Photon counting detector

Abstract

Photon counting detector (11) comprising: a columnar body assembly (31, 81) provided with a plurality of columnar bodies (31A) arranged mutually closely and adjacently, each of the columnar bodies (31A) having a length direction (Z) and an incident end surface (31in) receiving incident radiation, the incident radiation being converted into scintillation light which is transmitted in a direction in each of the columnar bodies (31A) along the length direction (Z), each of the columnar bodies (31A) having an emission end surface (31out) in the length direction (Z) thereof, the converted scintillation light being emitted outwardly from the emission end surface (31out), the emission end surfaces (31out) of the columnar bodies (31A) forming an emission surface of the columnar body assembly (31, 81); an optical connector (32) formed to oppose the emission surface of the columnar body assembly (31, 81), the optical connector (32) enabling a propagation range of the light emitted from the emission end surface (31out) of each of the columnar body elements (31A) to be adjusted; a group of APD clusters (52G) arranged to oppose the emission surface formed by the emission end surfaces (31out) via the optical connector (32) and formed by a plurality of APD clusters (52) arranged two-dimensionally, each of the APD clusters (52) serving as a pixel and being formed by N x N pieces (N is a positive integer of 2 or more) of APDs (51) having a light-receiving surface, the N x N pieces of APDs (51) being arranged two-dimensionally and providing output signals that are electrically combined by a wired OR circuit; a processing circuit (34) which processes an electrically combined output signal through the wired OR circuit of each of the plurality of APD clusters (52), where the optical connector (32) is adapted such that a propagation area of the light emitted from the emission end face (31out) of each of the columnar bodies (31A) is spread at least over the light receiving surfaces of the N × N pieces of APDs (51) configuring the individual APD clusters (52), and the processing circuit (34) comprises: a signal processing circuit (62) comprising: a plurality of measuring circuits (71-74, 77, 78), each of the measuring circuits (71-74, 77, 78) being arranged for each of the APD clusters (52), each of the measuring circuits (71-74, 77, 78) measuring, as the number of photons of light, an energy of the emitted light in each of a plurality of divided energy ranges for a predetermined period of time, based on the output signal provided from each of the plurality of APD clusters (52); and an adding circuit (76) which, to produce a sum, adds counts counted by a plurality of measuring circuits designated among the measuring circuits (71-74, 77, 78), the sum of the counts being regarded as scintillation light generated by a substantially single pulse of radiation, wherein a single APD cluster (52) is designated as a scintillation center APD cluster (52(i,j)) and is one of the APD clusters (52) connected to one of the measuring circuits which first counted up a given number of electrical pulses, wherein the plurality of designated measuring circuits is connected to a given number of APD clusters (52) designated among the APD clusters (52), wherein the given number of APD clusters (52) is Scintillation center APD clusters (52 (i, j)) are placed, wherein each of the measuring circuits (71-74, 77, 78) comprises Inhibition commanding means (73) which commands the given number of APD clusters (52) placed around the single APD cluster (52) to inhibit counting of the photons entering the given number of APD clusters (52) placed around the single APD cluster (52) for a predetermined period of time during which a signal measuring circuit connected to the single APD cluster (52) counts; Inhibition means (52, 74) arranged in each of the plurality of measuring circuits (71-74, 77, 78), the inhibition means (52, 74) inhibiting counting of the measuring circuits (71-74, 77, 78) when an inhibition command means (73) issues a command to inhibit counting; Position information calculating means (77) which calculates position information of the scintillation based on the scintillation center APD cluster (52 (i, j)); and an output circuit (78) which outputs position information indicative of the scintillation center APD cluster (52 (i, j)) and information indicative of the number of photons of the radiation in at least each of the energy ranges.

Description

TECHNICAL FIELD

[0001] The present invention relates to a photon-counting radiation detector which counts the number of photons of radiation or excitation light in each energy range thereof and acquires detection information based on information showing the counted number, and more particularly to a photon-counting detector capable of measuring, as the number of photons, the intensity of radiation having a wide wavelength range, including radiation such as X-rays or gamma rays or excitation light such as fluorescence.

[0002] In recent years, it has become necessary, for example in the medical field, to quickly detect radiation such as X-rays or gamma rays or excitation light such as fluorescence at each pixel.

[0003] One conventional detector with such a function is a gamma camera mounted in a nuclear medicine diagnostic device. This gamma camera receives gamma rays emitted from a nucleus-injected object body and outputs detection information indicating the magnitude of the gamma rays at each emission position. Conveniently, the gamma camera is provided with a collimator, a group of scintillators, light guides, and photomultipliers (PMTs) when viewed in the gamma-ray incoming direction. A position calculation unit is provided at the output side of this photomultiplier.

[0004] The array of scintillators is constructed such that a plurality of columnar scintillators are arranged densely and adjacent to each other, such that such scintillators have a front surface that serves as an input surface. The photomultipliers each have a hexagonal input surface and are densely arranged.

[0005] Gamma rays incident through one or more holes of the collimators are thus guided to enter one or more scintillators through the input surface of the scintillators. In such scintillators, scintillation light (light pulse) is generated by being excited by the incident gamma rays. The scintillation light enters one or more photomultipliers from the output surface of one or more scintillators via light guides. The one or more photomultipliers convert / convert light pulses into electrical signals to output electrical pulses proportional to amounts of incoming light to the position calculation unit. Based on the one or more output pulses, the position calculation circuit calculates light-emitting points, i.e., incident positions of the gamma rays.Accordingly, information indicating the emission positions and intensities (i.e., energy quantities) can be supplied from the position calculation circuit to an image display and / or storage.

[0006] In recent years, while being provided with such a basic scintillation structure, various types of developed scintillators are known, as shown in patent references 1 and 2. Other detectors are also described, for example, in DE 697 23 991 T2 and US 2014 / 0 021 354 A1. LIST OF CITATIONS[Patent Literature] [PTL1] US 7 375 341 B1 [PTL2] US 7 405 406 B1 [PTL3] JP 2010 - 91 483 A SUMMARY OF THE INVENTION[Technical Problem]

[0007] However, even though the scintillators shown in Patent References 1 and 2 above are used, versatile detectors capable of detecting gamma rays, X-rays, and weak excitation light in medical diagnostic devices have not been realized. This is because, unlike gamma rays, X-rays require detection at higher resolution levels. In addition, in X-ray detection, the number of photons of radiation incident on the detector is significantly larger (for example, 10,000 times), which makes the technical difficulty level for signal processing very high.

