JP2003084067A - X-ray detector, and x-ray ct device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent light from being leaked in a space between adjacent elements in a multi-element X-ray detector combined with scintillators and a silicon photo-diode array, and to effectively guide emitted light from the scintillators to the silicon photo-diode array to enhance an S/N ratio and spatial resolution. SOLUTION: The scintillators 1 and separation zones (dead zones) in order to separate channels in intermediates between the respective scintillators 1 are provided in positions corresponding to the separation zones for separating spaces between the channels in the photo-diode array 3 of multi-channel arranged with a prescribed pitch on a substrate, and grooves are provided for inserting partitioning walls reaching to an inside of an adhesive layer 4 for bonding the scintillators 1 and silicon photo-diodes, between the respective scintillators 1. A refractive index of an adhesive for forming the adhesive layer has a value slightly smaller than those of a reflection-preventive film provided in a photo-receiving surface of the photo-diode array 3 and the scintillators 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray detector for simultaneously detecting X-ray transmission data of a plurality of slices and an X-ray CT apparatus using the same, and particularly to electrical and optical crosstalk between respective detection elements. To increase the mounting density and make the characteristics of each detector uniform, resulting in high spatial resolution,
X-ray detector capable of detecting high S / N X-ray transmission data and this
X-rays suitable for obtaining high-quality tomographic images using an X-ray detector
Regarding CT equipment.

[0002]

2. Description of the Related Art An X-ray CT apparatus prevents image deterioration due to movement of organs in the human body, reduces the burden on the patient, and
In order to improve the throughput of the device, it is desired to reduce the time required to obtain one CT image. There are two methods to reduce this time. (1) Shortening the time required for one rotation of the scanner (2) Increasing the number of tomographic images that can be taken per one rotation of the scanner

Regarding (1), the rotation speed of the scanner is improved by reducing the weight of the X-ray tube which is the X-ray generator and the rotating portion of the apparatus, and the time is shortened by speeding up the signal processing. There is. On the other hand, with regard to (2), in the X-ray detector, the rows of X-ray detection elements that have been arranged one-dimensionally in the channel direction so far are divided into two rows in the slice direction (direction orthogonal to the channel direction) or This is achieved by arranging the above multiple columns.

With such a single X-ray exposure, two-dimensional
An X-ray CT device that collects X-ray data and obtains multiple CT images, that is, a multi-slice X-ray CT device (used for this
The X-ray detector is referred to as a multi-slice X-ray detector.) The X-ray CT system that was used in the past was called a single-slice type X-ray CT system.)
There is an advantage that the utilization efficiency of the line is also high.

The above-mentioned multi-slice type X-ray detector includes
Instead of a conventional ionization chamber type detector using xenon gas, a solid-state detector that can obtain high spatial resolution and high S / N (signal / noise) is used. This solid state detector
It consists of a scintillator that converts incident X-rays into light and a photodetector element such as a silicon photodiode that detects the light converted by this scintillator and outputs it as an electrical signal.
A large number of X-ray detection element groups are arranged in a substantially arc shape around the X-ray source in the channel direction and the slice direction orthogonal to the channel direction.

As described above, since the multi-slice type X-ray detector is constructed by arranging a large number of X-ray detecting elements in the channel direction and the slice direction, the output signals of these X-ray detecting elements are the same as those of the conventional single-ray detecting elements. The number is much larger than that of slice type X-ray detectors, and how to extract efficiently in a limited mounting space is a major issue.

As described above, since a multi-element array is required for the X-ray detector for the X-ray CT apparatus, it is not necessary to arrange single-channel chips as the photo-detecting element for converting the output light of the scintillator into an electric signal. Instead, a large number of photo-detecting element arrays disclosed in Japanese Patent Laid-Open No. 2000-316841 in which a plurality of channels are formed on one chip are used.

Since the photodetector array must be arranged with high density in a limited mounting space, a semiconductor device such as a silicon photodiode is generally used. Naturally, the multi-slice X-ray detector has a much larger number of X-ray detection elements than the conventional single-slice type X-ray detector, and it is necessary to make the detection characteristics of these individual X-ray detection elements uniform. Is also a big issue.

If there is a variation in the detection characteristics among the X-ray detection elements, annular false image noise (hereinafter, referred to as ring artifact) or the like occurs in the reconstructed CT image, which deteriorates the image quality. Also, if there is a variation in the detection characteristics of the X-ray detection element in the slice direction, even when measuring the image data of the same slice surface of the subject, it is measured by the position of the X-ray detection element in the slice direction There is a risk that the data will be different and the image quality of the CT image and the medical information obtained from the CT image will be different.

Despite measuring the image data of the same slice surface of the same subject, the CT images obtained will never be different due to the different characteristics of the X-ray detection elements used for the measurement. This should not happen. For this reason, the characteristics of the X-ray detection element are
It is necessary that the slice directions are sufficiently aligned.

From the above, in order to make the characteristic values of the X-ray detection elements uniform, the leakage amount of the electrical signal between the elements is required.
It is important to reduce (hereinafter referred to as electrical crosstalk) and the amount of leakage of X-rays or light (hereinafter referred to as optical crosstalk). The multi-slice type X-ray detector required to have such a feature is basically a system in which conventional single-slice type X-ray detectors are arranged side by side in the slice direction.

FIG. 9 shows a perspective view of the basic structure of a conventional single-slice type X-ray detector. In Figure 9, 1 is incident
A scintillator that converts X-rays 5 into light, 2a is a separator that separates the X-ray detection elements that are adjacent in the channel direction, and 3 is a silicon photodiode array that converts the light converted by the scintillator into an electrical signal. The scintillator 1 is adhered to the upper surfaces of a plurality of light receiving portions provided on the surface of the diode array, and the scintillator 1 and the separator 2a are arranged in parallel on the circuit board 6 at a predetermined pitch to form an X-ray detection element array. Further, 7 is a top reflection plate / shield plate for efficiently reflecting the light from the scintillator 1 to guide it to the silicon photodiode array 3 and for shielding the outside light from leaking into the detector.

