JP2001318154A - Radiation detector and its manufacturing method, and data correcting method for x-ray ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector which can be manufactured at a low cost by reducing collimator plates and its manufacturing method, and a data correcting method for an X-ray CT device which mathematically remove scattered rays. SOLUTION: Detector modules 1 having a plurality of detector elements are arranged arcuately around the focus of an X-ray tube and on joints between detector modules 1 and their adjacence parts, three channel-directional collimator plates 2 are formed at intervals corresponding to the width of one detector element 1 while converging on the X-ray tube focus. A collimator is manufactured by using a dedicated jig which is hollowed in the external shape of the collimator to have a groove into which a channel-directional collimator plate 2 can be inserted. This detector is used to estimate direct and scattered rays of transmitted X rays of a body to be inspected and data corrections for scattered-ray removal are made to obtain an X-ray image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus, and more particularly to a radiation detector in which a channel direction collimator is arranged corresponding to a detector element array and a data correction method for the X-ray CT apparatus using the same. About.

[0002]

2. Description of the Related Art As shown in FIG.
The X-ray radiated from the X-ray tube 16 is narrowed down to a fan-shaped X-ray beam 17 by the collimator of the emission port, and the X-ray tube 16 is arranged around the subject 18 and an arc-shaped X-ray tube arranged opposite thereto. The channel direction collimator plate 3 and the detector module 1 rotate, and the detector module 1 captures X-ray information transmitted through the subject 18, and processes the signal by a computer to obtain an X-ray tomographic image of the subject 18. Things. X-rays radiated from the X-ray tube 16 include those that travel straight through the subject 18 and those that are scattered by the subject 18, and take in only the former information to remove scattered rays entering obliquely, In order to prevent the crosstalk, a channel direction collimator plate 3 is provided in front of the detector module 1. This channel direction collimator plate 3 forms an X-ray shielding wall in front of the one-dimensionally arranged detector modules 1 with a material that is difficult to transmit X-rays for each channel. The detector module 1 comprises an X-ray tube 16 which converts an X-ray into a light, and a X-ray detector comprising a photodiode which detects the light converted by the scintillator and outputs it as an electric signal. And about 500 to 1000 channels arranged in an arc with the center as the center.

[0003] Due to the mechanical arrangement, 8 to 30 scintillators and photodiodes combined by optical bonding are arranged on a substrate to form a module. Numerals 1 are arranged continuously in a substantially arc shape on the circumference and combined with the channel direction collimator plate 3 to constitute a radiation detector for an X-ray CT apparatus. FIG. 8 shows the structure of the collimator. The collimator includes a plurality of channel direction collimator plates 3 provided in the channel direction, arc-shaped support plates 4 and 5 provided before and after in the slice direction, and both ends of the support plate 4 and the support plate 5 in the channel direction. It consists of a support rod 7 that supports the part. The channel direction collimator plate 3 is inserted and fixed between the two support plates 4 and 5 in the slice direction toward the incident direction of the X-ray beam 17 from the X-ray tube 16.

The channel-direction collimator plate 3 has a support plate 4 and a support plate 5 on both sides thereof, and is fixed with a fixing adhesive. This fixing and bonding work has a hollow space having a shape along the entire outer shape of the collimator, and is cut in advance into a jig frame having a number of vertical grooves along which the channel direction collimator plate 3 can be inserted. The channel direction collimator plate 3 and the support plate 4 or the support plate 5 are vertically inserted along the groove, and the channel direction collimator plate 3 is sequentially bonded to the support plate 4, and finally supported by the channel direction collimator plate 3. After the plate 5 is integrally bonded, it is manufactured by pulling out from the frame to either the upper or lower side. Alternatively, a groove into which both ends of the channel-direction collimator plate 3 can be inserted is provided on the inner surfaces of both support plates 4 and 5 having both ends fixed by the support rod 7, and the channel-direction collimator plate 3 is fitted into the groove to fix the groove. It is fixed with an adhesive. The directions in which the channel direction collimator plates 3 are fixed are bonded and fixed so that they converge in the direction of the focal point of the X-ray tube 16. When the grooves are provided and fixed, the grooves are processed so that the directions of the grooves converge in the focal direction of the X-ray tube 16, respectively.