[0008] The detector has a sensing section that converges X-rays or light into electrical signals. Therefore, the materials used in the sensing section and / or the structure of the sensing section are important factors for achieving superior detection characteristics. The material and / or structure of this sensing section are modified depending on different detection purposes, resulting in lower volume efficiency and higher parts costs. Therefore, the market desires the development of a detector that has a common structure for various diagnostic modalities, which becomes an important factor in reducing manufacturing costs. This is also useful for generalizing diagnostic modalities, which will help prevent higher medical costs.

[0009] Taking this point of view into account, the detector is ideal when various diagnostic modalities (including nuclear medicine diagnostic devices, X-ray CT scanners and fluorescent CT scanners) are provided with a detector having a common structure capable of detecting a wide range of wavelengths, ranging from radiation emitted by or transmitted through an object to faint light generated by excitation, which are parts of electromagnetic waves.

[0010] However, a photon-counting detector has recently become popular (refer to Patent Reference 3). This detector is configured to count the number of photons of X-rays for each pixel and obtain detection information using the counts.

[0011] Although this photon-counting detector can detect X-rays, it is not a detector that enables the aforementioned wide wavelength range of electromagnetic waves (such as X-rays, gamma rays, and weak fluorescent light that is excited) to be detected using a single common structure. This is because the technical difficulty level is high and far from current production due to the need to jointly incorporate a photon-counting detection structure used in at least one gamma-ray detection device into each electromagnetic wave detector.Practically, the reason is that the conventional photon counting detector does not have a means to optimally balance a plurality of parameters in all types of modalities, such as a necessary resolution level, counting rate characteristics, and energy ranges used.

[0012] The photon counting detector has been actively developed in recent years, but is not able to detect the above wide wavelength range of electromagnetic waves in a relatively simple structure.

[0013] The present invention has been made in view of the above object and is to provide a photon counting detector with a higher structural versatility, which is capable of easily adapting electromagnetic waves (such as X-rays, gamma rays and weakly excited fluorescent light) having a wide wavelength range to performance criteria required by various modalities using a common structure. [Solution to the problem]

[0014] To realize the above object, the photon counting detector (the photon counting type of detector) according to the present invention is provided as a detector for detecting radiation or weak light (weak-intensity light) generated by excitation.

[0015] As an exemplary embodiment, the detector is characterized in that the detector comprises a columnar body assembly provided with a plurality of columnar bodies mutually densely and adjacently arranged, each of the columnar bodies receiving incident radiation or light, converting the incident radiation into light or transmitting the incident light in a direction therealong, each of the columnar bodies having an emission end surface through which the converted light or the transmitted light is emitted to the outside, the emission end surfaces of the columnar bodies forming an emission surface; an optical connector formed to oppose the emission surface of the columnar body assembly, the optical connector capable of adjusting a propagation range of the light emitted from the emission end surface of each of the columnar body elements; a group of APD clusters arranged to face the emission surface via the optical connector and formed by a plurality of APD clusters arranged two-dimensionally, each of the APD clusters serving as a pixel and being formed by N × N pieces (N is a positive integer of 2 or more) of APDs having a light-receiving surface, the N × N pieces of APDs being arranged two-dimensionally and providing output signals electrically combined by a wired OR circuit; a processing circuit that processes an electrically combined output signal through the wired OR circuit of each of the plurality of APD clusters.

[0016] The optical connector is configured such that the propagation area of the light emitted from the emission end face of each of the columnar bodies is spread at least over the light receiving faces of the N × N pieces of APDs configuring the individual APD clusters.

[0017] The processing circuit has the following: a plurality of measuring circuits, each of the measuring circuits being arranged for each of the APD clusters, each of the measuring circuits being capable of measuring, as the number of photons of light, an energy of the emitted light in each of a plurality of divided energy ranges for a predetermined period of time based on the output signal provided from each of the plurality of APD clusters; an adding circuit that adds, to generate a sum, counts counted by a plurality of measuring circuits designated among the measuring circuits, the sum of the counts being considered as the scintillation light generated by a substantially single pulse of radiation, wherein a single APD cluster is designated as a scintillation center APD cluster and is one of the APD clusters connected to one of the measuring circuits that first counted up a given number of electrical pulses, the plurality of designated measuring circuits being connected to a given number of APD clusters designated among the APD clusters, the given number of APD clusters being placed around the scintillation center APD; Inhibition commanding means for commanding the given number of APD clusters placed around the single APD cluster to inhibit counting of the photons entering the given number of APD clusters placed around the single APD cluster for a predetermined period of time during which the signal measuring circuit connected to the single APD cluster is counting; Inhibition means arranged in each of the plurality of measuring circuits, the inhibition means inhibiting or preventing counting of the measuring circuits when the inhibition command means issues a command to inhibit counting; Position information calculating means which calculates position information of the scintillation based on the scintillation center APD cluster; and an output circuit that outputs position information indicative of the scintillation center APD cluster and information indicative of the number of photons of the radiation in at least each of the energy ranges. [Effect of the invention]

[0018] According to the photon counting detector of the present invention, an optical connector is provided, which is formed to oppose the emission surface of the columnar body array and is capable of adjusting a light propagation area of light emitted from the emission end face of each of the plurality of columnar bodies. Additionally, an APD cluster group is also provided, in which a plurality of APD clusters are two-dimensionally arranged. Each APD cluster corresponds to a single pixel. The APD cluster group is arranged to oppose the emission surface via the optical connector.In the APD cluster group, N × N (N is a positive integer of 2 or more) avalanche photodiodes (APDs), each having a light-receiving area, are two-dimensionally arranged. The output signals of the N × N APDs are combined by a wired logic addition circuit. Therefore, depending on the number of photons (i.e., a quantity of light) of pulsed light emitted from the respective columnar bodies of the columnar body array, the propagation range of the light (i.e., the propagation of light with a solid angle) propagating in the optical connector can be adjusted.Accordingly, a more accurate measurement with a desired level of resolution and with fewer countless photon counts can be provided by appropriately adjusting both the propagation range of pulses of light propagating in the optical connector and the light reception ranges associated with the respective APD clusters receiving the light pulses. In other words, when an object being measured is given as radiation or faint light (i.e., a propagating medium), this adjustment enables the detector of the present invention to detect the radiation or faint light using the common detection structure for both applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the attached drawings: Fig. 1 is an oblique perspective view outlining a detection system in which an X-ray detector (provided as a mode of the radiation detector) according to a photon counting detector of the present invention; Fig. 2 is a sectional view outlining the X-ray detector; Fig. 3 is a plan view showing a plane taken along a III-III line shown in Fig. 2 is shown; Fig. Figure 4 provides illustrations in (A) and (B) thereof showing propagation of an X-ray beam emitted from an X-ray tube and oblique incidence into a scintillation layer; Fig. 5 is a plan view showing a plane taken along a VV line in Fig. 2 shows; Fig. 6 is an illustration showing both a scintillation light beam propagated from a scintillator to an optical interconnect layer and, in one direction, a plurality of APD clusters receiving the scintillation light; Fig. 7 is an illustration pictorially showing how the detector is layered when the surface (the X-ray incident window) of the X-ray detector is viewed from a viewpoint placed in the X-ray beam entering the plane; Fig. 8 is a block diagram showing a circuit centered on one processing circuit section per physical pixel fabricated in a processing circuit layer; Fig. 9 is a view explaining a positional relationship between a single physical pixel and a sub-pixel generated by calculation; Fig. 10 provides in (A) and (B) thereof a view of a sub-pixel according to the embodiment and a photon-counting X-ray detection performed for each energy range; Fig. 11 is a flowchart explaining a detection process according to the embodiment; and Fig. 12 is a sectional view outlining a modification of the detector according to the present invention, which is constructed from compositions used except for an optical fiber plate (FOA). DESCRIPTION OF EMBODIMENTS

