimated by the correction means.
Either estimation in the slice direction or estimation in the two-dimensional direction of the slice direction and the channel direction,
Or a combination of the two.

(7) An X-ray computed tomography apparatus according to the present invention is the apparatus according to any one of the above (2), (3) and (4), and is provided outside the two-dimensional detection element array. The scattered radiation detector is further provided, and the scattered radiation intensity detected by the scattered radiation detector is used for the approximation when estimating the distribution of only the scattered radiation.

(8) An X-ray computed tomography apparatus according to the present invention is the apparatus according to any one of the above (2), (3) and (4), wherein the sum of the straight line and the scattered ray is calculated. In estimating a component (distribution), data from an element close to a detection element having the slice direction collimator is not used, and only data from a detection element at a position distant from the collimator is used. I do.

(9) The X-ray computed tomography apparatus of the present invention is the apparatus according to any one of the above (2), (3) and (4), wherein the scattered dose is subtracted from the scan data. Preferably, the predetermined scattered dose is subtracted while leaving the predetermined scattered dose, and the predetermined scattered dose is added to the detection element having the slice direction collimator.

(10) An X-ray computed tomography apparatus according to the present invention is the apparatus according to any one of the above (2), (3) and (4), and further includes a two-dimensional element array in a slice direction. In the vicinity of the center, the collimator plates of the collimator in the slice direction are arranged so as to be closely spaced in the slice direction.

(11) The X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (10), wherein the collimator plate is not disposed except near the center in the slice direction. I do.

(12) The X-ray computed tomography apparatus according to the above (1), wherein the collimator plate of the slice direction collimator is provided at an end of the two-dimensional element array in the slice direction. Is arranged.

(13) The X-ray computed tomography apparatus of the present invention irradiates a subject with X-rays, and transmits X-rays transmitted through the subject from a two-dimensional detection element array. In the X-ray computed tomography apparatus for detecting X-rays, a two-dimensional detection element array is provided between a predetermined detection element and a focal point, and shields direct rays of transmitted X-rays transmitted through the subject and scattered rays. Having a shielding means for allowing only the detection element to enter the detection element,
The detection element is used as a scattered radiation detection element.

(14) An X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (13),
Based on the scattered dose output from the scattered ray detection element,
The image processing apparatus further includes a correction unit that corrects scan data output from the two-dimensional detection element array, the correction unit including: a scattered radiation amount detected by the scattered radiation detection element;
The ratio of the amount of scattered radiation incident on each of the elements other than the scattered radiation detection element in the dimensional detection element array is stored, and at the time of actual scanning, the amount of scattered radiation detected by the scattered radiation detection element and Estimating the distribution of only the scattered radiation based on the ratio and subtracting the distribution of only the scattered radiation from the scan data, the data to be detected by the scattered radiation detection element in the absence of the shielding means, the surroundings The estimation is performed by performing channel replacement on the data of the detection elements.

(15) The X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (14), wherein the approximation method for estimating the distribution by the correction means is one of a curve approximation and a linear approximation. One or a combination of both.

(16) The X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (14), wherein the distribution is estimated by the correction means in the slice direction and in the slice direction and the channel direction. , Or a combination of the two in the two-dimensional direction.

(17) The X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (14), further comprising a scattered radiation detector arranged outside the two-dimensional detection element array. When estimating the distribution of only the scattered radiation, the scattered radiation intensity detected by the scattered radiation detector is used for the approximation.

(18) The X-ray computed tomography apparatus according to the present invention is the apparatus according to the above (14), wherein when the scattered dose is subtracted from the scan data, the scattered dose is subtracted leaving a predetermined scattered dose. It is characterized by.

[0043]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) The first embodiment relates to an X-ray CT equipped with a two-dimensional detector system for removing scattered radiation using a sparse collimator.

FIGS. 1, 2 and 3 show a first example of a two-dimensional detector system provided in the X-ray CT according to the present embodiment.
It is a perspective view which shows the 3rd example of a schematic structure.

