JP2016223951A - Radiation imaging apparatus, control method for same, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for acquiring an incident amount per energy band of an incident radiation in an indirect-type sensor.SOLUTION: A radiation imaging apparatus comprises: a scintillator; a sensor panel on which a plurality of pixels each having a photodetector for detecting light are disposed; and a processing unit. The processing unit generates a signal in response to the light detected by each photodetector, determines whether a plurality of signals generated by a pixel group including a pixel of interest and one or more pixels proximate to the pixel of interest out of the plurality of pixels in the same period have a specific distribution, obtains a count by which it is determined that the signals have the specific distribution for the pixel of interest, acquires an incident amount in a first energy band out of a radiation radiated to the pixel of interest on the basis of a value obtained by converting the count in accordance with a first coefficient, and acquires an incident amount in a second energy band out of the radiation radiated to the pixel of interest on the basis of a value obtained by converting the count in accordance with a second coefficient.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiation imaging apparatus, a control method thereof, and a program.

  2. Description of the Related Art A radiation imaging apparatus using a flat panel detector (hereinafter referred to as FPD) formed of a semiconductor material is known as an imaging apparatus used for medical image diagnosis and nondestructive inspection using radiation (X-rays). Such a radiation imaging apparatus can be used, for example, as a digital imaging apparatus for still images and moving images in medical image diagnosis.

  As the FPD, there are an integration type sensor and a photon counting type sensor. The integral type sensor measures the total amount of charge generated by the incidence of radiation. On the other hand, the photon counting type sensor identifies the energy (wavelength) of incident radiation and counts the number of times of detection of radiation for each of a plurality of energy levels. That is, since the photon counting type sensor has energy resolution, the diagnostic ability can be improved as compared with the integration type sensor.

  Patent Document 1 proposes a direct sensor that counts the number of times of detection of radiation by directly detecting the energy of radiation using CdTe. Patent Document 2 proposes an indirect type sensor that detects the intensity of light generated in a scintillator by the incidence of radiation and counts the number of times the light is detected.

Special table 2013-501226 gazette JP 2003-279411 A

  A single crystal of CdTe used for a direct sensor can be grown only to a few cm square. For this reason, it is difficult to increase the area of the direct type sensor, and it is very expensive. In addition, there is a method for realizing a direct sensor with a large area by depositing amorphous Se. However, a sensor manufactured by the method has a problem that operation is slow and temperature management is required.

  On the other hand, the indirect type sensor has the advantage that it is easy to increase the area and is inexpensive. However, Patent Document 2 does not describe obtaining an incident amount of radiation having specific energy.

  An object of the present invention is to provide a technique for acquiring an incident amount for each energy band of incident radiation in an indirect sensor.

  In view of the above problems, a radiation imaging apparatus according to some embodiments of the present invention includes a scintillator that converts radiation into light, a sensor panel that includes a plurality of pixels including a photodetector that detects light, and A radiation imaging apparatus including a processing unit, wherein the processing unit generates a signal according to the light detected by the photodetector, and one of the plurality of pixels and one adjacent to the target pixel It is determined whether a plurality of signals generated in the same period by the pixel group including the above pixels has a specific distribution, the number of times determined to have the specific distribution is counted for the pixel of interest, and according to the first coefficient Based on the value obtained by converting the number of times, it is obtained by acquiring the incident amount of the first energy band of the radiation irradiated toward the target pixel and converting the number of times according to the second coefficient. Based on There are, and acquires the incident amount of the second energy band of the radiation emitted toward the pixel of interest.

  The above means provides a technique for acquiring the incident amount for each energy band of incident radiation in the indirect sensor.