[0020] With reference to the accompanying drawings, a photon counting detector (photon counting type of detector) according to the present invention will now be described. [First embodiment]

[0021] First, with reference to the Fig. 1 to 11 a first embodiment of the photon counting radiation detector will be described.

[0022] Fig. Figure 1 outlines the configuration of a detection system in which a photon-counting radiation detector detects radiation emitted by a radiation source. The radiation source is, for example, an X-ray tube mounted in medical X-ray diagnostic devices or a nuclide injected into an object in nuclear medicine diagnostic devices. In X-ray diagnostic devices, X-rays emitted from the X-ray tube are transmitted through an object under examination. In nuclear diagnosis, gamma rays serve as a detection medium, with the gamma rays emitted by a nuclide injected into an object under examination.In the present embodiment, the radiation is referred to as ionized radiation which includes light of weak intensity, such as fluorescence, generated by excitation light, ie, weak light, so that the radiation is one of propagating media belonging to the field of electromagnetic waves in a broader sense.

[0023] Fig. 1 shows a detection system in which a photon-counting radiation detector is an X-ray detector. This photon-counting X-ray detector 11 (hereinafter referred to simply as a detector) is capable of processing the incident X-rays as streams of photons and is configured to detect the number of photons for each energy range and output the counts as detection information. The detector 11 is operable under the control of a controller 12, which controls its operation. The controller 12 is communicatively connected to an input device 13 and a display device 14, which are used for interactive or non-interactive communication of operated information and / or input and output information with an operator. Although not specifically shown, the controller 12 includes a driver circuit for driving the detector 11.

[0024] Furthermore, a processor 15 is provided on the output side of the detector 11, which is configured to process the detection information, such as reconstructing images based on the detection information.

[0025] As in Fig. 1, the detector is housed in an approximately box-shaped housing 21. This housing 21 is made of an X-ray non-transmitting material except for the upper surface, which is Fig. 1, and components necessary for detection are housed in the housing 21 as will be explained in detail later. One surface 21WD of the housing 21 (refer to Fig. 1) is formed of an element with a low X-ray absorption rate (e.g., carbon resin) and serves as an X-ray incident window. Such an element is selected for the purpose of ensuring the deliquescent of a scintillator that is later delated (when the scintillator has hygroscopicity), light shielding, and efficiently guiding light to a light-receiving surface by light reflection. The detector 11 is thus positioned to have its X-ray incident window 21WD facing the X-ray incoming direction.For example, in a case where the detector 11 is mounted in a dental panoramic X-ray imaging apparatus, the X-ray incident window 21WD is always directed toward the X-ray tube such that the detector and the X-ray tube are positionally controlled to provide the paired components rotating on a patient's head.

[0026] For the purpose of a simplified explanation of the box-shaped detector 11, three-dimensional orthogonal coordinates having an X, Y and Z axis are shown in Fig. 1, in which the X- and Y-axes are assigned to the edges of the X-ray incident window 21WD. According to these coordinate axes, a section along a lateral direction of the detector 11, ie, the X-axis (ie, a section taken along a II-II line in Fig. 1) in Fig. 2 will be shown.

[0027] In the shape of this section, along the longitudinal direction of the X-ray incident window 21WD, ie, the Z-axis, a scintillator layer 31 functioning as a columnar array, an optical interconnection layer 32 serving as an optical interconnection element, a photoelectric conversion layer 33, and a processing circuit layer 34 serving as a processing circuit are arranged in this order from the window.

[0028] With this configuration, when the X-ray beam (pulsed X-ray beams) reaches the X-ray incident window 21WD of the detector 11, the X-ray beams pass through the incident window 21WD and arrive at an incident surface (detailed later) of the scintillator layer 31 positioned below the window. In the scintillation layer 31, the incident pulsed X-rays are received by one or more scintillators (detailed later) acting as columnar bodies, causing the scintillators to scintillate light. This scintillated light is emitted as pulsed spread light (i.e., light spread two-dimensionally with an emission angle) from the emission surface (detailed later) of the scintillators to the optical interconnect layer 32.As explained below, in the present embodiment, the optical interconnection layer 32 is formed as a resin layer having a predetermined thickness in the Z-axis direction. Therefore, as explained in detail later, the optical interconnection layer 32 is formed such that the single pulsed propagated light enters a plurality of pixel areas of the photoelectric conversion layer 33. The corresponding pixels of the photoelectric conversion layer 33 each convert the incident pulsed light into an electrical pulse. These electrical pulses are processed in the processing circuit layer 34, resulting in output of electrical signals, i.e., a detection signal, from the circuit layer 34 depending on the incident X-rays.

[0029] In this way, detector 11 performs the function of converting the incident X-rays into electrical signals via scintillation light. Furthermore, in addition to the above configurations, detector 11 also has a configuration to ensure versatility for the objects being detected, which is inherent in the present application. This configuration will be explained in more detail below. Layers 31 to 34 will be explained in this order. < Scintillation layer>

[0030] The scintillation layer 31 is an array of a plurality of columnar bodies 31A which are arranged densely and adjacent to each other in a two-dimensional plane, ie, an XY plane, as shown in the Fig. 2 and Fig. 3. The columnar bodies 31A functioning as columnar bodies are cylindrical scintillators (micro-column scintillators: minimal columnar scintillator) having a fine radius and a predetermined length. Conveniently, the bodies are densely arranged in the XY plane to cause the length directions of such columnar bodies to align in the longitudinal direction, i.e., a Z-axis direction. The scintillators 31A calibrate, for example, a diameter of 20 µm and a length of 1.5 mm. Regarding the diameter, a given range of irregularities in size is allowable, so it is not always exactly 20 µm, thereby being an amount of approximately 20 µm with a given allowable band. The length of the scintillators can be changed depending on applications. For example, when detecting gamma rays, the length is allowed to be made larger than 1.5 mm, iethe scintillation layer 31 becomes thicker.