The two-dimensional detector system of this embodiment is configured as follows in any of the first to third configuration examples. That is, channel direction collimators (11, 21, 3, 3) for preventing scattered rays in the channel direction from being incident on the two-dimensional detection element array (10, 20, 30).
1) and a slice direction collimator (referred to as “sparse collimator”) (13, 23, 33) for preventing scattered rays in the slice direction from being incident on the detection element array, and a channel direction collimator ( 11,21,3
1) is constituted by providing a plurality of collimator plates (12, 22, 32) extending along the slice direction so as to have a close arrangement interval in the channel direction (in this example, all channels), and Collimator (13, 23, 33)
Is formed by providing a plurality of collimator plates (14, 24, 34) extending along the channel direction so that the arrangement intervals in the slice direction are coarse (sparse).

As shown in FIGS. 1 to 3, the two-dimensional detection element array has a cylindrical shape (10, 20) or a planar shape (30). Accordingly, the shape of the collimator in the channel direction is cylindrical (11, 21) or planar (31), and the shape of the collimator in slice direction is also cylindrical (13, 23) or planar (33).

The shape of the collimator plate is curved (1).
4, 24) or a planar shape (12, 22, 32, 34). In the channel direction collimator 21, one of the channel direction collimator plates 22 is composed of a plurality of (two in the figure) planar collimator plates. Also,
In the slice direction collimator 23, one of the slice direction collimator plates 24 is composed of a plurality of (eight in the figure) plane collimator plates.

Here, scattered radiation correction in the two-dimensional detector system configured as described above will be described.

(1) FIG. 4 is a diagram of the two-dimensional detector system viewed from the front (X-ray focal point side). FIG. 5 is a side view of the cross section of the detector, and X-rays are emitted from the left side of the paper. The X-ray intensity when an actual subject is photographed is as shown in FIG. As described above, the collimator plates for removing scattered radiation in the slice direction are provided so that the arrangement intervals in the channel direction are coarse (sparse). Only direct rays enter the detection elements (A, B, C, D), and direct rays and scattered rays (part of them) enter the detection elements (X2, X3, X6, X7, X10, X11, X14, X15). Is blocked by the collimator plate), and the detection elements (X1, X4, X5, X8, X9, X12, X13, X16)
Direct rays and scattered rays enter without any shielding action by the collimator plate.

(2) First, for each element, the amount of scattered radiation removed by the sparse collimator (the amount of scattered radiation incident with the sparse collimator in relation to the amount of scattered radiation incident when there is no collimator at all) Volume ratio). Such measurement is performed before actually scanning the subject. Here, for example, a water phantom or the like is used to irradiate uniform X-rays in the slice direction, or a phantom that simulates each part of the human body is used to irradiate X-rays whose intensity distribution in the slice direction is known. Measurement.

FIG. 7 shows a uniform X for a given phantom.
6 is a graph showing the X-ray intensity from a two-dimensional detector in a slice direction when a line is irradiated. In this case, the direct line intensities of all the elements are estimated based on the outputs from the elements (A, B, C, D) that detect only the direct lines. Also, outputs from elements (A, B, C, D) that detect only direct lines,
Elements that detect all direct and scattered rays (X1, X4, X5, X
8, X9, X12, X13, X16), the intensity of the incident scattered radiation is estimated from the difference from the output.

By subtracting the direct ray component from the measurement data for each element, the scattered ray component detected in each element is estimated, and the ratio between the incident scattered ray intensity and the detected scattered ray intensity is obtained. .

(3) Next, the subject is actually scanned.
FIG. 8 is a graph showing the X-ray intensity from the two-dimensional detector in the slice direction when the subject is actually scanned.

First, the component (distribution) of the direct line is estimated based on the output value from the detection element (A, B, C, D) having the collimator in the slice direction.

(4) Next, the component (distribution) of the sum of the direct ray and the scattered ray is estimated based on the output value from the detection element having no collimator in the slice direction. In this case, the data from the element close to the element with the collimator is not used, and the element (X
1, X4, X5, X8, X9, X12, X13, X16) is preferable from the viewpoint of obtaining appropriate accuracy.

(5) Next, by subtracting the previously estimated direct ray component (distribution) from the estimated sum of the direct ray and scattered ray component (distribution), the distribution of only the scattered ray at the front of the collimator is obtained. presume.