The figure which shows the structural example of the radiation imaging device which concerns on this invention. The figure which shows the structure of the sensor panel of the radiation imaging device of FIG. The figure which shows the structure of the sensor part of the radiation imaging device of FIG. The figure which shows the irradiation period and read-out period of the sensor panel of the radiation imaging device of FIG. The figure which shows operation | movement of each sensor part in the irradiation period of the radiation imaging device of FIG. The figure which shows the breadth of light emission of the scintillator of the radiation imaging device of FIG. The figure which shows the light emission distribution converted into the digital value of the radiation imaging device of FIG. The figure which shows the conversion part of the radiation imaging device of FIG. The figure which shows the example of the conversion coefficient of the radiation imaging device of FIG. The figure which shows operation | movement of each sensor part in the read-out period of the radiation imaging device of FIG. The figure which shows the structure of the sensor part of the radiation imaging device which concerns on 2nd Embodiment of this invention.

  Hereinafter, specific embodiments of a radiation imaging apparatus according to the present invention will be described with reference to the accompanying drawings. Note that, in the following description and drawings, common reference numerals are given to common configurations over a plurality of drawings. Therefore, a common configuration is described with reference to a plurality of drawings, and a description of a configuration with a common reference numeral is omitted as appropriate. The radiation in the present invention includes a beam having energy of the same degree or more, such as X-rays, β-rays, γ-rays, etc., which are beams formed by particles (including photons) emitted by radiation decay, such as X It can also include rays, particle rays, and cosmic rays.

<First Embodiment>
A radiation imaging apparatus 100 (or a “radiation imaging system”) according to a first embodiment of the present invention will be described. FIG. 1 shows a configuration example of a radiation imaging apparatus 100 according to the first embodiment. The radiation imaging apparatus 100 according to the first embodiment includes, for example, an irradiation unit 101 that irradiates a subject with radiation, an irradiation control unit 102 that controls the irradiation unit 101, and an imaging unit 104 that images a subject irradiated with radiation. And a processor 103. Each of the irradiation controller 102 and the processor 103 can be configured by a computer having a CPU, a memory, and the like. In the present embodiment, the irradiation control unit 102 and the processor 103 are configured separately, but are not limited thereto, and may be configured integrally. That is, the irradiation control unit 102 and the processor 103 may be configured by one computer having these functions.

  The imaging unit 104 includes, for example, a scintillator 105 that converts incident radiation into light, and a sensor panel 106. In the sensor panel 106, for example, a plurality of sensor units 201 each detecting light converted from radiation by the scintillator 105 are arranged so as to form a plurality of rows and a plurality of columns. The sensor unit 201 may be referred to as a “pixel”. Although details will be described later, each sensor unit 201 has a configuration for performing photon counting radiation imaging, and measures the number of incident photons of radiation based on the detection result of light.

  The processor 103 exchanges signals or data with the imaging unit 104, specifically controls the imaging unit 104 to perform radiation imaging, and receives signals obtained thereby from the imaging unit 104. This signal includes a measurement value of radiation photons. For example, the processor 103 generates image data for displaying a radiation image on a display unit (not shown) such as a display based on the measurement value. At this time, the processor 103 may perform a predetermined correction process on the image data. Further, the processor 103 supplies a signal for starting or ending radiation irradiation to the irradiation control unit 102.

  Next, the configuration of the sensor panel 106 will be described with reference to FIG. FIG. 2 is a diagram illustrating a configuration of the sensor panel 106. The sensor panel 106 can include a plurality of sensor units 201, a vertical scanning circuit 202, a horizontal scanning circuit 203, a column signal line 204, a signal line 205, an output line 206, a signal line 207, and a column selection circuit 208. Each of the plurality of sensor units 201 acquires the distribution of light generated in the scintillator 105. Next, the detection may be configured to count the number of times of detection of a specific distribution in the acquired light distribution. Each sensor unit 201 converts data of the number of detection times corresponding to one or more distributions into an incident amount for each energy band of radiation irradiated toward each sensor unit 201. When a signal is supplied via the signal line 205, each sensor unit 201 outputs incident amount data to the column selection circuit 208 via the column signal line 204.