[0031] The scintillators 31A are made of, for example, Ce:LaCl3, which is an X-ray / light conversion material. The X-ray characteristics of Ce:LaCl3 can be described as follows: the number of photons emitted is 60,000 / 1 MeV, and the density (gravity) is 5.2 g / cm 3is, the energy resolution is 3% (@ 662 KeV), a delay time is 18 nsec, and a wavelength band is 380 to 420 nm. This material has several advantages, including superior characteristics than NaI, which is a scintillator material used in general gamma cameras, in terms of energy resolution, detection sensitivity, response speed, afterglow characteristics, and other characteristics. Such advantages further include no hygroscopy and growth into columnar bodies with eutectic composition. It is also easier to use such scintillators for detecting gamma rays.

[0032] Accordingly, when an X-ray beam enters one of the two end faces of each of the scintillators 31A, ie, the face 31in (incident end face: refer to Fig. 4 (b)), the light (scintillation light) is generated by exciting incident light at a lengthwise position in the scintillator 31A. The generated scintillation light is held within the columnar body, but is spread toward the other surface 31 out (emission end face) of the columnar body in the length direction and emitted outward from the emission end face with a spreading in the emission angle. In the present embodiment, the term "outward" means "toward the optical interconnection layer 32."

[0033] The X-ray beam does not necessarily enter perpendicular to the incident end face 31 in each of the scintillators 31A, but enters obliquely thereto. As in Fig. 4 (a), this is the case because the X-ray beam is emitted from the X-ray focal point F of the X-ray tube 41 positionally opposite the detector 11 with a given spread of angles (ie, a fan angle). In a geometry shown in Fig. As shown in Figure 4 (a), an angle formed between the X-ray axis direction of the detector 11 and the edge of a fan-shaped X-ray beam is approximately 82 degrees. In this geometry, as shown in Fig. As shown in Figure 4(b), if it is assumed that an X-ray section B traveling along an edge of the beam and containing an X-ray photon excited by 100 keV enters a scintillator 31A' obliquely, the X-ray section has an oblique trace of approximately 500 µm and a spread of approximately 69 µm. This oblique incidence still makes it possible for one or more scintillators 31A through which the trace passes to generate scintillation light therein as probabilistic events. < Optical link layer >

[0034] The optical interconnect layer 32 will now be described. This optical interconnect layer 32 is configured to act as a boundary layer that defines the emission end face (i.e., the face composed of the other faces 31 outof the respective scintillators 31A) of the front-side scintillation layer 31 and the back-side photoelectric conversion layer 33. This optical connection layer 32 is formed by processing an optically transparent resin material into a plate-shaped member having a thickness L 0pt in the longitudinal direction, i.e., the Z-axis direction, which is appropriately selected according to applications of the detector 11. As the resin material that can be used, silicon-based resin is preferred, which is optically transparent and allows the refractive index thereof to be adjusted to a certain extent to adjust the propagation angle of the emitted light.

[0035] The optical interconnect layer 32 includes a wall 32W, wherein the layer 32 is made from a member having, for example, a white reflection surface for total reflection of the scintillation light from the outside periphery in the longitudinal direction. This wall 32W can be fabricated by coating an optical refraction agent on the wall for total refraction.

[0036] The thickness Lopt of this optical interconnect layer 32 is a significant factor and is set, for example, within a range of several tens of micrometers to several hundreds of micrometers, taking into account a balance among various factors such as a desired resolution level and desired counting characteristics.

[0037] As a modification, the optical interconnect layer 32 may be formed as an air layer. < Photoelectric conversion layer >

[0038] The photoelectric conversion layer 33 is a layered part composed of elements that receive the emitted light from the respective scintillators 31A and generates electric pulses in response to the received light.

[0039] In particular, as in Fig. As shown in Fig. 5, this photoelectric conversion layer 33 is composed of a plurality of avalanche photodiodes (APDs) 51, which are mutually densely and adjacently arranged two-dimensionally in the XY plane in the similar manner to the scintillation layer 31. The APDs 51 are each formed into a rectangular columnar shape of, for example, horizontal and vertical sizes of 10 µm × 10 µm, and the APDs are arranged two-dimensionally with electrical insulation layers inserted therebetween and mutually adjacent, so that the layer is afforested with the APDs. The rectangular columnar APDs 51 have a surface exposed to the optical interconnection layer 32, and light-receiving sections 51A for the scintillation light are formed on the surface.

[0040] Among these plural APDs 51, a given number of APDs composed of a given number of pieces in both the X and Y axes, for example, 10 pieces × 10 pieces (=100 pieces) are electrically connected to each other via a wired logic adding circuit (refer to Fig. 8, which will be described later) in the processing circuit layer 34 or at one end of each of the APDs, one end of which is electrically connected to the processing circuit layer. Thus, a given number of APDs among the APDs 51A (for example, 100 pieces, providing a rectangular area (for example, 150 µm × 150 µm), where the size of the gaps among the APDs is taken into account when they are manufactured)) forms an APD cluster 52.

[0041] In the detector 11 of the present embodiment, as shown in the Fig. 1 and Fig. 5, the connections using the wired logic adding circuits provide an equivalent arrangement in which a plurality of APD clusters 52 are arranged in a mutually adjacent manner in both the X-axis and Y-axis directions. Each of the APD clusters 52 serves as a pixel. In this way, the photoelectric conversion layer 33 is configured by a group of APD clusters composed of the two-dimensionally arranged plurality of APDs 52.

[0042] The group 52G of APD clusters 52, namely the photoelectric conversion layer 33, can be related to the size and shape of the scintillation layer 31, and such a relationship can be summarized below. The APD cluster group 52G is arranged around the emission end surfaces 31. outof the scintillators 31A via the optical interconnection layer 32. In this formation, the rectangular columnar APDs 51, the number of which is N × N pieces (N is a positive integer of 2 or more), are arranged, each APD having the light-receiving section 51A, and the rectangle having a side smaller than the radius of a section of each scintillator 31A perpendicular to the axial direction thereof. By combining the output signals from the N × N pieces of APDs with each other through the wired logic addition circuit, the one APD cluster 52 is formed. Physically, the area occupied by the one APD cluster 52 in the XY plane corresponds to one pixel.Incidentally, the present embodiment provides a calculation scheme, as will be described later, in which a comparison calculation is performed to divide each physical pixel into a pixel of a fractional ownership size (1 / 4 in the present embodiment), thereby generating finer sub-pixels. Through this calculation, information indicating the X-ray incident positions can be obtained for each sub-pixel.