In the above structure, the X-rays 5 incident on the detector
Is converted by the scintillator 1 into visible light having an intensity proportional to the intensity of the X-ray 5. The converted light is transmitted through the scintillator 1 while being repeatedly reflected by the inner surface and the surface of the upper reflector / shield plate 7, the surface of the separator 2a, the interface of the scintillator 1, or the surface, and the silicon photodiode. The light is guided to a light receiving portion provided on the surface of the array 3, photoelectrically converted, and detected as an electric signal (photocurrent) having an intensity proportional to the intensity of light, that is, the intensity of the X-ray 5.

By arranging the single-slice type X-ray detectors having such a structure in the slice direction, as described above, the optical crosstalk and the electrical crosstalk are reduced and the X-ray detector is reduced.
The multi-slice type X-ray detector must be constructed so that the detection characteristics between the line detection elements are uniform.

The characteristics of the X-ray detector are evaluated mainly by S / N and spatial resolution. S / N is the contribution rate of the incident X-ray 5 to the output signal, that is, the X-ray utilization efficiency and X-ray detector X
It is determined by the electric signal (noise signal) generated in the electric circuit system including the silicon photodiode 3 when the line is not incident. This X-ray utilization efficiency depends on the luminous efficiency (light conversion efficiency) of the scintillator 1, the silicon photodiode 3
Is determined by the photoelectric conversion efficiency, the space utilization efficiency that is the spatial X-ray utilization efficiency of the X-ray detector, and the light transmission efficiency in the X-ray detector.

The noise signal is mainly due to shot noise of the silicon photodiode 3, dark current due to recombination current in the depletion layer, and noise current of an electric circuit system such as a preamplifier for amplifying the output current of the silicon photodiode 3. is there. Among the factors that influence the X-ray utilization efficiency, the light emission efficiency (light conversion efficiency) of the scintillator 1 and the photoelectric conversion efficiency of the silicon photodiode array 3 are uniquely determined by their physical characteristics.
The space utilization efficiency is improved by reducing the region that does not contribute to the detection of the incident X-rays 5, that is, the region other than the scintillator 1, such as the space occupied by the separator 2a that separates the elements. The light transmission efficiency reduces self-absorption of light in the scintillator 1 and absorption of light on the surface of the upper reflection plate 7 and the surface of the separator 2a, and at the same time, the surface of the scintillator 1 having a large refractive index and the silicon photodiode. 3
It is improved by reducing the amount of light reflected on each surface by efficient optical coupling with the surface of the light receiving surface and capturing more light in the light receiving portion.

On the other hand, a factor that influences the spatial resolution of an image reconstructed using X-ray data obtained by such an X-ray detector is geometrically between the adjacent separators 2a shown in FIG. Distance, that is, the aperture width of each element of the X-ray detector. Physically and optically, electrical crosstalk between adjacent elements of the X-ray detector, and X-ray or optical crosstalk. . Furthermore, there is an image noise amount due to remarkable deterioration of S / N.

First, the spatial resolution is improved by narrowing the aperture width of each element of the X-ray detector, which is a geometric factor, in principle. In recent years, the aperture width of each detection element is often 1 mm or less because higher spatial resolution is required. However, there is a limit to the narrowing of the opening width. That is, when the aperture width is extremely narrowed, each X
Since the X-ray dose of the incident X-ray 5 to the line detection element also decreases, the output signal of the detection element becomes small, the S / N deteriorates, the image noise increases, and conversely the spatial resolution decreases.

Further, as the opening width is narrowed, the ratio of the space occupied by the separator 2a having a constant thickness inserted between the X-ray detecting elements increases, so that the space utilization efficiency also decreases. Further, the light emitted from the scintillator 1 when the aperture width becomes narrower, the self-absorption in the scintillator 1 or the frequency of reflection on the surfaces of the scintillator 1, the upper reflector 7 and the separator 2a increases. The light attenuation increases, and the light transmission efficiency decreases. As a result, the output signal of the X-ray detector is reduced, and the S / N is reduced.

When the amount of electrical crosstalk or optical crosstalk between the elements of adjacent X-ray detectors increases, the spatial resolution deteriorates. Conventionally, the following methods have been used to reduce these crosstalks. Means are used.
First, in the case of a multi-element silicon photodiode array, a method as shown in FIG. 10 is used to reduce electric crosstalk.

FIG. 10 is a cross-sectional structure of a PIN type multi-element silicon photodiode array capable of obtaining low noise, high sensitivity and a wide dynamic range. In FIG.
3a is an n-type semiconductor N ⁺ layer, 3b is an intrinsic semiconductor (i-type semiconductor) N ⁻ layer with a low impurity concentration in the region where the depletion layer spreads, and 3c provided on the surface are p-type semiconductor P ⁺ layers (light receiving Area).

A dead region I (N ⁻ ) layer, that is, 3b ′ exists between the plurality of light receiving regions 3c, and electrically separates the elements.
Then, in order to further ensure electrical isolation, 3a ′ (n-type semiconductor region) and 3c ′ (p-type semiconductor region) are locally formed in the dead region I (N ⁻ ) layer as isolation. There is. In FIG. 10, 3d is an anode electrode of the silicon photodiode, 3e is an antireflection film of the silicon photodiode, and 3f is a protective oxide film of the silicon photodiode.

As a method of preventing optical crosstalk, a method of filling a narrow gap between adjacent scintillators with a light reflecting material (white pigment) 2b also serving as an isolation wall as shown in FIG. 11 (Patent No. 1738475) or a metal separating plate as a separating wall between adjacent scintillators as shown in FIG.
Method for inserting 2a '(Patent No. 2720159 Publication, Patent No. 2720
No. 162) has been proposed. It should be noted that reference numeral 4 in FIGS. 11 and 12 denotes an adhesive layer for adhering the scintillator 1 and the silicon photodiode.