[0005] The collimator to which the channel direction collimator plate 3 is fixed is fixed with a fixing screw above a detector element on which a photodiode array and a scintillator array are mounted on a substrate. At this time, the positional accuracy of the collimator and the detector is set accurately, and the detection sensitivity of each detector is made uniform and maximum. Then, an integrated body of the collimator and the detector is attached to the main housing.

[0006]

The conventional X-ray CT apparatus is constructed as described above. However, a channel direction collimator plate 3 is provided for each element of the detector, and the number thereof is about 500. About 1000 sheets are used. The channel direction collimator plate 3 is made of a substance having a large atomic number such as molybdenum or tungsten, and is usually 0.1 to
It is finished to a predetermined dimension with a precision of 0.3 mm. Therefore, the material cost and the processing cost are increased, and the man-hour for assembling into the collimator requires time. Therefore, there is a problem that the price of the entire detector becomes expensive.

On the other hand, in X-ray image reconstruction of X-ray CT, transmission data of the subject considers only data of direct X-rays perpendicularly incident on the detector from the focal point, and is scattered by the subject. The scattered X-ray data whose
This is a factor that degrades the image quality of the line 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. To remove scattered radiation, prepare a scattered radiation removal collimator that physically removes scattered radiation over the entire scintillator, and prepare another scattered radiation detector that measures only scattered radiation and use the data. A method based on scattered radiation correction for mathematically removing scattered radiation has been put to practical use. Recently, the collimator method has become the mainstream, but there is a need for a method of obtaining a high-quality X-ray image in which scattered radiation components that cannot be removed by the collimator are mathematically removed even if the data processing takes time. ing.

The present invention has been made in view of the above circumstances, and reduces the number of channel direction collimator plates 3 for removing scattered radiation, thereby reducing material costs, processing costs, assembling man-hours, and inexpensively. An object of the present invention is to provide a radiation detector that can be manufactured and a manufacturing method thereof. Further, a data correction method for an X-ray CT apparatus capable of directly estimating the components of X-rays and scattered X-rays from output data of a detector element and mathematically removing the scattered rays to obtain a high-quality X-ray image. The purpose is to provide.

[0009]

In order to achieve the above object, a radiation detector according to the present invention comprises an X-ray having a solid state detector module on which a plurality of X-ray detector elements are arranged and a channel direction collimator plate. In a radiation detector for CT, a channel direction collimator plate is provided at a position corresponding to only a joint of a solid state detector module and an adjacent portion thereof.

Further, the method of manufacturing a radiation detector according to the present invention has a hollow space having a shape along the outer shape of the collimator, and corresponds to only the joint of the detector module and its adjacent portion along the inside of this space. The channel direction shielding plate is sequentially inserted along the groove into a jig frame having a vertical groove into which the side of the channel direction shielding plate can be inserted. In this method, a collimator manufactured by integrally bonding and then pulling out the upper or lower side from the frame body is disposed corresponding to the detector module.

Further, according to the present invention, there is provided a data correction method for an X-ray CT apparatus comprising the radiation detector according to the first aspect.
In the data correction method of the apparatus, the detection rate of the scattered radiation for each of the detector elements which is measured in advance before scanning is stored, and at the time of actual scanning, the detector having the channel direction collimator plate is used. Estimating the direct ray component distribution based on the output value from the element, estimating the component distribution of the sum of the direct ray and the scattered ray based on the output value from the detector element without the channel direction collimator plate,
The distribution of only the scattered radiation is estimated by subtracting the previously estimated direct radiation component distribution from the component distribution of the sum of the direct radiation and the scattered radiation thus estimated. Multiplying the detection rate of the scattered radiation to estimate the scattered dose incident on each of the detector elements, and subtracting the estimated scattered radiation from the scan data.

In the data correction method of the X-ray CT apparatus according to the present invention, the approximation method for estimating the distribution by the correction means is a method based on one of a curve approximation and a linear approximation or a combination of both.

