Signal processing device, signal processing method, positron emission tomography device, and configuration method

Abstract

The objective of the present invention is to provide a signal processing device capable of calculating the detection time at which a radiation detection device detects radiation by taking into account the characteristics of the radiation detection device. This signal processing device (3) for processing an output signal from a radiation detection device (2) including a plurality of scintillators, which emit fluorescence according to incident radiation, and a plurality of light-receiving elements, which detect fluorescence, comprises a processor that executes: an identification process for identifying, from the output signal, the detection time at which the light-receiving elements detected the fluorescence emitted by the scintillators and the imparted energy imparted to the light-receiving elements; and a calculation process for calculating, as the detection time at which the radiation detection device detected the fluorescence, a weighted average of the detection times detected by the light-receiving elements, wherein the weights are the n-th power (n is a real number greater than 1) of the energy corresponding to each of the light-receiving elements.

Description

Signal processing device, signal processing method, positron emission tomography device, and setting method

[0001] The present invention relates to a technology for processing a signal indicating that radiation has been detected in a radiographic apparatus that generates tomographic images of a living body.

[0002] Positron emission tomography (PECT) imaging devices are widely used to generate tomographic images of living organisms by detecting gamma rays emitted from the inside of the organism. In PECT imaging devices, gamma rays are typically detected using a radiation detection device in which detection units, each consisting of a scintillator that converts radiation (gamma rays) into light (fluorescence) and a photodetector that detects the light converted by the scintillator, are arranged in a matrix.

[0003] In order to improve the image quality of tomographic images, it is important to improve the time resolution of the radiation detection device, which is affected by the accuracy of the detection time when the radiation detection device detects fluorescence.

[0004] Non-Patent Document 1 discloses a signal processing device in which each of a plurality of light receiving elements included in a radiation detection device detects fluorescence, and the detection time is weighted by the energy imparted to each of the plurality of light receiving elements to determine an average detection time, which is calculated as the detection time T at which the radiation detection device detects radiation.

[0005] Dam, HT van, Borghi, G., Seifert, S. & Schaart, DR Sub-200 ps CRT in monolithic scintillator PET detectors using digital SiPM arrays and maximum likelihood interaction time estimation. Phys Med Biol 58, 3243-3257 (2013).

[0006] There are various types of radiation detection devices, each with different characteristics, such as different types and arrangements of scintillators and light-receiving elements, and different types and presence of reflective materials. However, the detection time of a radiation detection device is calculated using a method that does not take into account the characteristics of the radiation detection device. Therefore, there is room for improving the time resolution of the radiation detection device by optimizing the method for calculating the detection time of the radiation detection device.

[0007] One aspect of the present invention has been made in consideration of the above-mentioned problems, and aims to realize a signal processing device that can calculate the detection time at which a radiation detection device detects radiation, taking into account the characteristics of the radiation detection device.

[0008] A signal processing device processes an output signal from a radiation detection device, the radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation and a plurality of photodetectors that detect the fluorescence, and the signal processing device includes a processor that executes: an identification process that identifies, from the output signal, a detection time at which each photodetector detects the fluorescence emitted from the scintillator and an energy imparted to each photodetector; and a calculation process that calculates, as the detection time at which the radiation detection device detected the fluorescence, a weighted average of the detection times detected by each photodetector, where the weight is the nth power (n is a real number greater than 1) of the energy corresponding to each photodetector.

[0009] According to one aspect of the present invention, it is possible to realize a signal processing device capable of calculating the detection time at which a radiation detection device detects radiation, taking into account the characteristics of the radiation detection device.

[0010] Fig. 1 is a diagram showing an overview of a radiation imaging apparatus according to a first embodiment of the present invention. Fig. 2 is a diagram showing the configuration of a radiation imaging apparatus according to a first embodiment of the present invention. Fig. 3 is a diagram showing the configuration of a radiation detection apparatus according to a first embodiment of the present invention. Fig. 4 is a flow diagram showing the flow of a signal processing method performed by a signal processing apparatus according to a first embodiment of the present invention. Fig. 5 is a diagram showing the configuration of a radiation imaging apparatus according to a second embodiment of the present invention.