[0043] As a result, it is understood that the two-dimensionally arranged plural APD clusters 52 provide a structure equivalent to an arrangement in which a plurality of physical pixels are arranged two-dimensionally along the X-ray incident window 12WD.

[0044] Fig. Figure 6 depicts an event in which an X-ray beam enters the incident end face 31A of a scintillator 31A present in the scintillation layer 31. When received by the columnar scintillator 31A, the X-ray energy is absorbed by the fluorescent body constituting the scintillator 31, causing excitation or ionization in atomic nuclei within the fluorescent body, thus generating pulsed light using a portion of the absorbed energy. This light is called scintillation light. The scintillation light is then transmitted within the scintillator 31A and is emitted from the emitting end face 31. outemitted at a solid angle toward the optical interconnection layer 32. In the present embodiment, the thickness of Lopt of the optical interconnection layer 32 in the Z-axis direction is optimized such that the propagated light has a projection range extending over an area larger than the area of the one pixel, ie, the one APD cluster 52.

[0045] A reception process for the emitted scintillation light will now be described. Fig. 7 is an illustration pictorially showing a geometrically overlapped relationship among the scintillation layer 31, the photoelectric conversion layer 33, and the photoelectric conversion layer 33. The illustration shows a two-dimensional perspective view, drawn pictorially, obtained when the X-ray incident window 21WD is viewed in the X-ray incident direction, that is, from the upper right in the Z-axis direction. As shown, the two-dimensional arrangement of the plurality of scintillators 31A, the two-dimensional arrangement of the plurality of APDs 51, and the plurality of APD clusters (each constituting one pixel) are formed by electrically combining a specified number of the plurality of APDs 51 placed within each block enclosed in the plane.In the present embodiment, the optical interconnection layer 32 is a layer made of a resin material.

[0046] With reference to Fig. 8, a signal processing circuit 61 will now be described by way of example, which is formed in the processing circuit layer 34 at each physical pixel, ie, at each APD cluster 52. This signal processing circuit 61 is configured for each pixel in the processing circuit layer 34 using ASIC. The signal processing circuit 61, which is formed in Fig. 8 shows one of the APD clusters 52, ie a circuit which is electrically connected to a single physical pixel.

[0047] As in Fig. 8, all of the APDs of each APD cluster 52 (in this example, 225 (15 × 15) pieces of APDs of APD (1) - APD (225)) are electrically connected to an individual signal circuit section 62 via a wired logical addition circuit OR.

[0048] This signal circuit section 62 includes a comparator 71 electrically connected to the wired logical addition circuit OR, and a counter 72, a before / after determination circuit 72, and a timer arranged on the output side of the comparator 71. In addition, this signal circuit section 62 includes a group of circuits for identifying an X-ray incident pixel in the X-ray incident window 21WD and counting the X-ray energy as the number of X-ray photons in each energy range.

[0049] The group of circuits comprises a counting and adding circuit 76, a sub-pixel decision circuit 77, and an output circuit 78. Of these circuits, the counting and adding circuit 76 is connected to the output terminals (i.e., not shown wired logic adding circuits) of 8 of the ADP clusters 52 in which the 8 APD clusters 52 are placed close to each other and to the wired logic adding circuits OR in the same way as that shown in Fig. 8. The subpixel decision circuit 77 actually comprises a counter and a comparator and is connected to the output terminals of the closely (densely) placed 8 APD clusters 52.

[0050] For example, if attention is focused on an APD cluster 52 (i, j) in the example shown in Fig. 7, the nearby 8 APD clusters 52 are represented by 8 APD clusters 52(i-1, j-1), 52(i, j-1), 52(i+1, j-1), 52(i-1, j), 52(i+1, j), 52(i-1, j+1), 52(i, j+1), and 52(i+1, j+1), which positionally enclose the APD cluster 52(i, j). These 9 APD clusters temporarily provide a measurement target area RMEA in response to an X-ray photon incident at a certain position in the X-ray incident window 21WD at a certain moment.

[0051] In addition, subpixels which are virtually decided by the subpixel decision circuit 77 are represented by four rectangular (square) subpixels APD (i, j)-1, APD (i, j)-2, APD (i, j)-3 and APD (i, j)-4, which are now specifically generated by virtually dividing the APD cluster 52 (i, j).

[0052] The foregoing circuit will now be explained in detail, first, from the comparator 71, which is electrically connected to the wired logic addition circuit OR. This comparator 71 is supplied with a predetermined value, which is set to the wave height (intensity) of a pulse signal, as a threshold value. This threshold value is set as a value capable of distinguishing a counting signal from noise signals. Thus, the comparator 71 compares with the predetermined threshold value (i.e., the wavelength value) a pulse signal composed of a single electrical pulse or combined electrical pulses from the one or more APDs 51 supplied via the wired logic addition circuit OR. With this comparison, if the wave height value of the input signal is greater than the threshold value, a binary signal ("1") is output to the counter 72 of the next stage.A counting threshold value is also given to the counter 72. This counting threshold value is a different value used in deciding an actual X-ray incidence position. Using this threshold value, the counter is able to output a measurement start command signal to the next before / after determination circuit 73 only when the count of the counter 72 becomes a predetermined value, for example, "5 counts."

[0053] The term "before / after" of the before / after determination circuit 73 means before and after in time. When the measurement start signal is received from the counter 72, the before / after determination circuit 73 outputs an inhibition signal to a signal circuit section (not shown) connected to the individual APDs, which inhibits a predetermined number of neighboring APD clusters. In this embodiment, 25 APD clusters 52 are inhibited upon receipt of an addition request, and the 25 APD clusters 52 form an inhibited area RINHIBIT. This inhibited area R INHIBIT for the addition is exemplary in Fig. 7, and as shown by way of example, 25 APD clusters 52 are arranged, at the center of which a targeted APD cluster 52 (i, j) is placed. In response to receiving this inhibition signal, the signal circuit section of each of the 25 APD clusters 52 inhibits, for a preset period of time measured by the timer 74, an addition of electrical pulses generated by X-ray incidences immediately following an X-ray incidence currently being targeted.

[0054] The inhibition signal also serves as a trigger signal for the counting and adding circuit 72. Upon receipt of the inhibition signal, the timer 74 begins counting the preset time period. When it counts up to this preset time period, the timer 74 provides a reset signal to the counting and adding circuit 76.