(6) Then, by multiplying the distribution of only the estimated scattered radiation by the ratio previously obtained by the measurement of the phantom, the scattered dose incident on each element is estimated. By subtracting this from the original scan data,
An X-ray intensity distribution of only direct rays can be estimated.

The above various distributions are estimated by the following approximation method. That is, it is performed by one of curve approximation (curve fitting) and linear approximation, or a combination thereof. The distribution is estimated by either one of the estimation in the slice direction and the two-dimensional estimation including the channel direction, or a combination thereof.

According to the embodiment described above, the plurality of collimator plates (14, 2) extending in the channel direction are provided.
4, 34) are slice direction collimators (13, 23, 33) provided so that the arrangement intervals in the channel direction are coarse (sparse), so that the harmful effects of scattered radiation can be appropriately removed at low cost. can do.

Here, several modified examples relating to the scattered radiation removal by the sparse collimator of the present embodiment will be described.

(First Modification) FIG. 9 is a view for explaining a first modification. This modification relates to estimation of distribution of only scattered radiation on the front surface of the collimator.

As a procedure for such distribution estimation, as shown in FIG. 9, the direct line component distribution (detection with a slice direction collimator) estimated in the above (3) is performed based on the output value of the detection element having no slice direction collimator. The element (A,
B, C, D), the intensity at the corresponding slice position is subtracted to obtain the scattered dose (indicated by an arrow in FIG. 9) at the detection element having no collimator in the slice direction. The distribution of only the scattered radiation at the front of the collimator may be estimated from the value.

(Modification 2) FIG. 10 is a view for explaining Modification 2. This modification also relates to the estimation of the distribution of only the scattered radiation in front of the collimator.

As a procedure of the distribution estimation, as shown in FIG. 10, the component (distribution) of the sum of the direct ray and the scattered ray estimated by the same method as in the above (4) (from the detection element having no collimator in the slice direction). Estimated based on the output value of
A detection element having a slice-direction collimator is obtained by subtracting an output value of a detection element having a slice-direction collimator (A, B, C, D) from an intensity at a slice position corresponding to a detection element having a slice-direction collimator. May be estimated (indicated by an arrow in FIG. 10), and the distribution of only the scattered radiation in front of the collimator may be estimated from the value.

(Third Modification) FIGS. 11, 12 and 13 are diagrams for explaining a third modification. The present modification relates to a sparse collimator arrangement method.

FIG. 1 shows a sparse collimator arrangement method.
As shown in FIGS. 1 to 13, the central portion in the slice direction is not sparse, and all elements are provided with collimators. As a result, it is possible to reduce a correction error in a specific area (here, near the center) and obtain highly accurate direct line distribution data.

(Modification 4) FIGS. 14, 15 and 16 are diagrams for explaining Modification 4. FIG. This modification also relates to a sparse collimator arrangement method.

FIG. 1 shows a sparse collimator arrangement method.
As shown in FIGS. 4 to 16, the collimator is provided only in all the elements at the center in the slice direction. Also in this case, similarly to the third modification, it is possible to reduce a correction error near the center, and to obtain highly accurate direct line distribution data.

(Fifth Modification) FIGS. 17, 18 and 19 are diagrams for explaining a fifth modification. This modification also relates to a sparse collimator arrangement method.

FIG. 1 shows a sparse collimator arrangement method.
As shown in FIGS. 7 to 19, the detection element at the end in the slice direction is always provided with a collimator. In this case, in the estimation of the scattered radiation distribution, all interpolation can be performed, and highly accurate direct radiation distribution data can be obtained near the edge.

(Modification 6) FIGS. 20, 21, 22, and 23 are diagrams for explaining Modification 6. FIG. This modification relates to estimation of distribution of only scattered radiation on the front surface of the collimator.

In this modified example, as shown in FIGS. 20 to 22, a scattered radiation detector is arranged outside a detection element array for collecting actual projection data. Then, when estimating the distribution of only the scattered radiation, as shown in FIG. 23, the scattered radiation intensity measured by the outer scattered radiation detector is used for approximation.

(Modification 7) FIG. 24 is a view for explaining Modification 7. This modification also relates to the estimation of the distribution of only the scattered radiation on the front surface of the collimator.