[0024]

The conventional crosstalk reducing method as described above has the following problems. That is, in the structure shown in FIG. 11 of Japanese Patent No. 1738475, adjacent elements are separated by filling a narrow gap between the scintillators 1 with a light reflecting material 2a ′ also serving as an isolation wall. In this case, since the portion of the adhesive layer 4 that bonds the scintillator 1 and the silicon photodiode 3 does not have an optical separation portion, a problem such as occurrence of light crosstalk in the adhesive layer 4 can be considered.

Further, in the structure shown in FIG. 12 disclosed in Japanese Patent No. 2720159, after the scintillator 1 and the silicon photodiode 3 are bonded, the inside of the scintillator 1 and the silicon photodiode 3 are cut. , The position difference between the scintillator 1 and the silicon photodiode 3 can be prevented, and the silicon photodiode 3
Since the metal separator separator 2a is inserted to the inside as a separator wall, there is an advantage that crosstalk of light can be prevented, but on the other hand, due to the influence of microcracks generated when the surface of the silicon photodiode 3 is cut. Problems such as increase in leakage current and dark current of the silicon photodiode, decrease in S / N, and variation in characteristics of the X-ray detection element can be considered.

When the electrical / optical crosstalk reducing method having the above problems is used in a multi-slice type X-ray detector, the following problems can be considered. That is, in order to realize a two-dimensional multi-element detector for a multi-slice type X-ray CT device, it is necessary to make the silicon photodiode array, which is a photoelectric conversion element, also have a two-dimensional multi-element structure. In order to improve the spatial resolution of the structure, it is essential to improve the packaging density of the silicon photodiode array.

Therefore, in the multi-slice type X-ray detector, it is indispensable to reduce the area occupied by the non-light-receiving portion of the silicon photodiode array and use this portion as a wiring region to increase the packaging density. . Even if the conventional method disclosed in Japanese Patent No. 173847 or Japanese Patent No. 2720159 is adopted for the multi-slice type X-ray detector required to increase the packaging density, a predetermined spatial resolution is obtained. There is a limit to increasing the mounting density while ensuring S / N and.

Therefore, an object of the present invention is to reduce the electrical and optical crosstalk between the X-ray detecting elements, to increase the mounting density and to make the characteristics of each X-ray detecting element uniform, thereby achieving high spatial resolution, An object of the present invention is to provide an X-ray detector capable of detecting high S / N X-ray transmission data and an X-ray CT apparatus suitable for obtaining a high-quality tomographic image using this X-ray detector.

[0029]

The above object is achieved by the following.

(1) A scintillator that emits light by detecting incident radiation, a photodetector array having a light receiving region separated at least in the channel direction, and an isolation wall provided between the channels to separate the channels. An X-ray detection element array including and is mounted on a substrate, and a plurality of X-ray detection element arrays mounted on this substrate are formed in a polygon shape at a substantially equal angular pitch on a substantially arc centered on the focal point of the X-ray tube in the channel direction. In the arrayed X-ray detector, a separation band that separates the channels between the respective light receiving portions for each channel of the photodetector array, and between the channels of the scintillator corresponding to the range of the separation band, and A groove reaching to the inside of an adhesive layer for adhering the photodetection element and the scintillator is provided, and the bottom of the groove is the photodetection element in the adhesive layer. Present in the near surface position, configured such that the partition wall in the groove reaches a position where it reaches the bottom of the groove.

(2) The distance between the bottom of the groove and the surface of the dead zone of the photodetector is equal to or narrower than the groove width of the groove.

(3) The adhesive for adhering the photodetection element and the scintillator is bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol A
An epoxy resin of any of D-type epoxy resins, or an epoxy resin composed of a mixture thereof and an amine-based or polyamide-based curing agent are mixed, and the refractive index of the adhesive is the same as that of the photodetection element. The antireflection film provided on the surface of the light receiving portion and the refractive index of the scintillator are made slightly smaller.

(4) A spacer made of a colorless and transparent substance having a refractive index in the range of 1.4 to 1.6 is provided in the adhesive layer to keep the thickness of the adhesive layer uniform.

(5) X-ray tube for irradiating the subject with an X-ray beam, and X-ray detection for detecting the X-rays transmitted through the subject and arranged to face the X-ray tube and converting the X-rays into electrical signals Bowl and this
A preamplifier for amplifying the output signal of the X-ray detector, an AD converter for converting an analog output signal from this preamplifier into a digital signal, and holding at least the X-ray tube and the X-ray detector, An X-ray CT apparatus including a rotating disk that is rotationally driven around, a scan condition setting unit that sets a scan condition, and an image processing unit that reconstructs an X-ray image based on the output signal of the AD converter. Yes, the X
The X-ray detectors (1) to (4) above are used as the line detector.

In the X-ray detector having the above structure, when the light emitted from the individually separated scintillator leaks through the adhesive layer to the adjacent scintillator or each light receiving portion of the photodiode array as the photodetecting element. Must pass through the separation band between each light receiving portion of the above photodiode array. However, the groove is provided in the adhesive layer of the separation zone so that the bottom reaches a position closer to the surface of the photodiode array in the adhesive layer, and the separator which reaches the bottom of the groove is provided in the groove. (Isolation wall) is inserted. Therefore, most of the light reaching the separation band is blocked by the separator, and does not leak into the respective light receiving portions of the adjacent scintillator or photodiode array. However, there is a slight possibility that a small amount of light may pass through an extremely narrow gap between the separator and the surface of the separation band of the photodiode array. In order to reduce the refractive index, the refractive index of the adhesive forming the adhesive layer is slightly smaller than the refractive indexes of the antireflection film and the scintillator provided on the surface of the light receiving portion of the photodiode array. In this way, by making the refractive index of the adhesive slightly smaller than the refractive index of the antireflection film and the scintillator provided on the surface of the light receiving portion of the photodiode array,

A) The light emitted from the scintillator having a large refractive index is less reflected at the interface between the scintillator and the adhesive having a smaller refractive index, and is more likely to go out of the scintillator, that is, toward the adhesive.