[0011] First Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS.

[0012] (Outline of Radiation Imaging Apparatus) An outline of a radiation imaging apparatus 1 according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram for explaining the outline of the radiation imaging apparatus 1.

[0013] 1, the radiographic imaging device 1 includes a ring-shaped arrangement of a radiation detection device 2 that detects radiation emitted from inside a living body and a signal processing device 3 that processes an output signal from the radiation detection device 2. As an example, the radiographic imaging device 1 is a positron emission tomography (PET) device that detects gamma rays, a type of radiation emitted from inside a living body, and generates a tomographic image of the living body based on the detected gamma rays.

[0014] First and second radiation rays emitted in opposite directions from a radiation source inside a living body are incident on two of the radiation detection devices 2 arranged in a ring shape, each of which faces the other. The radiation detection devices 2 include a plurality of scintillators that convert the incident radiation into fluorescence, and a plurality of light-receiving elements that detect the fluorescence. When the light-receiving elements detect fluorescence, they output a signal indicating that they have detected the fluorescence. Based on the signal, the signal processing device 3 calculates the detection time T and the deposited energy E at which the radiation detection devices 2 detected the radiation.

[0015] In conventional radiation imaging devices, the time when the first light-receiving element detected the fluorescence was used as the detection time T, or multiple light-receiving elements with fast detection times were selected, and the detection times when each of the selected light-receiving elements detected the fluorescence were weighted by the imparted energy of each of the light-receiving elements to determine the average detection time as the detection time T. However, these methods of calculating the detection time T did not accurately take into account the characteristics of the radiation detection device 2.

[0016] In response to this, the radiation imaging device 1 selects m (m is an integer equal to or greater than 2) light receiving elements or multiple light receiving elements with the largest imparted energy, starting from the light receiving elements with the earliest detection times at which they detected the fluorescence, and weights the detection times at which each of the selected light receiving elements detected the fluorescence by the nth power of the imparted energy of each of the light receiving elements to determine the average detection time as the detection time T. The value of n may be any real number greater than 1, but is preferably an integer greater than 1. The value of n is set arbitrarily in consideration of the characteristics of the radiation detection device 2. Specifically, this makes it possible to calculate the detection time T taking into consideration the characteristics of the radiation detection device 2, which contributes to improving the temporal resolution of the radiation detection device 2. Furthermore, improving the temporal resolution of the radiation detection device 2 makes it possible to realize a radiation imaging device 1 with improved image quality for tomographic images.

[0017] (Configuration of Radiation Imaging Apparatus) The configuration of a radiation imaging apparatus 1 according to one embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is a diagram showing the configuration of the radiation imaging apparatus 1. In order to prevent the drawing from becoming too complicated, Fig. 2 shows only one radiation detection device 2 and one signal processing device 3, which are arranged in a ring shape in the radiation imaging apparatus 1 shown in Fig. 1.

[0018] The radiation detection device 2 is used to detect radiation emitted from inside a living body in the radiation imaging device 1. The radiation detection device 2 includes a detection unit 21 and a detection circuit 22.

[0019] The detection unit 21 includes a scintillator array 211 and a light receiving element array 212 .

[0020] The scintillator array 211 includes a plurality of scintillators. Each scintillator is a conversion element (for example, a crystal) that converts radiation (for example, gamma rays) into light (fluorescence). In this embodiment, each scintillator constituting the scintillator array 211 is made of Fast-LGSO (Ce:Lu ｘ Gd （２－ｘ） SiO ５ Other scintillator materials include LYSO (Lutetium Yttrium Orthosilicate), GAGG (Gd３ (Ga, Al) ５ O １２ (Ce)) and LFS (Lutetium Fine Silicate).

[0021] The light receiving element array 212 includes a plurality of light receiving elements arranged in a matrix. Each light receiving element amplifies the fluorescence emitted by the scintillator and then outputs an analog detection signal Sa. In this embodiment, an MPPC (Multi Pixel photon counter), which is a type of SiPM (Silicon Photo Multiplier), is used as the light receiving element constituting the light receiving element array 212, but other SiPMs can also be used.