When the estimated scattered dose is subtracted from the sum of the direct ray and the scattered ray to obtain the direct dose, as shown in FIG. 24, 100% of the calculated scattered dose is obtained.
, And leave a predetermined scattered dose (here, 10
%). In other words, subtraction of the amount of the scattered radiation remaining in the data from the scattered radiation component (estimated distribution) incident on the detector is subtracted from the data of the sum component of the direct radiation and the scattered radiation.

In this case, as a matter of course, for a detecting element having a collimator in the slice direction, the scattered radiation is added in a reverse manner so as to include a set amount of scattered radiation.

Here, an example of a more specific hardware configuration of the X-ray CT according to the present embodiment and a specific processing flow relating to scattered radiation correction will be described.

FIG. 25 is a block diagram showing a specific hardware configuration of the X-ray CT according to the present embodiment. The X-ray tube F and the main detector M are provided so as to be rotatable around the subject H so as to sandwich the subject H therebetween. The X-ray tube F is supplied with a high voltage from a high voltage generator V controlled by the host controller C.

The main detector M is connected to the main detector data collection device MD. When a scattered radiation detector is provided, the scattered radiation detector S is provided at the end of the main detector M, and the scattered radiation detector data collection device SD is provided.

Further, various storage devices and arithmetic units according to the features of the present invention are provided. That is, the first storage device 3 that stores the scan data collected by the main detector data collection device MD (and the scattered radiation data collection device SD).
01, a first arithmetic unit 302 for estimating a direct line intensity distribution from data of an element for detecting only a direct line, a second storage device 303 for storing a direct line intensity distribution, and an element for detecting a direct line + scattered ray. A second arithmetic unit 304 for estimating the intensity distribution of direct rays and scattered rays from the data, a third storage device 305 for storing the intensity distribution of direct rays and scattered rays, and a storage device of the second and third storage devices. A third computing unit 306 for estimating the intensity distribution of the incident scattered radiation from the difference, a fourth storage device 310 for storing the incident scattered radiation intensity distribution, and a scatter detected by subtracting the direct ray component from the scan data. A fourth arithmetic unit 307 for estimating the line distribution, a fifth storage device for storing the detected scattered radiation intensity distribution, and calculating a distribution of a ratio of the detected scattered radiation to the incident scattered radiation intensity. Fifth arithmetic unit 309, input The sixth storage device 315 stores the distribution of the ratio of the detected scattered radiation with respect to the scattered radiation intensity, and the incident scattered radiation distribution stored in the fourth storage device 310 and the sixth storage device 315. A sixth computing unit 311 for estimating the detected scattered radiation intensity distribution from the stored ratio of (detected scattered radiation intensity) / (incident scattered radiation intensity);
A seventh storage device 312 that stores the detected scattered radiation intensity distribution estimated by the calculation unit 312, and subtracts the scattered radiation component stored in the seventh storage device 312 from the collected scan data to obtain only direct rays. 7th to estimate projection data
And an eighth storage device 314 for storing projection data of only direct lines.

FIG. 26 is a flowchart showing the flow of processing according to a specific example of scattered radiation correction according to this embodiment.
This processing includes scattered radiation correction data collection processing S100, scattered radiation correction processing S200 during actual subject scanning, reconstruction processing S300, and image display and image recording processing S4.
00 is roughly classified.

As shown in the figure, the scattered radiation correction data collection processing S100 is a collection of projection data (direct rays + scattered rays) of an object (phantom) having a uniform distribution, S101, and data from an element that detects only direct rays. Extraction S102, calculation of direct ray intensity by averaging S103, extraction of elements for detecting direct ray + scattered ray S104, calculation of direct ray + scattered ray intensity by averaging S105, direct ray intensity from direct ray + scattered ray intensity Calculation of incident scattered radiation intensity by subtraction of S106, calculation of detected scattered radiation intensity of each element by subtraction of direct radiation intensity from projection data S107, and ratio of incident scattered radiation to detected scattered radiation (distribution correction data) Is calculated by S108.

