JPH0436687A - Radiation detector - Google Patents

Abstract

PURPOSE:To reduce the image ring artifact of an X-ray CT device by specifying the width of a substrate supporting a photoelectric conversion element array, and setting the width of the array less than that of the substrate. CONSTITUTION:A scintillator array 1 which converts X-rays to light, the photoe lectric conversion element array 2, and the substrate 3 are laminated on a radiation detection block 4. A detector is comprised by arranging plural blocks 4 in polyhedral shape along a circular arc. At this time, assuming the pitch of the array 2 as (a), the number of channels of the array in the block 4 as (c), the radius of the circular arc as (r), and the sum of width of the arrays 1, 2 as (d), and assuming the substrate (b) as a X c X (r+d)/r>b, no contact of neighboring substrates (b) occurs, and no pitch deviation at a terminal part occurs. also, when it is b<aXc, the deterioration of the array 2 due to handling in a packaging process can be remarkable reduced. Therefore, the ring arcthifact generating uniquely in a terminal channel can be reduced by setting the width (b) of the substrate within such range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an X-ray tomography apparatus, and particularly to medical
Regarding CT equipment.

[Prior Art] As a detector for an X#CT device, a solid-state detector consisting of a scintillator that converts X-rays into light and a photodiode as a photoelectric conversion element that converts this light into an electrical signal has been proposed in recent years. ing. This is one of the technologies that is currently attracting attention because it inherently has a good S/N ratio of images. A detector with this structure has a block structure in which a plurality of elements are formed together in order to simplify the assembly process and achieve highly accurate element arrangement. A plurality of the radiation detection element blocks are arranged in a polyhedral shape along an arc centered on the radiation generating part to detect an X-ray transmission image (one-dimensional image) of the subject. In this case, the characteristics of the elements at the end of the block are often slightly different from those of other elements.

On the other hand, in the third-generation X1iCT apparatus, variations in the sensitivity of the CT detector between elements cause ring artifacts to occur on CT images. Therefore, when a detector having the above-mentioned block structure is used, ring artifacts often appear at locations on the image corresponding to block joints. Examples of detector mounting methods to reduce this include fixing a block-shaped detector and devising joints between blocks. However, with the recent advances in the performance of medical diagnosis,
With the increasing functionality, demands from users have become stricter, and conventional mounting methods have not been sufficient to reduce ring artifacts.

On the other hand, regarding the relationship between the characteristics of the detection element and the ring artifact, for example, there is a study by Parker et al. (Medical Physics Vol. 9, July/August issue).

(1982, pp. 531-539). However, until now, little consideration has been given to the relationship between elements having a polyhedral block structure and images.

The reason for this is that the structure of the ionization chamber, which is a conventionally widely used detector, does not require a polyhedral structure, and there is essentially no variation in element characteristics. That is, only when block-shaped elements such as scintillators and photoelectric conversion elements are arranged in a polyhedral shape,
Removal of ring artifacts has become an important issue.

Therefore, we studied the basic characteristics of block-shaped detectors arranged in a polyhedral shape, devised a structure of a detection element block that is less likely to cause variations in detector sensitivity, and arrived at the present invention.

In addition, as a prior art related to the present invention, "Unexamined Japanese Patent Publication No. 1983
-88078J r JP-A-63-151886J, etc. can be mentioned.

[Problems to be Solved by the Invention] The present invention aims to reduce image ring artifacts in an XICT device.6 [Means for Solving the Problems] As a means for solving the above problems, radiation is converted into light. A plurality of radiation detection blocks each consisting of a scintillator array, a photoelectric conversion element array for converting glare into electrical signals, and a substrate supporting the photoelectric conversion element array are arranged in a polyhedral shape along an arc. In a radiation detector, when the pitch of the photoelectric conversion element array is a, the radius of the arc of the number of channels in the array in a block is r, and the sum of the thicknesses of the scintillator and the photoelectric conversion element is d, the substrate width is We propose a radiation detector characterized in that a*c*(r+d)/r>b>a*c and the photoelectric conversion element array width e is smaller than the substrate width.

[Function] In the present invention, since the photoelectric conversion element array width is smaller than the substrate width, an increase in dark current in the end channel can be prevented by handling in the detector mounting process. In addition, since the substrate width is smaller than a tree C tree (r+d)/r, pitch deviation of end elements does not occur when a plurality of blocks are arranged in a polyhedral shape. Therefore, it is possible to reduce ring artifacts that have specifically occurred in the end channels.

[Embodiment] First, FIG. 2 shows a block diagram of an X-ray CT apparatus to which the present invention is applied. X-ray flux 12 emitted from X-ray tube 11 passes through object 13 and is detected by detection section 14 . That is, here the X-ray intensity signal is converted into a current signal. This portion may be kept at a constant temperature by a temperature control section, which is not shown in this embodiment. The current signal from the detection section 14 is converted into a voltage signal by the detection circuit section 15. This voltage signal is converted from an analog signal to a digital signal by the A/D converter 16 and sent to the signal processor 17.

The signal processing section 17 performs signal correction, for example, sensitivity correction and offset correction for each channel of the detection section and detection circuit section. One-dimensional projection data is obtained from the data group corrected in this way.