[0022] The scintillator array 211 and the light receiving element array 212 are optically connected. For example, in the detection unit 21, the scintillator array 211 and the light receiving element array 212 are optically connected such that the bottom surfaces of the scintillators constituting the scintillator array 211 are optically connected to the light receiving surfaces of the light receiving elements constituting the light receiving element array. Furthermore, in the detection unit 21, the scintillator array 211 and the light receiving element array 212 are optically connected via a light guide. An example of the configuration of the detection unit 21 in which the scintillator array 211 and the light receiving element array 212 are optically connected in this manner will be described with reference to FIG. 3. FIG. 3 is a diagram showing an example of the configuration of the detection unit 21 provided in the radiation detection device 2. (a), (c), and (e) of FIG. 3 are perspective views of the detection unit 21, and (b), (d), and (f) of FIG. 3 are plan views of the detection unit 21.

[0023] As shown in Fig. 3(a), for example, the detection unit 21 is configured so that each scintillator constituting the scintillator array 211 is optically connected one-to-one to each light-receiving element constituting the light-receiving element array 212. In the detection unit 21 configured in this manner, a reflective material may be appropriately disposed between each scintillator constituting the scintillator array 211, as shown in Fig. 3(b). In Fig. 3, the reflective material is disposed in the region between each scintillator indicated by a solid line, and the region indicated by a dotted line indicates that the scintillators are optically connected.

[0024] 3(a) and 3(b), radiation incident on the scintillator of the detection unit 21 is converted into fluorescence and reaches the light-receiving surface of the light-receiving element optically connected to the scintillator. Similarly, the light-receiving element that detects the fluorescence outputs an analog detection signal Sa corresponding to the fluorescence to the detection circuit 22.

[0025] Furthermore, the detection unit 21 may be configured such that a light guide 213 is disposed between the scintillator array 211 and the light receiving element array 212, as shown in FIG. 3( c). In this configuration, the scintillator array 211 and the light receiving element array 212 are optically connected via the light guide 213. Here, the light guide 213 serves to distribute the fluorescence received from the scintillator to each light receiving element. Note that even in the detection unit 21 configured in this manner, a reflective material may be appropriately disposed between each scintillator constituting the scintillator array 211, as shown in FIG. 3( d).

[0026] Radiation incident on the scintillator of the detection unit 21 having the configuration shown in Figures 3(c) and 3(d) is converted into fluorescence and reaches the light guide 213. The fluorescence that reaches the light guide 213 is distributed to the light-receiving surfaces of the light-receiving elements. The light-receiving elements that detect the distributed fluorescence output analog detection signals Sa corresponding to the fluorescence to the detection circuit 22.

[0027] 3( e), the detection unit 21 may be configured such that four scintillators are optically connected to each light-receiving element that constitutes the light-receiving element array 212. In this case, the area of ​​the light-receiving surface of each light-receiving element is four times the area of ​​the bottom surface of each scintillator that constitutes the scintillator array 211. In the detection unit 21 configured in this manner, a reflective material may be appropriately disposed in part or all of the spaces between each scintillator, as shown in FIG. 3( f). Furthermore, adjacent regions where no reflective material is disposed may be optically connected to each other by an optical adhesive or the like.

[0028] 3(e) and 3(f), radiation incident on the scintillator of the detection unit 21 is converted into fluorescence, reflected in the area where the reflective material is arranged, and transmitted through other adjacent scintillators in the optically connected area before reaching the light-receiving surface of the light-receiving element. The light-receiving element that detects the fluorescence outputs an analog detection signal Sa corresponding to the fluorescence to the detection circuit 22.

[0029] The configuration of the radiation imaging apparatus 1 will now be described with reference to FIG.