Further, the scattered radiation correction processing S200 at the time of actual scanning of the subject is performed by collecting projection data (direct rays + scattered rays) of the actual subject S201, extracting data S202 from elements that detect only direct rays, and interpolation processing. Calculation of the approximate distribution of direct ray + scattered ray intensity S203, extraction of the element detecting the direct ray + scattered ray S204, calculation of the approximate distribution of direct ray + scattered ray intensity by interpolation processing S205, direct calculation from the direct ray + scattered ray intensity distribution Calculating the incident scattered radiation intensity distribution by subtracting the line intensity distribution S206, calculating the incident scattered radiation intensity distribution by multiplying the incident scattered radiation intensity distribution by distribution correction data, and calculating the detected scattered radiation distribution from the projection data It is configured by calculation S208 of the projection data of only the direct line by the subtraction.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the second embodiment, a scattered radiation detection element is provided in a two-dimensional detector system, and scattered radiation is removed by channel replacement.

FIGS. 27 to 33 are diagrams for explaining the present embodiment.

(1) First, in the two-dimensional detector system of the present embodiment, the slice direction collimator is not provided for all the elements in the slice direction. That is, the collimator is not provided at all, or the sparse collimator of the first embodiment is provided.

(2) In the two-dimensional detector system of the present embodiment, the scattered radiation detecting element is arranged inside the detecting element row for collecting actual projection data. That is, as shown in FIG. 27 to FIG. 28, the shielding member 20 is separated from the detection element between the scattered radiation detection element and the focal point.
By disposing 0, direct rays are shielded and only scattered rays enter, so that the detection element is used as a scattered ray detection element.

The scattered radiation correction in the two-dimensional detector system configured as described above will be described.

FIG. 27 is a view of the two-dimensional detector system of this embodiment as viewed from the front (X-ray focal point side). FIG. 28 is a cross-sectional view of the detector when viewed from the side. In FIG. 28, X-rays are emitted from the left side of the drawing.
FIG. 29 is a graph showing the X-ray intensity when an actual subject is photographed. The amount of incident scattered radiation differs depending on the position of the element in the slice direction and the sparsely arranged shielding member. For example, the scattered radiation detected by the scattered radiation detector is a part of the entire scattered radiation (it is reduced by the amount of the scattered radiation absorbed by the shielding material).

(3) The ratio between the amount of scattered radiation detected by the scattered radiation detection element and the amount of scattered radiation detected for each element for collecting actual projection data is measured in advance.
For example, using a water phantom or the like to irradiate uniform X-rays in the slice direction, or using a phantom that assumes various parts of the human body and irradiating X-rays with a known intensity distribution in the slice direction I do.

FIG. 30 is a graph showing the X-ray intensity from the two-dimensional detector in the slice direction when a predetermined phantom is irradiated with uniform X-rays. In this case, the direct line intensities of all the elements are estimated from the difference between the outputs from the scattered ray detection elements (A, B, C, D) and the outputs from the elements around the scattered ray detection elements. Next, as shown in FIG.
For each element for which projection data is collected, the direct ray component is subtracted from the measured data to estimate the scattered ray component detected by each element, and the amount of scattered radiation detected by the scattered ray detection element and the actual projection The ratio with the scattered radiation intensity detected by each element for collecting data is determined.

(4) Next, the subject is actually scanned.
First, the distribution of the scattered radiation detected by each element that collects projection data is estimated from the amount of scattered radiation detected by the scattered radiation detection element and the ratio measured in advance in (3). .

(5) Next, as shown in FIG. 32, the distribution of only the estimated scattered radiation is subtracted from the original scan data.

(6) As shown in FIG. 33, the projection data to be detected by the scattered radiation detecting element arranged inside is estimated from the data of peripheral elements by using channel replacement.
This makes it possible to obtain direct line projection data of the entire subject.

The above various distributions are estimated by the following approximation method. That is, it is performed by one of curve approximation (curve fitting) and linear approximation, or a combination thereof. The distribution is estimated by either one of the estimation in the slice direction and the two-dimensional estimation including the channel direction, or a combination thereof.

According to the present embodiment described above, no collimator in the slice direction is provided, or a sparse collimator is provided. Therefore, similarly to the first embodiment, the harmful effects of scattered radiation can be appropriately reduced at low cost. Can be removed.