(B) The critical angle of light incident on the light receiving portion of the photodiode array having a large refractive index and the scintillator becomes small. As a result, the incident angle of light that can be incident on the light receiving portion of the photodiode array and the scintillator from the outside is limited within the range of the above-described small critical angle.

(C) Light from the side of the light-receiving portion of the photodiode array having a large refractive index and the scintillator from the adhesive side having a small refractive index is limited within the range of the critical angle, and light having a large incident angle exceeding the critical angle is detected. The light is totally reflected by the surface of the light receiving portion of the photodiode array and the surface of the scintillator, and does not enter the light receiving portion of the photodiode array and the scintillator.

Of the light passing through an extremely narrow gap between the separator and the surface of the separation band of the photodiode array, most of the light having a small incident angle that can be incident on the surface of the photodiode array and the scintillator. Is absorbed by multiple reflections on the surface of the separation band of the photodiode array and the surface of the separator in the plate thickness direction, which is an extremely narrow gap, and does not reach the light receiving portion or the scintillator of the adjacent photodiode array. On the other hand, light with a large incident angle that can pass through the gap without being absorbed by the gap exceeds the critical angle of the light receiving portion or the scintillator surface of the adjacent photodiode array, so the light receiving portion surface of the photodiode array and the scintillator surface. Is totally reflected by and does not enter the light receiving portion of the photodiode array and the scintillator. Therefore, crosstalk of light between adjacent elements can be suppressed, and spatial resolution can be improved.

Further, since it is not necessary to cut and separate each detecting element to the inside of the photodiode disclosed in Japanese Patent No. 2720159 shown in FIG. 12, the silicon photodiode due to the influence of microcracks or the like generated during processing. It is possible to solve problems such as a decrease in S / N and variations in detector characteristics due to an increase in leakage current and dark current.
Furthermore, since the separation band part of the silicon photodiode can be effectively used as a wiring area, a multi-element solid X-ray detector suitable for a multi-slice type X-ray CT device with a two-dimensional element array can be realized. It is possible to provide an X-ray CT apparatus which can obtain a plurality of high-quality slice tomographic images at one time using a scanning device.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. << X-ray detector >> Regarding the X-ray detector according to the present invention, FIGS.
Will be described with reference to. FIG. 1 illustrates the present invention as a multi-slice type X.
Perspective view of a two-dimensional multi-element X-ray detector used for the X-ray detector for the X-ray CT apparatus, FIG. 2 is a cross-sectional view showing a state in which a groove for optically separating and isolating the scintillator is formed (channel direction, slice Direction is an arbitrary sectional view), FIG. 3 is a sectional view of the first embodiment of the two-dimensional multi-element detector of FIG. 1 (channel direction, slice direction is an arbitrary sectional view), FIG. 4 is a second embodiment. FIG. 5 is a cross-sectional view for explaining the configuration of each of the cross-sectional views when used in the channel direction, and FIG. 5 is a cross-sectional view for explaining the configuration of the adhesive layer of the detection element of the first and second embodiments Slice direction cross-sectional view of the slice portion, FIG. 6 is a cross-sectional view of the silicon photodiode array of the first and second embodiments for the two-dimensional multi-element detector of FIG. 1 (channel direction, slice direction is any cross-sectional view ). 1 to 6, the same reference numerals indicate the same parts.

In FIG. 1, reference numeral 5 denotes an incident X-ray, and 7 is provided for the purpose of blocking external light incident on the detector and efficiently reflecting the light emitted from the scintillator 1 to guide it to the silicon photodiode array 3. 3 shows the prepared upper reflector. The inside of the detector is adhered to the upper surface of each of the plurality of light receiving portions provided on the surface of the two-dimensional silicon photodiode array 3 and is separated on the circuit board 6 together with the separator plate 2a in the channel direction and the separator plate 2a 'in the slice direction. Two-dimensional X-ray detector array is formed by arranging two-dimensionally in parallel at a pitch. The two-dimensional X-ray detection element array of the embodiment of FIG. 1 is compatible with 12 channels and 4 slices (each channel is divided into 4 in the longitudinal direction). Therefore, in the X-ray CT apparatus equipped with the X-ray detector incorporating the two-dimensional X-ray detection element array of FIG. 1, a multi-slice X-ray that simultaneously obtains 4 slice (4 tomographic) tomographic images in one scan is obtained. A line CT device can be configured. The optical crosstalk and electrical crosstalk of the two-dimensional multi-element solid-state X-ray detector having such a configuration are reduced by the following examples.

(First Embodiment) In FIG. 2, 1 is an incident X
A scintillator that converts a line into light, 1a is a groove formed to insert a separator that optically separates and separates adjacent scintillators, and 3 and 3a convert the light converted by the scintillator 1 into an electric signal. The two-dimensional silicon photodiode array, 4 is an adhesive (adhesive layer) that optically and mechanically connects the scintillator 1 and the two-dimensional silicon photodiode array 3.

The procedure for forming this structure is that the adhesive 4 is applied to the light-receiving surface of the two-dimensional silicon photodiode array 3.
Using, the scintillator 1 molded into a predetermined size and thickness is adhered and fixed. As the adhesive (adhesive layer) 4 that optically and mechanically bonds, a highly transparent and stable X-ray is used. Further, the refractive index n of the adhesive is optimal depending on the type of antireflection film of the light receiving part of the silicon photodiode array used and the type of scintillator, but generally n = 1.4 to 1.6, for example Epoxy resin consisting of any one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, or a mixture thereof and a reactive diluent for viscosity adjustment and a silane cup as a resin modifier. Those mixed with a ring agent are desirable. A polyamide-based curing agent such as 3,9-bis (3-aminopropyl) -2,4,8,10-tetrapyro [5,5] undecane: (ATU), or an amine-based curing agent is used as the curing agent. .