[0030] The detection circuit 22 converts an analog detection signal Sa output from the light receiving element that detects the fluorescence into a digital detection signal Sb. The digital detection signal Sb includes an element identifier i, an applied energy E ｉ , detection time T ｉ Includes:

[0031] The element identifier i is information for identifying the light receiving element that detected the fluorescence. The element identifier i is, for example, an element number assigned to each light receiving element array that constitutes the light receiving element array 212. In the following, the light receiving element identified by the element identifier i will be referred to as the light receiving element 212U. ｉ Let's say.

[0032] 2, when the detection unit 21 has a light receiving element array 212 consisting of 8×8=64 light receiving elements, each of the 64 light receiving elements is assigned an element number 1 to 64. In this case, the digital detection signal Sb includes an element identifier i, which is one of the element numbers 1 to 64. If the element identifier i is element number 4, the light receiving element 212U assigned element number 4 is ４ indicates that fluorescence was detected.

[0033] Imparted energy E ｉ is the light receiving element 212U represented by the element identifier i included in the digital detection signal Sb. ｉ represents the applied energy E ｉ is the light receiving element 212U ｉ is derived from the energy of the detected fluorescence.

[0034] The detection time Ti is the time when the light receiving element 212U is detected by the element identifier i included in the digital detection signal Sb. ｉrepresents the detection time when fluorescence was detected.

[0035] When the element identifier i indicates a plurality of element numbers, the digital detection signal Sb is output from the light receiving element 212U indicated by the element number. ｉ Each detection time T ｉ and imparted energy E ｉ Contains:

[0036] Here, the digital detection signal Sb is output from the light receiving element 212U ｉ The analog detection signal Sa is generated by processing one event, i.e., a time width (for example, on the order of picoseconds) corresponding to the incidence of one radiation, for each event. This is to enable the radiation detection device 2 to process a larger number of events.

[0037] The signal processing device 3 is a device that processes the digital detection signal Sb output from the detection circuit 22. As an example, the signal processing device 3 is a device that calculates the detection time T at which the radiation detection device 2 detects radiation based on the digital detection signal Sb output from the detection circuit 22.

[0038] The signal processing device 3 includes a processor 31, a primary memory 32, a secondary memory 33, an input / output interface 34, and a bus 35. The processor 31, the primary memory 32, the secondary memory 33, and the input / output interface 34 are connected to each other via the bus 35.

[0039] A signal processing program P (for executing a signal processing method described below) and a mathematical formula (for calculating a detection time T described below) are stored (non-volatilely) in the secondary memory 33. The processor 31 loads the signal processing program P stored in the secondary memory 33 onto the primary memory 32. Then, the processor 31 executes each process included in the signal processing method described below in accordance with instructions included in the signal processing program P loaded onto the primary memory 32.

[0040] An example of a device that can be used as the processor 31 is a CPU (Central Processing Unit). An example of a device that can be used as the primary memory 32 is a semiconductor RAM (Random Access Memory). An example of a device that can be used as the secondary memory 33 is a HDD (Hard Disk Drive).

[0041] An input device and / or an output device are connected to the input / output interface 34. An example of an input device connected to the input / output interface 34 is a keyboard. An example of an output device connected to the input / output interface 34 is a display.

[0042] Examples of interfaces that can be used as the input / output interface 34 include a PCI (Peripheral Component Interconnect) interface and a USB (Universal Serial Bus).

[0043] The signal processing program P may be recorded on a computer-readable, non-transitory, tangible recording medium. This recording medium may be the secondary memory 33 or another recording medium. For example, a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, etc. may be used as the other recording medium.

[0044] (Signal Processing Method) A signal processing method M1 performed by the signal processing device 3 will be described with reference to Fig. 4. Fig. 4 is a flow chart showing the flow of the signal processing method M1.

[0045] As shown in Fig. 4 , the signal processing method M1 includes a specifying process M11 and a calculating process M12. The timing at which the signal processing device 3 executes each process of the signal processing method M1 can be set arbitrarily. For example, the signal processing device 3 may execute each process shown in Fig. 4 at predetermined time intervals (e.g., one second), or may execute each process every time the signal processing device 3 receives the digital detection signal Sb from the detection circuit 22 of the radiation detection device 2.