The radiation detector of the present invention is configured as described above, and has a channel direction collimator plate at a position corresponding to only a joint of the solid state detector module and an adjacent portion thereof. The total cost can be reduced by considerably reducing the number of materials, processing costs, and assembly man-hours. Further, in the method of manufacturing the radiation detector according to the present invention, since a manufacturing jig dedicated to the collimator is used, the radiation detector can be finished easily and accurately.

In the data correction method for an X-ray CT apparatus according to the present invention, the detection rate of scattered radiation is measured in advance and stored before scanning, and the data is detected from a detector element having a channel direction collimator plate at the time of actual scanning. The direct ray component distribution is estimated based on the output value, and the distribution of only the scattered rays is estimated by subtracting from the component distribution of the sum of the direct rays and the scattered rays from the detector element having no channel direction collimator plate, Since the scattered radiation is estimated by multiplying the scattered radiation detection rate and subtracted from the scan data, there is no need to provide a channel direction collimator plate corresponding to each detector element, and scattered radiation is eliminated. A clear X-ray image can be obtained. The approximation method in the data correction method of the X-ray CT apparatus according to the present invention is a method based on one of a curve approximation and a linear approximation or a combination of both, and is an optimal approximation method based on an X-ray transmission image of the subject. Can be selected.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the radiation detector of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a cross section in the channel direction of the radiation detector. FIG. 2 is an enlarged view of a cross section in the channel direction. The radiation detector includes a plurality of detector modules 1 that are arranged in a substantially arc shape around the X-ray tube focal point and formed in a polygonal shape,
Three channel direction collimator plates 2 provided in an upper position corresponding to the vicinity of each joint of the detector module 1 so as to converge in the X-ray tube focal direction, and the channel direction collimator plate 2 and the detector module 1 Are supported from both ends in the slice direction.

A plurality of detector elements 15 are arranged in one detector module 1, and the upper part of the joint of each detector module 1 and the adjacent part thereof correspond to the width of one detector element 15. Three channel direction collimator plates 2 are provided at intervals. For example, assuming that the detector module 1 is constituted by collecting 24 channels of the detector elements 15 and arranging them on 40 arcs centering on the focal point of the X-ray tube, the detector elements 15 are 960 in total. Consists of channels. Conventionally, since the channel direction collimator plate 2 is provided for each detector element 96, 961 sheets are required. On the other hand, this detector requires only 121 channel direction collimator plates 2. That requires less work time, which leads to cost reduction. Further, the number of expensive channel direction collimator plates 2 is reduced to 1/8.
, The cost can be further reduced.

In this radiation detector, as shown in FIG. 2, a detector module 1 in which a scintillator array 9 and a photodiode array 10 are formed on a substrate 11 provided below is provided. The channel direction collimator plates 2 are provided on both sides at a center position corresponding to the upper part of the joint with the neighbor of 1 and on both sides thereof at intervals corresponding to the width of one detector element 15. The channel direction collimator plate 2 is fixedly supported at both ends in the slice direction by a support plate 8 and a support plate 8a (not shown). The height of the support plate 8 is made smaller than the height of the channel direction collimator plate 2 in manufacturing. The channel direction collimator 2 is manufactured so as to face the X-ray tube focal direction.

Generally, in order to mount the channel direction collimator plate 2 on the detector module 1, it is necessary to mount it with very high accuracy. The collimator formed by the channel direction collimator plate 2 of the present detector is assembled using a dedicated manufacturing jig described below, and the width of the support plate 8 is larger than the height of the channel direction collimator plate 2 in structure. The end of the collimator plate 2 in the channel direction is visible from the front. Therefore, by paying attention to the position of the provided channel direction collimator plate 2 and the end face of the scintillator array 9 at the joint of the detector modules 1, the array of the detector modules 1 can be attached with high accuracy.

Next, a method for manufacturing the radiation detector will be described with reference to FIG. First, a jig 14 having a groove 13 into which a channel-direction collimator plate 2 can be inserted by cutting the inside into a channel-direction collimator shape.
Prepare The grooves 13 are formed with three grooves 13 at positions on the collimator side corresponding to the joints of the detector modules 1, and are formed corresponding to the joints of the detector modules 1. The hollow shape of the jig 14 is the X-ray tube focus 1
2, the width of which is equal to the height in which the channel direction collimator plate 2 can be inserted, and the groove 13
Is convergently formed in the direction of the X-ray tube focal point 12.