In the third generation X@CT, a large amount of projection data is acquired while simultaneously rotating the X-ray tube 11 and the detection unit 14, and a tomographic image is calculated based on this data. The image processing section 18 performs this calculation. The tomographic image obtained by the calculation is displayed on the image display section 19. Each component of the CT apparatus is controlled by a control section 20.

Next, using FIG. 3, detecting element block 4 used in the present invention.
I will explain about it.

The radiation detection element 30 consists of a scintillator and a photoelectric conversion element. The X-rays are converted into light by a scintillator, and this light is converted into a current signal by a photoelectric conversion element, such as a Si photodiode, which is optically in close contact with the scintillator. The output of this photodiode is sent to a detection circuit section, for example, a current-voltage conversion circuit (not shown) using an OP amplifier, via a conductor (not shown) on the board 3 and a connector 32. The voltage is converted. In such a block, since the photodiodes are fabricated from a single wafer, it is difficult to arrange the elements on a circular arc.

Therefore, a plurality of such planar blocks are arranged in a polyhedral shape. In this case, it was found that the end elements (1 channel and 18 channel in the figure) exhibit characteristics different from other elements. That is, during the detector mounting process, the dark current of the photoelectric conversion element in the end channel increased as shown in FIG. Therefore, this large dark current in the end channel caused a non-linear response in the end element, causing ring artifacts in both CT images. In such cases, the substrate width is usually made larger than the photoelectric conversion element width to prevent deterioration of element characteristics during handling during the detector mounting process.

However, in such a detector, many blocks are arranged in a polyhedral shape, so if the substrate width is extremely large compared to the block width calculated from the detection element pitch, a shift in the element pitch will occur, and the quality of both CT images may deteriorate. Understood. Therefore, we investigated the optimal value for the board width.

This will be explained below using FIG.

The radiation detection block 4 is formed by laminating a scintillator array 1, a photoelectric conversion element array 2, and a substrate 3. XAiC by arranging a plurality of these blocks in a polyhedral shape along an arc
This is a radiation detector for T. The pitch of the photoelectric conversion element array 2 is a, the number of channels in the array in a block is c, the radius of the circular arc is r, and the sum of the thicknesses of the scintillator and photoelectric conversion element is d.
, and if the substrate width is set as (r+d)/r>b, then adjacent substrates will not come into contact with each other, so no pitch deviation will occur at the end of the block, and the CT
It is suitable as a detector for Furthermore, the deterioration of the detection element caused by the substrate *b was significantly reduced. Therefore, the optimum range of substrate width is a*c lines (r+d)/r>b>a*c.

It has been found that by setting the substrate width as described above, the photoelectric conversion element width can be made smaller than the substrate width, and there is no deviation in the element pitch at the end of the block and the quality of both CT images does not deteriorate.

An example of a specific detector structure will be described below.

When considering a 3rd generation XICT device for the whole body, 1. For example, the thickness of the detection element and the radius of the block arrangement, respectively, d = 1.50 mm r = 1200. oomm, the board width is a*c*1.0013>b>a>*c, which is suitable for handling in the mounting process. Furthermore, the detection pitch and the number of elements in the block are, for example, a"1.00mm c=24.o.

If the width is set as 24.03>b>2.00. Therefore, if the substrate width is 24.02 mm and the photoelectric conversion element width is 24.00 mm, the substrate width will be 0.010 mm wider at both ends than the photoelectric conversion element.
It is possible to prevent element deterioration due to handling of the end of the block.

[Effects of the Invention] In the present invention, since the photoelectric conversion element array width is smaller than the substrate width, an increase in dark current in the end channel due to handling in the detector mounting process can be prevented. Further, since the substrate width is made smaller than B lines c*(r+d)/r, pitch deviation of the end elements does not occur when a plurality of blocks are arranged in a polyhedral shape. Therefore, it is possible to reduce ring artifacts that have specifically occurred in the end channels.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of a radiation detector according to an embodiment of the present invention, FIG. 2 is a block diagram of an X-ray CT apparatus to which the present invention is applied, and FIG. 3 is a detection section used in the present invention. FIG. 4 is a dark current characteristic diagram of an X-ray detection element for explaining the present invention in detail. Figure Z (enemy w supplement)

Claims (1)

[Claims] 1. A radiation detection block comprising a scintillator array that converts radiation into light, a photoelectric conversion element array that converts each of the lights into electrical signals, and a substrate that supports the photoelectric conversion element array. , in a radiation detector consisting of a plurality of photoelectric conversion element arrays arranged in a polyhedral shape along an arc, the pitch of the photoelectric conversion element array is a, and the number of channels of the array in a block is c.
, the radius of the arc is r, and the sum of the thicknesses of the scintillator and the photoelectric conversion element is d, then the substrate width b is a*c*(r+d)/r>b>a*c, and the photoelectric conversion A radiation detector characterized in that an element array width e is smaller than a substrate width b. 2. In a radiation detector consisting of a laminated scintillator array that converts radiation into light, a photoelectric conversion element array that converts each light into an electrical signal, and a substrate that supports the photoelectric conversion element array, the width of the substrate is determined by the width of the photoelectric conversion element array. When the pitch of the element array is a, the number of channels in the array in a block is c, and the sum of the thicknesses of the scintillator and photoelectric conversion element is d,
A radiation detector characterized in that a substrate width b satisfies a*c*1.0013>b>a*c.