[0046] The identification process M11 is a process for the signal processing device 3 to identify information about the light receiving element that detected the fluorescence. In the identification process M11, the processor 31 of the signal processing device 3 extracts, from the digital detection signal Sb received from the detection circuit 22 of the radiation detection device 2, the element identifier i, the light receiving element 212U, and the like as information about the light receiving element that detected the fluorescence. ｉ The detection time T ｉ and light receiving element 212U ｉ The imparted energy E ｉ Identify.

[0047] Calculation process M12 is a process for calculating the detection time T at which the radiation detection device 2 detected the radiation. In calculation process M12, the processor 31 of the signal processing device 3 calculates the detection time T at which the radiation detection device 2 detected the radiation based on information related to the light receiving element that detected the fluorescence identified in identification process M11 and equation (1).

[0048] First, the processor 31 of the signal processing device 3 selects m (m is any natural number equal to or greater than 1) light-receiving elements from the light-receiving elements that detected the fluorescence, and obtains an element identifier i for identifying each of the m light-receiving elements, a detection time T ｉ , and the applied energy E ｉ The processor 31 extracts the detection time T from the light receiving element that detected the fluorescence identified in the identification process M11. ｉ Alternatively, the m light receiving elements may be selected in order of the applied energy E ｉ Alternatively, the m light receiving elements may be selected in descending order of magnitude.

[0049] Furthermore, the processor 31 of the signal processing device 3 assigns a new element identifier k to the selected m light receiving elements. For example, the element identifier k is an element number assigned to the light receiving element. ｉ When m light receiving elements are selected in the order of the earliest, element numbers 1 to m are assigned in the order of the earliest, and the applied energy E ｉ When m light receiving elements are selected in descending order of the element identifier k, element numbers 1 to m are assigned in ascending order. Hereinafter, the light receiving element represented by element identifier k is referred to as the light receiving element 212U. ｋ and the light receiving element 212Uｋ The time when the fluorescence is detected is the detection time T ｋ and the light receiving element 212U ｋ The energy imparted to ｋ Let's say.

[0050] Next, the processor 31 of the signal processing device 3 calculates the detection time T ｋ and imparted energy E ｋ By substituting the above, the detection time T at which the radiation detection device 2 detects radiation is calculated.

[0051] k: element identifier T: detection time when the radiation detection device detects the fluorescence T ｋ : Detection time when the light receiving element detects the fluorescence E ｋ : Energy imparted to the light receiving element m: Number of light receiving elements used to calculate the detection time when the radiation detection device detects fluorescence

[0052] Here, the value of n may be any real number greater than 1, and is preferably an integer greater than 1. As an example, the value of n varies depending on the characteristics of the radiation detection device 2. For example, in the case where the fluorescence generated by incident radiation in the radiation detection device 2 spreads and is detected by multiple light receiving elements, the value of m is made large and the value of n is made a real number equal to or greater than 3. In the case where the fluorescence does not spread but is detected by a single light receiving element (for example, as shown in FIGS. 3(a) to 3(d)), the values ​​of m and n are made real numbers close to 1.

[0053] (Example of Radiation Imaging Apparatus) An example of the radiation imaging apparatus 1 will be described below.

[0054] The radiation detection device 2 included in the radiographic imaging device 1 according to the example and comparative example has the configuration shown in FIGS. 3( a) and 3(b). A scintillator array composed of 14 x 14 = 196 scintillators was used as the scintillator array 211. A prismatic Fast-LGSO with a height of 1.5 mm and a square base with sides of 1.45 mm was used as the scintillator. Furthermore, an MPPC with a square light-receiving surface with sides of 3 mm was used as the light-receiving element array 212. Furthermore, the radiation detection devices 2 were composed of a radiation detection device using a specular reflector (ESR) and a radiation detection device using a diffuse reflector (Lumirror) as reflectors disposed between the scintillator array 211.