  The vertical scanning circuit 202 sequentially switches the signal line 205 that supplies a signal so that incident amount data is output from each sensor unit 201. When a signal is supplied via the signal line 207, the column selection circuit 208 outputs the incident amount data output from each sensor unit 201 to the output line 206 as output data DATA. Further, the horizontal scanning circuit 203 sequentially switches the signal line 207 that supplies a signal so that the operation of outputting the incident amount data to the output line 206 is sequentially performed in the plurality of column selection circuits 208. Here, in order to simplify the description, FIG. 2 shows the sensor panel 106 in which the sensor units 201 of 3 rows × 3 columns are arranged, but the sensor panel 106 in which more sensor units 201 are arranged is used. May be. For example, in a 17-inch sensor panel 106 (FPD), the sensor unit 201 of about 2800 rows × about 2800 columns can be arranged. Further, for example, the sensor panel 106 is not limited to a form in which the sensor units 201 are arranged in a two-dimensional array, and may be a line-shaped sensor panel 106 in which the sensor units 201 are arranged in a one-dimensional manner. .

  Next, the configuration of the sensor unit 201 will be described with reference to FIG. FIG. 3 is a diagram illustrating a configuration of the sensor unit 201. Each sensor unit 201 of the sensor panel 106 may include, for example, a detection element 301 that is a photodetector, a processing unit 330, an output unit 305, and a reference voltage unit that supplies a reference voltage 306. The processing unit 330 may include a voltage conversion unit 302, a comparison unit 303, a memory 304, a determination unit 307, and a conversion unit 130. The detection element 301 is a photoelectric converter that detects light generated by the scintillator 105 when radiation enters the scintillator 105 and generates a signal. As the detection element 301, a known photoelectric conversion element such as a photodiode may be used. The voltage conversion unit 302 uses, for example, a differentiation circuit, converts the signal generated by the detection element 301 into a voltage pulse signal, and outputs the voltage pulse signal to the comparison unit 303. The comparison unit 303 compares the voltage value of the pulse signal output from the voltage conversion unit 302 with the reference voltage 306, and generates, for example, a binary signal as a comparison result signal corresponding to the comparison result. When the voltage value of the pulse signal output from the voltage converter 302 is equal to or higher than the voltage value of the reference voltage 306, the comparator 303 outputs a digital value “1” as a signal corresponding to the comparison result. On the other hand, when the voltage value of the pulse signal output from the voltage conversion unit 302 is smaller than the reference voltage 306, the comparison unit 303 outputs a digital value “0” as a signal corresponding to the comparison result. The reference voltage 306 supplied to the comparison unit 303 can be set to have a common value for all the sensor units 201 in the sensor panel 106. When radiation is incident on the scintillator 105 and converted into light, the comparator 303 generates a binary digital signal via the voltage converter 302 in accordance with the light detected by the detection element 301.

  The determination unit 307 acquires a signal pattern 309 including a plurality of digital value signals output from the comparison unit 303 of the plurality of sensor units 201 (pixel group) in the same period. The determination unit 307 obtains a signal pattern 309 composed of a plurality of signals output from each sensor unit 201 during the same period, thereby distributing the light converted by the scintillator 105 from one radiation photon of the incident radiation. Can get the spread of.

  Next, the determination unit 307 determines whether or not the signal pattern 309 has a specific distribution. If the determination unit 307 determines that the signal pattern 309 has a specific distribution, the determination unit 307 counts the number of times the specific distribution is detected in a predetermined period. Specifically, the determination unit 307 compares the acquired signal pattern 309 with a reference pattern 308 representing a preset light distribution. If it is determined that the signal pattern 309 and the reference pattern 308 match, the determination unit 307 determines that a distribution corresponding to the reference pattern 308 has been detected, and outputs a distribution detection signal that adds 1 to the count value of the memory 304. To do. When the signal pattern 309 and the reference pattern 308 do not match, the determination unit 307 does not output a distribution detection signal indicating that the distribution is detected and does not change the count value of the memory 304. The determination unit 307 and the memory 304 count the number of times that the signal pattern 309 matches the reference pattern 308 and it is determined that a specific distribution is detected. The reference pattern 308 may be recorded in, for example, a memory in the determination unit 307 or may be given from the outside of the determination unit 307.