The thickness of the adhesive (adhesive layer) 4 influences the optical crosstalk amount, and if the thickness is too thick, the crosstalk amount increases, and if the thickness is too thin, air bubbles are likely to be mixed in. Problems such as weak mechanical strength occur. For this reason,
It is important to select the thickness of the adhesive (adhesive layer) 4, and the isolation wall (Fig.
1 or less of the width of the separator 2a, 2a '), 0.05 mm or less when the width of the separator wall (separator 2a, 2a' of Figure 1) is 0.1mm (practically 0.01mm ~ 0.02 mm) is desirable. Further, if the thickness of the adhesive layer is not uniform, the optical crosstalk amount may be partially increased, and the surface of the silicon photodiode array may be damaged during the groove forming process described later. Therefore, it is necessary to keep the thickness of the adhesive layer uniform. A means for making the thickness of the adhesive layer uniform can be achieved by inserting a spacer 8 between the scintillator 1 and the silicon photodiode array 3 as shown in FIG.

The spacer 8 inserted in the adhesive layer which is an optical path from the scintillator 1 to the light receiving portion of the silicon photodiode array 3 should not interfere with the light from the scintillator 1. Depending on the material, it may cause unevenness in the sensitivity of the detector, so it is necessary to pay sufficient attention when selecting the material. As the material, it is colorless and transparent, has high durability against X-rays (especially one that does not cause optical changes such as coloring), and to prevent light from bending,
It is required that the refractive index is close to that of the adhesive used (n = 1.4 to 1.6). As a specific example, it is convenient to use a true spherical spacer made of resin, glass, or quartz having a uniform diameter, or a round bar or pipe made of a similar material having a uniform diameter. In addition, 9 is an adhesive layer.

Next, as shown in FIG. 2, a groove 1a (not shown) having a predetermined width is formed along the separation band at a position corresponding to the separation band of the two-dimensional silicon photodiode array 3 of the scintillator 1. Form. The depth of the groove 1a is preferably set so that the bottom of the groove 1a is closer to the surface of the two-dimensional silicon photodiode array 3 within the range of the adhesive layer 4. As a groove forming processing means, a dicing saw using a thin blade diamond grindstone or a wire saw
(A free abrasive grain or a wire in which diamond abrasive grains are electroformed) is used.

In FIG. 2, the scintillator is divided into eight channels by forming a groove in order to correspond to a silicon photodiode array whose channel direction is eight channels.

FIG. 6 shows a detailed cross section of the two-dimensional silicon photodiode array 3 shown in FIG. The silicon photodiode array used for the X-ray detector for X-ray CT apparatus is required to convert the weak light from the scintillator into an electric signal.
Therefore, in order to obtain a wide dynamic range, high quantum efficiency, and fast response speed, the intrinsic semiconductor (i-type semiconductor) layer 3b in which the impurity concentration in the region where the depletion layer spreads between the p-type semiconductor 3c and the n-type semiconductor 3a is low is reduced. It is desirable to use a pin type silicon photodiode having In order to further reduce the capacitance and dark current to improve the S / N of the detector, it is desirable to use the substrate (wafer) of the pin type silicon photodiode as an epitaxial substrate.

The refractive index of the p-type semiconductor 3c which is the light receiving region is n≈
Adhesive (adhesive layer) 4 that is as large as 3.5 and is in contact with the surface
Since the difference in the refractive index (n≈1.5) between and is large, the critical angle for incident light becomes small, and the amount of reflection on the surface of the p-type semiconductor 3c increases. Therefore, the refractive index n is 1.4 or less for the purpose of efficiently entering the light on the light incident side surface of the p-type semiconductor 3c.
An antireflection film 3e (SiO ₂ film, SiN film, etc.) of about 2.7 is provided. Further, the anode electrode 3d (A1) for extracting a signal current (photocurrent) is formed on a part of the surface of the p-type semiconductor 3c which is a light receiving region.
A thin film, etc., and the surface is a protective film for the purpose of corrosion prevention 3
Cover with f (SiO ₂ film, etc.). It should be noted that 3g and 3h will be described later, and other reference numerals other than the above are the same as those in the conventional technique of FIG.

FIG. 3 shows a state in which a separator 2a is inserted for the purpose of optically separating adjacent channels into the groove 1a formed for channel separation in FIG. The separator 2a is inserted so that its lower portion reaches the bottom of the groove 1a, and its upper portion is slightly protruded from the surface of the scintillator 1.

The separator 2a uses a thin metal plate as a material,
Polishing the surface, plating, resin coating, PVD, CVD
A mirror surface is formed by such means as the above, and an optical reflection enhancing film (a mirror surface that reflects light to obtain a higher reflectance) is formed on the surface, and the light from the scintillator 1 is efficiently reflected to the silicon photodiode. It should be led to the light receiving part of the array 3. Here, a more specific description will be given by adding numerical values to the present embodiment. Assuming that the pitch of the detector in the channel direction is 1 mm, the opening width of the detector (that is, the width of the scintillator 1) is 0.9 mm, and the width of the separating wall (separating plates 2a and 2a ') is 0.1 mm.
mm is appropriate. On the other hand, the dimensions on the side of the silicon photodiode array to be combined are as shown in FIG.
c) and the light receiving portion (p-type semiconductor 3c) pitch is 1 mm, the width of the light receiving portion (p-type semiconductor 3c) is 0.7 mm ~ 0.8 mm, the opening width of the detector (i.e. the width of the scintillator 1) Set smaller than 0.9mm.