The channel direction collimator plate 2 is made of a material having a large atomic number, such as molybdenum or tungsten, and has a thickness of usually 0.1 to 0.3 mm. If the collimator has a problem in mechanical strength, the inexpensive F
A plate of e, Cu, or an alloy thereof may be used. These channel direction collimator plates 2 are configured such that, when combined with the support plate 8 and the support plate 8a, they face the focal direction. The support plate 8 and the support plate 8a are usually made of aluminum or stainless steel having a thickness of about 5 to 10 mm, but aluminum is most suitable from the viewpoint of workability. The support plate 8 is formed in an arc shape so as to form a part of an arc centered on the X-ray tube focal point 12 so as to be accommodated in the hollow portion of the jig 14, and has a shape different from that of the hollow portion. It is formed a little smaller.

First, the jig 14 is fixed to a predetermined position of the support plate 8a with a positioning pin or the like. This jig 1
The hollow portion 4 is cut out in an arc shape that forms a part of an arc centered on the X-ray tube focal position so as to follow the entire outer shape of the collimator portion by wire electric discharge machining or the like, and is cut out to a certain width. A groove 13 is formed in the inner part of the arc-shaped portion so as to face left and right. However, three grooves 13 are formed at positions on the collimator side corresponding to the joints of the detector module 1.

First, the channel-direction collimator plate 2 is inserted into all the grooves 13, and the support plate 8a is once removed from the jig 14. Then, the adhesive plate is applied to the contact portion with the channel-direction collimator plate 2 with an adhesive. Is adhered to the channel direction collimator plate 2 by fixing it to the jig 14 again. Finally, the support plate 8 is fixed by bonding. The collimator is completed by pulling the completed product from the jig 14 below the support plate 8a. Then, as shown in FIG. 2, the scintillator array 9, the photodiode array 1
On the substrate 11 on which the scanning circuit (not shown) is mounted, the collimator is aligned, and the upper collimator and the lower detector array are matched. Fix with.

Next, a data correction method of the X-ray CT apparatus using the radiation detector will be described. Although the actual collimator and the detector module 1 have a structure arranged on an arc, the collimator plate 2 in the channel direction is actually effective.
However, as shown in FIG. 4, it can be schematically represented in a state where the detector modules 1 are arranged on an array. FIG. 5 is a graph showing the X-ray intensity from the detector element 15 in the channel direction when uniform X-rays are irradiated using a water phantom, an acrylic phantom, or the like. in this case,
From the arrangement of the detector elements 15 from which the scattered radiation can be completely removed and the shape of this graph, the intensity of only the direct ray and the intensity distribution of the incident scattered ray plus the direct ray can be predicted. By subtracting both, the intensity of the scattered radiation detected by each detector element 15 and the intensity of the incident scattered radiation can be derived. Here, the scattered ray detection rate is defined as: scattered ray intensity detected by each detector element 15 / incident scattered ray intensity, and each detector element 15 has a scattered ray detection rate as a parameter.

FIG. 6 is a graph showing the X-ray intensity from the detector element 15 when an actual subject is scanned.
From this graph, a direct ray distribution can be predicted by the detector element 15 having the channel direction collimator plate 2, and in FIG. 5, the detector element 15 that has detected the incident scattered ray + the direct ray predicts the incident scattered ray + the direct ray distribution. Is possible. By subtracting these distribution predictions, the intensity of only the scattered radiation incident on each detector element 15 can be derived. Then, by multiplying the estimated distribution of only the scattered radiation by the scattered radiation detection rate previously obtained by the measurement of the phantom, the scattered dose incident on each detector element 15 is estimated. By subtracting this from the original scan data, the X-ray intensity distribution of only direct rays can be estimated.