  Here, the determination of the distribution detection for adding 1 to the count value of the memory 304 is not limited to the comparison between the signal pattern 309 and the reference pattern 308. For example, an adder circuit that adds the outputs of the comparison units 303 of the adjacent sensor units 201 may be used, and the determination unit 307 may cause the memory 304 to count according to the total value of the digital values output from the comparison unit 303. . For example, the output from the comparison unit 303 of the sensor unit 201 is “1”, and the total output from the comparison unit 303 of the sensor unit 201 and the four sensor units 201 adjacent to the sensor unit 201 in the vertical and horizontal directions is “ 2 ”or more. In this case, the determination unit 307 may add 1 to the count value of the memory 304, assuming that a specific distribution is detected. The determination unit 307 detects that light is detected not only by one sensor unit 201 but also by a plurality of sensor units 201 adjacent to the sensor unit 201, and light emitted from the scintillator 105 is detected by spreading to the plurality of sensor units 201. Can be determined.

  The signal pattern 309 is a multi-bit digital value composed of the output of the comparison unit 303 of the sensor unit 201 and the outputs of the comparison units 303 of the four sensor units 201 that are vertically and horizontally adjacent to the sensor unit 201. sell. That is, the signal pattern 309 is a digital value based on a plurality of signals reflecting the distribution of light emission when radiation photons are converted into light in the scintillator 105. In the configuration shown in FIG. 3, since one comparison unit 303 is arranged for the sensor unit 201, the signal pattern 309 is a 5-bit digital value. However, the present embodiment is not limited to this. For example, a plurality of comparison units 303 having different reference voltages 306 may be arranged for each sensor unit 201 to perform multi-level determination. By arranging a plurality of comparison units 303, each sensor unit 201 can count the number of detections for a plurality of levels of light emission distribution related to light intensity.

  The conversion unit 130 that converts the count value stored in the memory 304 into an incident amount for each energy band of incident radiation will be described later. The output unit 305 receives incident amount data DATA for each energy band of the radiation converted by the conversion unit 130 when a signal is supplied from the vertical scanning circuit 202 via the signal line 205 connected to the output unit 305. Is supplied to the column selection circuit 208 via the column signal line 204. After that, when a signal is supplied to the column selection circuit 208 via the signal line 207, incident amount data DATA for each energy band of incident radiation is output to the processor 103.

  In the configuration illustrated in FIG. 3, two determination units 307, which are a determination unit 307 </ b> R and a determination unit 307 </ b> B, are arranged in each sensor unit 201. The determination unit 307R and the determination unit 307B perform determination on the signal pattern 309 using different reference patterns 308, respectively. A reference pattern 308R is provided to the determination unit 307R, and a reference pattern 308B is provided to the determination unit 307B. Two memories 304R, a memory 304R connected to the determination unit 307R and a memory 304B connected to the determination unit 307B, are arranged. When the determination unit 307R determines that the signal pattern 309 matches the reference pattern 308R, the determination unit 307 adds 1 to the count value of the memory 304R. If the determination unit 307B determines that the signal pattern 309 and the reference pattern 308B match, the determination unit 307B adds 1 to the count value of the memory 304B. In the present embodiment, a plurality of determination units 307 and a memory 304 are arranged to acquire the incident amount of radiation photons having a plurality of specific energies.

  In the present embodiment, an example in which two determination units 307 are arranged in one sensor unit 201 is shown, but the present invention is not limited to this. For example, only one determination unit 307 may be arranged. Further, for example, three or more determination units 307 may be arranged, and it may be determined whether different reference patterns 308 and signal patterns 309 match each other. 3 shows an example in which two memories 304 are arranged. However, the present invention is not limited to this. For example, only one memory 304 may be arranged in accordance with the number of determination units 307 to be arranged. In addition, three or more memories 304 may be arranged. Further, the signal pattern 309 is configured by outputs of the comparison unit 303 of five sensor units of the sensor unit 201 and four sensor units adjacent to the sensor unit 201 in the vertical and horizontal directions in the present embodiment. However, the signal pattern 309 is obtained, for example, from the outputs of the two sensor units 201 adjacent to each other, the four sensor units 201 obliquely adjacent to the sensor unit 201, or the comparison unit 303 of the sensor unit 201 that is two or more away from each other. It may be configured. In addition, the signal pattern 309 may be configured by, for example, the output of the comparison unit 303 of nine sensor units of the sensor unit 201 and eight sensor units adjacent to the periphery of the sensor unit 201. The scintillator 105 emits light by the incidence of radiation, and is generated in the same period by the sensor unit 201 that is one pixel of interest among the plurality of sensor units 201 and one or more sensor units that are close to the sensor unit 201 of interest. Any configuration may be used as long as the spread of the emission distribution is acquired. Then, the determination unit 307 acquires the distribution of light emission generated during the same period for each sensor unit 201 of interest, and determines whether or not the light distribution has a specific distribution.