Here, some modified examples relating to the scattered radiation removal of the present embodiment will be described.

That is, a scattered ray detector is also arranged outside the detection element array for collecting actual projection data, and when estimating the distribution of only scattered rays, measurement was performed by the outer scattered ray detector. The scattered radiation intensity may be used for approximation.

Also, from the sum of the direct rays and the scattered rays,
When the scattered dose is subtracted, the calculated scattered dose is 100
Alternatively, a predetermined scattered dose may be left without subtracting%.

The present invention is not limited to the above-described embodiment, but can be implemented with various modifications.

[0101]

As described above, according to the present invention, it is possible to provide an X-ray computed tomography apparatus equipped with a detector system for removing the adverse effects of scattered radiation at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first schematic configuration example of a two-dimensional detector system provided in an X-ray computed tomography apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a second schematic configuration example of the two-dimensional detector system.

FIG. 3 is a perspective view showing a third schematic configuration example of the two-dimensional detector system.

FIG. 4 is a view of the two-dimensional detector system as viewed from the front (X-ray focal point side).

FIG. 5 is a side view of a cross section of the two-dimensional detector system.

FIG. 6 is a diagram illustrating X-ray intensity when an actual subject is imaged.

FIG. 7 is a graph showing the X-ray intensity from a two-dimensional detector in a slice direction when a predetermined phantom is irradiated with uniform X-rays.

FIG. 8 is a graph showing the X-ray intensity from a two-dimensional detector in a slice direction when an object is actually scanned.

FIG. 9 is a diagram showing a first modification of the first embodiment.

FIG. 10 is a diagram showing a modification 2 of the first embodiment.

FIG. 11 is a view for explaining a third modification of the first embodiment;

FIG. 12 is a view for explaining a third modification of the first embodiment;

FIG. 13 is a view for explaining a third modification of the first embodiment;

FIG. 14 is a view for explaining a fourth modification of the first embodiment;

FIG. 15 is a view for explaining a fourth modification of the first embodiment;

FIG. 16 is a view for explaining a fourth modification of the first embodiment;

FIG. 17 is a diagram illustrating Modification Example 5 of the first embodiment.

FIG. 18 is a view for explaining a fifth modification of the first embodiment;

FIG. 19 is a view for explaining Modification Example 5 of the first embodiment.

FIG. 20 is a view for explaining a modification 6 of the first embodiment.

FIG. 21 is a view for explaining a modification 6 of the first embodiment.

FIG. 22 is a view for explaining a modification 6 of the first embodiment.

FIG. 23 is a view for explaining a modification 6 of the first embodiment.

FIG. 24 is a view for explaining a seventh modification of the first embodiment;

FIG. 25 is a block diagram showing a specific hardware configuration of the X-ray CT according to the first embodiment.

FIG. 26 is a flowchart showing the flow of a process according to a specific example of scattered radiation correction according to the first embodiment.

FIG. 27 is a front view showing a configuration of a two-dimensional detector system provided in an X-ray computed tomography apparatus according to a second embodiment of the present invention.

FIG. 28 is a sectional view showing a configuration of a two-dimensional detector system provided in the X-ray computed tomography apparatus according to the second embodiment of the present invention.

FIG. 29 is a graph showing an X-ray intensity when an actual subject is photographed.

FIG. 30 shows a case where a predetermined phantom is irradiated with uniform X-rays, and the X-rays from the two-dimensional detector in the slice direction are obtained.
4 is a graph showing line intensity.

FIG. 31 shows the amount of scattered radiation detected by the scattered radiation detection element,
9 is a graph for explaining a process of deriving a ratio with a scattered radiation intensity detected by each element that collects actual projection data.

FIG. 32 is a graph for explaining a process of subtracting an estimated distribution of only scattered radiation from original scan data.

FIG. 33 is a diagram showing a detection element for estimating projection data by channel replacement.

FIG. 34 is a view showing a detector system provided in an X-ray CT according to a conventional example of the present invention.

FIG. 35 is a diagram for explaining removal of scattered radiation by a collimator according to a conventional example of the present invention.