The surface of the light receiving portion (p-type semiconductor 3c) is an antireflection film 3e (SiO ₂ film, which is a transparent optical thin film having a refractive index n of about 1.4 to 2.7, for the purpose of efficiently entering light. SiN film).

The width of the separation band (dead zone: i-type semiconductor region where the p-type semiconductor is not formed) 3b for separating elements provided between the light-receiving portions (p-type semiconductor 3c) is 0.3 mm (the light-receiving portion Width is 0.
(8 mm is 0.2 mm) and the width of this area is the isolation wall
Be sure to make it wider than the width of (separator 2a). Further, to prevent electrical crosstalk in this region, locally formed for the purpose of more sure electrical isolation 3a '(n-type semiconductor region), 3c' (p-type semiconductor region), 3a ' The width of each (n-type semiconductor region) is 0.03 mm to 0.05 mm (0.02 mm to 0.03 mm when the width of the light receiving part is 0.8 mm), the first layer insulation protection on the surface of the substrate separation zone (dead zone) Anode electrode 3d (A1 thin film) for extracting the signal current (photocurrent) of each light receiving part (p-type semiconductor 3c) between the film 3f (SiO ₂ film etc.) and the second layer 3e (SiN film etc.) Signal lead-out wiring 3d '(A1 thin film etc.) shown in Figure 1 connected to
To provide. In addition, a light-shielding film 3g (metal thin film such as A1, Ag, etc.) is provided on the second layer 3e (SiN film, etc.) to block light from entering the dead zone. Covering with a light absorbing film 3h that exhibits black or gray black and absorbs light (a thin film of carbon and a carbon compound, a metal sulfide, an oxide, or the like) is also an effective means for preventing light crosstalk.

(Second Embodiment) FIG. 4 is a sectional view (arbitrary sectional view in the channel direction) of a second embodiment of the two-dimensional X-ray detection element array of FIG. In FIG. 4, in order to optically separate adjacent channels in the groove 1a formed for channel separation in FIG. 2, except for filling the isolation wall 2 shown in FIG. The structure is almost the same as that of the embodiment, and the same reference numerals in the drawings indicate the same parts.
For the only different separating wall 2, a white pigment mixed with a binder is used instead of the separating plate 2a. Similar to the first embodiment, the isolation wall 2 is filled up to the position where the lower portion of the isolation wall 2 reaches the bottom of the groove 1a. TiO ₂ (use rutile type to maintain stable state), BaSO ₄ , Mg as white pigment
A material having a high reflectance such as O is used, and a resin having high durability against X-rays, such as an epoxy resin, is used as a binder.

According to the embodiments of FIGS. 3 and 4 described above, the light emitted from the scintillator 1 of the X-ray detection element array is separated by the separator 2a, the surface of the upper reflection plate, the interface of the scintillator 1, or the surface. Scintillator 1 with repeated reflections
Is emitted to the adhesive layer 4 and further penetrates the adhesive layer 4 to be guided to each light receiving portion (p-type semiconductor 3c) of the silicon photodiode array 3 and photoelectrically converted, and as an electric signal (photocurrent). To be detected. However, the light emitted to the adhesive layer 4 is transmitted to each light receiving portion (p-type semiconductor) of the silicon photodiode array.
Some do not go to 3c), but some go in the adhesive layer 4 in the lateral direction, that is, toward the adjacent element, and this light is incident on the light receiving portion of the adjacent silicon photodiode array, and this crosses the light. It becomes a factor of talk.

However, according to the above-described embodiment of the present invention, when the light emitted from the scintillator leaks through the adhesive layer to each light receiving portion of the adjacent scintillator or photodiode array, the photodiode array described above is always used. Through the separation band between each of the light receiving parts. However, the groove is provided in the adhesive layer of the separation zone so that the bottom reaches a position closer to the surface of the photodiode array in the adhesive layer, and the separator which reaches the bottom of the groove is provided in the groove. (Isolation wall) is inserted. Therefore,
Most of the light that has reached the separation band is blocked by the separator, and does not leak into the light-receiving portions of the adjacent scintillator or photodiode array. However, not all of the light is obstructed, and only slightly, but a small amount of light passes through the very narrow air gap between the separator and the surface of the separation band of the photodiode array.

In the present invention, even the slight amount of light passing through the extremely narrow gap between the separator and the surface of the separation band of the photodiode array is dealt with by the following means. That is, as described above, the adhesive that forms the adhesive layer has a refractive index that is slightly smaller than the refractive indexes of the antireflection film and the scintillator provided on the surface of the light receiving portion of the photodiode array. in this way,
When an adhesive having a refractive index slightly smaller than that of the antireflection film and scintillator provided on the light receiving surface of the photodiode array is used, the separation band of the separator and the photodiode array is used. Of the light passing through the extremely narrow gap with the surface, most of the light with a small incident angle that can enter the surface of the photodiode array and the scintillator is the separation band of the photodiode array where the gap is very narrow. It is absorbed by multiple reflections on the surface and the surface of the separator in the plate thickness direction, and does not reach the light receiving portion or the scintillator of the adjacent photodiode array.

On the other hand, the light having a large incident angle that is not absorbed by the gap and can pass through the gap exceeds the critical angle of the light receiving portion of the adjacent photodiode array or the surface of the scintillator, and therefore the light receiving portion surface of the photodiode array. The light is totally reflected by the surface of the scintillator and does not enter the light receiving portion of the photodiode array and the scintillator. Therefore, crosstalk of light between adjacent elements can be suppressed, and spatial resolution can be improved. Further, by having the above structure, because it is not necessary to cut and separate each detection element up to the inside of the photodiode 3 as disclosed in Japanese Patent No. 2720159, due to the influence of micro cracks or the like generated during processing. It is possible to solve problems such as a decrease in S / N and variations in detector characteristics due to an increase in leakage current and dark current of the silicon photodiode.