  Next, driving of the radiation imaging system in the present embodiment will be described. FIG. 4 is a diagram illustrating the drive timing of the sensor panel 106 of the imaging unit 104. The waveform in FIG. 4 represents a radiation irradiation period and a data DATA reading period with the horizontal axis as time. In FIG. 4, during the radiation irradiation period, the irradiation unit 101 irradiates the subject with radiation, the radiation incident on the sensor panel 106 is converted into light by the scintillator 105, the spread of the light distribution is acquired, and the reference pattern 308 This is the period during which the number of matches is counted. The readout period is a period in which data DATA obtained by converting the number of detections obtained during the radiation irradiation period into an incident amount for each incident energy band is output from the sensor panel 106. As shown in FIG. 4, the sensor panel 106 can acquire a moving image by alternately performing the radiation irradiation period and the reading period. Further, for example, a still image may be acquired by performing a radiation irradiation period and a reading period once.

  Next, the operation in the radiation irradiation period in the sensor unit 201 configured as shown in FIG. 3 will be described with reference to FIG. FIG. 5 shows drive timings during radiation irradiation of the voltage conversion unit 302, the comparison unit 303, and the memory 304. 5 represents the output of the voltage conversion unit 302, the output of the comparison unit 303, and the count value of the memory 304 with the horizontal axis as time. Radiation photons enter the imaging unit 104 and are converted into light by the scintillator 105. An electric signal resulting from the light detected by the detection element 301 is converted into a voltage pulse by the voltage converter 302. When the voltage pulse of the voltage conversion unit 302 exceeds the reference voltage 306, a digital value “1” is output from the comparison unit 303. In the present embodiment, as described above, the determination unit 307 that compares the signal pattern 309 and the reference pattern 308 exists between the comparison unit 303 and the memory 304. When the signal pattern 309, which is a plurality of signals output from the comparison unit 303 of the plurality of sensor units 201 (pixel group), matches the reference pattern 308R, the determination unit 307R sets the count value of the memory 304R to 1. Add. Similarly, when both the signal pattern 309 and the reference pattern 308B match, the determination unit 307B adds 1 to the count value of the memory 304B. The number of times that the determination unit 307 determines that the signal pattern 309 matches the reference pattern 308 is counted as the number of detection times when a specific distribution is detected and stored in the memory 304.

  Next, a method for converting the number of detections obtained during the radiation irradiation period into an incident amount of radiation having specific energy will be described with reference to FIGS. FIG. 6 is a diagram showing the relationship between the energy of incident radiation and the light emission distribution of the scintillator 105. In the configuration shown in FIG. 6, radiation enters from the upper side of the figure, and in the imaging unit 104, the scintillator 105 and the sensor panel 106 (detection element 301) are arranged in this order from the side on which the radiation is incident. The plurality of radiation photons constituting the radiation have various energies. As shown in FIG. 6 (a), radiation photons having low energy are likely to be absorbed far from the detection element 301 and closer to the radiation incident side. In this case, the light converted from the radiation by the scintillator 105 is diffused widely in the scintillator 105, and is thus detected by the detection elements 301 of the multiple sensor units 201. On the other hand, radiation photons having high energy are less likely to be absorbed by the scintillator 105 than radiation photons having low energy. For this reason, it may be absorbed on the radiation incident side as shown in FIG. 6A, or may be absorbed near the detection element 301 as shown in FIG. 6B. When absorbed in the vicinity of the detection element 301 as shown in FIG. 6B, the light converted from the radiation by the scintillator 105 is not diffused as compared with the case of FIG. It is detected by the detection element 301 of the unit 201.