[0055] In response to receiving the trigger signal, the counting and summing circuit 76 is able to detect that the targeted APD cluster 52 (i, j) which positionally represents a current x-ray incidence position (for example, in Fig. 7 by a scintillation position P) (namely, a scintillation center APD cluster) should be treated by the counting and adding circuit 76 itself. Accordingly, this counting and adding circuit 76 counts, for each energy range (band), the number of electrical pulse signals output from each of the eight APD clusters 52, which consist of APD clusters 52(i-1, j-1), 52(i, j-1), 52(i+1, j-1), 52(i-1, j), 52(i+1, j), 52(i-1, j+1), 52(i, j+1), and 52(i+1, j+1), which have a measurement target range R MEAwhose center is the targeted APC cluster 52 (i, j), and which are placed to surround the targeted APD cluster 52 (i, j). The counting & adding circuit 76 adds the counts to each other for each energy range. This counting measurement for each of the X-ray energy ranges can be performed by a circuit similar to the conventionally known photon counting circuits. The electrical pulse signals are generated in response to the X-ray photon incident events in the scintillator 31A. It is therefore understood that the foregoing individual measurement of the number of electrical pulse signals and the addition of the number of counts obtained from the measurement target area R MEA (formed in particular by the preceding nine APD clusters 52), exactly equivalent to counting the photons over the entire measurement target area R MEA is.

[0056] The energy ranges are shown in (B) of the Fig. 10, set to have, for example, three energy ranges BIN1, BIN2, BIN3, which are divided along the abscissa axis scaled to an X-ray photon energy [KeV]. Alternatively, the number of energy ranges can be two or one.

[0057] As in Fig. As shown in Figure 11, the counting and adding circuit 76 repeatedly performs the foregoing measurement and addition based on a predetermined minute repetition time Δt during a given cycle T (FPS) starting from the input of the inhibition signal to the input of the reset signal. This circuit 76 provides the added values to the output circuit 78 individually for each of the energy ranges BIN1, BIN2, and BIN3.

[0058] The sub-pixel decision circuit 77 is provided with four counters and two comparators, and based on comparison results by the comparators, it decides in a finer manner a current X-ray incident position (for example, a scintillating point P which is in Fig. 7). Conveniently, the APD cluster 52 (i, j) into which the X-ray beam has now entered, namely the single physical pixel, is virtually divided into 1 / 4-size subpixels by the preceding comparison calculation. Furthermore, the circuit 77 determines to which of the four subpixels the X-ray incident position positionally belongs.

[0059] For example, in the example shown in Fig. 9, assume that, as the APD cluster 52, an X-ray incident position P in the physical pixel formed by an APD cluster 52 (i, j). In this example, by the four counters (not shown) of the sub-pixel decision circuit 77, electric pulse signals output from four APDs of APD (i-1, j), APD (i+1, j), APD (i, j-1), and APD (i, j+1) placed on the front, side, and back sides are counted for a predetermined time period t. k (reference is made to Fig. 11). Given these counts as K1, K2, K3, and K4, the two comparators perform a determination including comparative calculations of: K1 <K2 K3 <K4.

[0060] As a result, any of the following determination results 1 to 4 will come out. Determination result 1: K1 ≥ K2 and K3 ≥ K4 Determination result 2: K1 < K2 and K3 ≥ K4 Determination result 3: K1 ≥ K2 and K3 < K4 and Determination result 4: K1 < K2 and K3 < K4.

[0061] That is, when the determination result 1 comes out, the X-ray incident position P is determined as an upper left 1 / 4-size sub-pixel APD(i,j)-1 in the APD cluster 52(i,j). When the determination result 2 comes out, the X-ray incident position P is determined as an upper right 1 / 4-size sub-pixel APD(i,j)-2, and when the determination result 3 comes out, the X-ray incident position P is determined as a lower left 1 / 4-size sub-pixel APD(i,j)-3. Similarly, when the determination result 4 comes out, the X-ray incident position P is determined as a lower left 1 / 4-size sub-pixel APD(i,j)-4 (refer to an illustration of the Fig. 4).

[0062] The sub-pixel decision circuit 77 converts the calculated determination result into binary information and provides the output circuit 78 with the binary position information as position information of a sub-pixel.

[0063] The output circuit 78 is, as shown, provided with counters 78A to 78C, which count the number of photons each time for each of the energy ranges BIN1, BIN2, and BIN3, and a position information generator 78D. Each counter 78A to 78C is responsible for the calculation for each of the energy ranges BIN1 (to BIN3) assigned to the counters, respectively. Specifically, the counter 78A (to 78C) receives a count (an added value) corresponding to the number of X-ray photons from the entire measurement target area R MEA which is sent by the counting & adding circuit 76 at each sampling time Δt, and increments the count.

[0064] In addition, the position information generator 78D receives position information indicating the positionally decided sub-pixel sent from the sub-pixel decision circuit 77. Accordingly, the generator 78D generates the X-ray incident position P on the X-ray incident window 21WD at a resolution level corresponding to the sub-pixel size based on the received position information of the decided sub-pixel and the preset default position information about each of the APD clusters 52.

[0065] The output circuit 78 is configured to output to the outside serially at a constant rate T (FPS) both the counts incremented by the counters 78A to 78C in each of the individual energy ranges BIN1 to BIN3 and the position information showing the X-ray incident position P generated by the position information generator 78D.

[0066] As described, the acquisition operations can be summarized as follows: In Fig. In Fig. 7, reference numeral 52 (i, j) indicates a single APD cluster 52, which positionally includes a scintillator 31A that has scintillated in response to the previous X-ray incidence among the two-dimensionally arranged multiple APD clusters 52 (i.e., two-dimensionally arranged multiple pixels). The suffixes i and j indicate the position, shown pixel by pixel in the X-axis and Y-axis directions on the XY plane provided by the X-ray incidence window 21W.

[0067] Fig. Figure 7 shows an event in which the X-ray radiation entered the position P as an incident X-ray beam. In this case, in the X-ray incident window 21WD, which is shown in Fig. As shown in Fig. 7, the APD cluster 52 containing the scintillator 31A that has scintillated in response to the X-ray incidence is placed at the third position from the left in the X-axis direction and the third position from the upper side in the Y-axis direction. To surround this APD cluster 51(i,j), the area containing eight APD clusters 52(i-1,j-1), 52(i,j-1), 52(i+1,j-1), 52(i-1,j), 52(i+1,j), 52(i-1,j+1), 52(i,j+1), and 52(i+1,j+1), namely, the measurement target area R IMA In other words, a total of nine APD clusters 52 containing the centrally targeted APD cluster 52 (i, j) are subjected to the preceding signal processing, including signal addition. In this processing, the preceding inhibited area R INHIBIT which is a range for excluding signals which are in the range R INHIBITgenerated by being added in the signal adding process.