FIG. 36 is a diagram showing a configuration of an SSD using a collimator method according to a conventional example of the present invention.

FIG. 37 shows a cone beam X-ray CT according to a conventional example of the present invention.
The figure which shows arrangement | positioning of the detector system in FIG.

FIG. 38 is a view for explaining removal of scattered light in the slice direction by the slice direction collimator according to the conventional example of the present invention.

FIG. 39 is a diagram showing a configuration example of a collimator according to a conventional example of the present invention.

FIG. 40 is a diagram showing a configuration example of a collimator according to a conventional example of the present invention.

FIG. 41 is a diagram showing a configuration example of a collimator according to a conventional example of the present invention.

FIG. 42 is a view of a two-dimensional detection element array according to a conventional example of the invention as viewed from the front (X-ray focal point side).

FIG. 43 is a view showing a cross section of a two-dimensional detection element array according to a conventional example of the present invention when viewed from the side.

FIG. 44 is a graph showing an X-ray intensity when a subject according to a conventional example of the present invention is actually photographed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Two-dimensional detection element array 11 ... Channel direction collimator 12 ... Channel direction collimator plate 13 ... Slice direction collimator 14 ... Slice direction collimator plate F ... Focus

Claims (18)

[Claims] An X-ray computed tomography apparatus for irradiating a subject with X-rays and detecting transmitted X-rays transmitted through the subject by a two-dimensional detector system including a two-dimensional detection element array, The two-dimensional detector system includes a channel direction collimator that prevents scattered rays in a channel direction from being incident on the two-dimensional detector element array, and a scattered ray in a slice direction that is incident on the two-dimensional detector element array. The channel direction collimator, wherein the channel direction collimator comprises a plurality of collimator plates extending along the slice direction, arranged so as to be closely spaced in the channel direction, and the slice direction collimator. Is such that a plurality of collimator plates extending along the channel direction has a coarse arrangement interval in the slice direction. An X-ray computed tomography apparatus characterized by being arranged. 2. The apparatus according to claim 1, further comprising a correction unit configured to estimate a scattered dose included in the scan data output from the two-dimensional detection element array and to correct the scan data based on the estimated scattered dose. A scattered radiation removal rate for each element of the two-dimensional detection element array, which is measured in advance, is stored, and at the time of actual scanning, a direct line based on an output value from the detection element having the slice direction collimator is stored. Estimating the component distribution, estimating the component distribution of the sum of the straight line and the scattered ray based on the output value from the detection element having no slice direction collimator, thereby estimating the component of the sum of the straight line and the scattered ray The distribution of only the scattered radiation is estimated by subtracting the previously estimated straight-line component distribution from the distribution. Scattering dose is incident on each of said elements by multiplying the rate of removal of scattered radiation estimated, X-rays computed tomography system according to claim 1, wherein the subtracting from the scan data. 3. The apparatus according to claim 1, further comprising a correction unit configured to estimate a scattered dose included in the scan data output from the two-dimensional detection element array and to correct the scan data based on the estimated scattered dose. A scattered radiation removal rate for each element of the two-dimensional detection element array, which is measured in advance, is stored. During an actual scan, a direct ray component is determined based on an output value from the detection element having the slice direction collimator. By estimating the distribution, from the output value from the detection element having no slice direction collimator, by subtracting the direct ray component previously estimated, the value of only the scattered radiation of the detection element is estimated, Estimating the distribution of only the entire scattered radiation based on the value of only the scattered radiation, and multiplying the distribution of the entire scattered radiation only by the scattered radiation removal rate, Estimating the scatter dose is incident on each element, X-rays computed tomography system according to claim 1, wherein the subtracting from the scan data. 4. The apparatus according to claim 1, further comprising: a correcting unit configured to estimate a scattered dose included in the scan data output from the two-dimensional detection element array and to correct the scan data based on the estimated scattered dose. A scattered radiation removal rate for each element of the two-dimensional detection element array, which is measured in advance, is stored. Based on an output value from a detection element having no slice direction collimator, a sum of a straight line and a scattered ray is calculated. By estimating the