[0055] In this example, the time resolution was evaluated by calculating the detection time T at which the radiation detection device 2 detected radiation by changing the values ​​of m and n in the above-mentioned formula (1). In this example, the time resolution of the radiation detection device 2 was also evaluated in both cases where m light receiving elements were selected in descending order of the fluorescence detection time (TS-EEWA) and where m light receiving elements were selected in descending order of the applied energy (ES-EEWA).

[0056] In this comparative example, the detection time T at which the radiation detection device 2 described above detected radiation was calculated using the following formula (2), and the time resolution was evaluated as the time resolution of the radiation detection device 2. Note that in this comparative example, only the case where m light receiving elements were selected in descending order of the fluorescence detection time (TS-EEWA) was evaluated.

[0057] k: element identifier T: detection time when the radiation detection device detects the fluorescence T ｋ : Detection time when the light receiving element detects the fluorescence E ｋ : Energy imparted to the light receiving element m: Number of light receiving elements used to calculate the detection time when the radiation detection device detects fluorescence

[0058] The results of evaluating the time resolution of the radiation detection device 2 included in the radiation imaging device 1 according to the example and the comparative example are shown in Tables 1 and 2. In the example and the comparative example, the time resolution was evaluated as the time resolution.

[0059]

[0060]

[0061] According to the radiation imaging apparatus 1 of this embodiment, it can be seen from Tables 1 and 2 that the time resolution of the radiation detection apparatus 2 is significantly improved when the value of n in formula (1) is set to n = 3 or n = 4. It can also be seen from Tables 1 and 2 that the optimal values ​​of m and n differ depending on the type of reflective material. In other words, it can be seen that setting the values ​​of m and n according to the characteristics of the radiation detection apparatus 2 is important for improving the time resolution.

[0062] Another embodiment (embodiment 2) of the present invention will be described with reference to Fig. 5. Fig. 5 is a diagram showing the configuration of a radiographic apparatus 1A according to embodiment 2. For ease of explanation, members having the same functions as those described in the above embodiment are denoted by the same reference numerals, and their description will not be repeated.

[0063] (Configuration of Radiation Imaging Apparatus) A radiation imaging apparatus 1A according to the second embodiment of the present invention differs from the radiation imaging apparatus 1 according to the first embodiment in that the signal processing device 3 includes a setting circuit 36, as shown in FIG.

[0064] The setting circuit 36 ​​is a circuit for setting the values ​​of m and n in equation (1) used to calculate the detection time T at which the radiation detection device 2 detects radiation. As an example, the setting circuit 36 ​​sets the values ​​of m and n according to the characteristics of the radiation detection device 2.

[0065] (Flow of Setting Method M2) The setting method M2 performed by the setting circuit 36 ​​will now be described. Setting method M2 includes a determination step M21 in which the values ​​of m and n included in formula (1) are optimized according to the characteristics of the radiation detection device 2. The timing at which the setting circuit 36 ​​performs setting method M2 can be set arbitrarily as long as it is before the signal processing device 3 performs each process of the signal processing method M1 described above. For example, the setting circuit 36 ​​performs the process of setting method M2 when the radiation detection device 2 connected to the signal processing device 3 is changed to another radiation detection device.

[0066] The determination step M21 is a step in which the setting circuit 36 ​​optimizes the values ​​of m and n in formula (1) based on information about the characteristics of the radiation detection device 2. In the determination step M21, the setting circuit 36 ​​optimizes the values ​​of m and n by referring to information about the characteristics of the radiation detection device 2 input from the input device of the input / output interface 34. Here, the information about the characteristics of the radiation detection device 2 includes at least one of the types of scintillators that make up the scintillator array 211, the light receiving elements that make up the light receiving element array 212, and the reflective material disposed between the scintillators, and the positional relationship between the scintillator array 211 and the light receiving element array 212 (see FIG. 3 ). In this way, by optimizing the values ​​of m and n in formula (1) according to the characteristics of the radiation detection device 2, it is possible to calculate an optimal detection time T regardless of the type of radiation detection device 2. This allows the same signal processing device 3 to be used even when radiation detection devices 2 with different characteristics are used, thereby providing high versatility.