Although the embodiments shown in FIGS. 3 and 4 have been described as being applied to the detecting elements in the channel direction, the detecting elements in the slice direction are also used in the same manner, and these are combined to detect the multi-slice type X-ray. It constitutes a container.

<< Multi-Slice X-ray CT Apparatus >> FIG. 7 shows a multi-slice X-ray detector of the present invention mounted on a scanner rotating plate, and FIG. 8 shows a multi-slice X-ray CT apparatus of the present invention. The block diagram of the whole system is shown.

In FIG. 8, the multi-slice X-ray of the present invention is shown.
The entire system of the CT device is composed of three units: a scanner 45, a console 46, and an image processing device 47. A scanner rotating plate 35 is rotatably supported at the center of the scanner 45. An X-ray tube 36 and an X-ray detector 38 are mounted on the scanner rotary plate 35 so as to face each other with an opening 41 provided in the center interposed therebetween.

According to FIG. 7, X-ray detection on the scanner rotary plate 35
The arrangement of 38 will be described. The X-ray detector 38 is the scanner rotating plate 35.
The X-ray tube 3 with the subject 42 inserted in the opening 41 above interposed therebetween
It is arranged so as to face 6. The X-ray detector 38 is housed in the detector container 37 together with the collimator plate 39.
The X-ray detector 38 is composed of a plurality of X-ray detection element arrays 10, and these X-ray detection element arrays 10 are arranged in a polygonal shape with the focal point of the X-ray tube 36 as the center. Scattering X incident on the front surface of the X-ray detector array 10 from directions other than the focal direction
Collimator plates 39 for preventing rays from entering the X-ray detection element array 10 are arranged in a radial pattern centered on the focal point of the X-ray tube 36. Further, on the front surface of the X-ray tube 36, for narrowing the X-ray beam in the slice direction and the channel direction,
An X-ray beam collimator 49 is arranged. X-ray detector 38
The measurement by means of inserting the subject 42 into the opening 41, irradiating the subject 42 with X-rays emitted from the focus of the X-ray tube 36 while rotating the scanner rotating plate 35, and from each direction of the subject 42. The X-ray transmission amount of is measured. At this time, the X-ray beam collimator 49 limits the thickness in the slice direction and the width in the channel direction of the X-ray beam from the focal point of the X-ray tube 36. X-ray detector 38
The output from is connected to amplifier 40. The output signal is amplified to a proper level by the amplifier 40, then analog-digital converted, and sent to the subsequent image processing apparatus.

In FIG. 8, the keyboard 5 is attached to the console 46.
4, a scan condition setting circuit 55, an image display device 53 and the like are included to control the scanner 45 and display a slice image of the subject 42.

The scan conditions of the scanner 45 input from the keyboard 54 of the console 46 are input to the scan condition setting circuit 55. In this embodiment, the slice configuration signal (information indicating the slice thickness × the number of slices) 65 is sent to the scanner 45 based on the information about the slice thickness in the scan conditions.
Then, the image addition signal 66 is sent to the image processing device 47, respectively.

The slice configuration signal 65 is received by the scanner control circuit 48 of the scanner 45, where the slice configuration signal 65 is
A collimator aperture control signal 67 and a detector switch switching control signal 68 are generated based on the above, and the respective signals 67 and 68 are sent to the X-ray beam collimator 49 and the X-ray detector 38, and the slice of the X-ray beam is sliced according to the scanning conditions. Thickness and X-ray detector 38
A switching condition of a switch circuit (not shown) for the output signal of the X-ray detection element in the slice direction is set therein. X-ray detector 3
The output from 8 is amplified by the amplification circuit 40, then analog-digital converted, and sent to the image processing device 47 as measurement data 69 for a plurality of slices.

The image processing device 47 includes an image reconstruction circuit 50,
An image adding circuit 51, a magnetic disk device 52 and the like are included.
In this image processing device 47, the measurement data 69 sent from the scanner 45 is created by the image reconstruction circuit 50 into slice images at a plurality of slice positions corresponding to the array in the slice direction of the X-ray detection elements of the X-ray detector 38. Then, the plurality of slice images are sent to the image adding circuit 51. The image addition circuit 51 performs addition processing between the reconstructed slice images in accordance with the image addition signal 66 sent from the scan condition setting circuit 55 of the console 46. The final image data 70 thus obtained is sent to the image display device 53 of the console 46 and is also stored in the storage device such as the magnetic disk device 52.

The multi-slice type X-ray CT apparatus of the present invention described above reduces the optical crosstalk and electrical crosstalk of each X-ray detection element in the channel direction and the slice direction to reduce the space between the X-ray detection elements. Since the X-ray detection characteristics can be made uniform, by performing image reconstruction using the data detected by the multi-slice type X-ray detector configured by combining these X-ray detection elements, it is possible to perform multiple diagnostics with high diagnostic ability. It is possible to provide an X-ray CT apparatus that can obtain slice slice tomographic images at once.

[0069]

As described above, each X-ray detecting element constituting the multi-element solid X-ray detector of the present invention has a separation band for separating channels between the scintillators of the X-ray detecting element,
Grooves are provided between the channels of each scintillator and into the adhesive layer for adhering the scintillator and the silicon photodiode, and grooves for inserting isolation walls are provided. The structure is located near the diode surface, and a separating wall (or a separating plate) is inserted into the groove to a position reaching the bottom of the groove. The effects of the X-ray detector configured by combining the X-ray detection elements of this structure and the X-ray CT apparatus using the same are summarized as follows.

(1) When the light emitted from the individually separated scintillators tries to leak through the adhesive layer to each light receiving portion of the adjacent scintillator or photodiode array, the isolation protruding to the inside of the adhesive layer is used. Wall (or separator)
The optical crosstalk can be reduced because they are shielded by and do not leak each other.