component distribution, subtracting the output value from the detection element having the slice direction collimator from the component distribution of the sum of the previously estimated straight line and scattered ray, the value of only the scattered ray of the detection element is calculated. Estimating the distribution of only the entire scattered radiation from the value of only the scattered radiation, and multiplying the distribution of the entire scattered radiation only by the removal rate of the scattered radiation. X-ray computed tomography apparatus of claim 1, estimating the scatter dose is incident, and wherein the subtracting from the scan data for each. 5. The method according to claim 2, wherein the approximation method in estimating the distribution by the correction means is one of curve approximation and straight line approximation, or a combination of both. 2. The X-ray computed tomography apparatus according to claim 1. 6. The method according to claim 1, wherein the distribution is estimated by the correction means by one of a slice direction and a two-dimensional direction of a slice direction and a channel direction, or a combination of both. The X-ray computed tomography apparatus according to claim 2. 7. A scattered radiation detector arranged outside the two-dimensional detection element array, wherein the scattered radiation intensity detected by the scattered radiation detector when estimating the distribution of only the scattered radiation is provided. The X-ray computed tomography apparatus according to claim 2, wherein is used for the approximation. 8. When estimating the component distribution of the sum of the straight line and the scattered ray, data from an element close to a detection element having the slice direction collimator is not used, and a position far from the collimator is detected. The X-ray computed tomography apparatus according to claim 2, wherein only data from the element is used. 9. When subtracting a scattered dose from the scan data, the scattered dose is subtracted while leaving a predetermined scattered dose, and the predetermined scattered dose is added to a detection element having the slice direction collimator. The X-ray computed tomography apparatus according to claim 2. 10. The apparatus according to claim 1, wherein the collimator plates of the collimator in the slice direction are arranged close to each other in the slice direction near the center of the two-dimensional element array in the slice direction. 2. The X-ray computed tomography apparatus according to claim 1. 11. The X-ray computed tomography apparatus according to claim 10, wherein the collimator plate is not disposed except in the vicinity of the center in the slice direction. 12. The X-ray computed tomography apparatus according to claim 1, wherein a collimator plate of the slice direction collimator is arranged at an end of the two-dimensional element array in a slice direction. 13. An X-ray computed tomography apparatus for irradiating a subject with X-rays and detecting transmitted X-rays transmitted through the subject by a two-dimensional detector system including a two-dimensional detection element array, Shielding means provided between a predetermined detection element and a focal point in the two-dimensional detection element array, for shielding direct rays of transmitted X-rays transmitted through the subject and for allowing only scattered rays to enter the detection element; An X-ray computed tomography apparatus, characterized in that the detection element is used as a scattered radiation detection element. 14. A scattered radiation detecting element, comprising: a correcting means for correcting scan data outputted from the two-dimensional detecting element array based on a scattered dose outputted from the scattered radiation detecting element. And the ratio of the amount of scattered radiation detected in the two-dimensional detection element array to the amount of scattered radiation incident on each of the elements other than the scattered radiation detection element is stored. Estimating the distribution of only the scattered radiation based on the amount of the scattered radiation detected by the line detection element and the ratio, subtracting the distribution of only the scattered radiation from the scan data, and the scattered radiation when there is no shielding means. 2. The data to be detected by a detection element is estimated by performing channel replacement on data of peripheral detection elements.
4. The X-ray computed tomography apparatus according to 3. 15. An approximation method for estimating a distribution by the correction unit includes one of a curve approximation and a straight line approximation.
The X-ray computed tomography apparatus according to claim 14, wherein the apparatus is based on a combination of the two. 16. The distribution estimation by the correction means is based on either one of estimation in a slice direction and estimation in a two-dimensional direction of a slice direction and a channel direction, or a combination of both. The X-ray computed tomography apparatus according to claim 14. 17. A scattered radiation detector disposed outside the two-dimensional detection element array, the scattered radiation intensity detected by the scattered radiation detector when estimating the distribution of only the scattered radiation. The X-ray computed tomography apparatus according to claim 14, wherein is used for the approximation. 18. The X-ray computed tomography apparatus according to claim 14, wherein when the scattered dose is subtracted from the scan data, a predetermined scattered dose is subtracted.