[0067] The processor 31 of the signal processing device 3 calculates the detection time T at which the radiation detection device 2 detects radiation based on equation (1) using the values ​​of m and n optimized in the above-mentioned determination step M21.

[0068] (Summary) A signal processing device according to aspect 1 of the present embodiment is a signal processing device that processes an output signal from a radiation detection device, the radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation and a plurality of light receiving elements that detect the fluorescence, and the signal processing device includes a processor that executes: an identification process that identifies, from the output signal, a detection time at which each light receiving element detects the fluorescence emitted from the scintillator and an energy imparted to each light receiving element; and a calculation process that calculates, as the detection time at which the radiation detection device detected the fluorescence, a weighted average of the detection times detected by each light receiving element, where the weight is the nth power (n is a real number greater than 1) of the energy corresponding to each light receiving element.

[0069] With the above configuration, it is possible to calculate an optimum detection time that contributes to improving the time resolution of the radiation detection device.

[0070] In the signal processing device according to Aspect 2 of this embodiment, in Aspect 1, the processor calculates the detection time at which the radiation detection device detects fluorescence using the following formula (1) in the calculation process.

[0071] k: element identifier T: detection time when the radiation detection device detects the fluorescence T ｋ : Detection time when the light receiving element detects the fluorescence E ｋ : Energy imparted to the light receiving element m: Number of light receiving elements used to calculate the detection time when the radiation detection device detects fluorescence

[0072] With the above configuration, it is possible to calculate an optimum detection time that contributes to improving the time resolution of the radiation detection device.

[0073] A signal processing device according to aspect 3 of the present embodiment is the signal processing device according to aspect 1 or 2, wherein the processor, in the identification process, selects m (m is an integer of 2 or more) light-receiving elements from the plurality of light-receiving elements that detected the fluorescence, and calculates the detection time T corresponding to each of the selected m light-receiving elements. ｋ and the applied energy E ｋ Based on this, the detection time at which the radiation detection device detected the fluorescence is identified.

[0074] With the above configuration, the detection time at which the radiation detection device detects fluorescence can be calculated based on information from the m light receiving elements, and therefore the detection time can be calculated efficiently.

[0075] In a signal processing device according to aspect 4 of this embodiment, in the above-mentioned aspect 3, the processor selects m light receiving elements from the plurality of light receiving elements that detected the fluorescence in the identification process in order of the earliest detection time.

[0076] With the above configuration, when the relationship between the energy imparted to each light receiving element and the detection time of each light receiving element is linear, the detection time at which the radiation detection device detects fluorescence can be calculated with high accuracy.

[0077] A signal processing device according to aspect 5 of this embodiment is the same as in aspect 3 above, wherein the processor selects m light receiving elements from the plurality of light receiving elements that detected the fluorescence in the calculation process in descending order of the applied energy.

[0078] With the above configuration, even if the relationship between the detection time at which each light receiving element detects fluorescence and the energy applied to each light receiving element is not linear, the detection time at which the radiation detection device detects fluorescence can be calculated with high accuracy.

[0079] A positron emission tomography apparatus according to a sixth aspect of this embodiment includes the signal processing apparatus according to any one of the first to fifth aspects and the radiation detection apparatus.

[0080] With the above configuration, it is possible to acquire a tomographic image of a living body with improved image quality.

[0081] A setting method according to a seventh aspect of the present embodiment is a setting method for a signal processing device that processes an output signal from a radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation and a plurality of light receiving elements that detect the fluorescence from the scintillators, the setting method setting a mathematical formula for calculating a detection time at which the radiation detection device detects fluorescence, the method using the following formula (1) as the mathematical formula, and including a determination step of optimizing the values ​​of m and n included in formula (1) in accordance with the characteristics of the radiation detection device:

[0082] k: element identifier T: detection time when the radiation detection device detects the fluorescence T ｋ : Detection time when the light receiving element detects the fluorescence E ｋ : Energy imparted to the light receiving element m: Number of light receiving elements used to calculate the detection time when the radiation detection device detects fluorescence

[0083] With the above configuration, it is possible to calculate the detection time at which the radiation detection device detects fluorescence, depending on the characteristics of the radiation detection device.