  The depth at which the radiation is absorbed by the scintillator 105 differs depending on the difference in energy of the incident radiation photons. If the depth in the scintillator where radiation photons are converted to light is different, the spread of the emission distribution is also different accordingly. As a result, the radiation imaging apparatus 100 has a resolution of energy with respect to the incident radiation, and the amount of incidence is determined for each specific energy band of the radiation among the radiation irradiated toward each sensor unit 201. Can be detected.

  Here, the energy resolution can be improved as the difference in the spread of the light emission distribution due to the difference in the energy of the radiation increases. The spread of the emission distribution can vary greatly depending on the thickness 702 of the scintillator 105. As the thickness 702 of the scintillator 105 is thicker, the light emitted by the radiation absorbed in the vicinity of the radiation incident surface spreads to more detection elements 301 of the sensor unit 201. In order to diffuse the light emission by the radiation photons absorbed in the vicinity of the radiation incident surface to a wider range, the thickness 702 of the scintillator 105 is, for example, larger than the pitch of the sensor units 201 in which the detection elements 301 are arranged. Good.

  Further, in order to increase the accuracy of energy resolution, an absorption layer 701 may be disposed on the side opposite to the side facing the detection element 301 of the scintillator 105, in the case of the configuration shown in FIG. The light emitted from the scintillator 105 can diffuse in various directions. Even when light is emitted in a region close to the detection element 301, the light can be diffused in directions other than the direction toward the detection element 301 as shown in FIG. When the reflectance of light is high on the surface of the scintillator 105, the diffused light can be reflected by the surface and enter the detection element 301. This reflected light is emitted in the vicinity of the detection element 301, and can be directly extended to the detection elements 301 of the plurality of sensor units 201 as compared with the light incident on the detection element 301. For this reason, there is a possibility that a difference from the light emission distribution of the light emitted at a position away from the detection element 301 hardly occurs. In order to prevent diffusion of light due to the reflection, an absorption layer 701 is preferably provided. For example, when the light emitted from the scintillator 105 is incident on the absorption layer 701, the absorption layer 701 may absorb 10% or more of the light.

  In the present embodiment, as shown in FIG. 6, in the imaging unit 104, the scintillator 105 and the sensor panel 106 are arranged in this order from the radiation incident side. However, the arrangement of the scintillator 105 and the detection element 301 is not limited to this. The radiation may enter the scintillator 105 after entering the sensor panel 106 and passing through the sensor panel 106. In this case, radiation photons having low energy are absorbed near the detection element 301 of the scintillator 105. The light converted from the radiation by the scintillator 105 is detected by, for example, the detection element 301 of one sensor unit 201 without widely diffusing in the scintillator 105. On the other hand, radiation photons having high energy are less likely to be absorbed by the scintillator 105 than radiation photons having low energy. For this reason, for example, light emitted by radiation absorbed by the scintillator at a location distant from the detection element 301 is diffused widely in the scintillator 105 and detected by the detection elements 301 of the multiple sensor units 201. Thus, even when radiation is incident from the sensor panel 106 side, the spread of light emission varies depending on the difference in the light emission depth. Thereby, the radiation imaging apparatus 100 can detect the energy and the incident amount of the incident radiation among the radiation irradiated toward each sensor unit 201.

  FIG. 7 shows a signal pattern 309 in which light emission is detected by the detection element 301 of the sensor unit 201 and converted into a digital value by the comparison unit 303. The sensor panel 106 configured as shown in FIG. 2 has sensor units 201 arranged in a two-dimensional array of X rows × Y columns. FIG. 8 shows digital values from the comparison unit 303 of the sensor unit 201 of 5 rows × 5 columns.