[0068] Under such a condition, the signal circuit section 62, which is in Fig. 8, which leads to the fact that, as shown in Fig. 10 (A), an X-ray incident position P, which is finer in size than the physical pixel, is decided as a subpixel. At the same time, as conceptually shown in Fig. 10 (B), a statistical count of X-ray photons is obtained for each range BIN1 (to BIN3) at the subpixel, which is, for example, P(i,j)-4. In this way, the photon counting type of X-ray intensity detection can be performed for each of the energy ranges.

[0069] The preceding X-ray acquisition for each of the APD clusters is performed at cycle T. In each cycle of this acquisition, if there is another X-ray incidence into an APD cluster 52 which is positionally related to the inhibited area R INHIBIT belongs to inhibit the detection of the APD cluster 52, which has received another X-ray incidence, during this cycle T.

[0070] In contrast, if there is an X-ray incidence at a different position on an APD cluster 52 which is outside the inhibited area R INHIBIT is placed, the detection in a different measurement target area R MEA start, since such a different measurement target range R MEA not with the inhibited area R INHIBIT overlaps, which is now being processed.

[0071] Furthermore, Fig. 7 other positions P1 and P2 different from the preceding exemplary X-ray incidence position P. At each of these positions P1 and P2, the preceding acquisition is performed in sequence every cycle T by targeting an APD cluster in which each of such positions P1 and P2 is included.

[0072] In this way, the detector 11 according to the present embodiment, as shown in Fig. 2, the layered structure is provided with the scintillation layer 31, the optical interconnection layer 32, a photoelectric conversion layer 33 having the APD clusters 52, and the processing circuit layer 34. With the same layered structural configuration directed to different applications, it is still possible to apply this detector to such applications by adjusting the thickness Lopt of the optical interconnection layer 32 regardless of the number of photons. Such applications include X-rays emitted by X-ray tubes, gamma rays emitted by nuclides administered into a patient's body, and weak fluorescence excited by excitation light.That is, in consideration of the balance between two parameters, which consist of a desired resolution level and a degree of accuracy required for photon counting, both the pixel size and the thickness Lopt of the optical interconnect layer 32 can be decided. In other words, this thickness Lopt can be decided depending on a perspective of detecting pulsed light propagating at a solid angle and diffused into the optical interconnect layer 32 by using how many APD clusters 52 center a scintillating point in a shared manner among the APD clusters and with no error detection.

[0073] Accordingly, by using the layered structure according to the embodiment in the detector, it is possible to easily provide versatile detectors that enable detection of not only gamma rays but also X-rays and weak excited light, which can thus be used by various medical modalities.

[0074] In the foregoing embodiment, the sub-pixel decision circuit 77 may be omitted from its arrangement, which means that, keeping the sizes of the physical pixels without being converted into sub-pixels, the number of photons in each energy range is counted. [Modifications]

[0075] The detector 11 according to the previous embodiment was described as an example provided with the processing circuit layer 31, but the sensor section will not be limited to this structure. For example, there may be an alternatively structured detector in which ultraviolet light, visible light, or X-rays can be used as the excitation light irradiated onto a fluorescent substance such that the excitation allows weak light (fluorescence, phosphorescence, or other weak light) emitted from the fluorescent substance to be detected.

[0076] An example showing a low-light detector 81 is shown in Fig. 12, in which, instead of inserting the foregoing scintillating layer, an optical fiber plate (FOP) 82 is mounted. This optical fiber plate 82 is mainly composed of a plurality of constant-length optical fibers 82A arranged close and adjacent to each other. The remaining configurations are the same as or equivalent to those shown in Fig. 2 are shown.

[0077] This weak light detector 81 is capable of operating as a highly sensitive two-dimensional optical sensor with an optical directivity. For this sensing, the optical fiber plate 82 has a front surface (i.e., an incident window 21WD) through which excited weak light is allowed to enter within the directivity. The incident weak light is propagated in the optical fibers 82A and emitted as diffused light into the preceding optical interconnect layer 32. The diffused light then forms one or more APD clusters 52 in the same manner as described above.

[0078] In this detector, similar to the previous one, depending on an intensity range of an incident weak light, the thickness Lopt of the optical connection layer 32, the size of the measurement target area R MEAand the size of the inhibited area R INHIBIT It can be optimized taking into account desired levels of both resolution and accuracy of counting the number of photons. When dedicated to detecting weak light, the signal circuit section 62 can be simplified more than the foregoing, since it is sufficient to detect only the positions and intensities of the weak light. For example, the comparator 71, the counter 72, and the before / after determination circuit 73 may be omitted from the circuit, and / or the sub-pixel decision circuit 77 may be omitted therefrom. It can be simply configured such that information indicating both an optical position at which incidence of light is first made and the intensity of the light at the first position is repeatedly output for each pixel at a constant frame rate.

[0079] Therefore, even if an assumption is made that only weak light is detected (i.e., imaging in which a CCD sensor or a CMOS sensor cannot be employed or a wider dynamic range is desired), near-distance imaging is performed from a closely approaching position to an object, linearly incident light should be selected, or a particularly improved resolution level is required, it is possible to provide a detector that estimates both excitation positions of light that is excited and amounts of the excited light. In addition, considering such characteristics, this exemplary weak light detector can be applied to dark-field cameras or optical topography. LIST OF REFERENCE SYMBOLS 11 Photon counting detector (photon counting type radiation detector), 12 controllers or controls, 15 processor, 21 housings, 21WD X-ray incidence window, 31 scintillation layer (columnar body arrangement), 31A scintillator, 32 Optical link layer (optical connector), 33 Photoelectric conversion layer (APD cluster group), 34 processing circuit layer (processing circuit), 51 APD (Avalanche Photodiode), 52 (APD cluster), 61 signal processing circuit, 62 signal circuit section, 81 Low-light detector (photon counting detector), 82 Optical Fiber Plate (FOP) (Column-shaped body arrangement), 82A Optical Fiber, R MEA measurement target range, R INHIBIT Inhibited area