[0084] A signal processing method according to aspect 8 of the present embodiment is a signal processing method for processing an output signal from a radiation detection device, the radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation and a plurality of photodetectors that detect the fluorescence, and the signal processing method includes: an identification process for identifying, from the output signal, the detection time at which each photodetector detected the fluorescence emitted from the scintillator and the energy imparted to each photodetector; and a calculation process for calculating, as the detection time at which the radiation detection device detected the fluorescence, a weighted average of the detection times detected by each photodetector, where the weight is the nth power (n is a real number greater than 1) of the energy corresponding to each photodetector.

[0085] With the above configuration, it is possible to calculate an optimum detection time that contributes to improving the time resolution of the radiation detection device.

[0086] (Additional Notes) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0087] REFERENCE SIGNS LIST 1 Radiation imaging device 2 Radiation detection device 3 Signal processing device 211 Scintillator array 212 Light receiving element array

Claims

1. A signal processing device that processes an output signal from a radiation detection device, the radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation, and a plurality of light receiving elements that detect the fluorescence, the signal processing device comprising a processor that executes an identification process that identifies, from the output signal, the detection time at which each light receiving element detected the fluorescence emitted by the scintillator and the energy imparted to each light receiving element, and a calculation process that calculates a weighted average of the detection times detected by each light receiving element, the weighted average being the nth power (n is a real number greater than 1) of the energy corresponding to each light receiving element, as the detection time at which the radiation detection device detected the fluorescence.

2. The signal processing device according to claim 1, characterized in that, in the calculation process, the processor calculates the detection time at which the radiation detection device detects the fluorescence using the following formula (1): k: element identifier T: detection time when the radiation detection device detects the fluorescence T ｋ E: Detection time when the light receiving element detects the fluorescence ｋ m: the number of light receiving elements used to calculate the detection time when the radiation detection device detects the fluorescence 3. In the identification process, the processor selects m (m is an integer of 2 or more) light receiving elements from the plurality of light receiving elements that detect the fluorescence, and calculates detection times T ｋ and the applied energy E ｋ The signal processing device according to claim 2 , further comprising: determining a detection time T at which the radiation detection device detects the fluorescence in accordance with the formula (1) based on the above formula:

4. The signal processing device according to claim 3, characterized in that, in the identification process, the processor selects m light receiving elements from the plurality of light receiving elements that have detected the fluorescence in order of the earliest detection time.

5. The signal processing device according to claim 3, characterized in that, in the identification process, the processor selects m light receiving elements from the plurality of light receiving elements that have detected the fluorescence in descending order of the applied energy.

6. A positron emission tomography apparatus comprising: a signal processing device according to any one of claims 1 to 5; and the radiation detection device.

7. A method for setting a formula for calculating a detection time at which the radiation detection device detects the fluorescence in a signal processing device that processes an output signal from a radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation, and a plurality of light receiving elements that detect the fluorescence from the scintillators, the method using the following formula (1) as the formula, and including a determination step of optimizing the values ​​of m and n included in the following formula (1) in accordance with the characteristics of the radiation detection device. k: element identifier T: detection time when the radiation detection device detects the fluorescence T ｋ E: Detection time when the light receiving element detects the fluorescence ｋ m: the number of light receiving elements used to calculate the detection time when the radiation detection device detects the fluorescence 8. A signal processing method for processing an output signal from a radiation detection device, the radiation detection device including a plurality of scintillators that emit fluorescence in response to incident radiation, and a plurality of light receiving elements that detect the fluorescence, the signal processing method comprising: an identification process for identifying, from the output signal, a detection time at which each light receiving element detects the fluorescence emitted by the scintillator and an energy imparted to each light receiving element; and a calculation process for calculating, as the detection time at which the radiation detection device detected the fluorescence, a weighted average of the detection times detected by each light receiving element, the weight being the nth power (n is a real number greater than 1) of the energy corresponding to each light receiving element.

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