The direct ray component distribution and the scattered ray component distribution described above are estimated by a linear approximation method, a curve approximation method, or a combination thereof. The linear approximation method is a method of connecting the output level points of the detector elements 15 to form a component distribution. However, in order to maintain the shape near the edge, dense sampling points are required. A sparse sample point is sufficient. Therefore, in some cases, accurate approximation can be performed by using a combination of the linear approximation method and the curve approximation method.

[0026]

According to the radiation detector of the present invention, the collimator plate in the channel direction is arranged only at the joint of the detector module and the upper part of the adjoining part of the detector module. And the cost of the entire detector can be reduced by reducing material costs, processing costs, and assembly man-hours. Further, in the manufacturing method, the position of the collimator and the detector array can be easily adjusted using a dedicated manufacturing jig, and the finishing can be performed with high accuracy. And X using this radiation detector
In a line CT apparatus, direct rays and scattered rays are estimated from acquired data, and data correction is performed by a curve approximation method or a straight line approximation method to obtain a clear X-ray image from which scattered rays are removed.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a detector unit of an X-ray CT imaging apparatus according to the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of a detector section of the X-ray CT imaging apparatus of the present invention.

FIG. 3 is a diagram for explaining a method of manufacturing a collimator of the X-ray CT imaging apparatus of the present invention.

FIG. 4 is a diagram schematically showing a detector unit of the X-ray CT imaging apparatus of the present invention.

FIG. 5 is a diagram showing an X-ray intensity output from a detector with a uniform X-ray absorber set in the X-ray CT imaging apparatus of the present invention.

FIG. 6 is a diagram showing an X-ray intensity output from a detector when a subject is scanned by the X-ray CT imaging apparatus of the present invention.

FIG. 7 is a diagram for explaining the principle of a conventional X-ray CT apparatus.

FIG. 8 is a diagram showing a collimator of a conventional X-ray CT apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Detector module 2 ... Channel direction collimator plate 3 ... Channel direction collimator plate 4 ... Support plate 5 ... Support plate 6 ... Base 7 ... Support rod 8 ... Support plate 9 ... Scintillator array 10 ... Photodiode 11 ... Substrate 12 ... X Tube focus 13 ... Groove 14 ... Jig 15 ... Detector element 16 ... X-ray tube 17 ... X-ray beam 18 ... Subject

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 31/09 H01L 31/00 A

Claims (4)

[Claims] 1. A radiation detector for X-ray CT having a solid state detector module in which a plurality of X-ray detector elements are arranged and a channel direction collimator plate, wherein only a joint between the solid state detector modules and an adjacent part thereof are provided. A radiation detector comprising a channel direction collimator plate at a corresponding position. 2. A hollow space having a shape following the outer shape of the collimator, and a side portion of the channel direction shielding plate is formed along the inside of the space at a position corresponding to only a joint of the detector module and an adjacent portion thereof. A channel direction shielding plate is sequentially inserted along the groove into a jig frame having a vertical groove that can be inserted thereinto. Finally, the upper and lower surfaces of the plate are integrally bonded to the support, and then the frame is attached to the frame. A collimator manufactured by pulling it up or down from the body,
2. The method according to claim 1, wherein the radiation detector is arranged corresponding to the detector module. 3. A data correction method for an X-ray CT apparatus provided with a radiation detector according to claim 1, wherein the detection rate of the scattered radiation for each of the detector elements measured in advance before scanning is determined. At the time of actual scanning, the direct line component distribution is estimated based on the output value from the detector element having the channel direction collimator plate, and the output value from the detector element not having the channel direction collimator plate is calculated. Estimate the component distribution of the sum of direct rays and scattered rays based on this, and subtract the previously estimated direct ray component distribution from the estimated component distribution of the sum of the direct rays and scattered rays to obtain only the scattered rays. Estimating the distribution, multiplying the distribution of only the estimated scattered radiation by the detection rate of the scattered radiation to estimate the scattered dose incident on each of the detector elements, Data correction method of the X-ray CT apparatus characterized by subtracting from Ndeta. 4. The data correction of an X-ray CT apparatus according to claim 3, wherein an approximation method in estimating the distribution by said correction means is one of a curve approximation and a linear approximation, or a combination of both. Method.