(2) Since it is not necessary to provide a region for cutting and separating each detecting element to the inside of the silicon photodiode,
It is possible to reduce the leakage current and dark current of the silicon photodiode due to the influence of microcracks generated during the processing of cutting and separating, and to reduce the electrical crosstalk.

(3) Since the separation band (dead zone) of the photodiode array at the position corresponding to the above separation band can be used as the wiring region, the packaging density can be improved.

(4) With the above electrical and optical crosstalk reducing means, variations in X-ray detection characteristics among X-ray detection elements are small, resolution and S / N can be improved, and packaging density can be improved. X-ray detector becomes possible, this X
It is possible to provide an X-ray CT apparatus that can obtain a plurality of high-quality slice tomographic images at once by using the line detector in a multi-slice type X-ray CT apparatus having a particularly large number of X-ray detection elements.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a two-dimensional multi-element detector of the present invention used for an X-ray detector of a multi-slice type X-ray CT apparatus.

FIG. 2 is a cross-sectional view showing a state in which a groove for optically separating and isolating a scintillator of a two-dimensional multi-element detector according to the present invention is formed.

FIG. 3 is a sectional view of the two-dimensional multi-element detector according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a two-dimensional multi-element detector according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view for explaining the configuration of an adhesive layer of the X-ray detection element according to the first and second embodiments of the present invention.

FIG. 6 is a sectional view of the silicon photodiode array of the first and second embodiments of the two-dimensional multi-element detector according to the present invention.

FIG. 7 is a diagram in which the multi-slice type X-ray detector of the present invention is mounted on a scanner rotating plate.

FIG. 8 is a block diagram of the entire system of the multi-slice X-ray CT apparatus of the present invention.

FIG. 9 is a perspective view showing the basic structure of a conventional multi-element solid X-ray detector.

FIG. 10 is a sectional view of a general PIN-type multi-element silicon photodiode array.

FIG. 11 is a sectional view of a conventional multi-element solid X-ray detector.

FIG. 12 is a sectional view of a conventional multi-element solid-state X-ray detector.

[Explanation of symbols]

1 ... scintillator, 2 ... isolation wall, 2a, 2a '... isolation plate, 3
… Silicon photodiode array, 3a… Si photodiode n-type semiconductor N ⁺ layer, 3a ′… Si photodiode local n-type semiconductor region, 3b… Si photodiode intrinsic semiconductor (i-type semiconductor) N ⁻ layer, 3c… Si Photodiode p-type semiconductor
P ⁺ layer (light receiving area), 3c '… Si photodiode local p-type semiconductor region, 3d… Si photodiode anode electrode, 3
d '... Si photodiode signal extraction wiring, 3e ... Si photodiode anti-reflection film, 3f ... Si photodiode protective oxide film, 3g ... Si photodiode light-shielding film / light reflection film,
4 ... Adhesive (adhesive layer), 5 ... Incident X-ray, 6 ... Circuit board,
7 ... Top reflector, 10 ... X-ray detecting element, 35 ... Scanner rotating plate, 36 ... X-ray tube, 37 ... Detector container, 38 ... X-ray detector, 39 ... Collimator plate, 40 ... Amplifier, 41 ... Opening Parts, 42 ... Subject, 45 ... Scanner, 46 ... Operation console, 4
7 ... Image processing device, 49 ... X-ray beam collimator

Claims (5)

[Claims] 1. A scintillator that emits light by detecting incident radiation, a photodetector array having a light receiving region separated at least in the channel direction, and an isolation wall provided between the channels to separate the channels. An X-ray detection element array including the above is mounted on a substrate, and a plurality of X-ray detection element arrays mounted on this substrate are arrayed in a polygon on a substantially circular arc centered on the focal point of the X-ray tube in the channel direction at a substantially equal angular pitch. In the X-ray detector, the separation band that separates the channels between the respective light receiving portions for each channel of the photodetector array, the channels of the scintillator corresponding to the range of the separation band, and A groove reaching to the inside of an adhesive layer for adhering the photodetector and the scintillator is provided, and the bottom of the groove is the photodetector in the adhesive layer. An X-ray detector existing at a position close to the surface and configured to reach the position where the partition wall reaches the bottom of the groove in the groove. 2. The X according to claim 1, wherein a distance between the bottom of the groove and a surface of the dead zone of the photodetector is equal to or narrower than the groove width of the groove. Line detector. 3. The adhesive for adhering the photodetection element and the scintillator is bisphenol A type epoxy resin,
Bisphenol F type epoxy resin, Bisphenol AD
Epoxy resin of any type epoxy resin or a mixture thereof, and an amine-based or polyamide-based curing agent are mixed, and the refractive index of the adhesive is the The X-ray detector according to claim 1 or 2, wherein the antireflection film provided on the surface of the portion and the refractive index of the scintillator are slightly smaller. 4. A spacer made of a colorless and transparent substance having a refractive index in the range of 1.4 to 1.6 is provided in the adhesive layer to keep the thickness of the adhesive layer uniform. The X-ray detector according to claim 3, which is characterized in that. 5. An X-ray tube for irradiating a subject with an X-ray beam, and an X-ray detector that is arranged so as to face the X-ray tube and detects the X-rays that have passed through the subject and converts it into an electrical signal. A preamplifier for amplifying the output signal of the X-ray detector, an AD converter for converting an analog output signal from the preamplifier into a digital signal, and at least the X-ray tube and the X-ray tube.
A rotary disk that holds a line detector and is driven to rotate around the subject, a scan condition setting unit that sets scan conditions, and an X-ray image is reconstructed based on the output signal of the AD converter. An X-ray CT apparatus including an image processing means, wherein the X-ray detector according to any one of claims 1 to 4 is used as the X-ray detector.