Claims

[1] Photon counting detector (11) comprising: a columnar body assembly (31, 81) provided with a plurality of columnar bodies (31A) arranged mutually closely and adjacently, each of the columnar bodies (31A) having a length direction (Z) and an incident end surface (31in) receiving incident radiation, the incident radiation being converted into scintillation light which is transmitted in a direction in each of the columnar bodies (31A) along the length direction (Z), each of the columnar bodies (31A) having an emission end surface (31out) in the length direction (Z) thereof, the converted scintillation light being emitted outwardly from the emission end surface (31out), the emission end surfaces (31out) of the columnar bodies (31A) forming an emission surface of the columnar body assembly (31, 81); an optical connector (32) formed to oppose the emission surface of the columnar body assembly (31, 81), the optical connector (32) enabling a propagation range of the light emitted from the emission end surface (31out) of each of the columnar body elements (31A) to be adjusted; a group of APD clusters (52G) arranged to oppose the emission surface formed by the emission end surfaces (31out) via the optical connector (32) and formed by a plurality of APD clusters (52) arranged two-dimensionally, each of the APD clusters (52) serving as a pixel and being formed by N x N pieces (N is a positive integer of 2 or more) of APDs (51) having a light-receiving surface, the N x N pieces of APDs (51) being arranged two-dimensionally and providing output signals that are electrically combined by a wired OR circuit; a processing circuit (34) which processes an electrically combined output signal through the wired OR circuit of each of the plurality of APD clusters (52), where the optical connector (32) is adapted such that a propagation area of the light emitted from the emission end face (31out) of each of the columnar bodies (31A) is spread at least over the light receiving surfaces of the N × N pieces of APDs (51) configuring the individual APD clusters (52), and the processing circuit (34) comprises: a signal processing circuit (62) comprising: a plurality of measuring circuits (71-74, 77, 78), each of the measuring circuits (71-74, 77, 78) being arranged for each of the APD clusters (52), each of the measuring circuits (71-74, 77, 78) measuring, as the number of photons of light, an energy of the emitted light in each of a plurality of divided energy ranges for a predetermined period of time, based on the output signal provided from each of the plurality of APD clusters (52); and an adding circuit (76) which, to produce a sum, adds counts counted by a plurality of measuring circuits designated among the measuring circuits (71-74, 77, 78), the sum of the counts being regarded as scintillation light generated by a substantially single pulse of radiation, wherein a single APD cluster (52) is designated as a scintillation center APD cluster (52(i,j)) and is one of the APD clusters (52) connected to one of the measuring circuits which first counted up a given number of electrical pulses, wherein the plurality of designated measuring circuits is connected to a given number of APD clusters (52) designated among the APD clusters (52), wherein the given number of APD clusters (52) is Scintillation center APD clusters (52 (i, j)) are placed, wherein each of the measuring circuits (71-74, 77, 78) comprises Inhibition commanding means (73) which commands the given number of APD clusters (52) placed around the single APD cluster (52) to inhibit counting of the photons entering the given number of APD clusters (52) placed around the single APD cluster (52) for a predetermined period of time during which a signal measuring circuit connected to the single APD cluster (52) counts; Inhibition means (52, 74) arranged in each of the plurality of measuring circuits (71-74, 77, 78), the inhibition means (52, 74) inhibiting counting of the measuring circuits (71-74, 77, 78) when an inhibition command means (73) issues a command to inhibit counting; Position information calculating means (77) which calculates position information of the scintillation based on the scintillation center APD cluster (52 (i, j)); and an output circuit (78) which outputs position information indicative of the scintillation center APD cluster (52 (i, j)) and information indicative of the number of photons of the radiation in at least each of the energy ranges. [2] Photon counting detector (11) according to claim 1, characterized by that the columnar body arrangement (31) is formed as a scintillator (31A) which emits the scintillation light towards the group of APD clusters (52) via the optical connector (32) depending on an amount of incident radiation from the emission surface for each of the columnar bodies (31A). [3] Photon counting detector (11) according to claim 2, characterized by that the incident end face of each of the plurality of columnar bodies (31A) is provided as a part of an incident surface of the scintillator (31A), the incident surface receiving the incidence of the radiation into the scintillator (31A). [4] Photon counting detector (11) according to claim 1, characterized by , that each of the columnar bodies (31A) is constructed from an optical fiber (82A); and the columnar body assembly (31) is provided as an optical fiber plate (82) having the emission surface, the optical fiber plate (82) being produced by combining a plurality of the optical fibers (82A) close and adjacent to each other. [5] Photon counting detector (11) according to claim 3, characterized by , that each of the columnar bodies (31A) has a diameter of several dozen micrometers; each of the APDs (51) has a surface area of 10 µm × 10 µm; the “N × N” pieces consist of 15 × 15 pieces; each of the APD clusters (52) combined by a wired logic addition circuit is less than 200 µm × 200 µm; a duration for counting the number of photons is a time period during which a pulse of radiation is considered to have decayed sufficiently; and the given number of APD clusters (52) placed around the single APD cluster (52) is eight in number, the eight APD clusters (52) being placed on four sides of the single APD. [6] Photon counting detector (11) according to one of claims 2, 3 and 5, characterized by , that the position information calculation means (77) comprises comparison means which mutually compare the number of photons output from the APD clusters (52) placed around the single APD cluster (52) to virtually divide the single APD cluster (52) into a plurality of sub-clusters, the position information calculating means (77) decides that the scintillation center is located at one of the plurality of sub-clusters based on a compared result in the comparing means, and outputs a position of the decided sub-cluster as the position information of the scintillation. [7] Photon counting detector (11) according to one of claims 2, 3, 5 and 6, characterized by , that at higher energy of the radiation to be detected, the respective columnar bodies (31A) of the scintillator (31A) are lengthened in the longitudinal direction, the thickness of the scintillator (31A) in the optical connector (32) between the scintillator (31A) and the group of APD clusters (52G) is increased and the size of the APD clusters (52) is effectively made larger. [8] Photon counting detector (11) according to one of claims 2, 3 and 5 to 7, characterized by , that the scintillator (31A), the optical connector (32) and the group of APD clusters (52G) and the processing circuit (34) are structured as a module of a predetermined size; the detector (11) comprises optical shielding means arranged on at least an outer periphery of the scintillator (31A) and an outer periphery of the optical connector (32), the optical shielding means shielding the incidence of external light; and the plurality of columnar bodies of the scintillator (31A) and the group of APD clusters (52G) have a dead space provided between the bodies and between the APD clusters (52), the dead space emitting no light and being made smaller than a size of the pixel. [9] Photon counting detector (11) according to claim 3, characterized by that the scintillator (31A) has a light attenuation time equal to or less than 25 ns and a relative density of 5 or more. [10] Photon counting detector (11) according to one of claims 2, 3 and 5 to 9, characterized by that the columnar bodies of the scintillator (31A) are made of CeLaCl3. [11] Photon counting detector (11) according to one of claims 1 to 10 characterized by that the processing circuit (34) is structured as an ASIC. [12] Photon counting detector (11) according to one of claims 1 to 11, characterized by that the light receiving surface of each of the APDs (52) is shaped as a rectangle having a side smaller than a length of a section of the respective columnar bodies (31A), the section being perpendicular to the length direction of each of the respective columnar bodies (31A).

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