  As shown in FIG. 6A, when radiation is absorbed and emitted at a location away from the detection element 301 of the scintillator 105, the light is emitted at a location away from the detection element 301, so that the light diffuses within the scintillator 105. The distribution of light emission spreads over the plurality of sensor units 201. In this case, the digital value from the comparison unit 303 of each sensor unit 201 indicates that light is detected by the adjacent sensor unit 201 with the sensor unit 201A as the target pixel as the center as shown in FIG. 7A. It can be a signal pattern 309R. This signal pattern 309R matches the reference pattern 308R for identifying that light is detected by the sensor unit 201A and the plurality of sensor units 201 adjacent to the sensor unit 201A. Therefore, the determination unit 307R determines that the signal pattern 309A matches the reference pattern 308R, and adds 1 to the count value of the memory 304R.

  On the other hand, as shown in FIG. 6B, when the radiation is absorbed and emitted near the detection element 301 of the scintillator 105, the light is emitted near the detection element 301. For this reason, the distribution of light emission does not spread over the plurality of sensor units 201, and is detected by only one sensor unit 201A, for example. In this case, the digital value from the comparison unit 303 of each sensor unit 201 can be a signal pattern 309B in which light is detected only by the sensor unit 201A as shown in FIG. 7B. This signal pattern 309B coincides with a reference pattern 308B for identifying that light is detected only by the sensor unit 201A and light is not detected by the adjacent sensor unit 201. Therefore, the determination unit 307B determines that the signal pattern 309B matches the reference pattern 308B, and adds 1 to the count value of the memory 304B. As described above, the number of detections where the determination unit 307 and the memory 304 determine that the signal pattern 309 matches the reference pattern 308 and a specific distribution is detected is counted for each sensor unit 201.

  Next, a method for acquiring the incident amount for each specific energy band of incident radiation from the count value of the number of detection times obtained for each sensor unit 201 will be described. FIG. 8 shows an example of a conversion unit 130 that converts the number of detections into the amount of incident radiation, and FIG. 9 shows an example of a conversion coefficient that is a coefficient for converting the number of detections into the amount of incident radiation. In the following example, a case will be described in which radiation energy is divided into two energy bands with a certain threshold (for example, 60 keV) as a boundary, and the incident amount of radiation is acquired for each energy band. Energy lower than this threshold is called low energy, and energy higher than this threshold is called high energy.

  Radiation having low energy is necessarily absorbed on the incident surface side of the scintillator 105 and the distribution of light emission is broadened, and radiation having high energy is always absorbed at a location away from the incident surface side of the scintillator 105 and the distribution of light emission is narrow. Not necessarily. Radiation having low energy is likely to be absorbed on the incident surface side of the scintillator 105, and radiation having high energy is likely to be absorbed almost uniformly by the scintillator 105. For this reason, each count value of the memory 304R and the memory 304B, which is the number of detections of the signal pattern 309 that matches each reference pattern 308, is converted into an incident amount of radiation for each energy band according to the conversion coefficient shown in FIG. The conversion coefficient is a coefficient representing the relationship between the energy of the radiation photons and the possibility that the signal pattern 309 obtained by converting the radiation photons into light matches the reference pattern 308. For example, each count value is converted by multiplying the count value of the memory 304R by a coefficient L and a coefficient H, and the count value of the memory 304B by a coefficient L 'and a coefficient H'. In the configuration of the conversion unit 130 illustrated in FIG. 8, the count value of the memory 304 </ b> R that has detected that the distribution of detecting light in the signal pattern 309 is wide is multiplied by a coefficient L = 0.6. Thereby, the conversion incident amount caused by the low-energy radiation among the count values of the memory 304R is calculated. Also, the count value in the memory 304R is multiplied by a coefficient H = 0.4, and the converted incident amount due to high energy radiation in the count value in the memory 304R is calculated. Similarly, the count value of the memory 304B that has detected that the light detection distribution of the signal pattern 309 is narrow is multiplied by a coefficient L ′ = 0.1, and the low energy radiation in the count value of the memory 304B is multiplied. The resulting conversion incident amount is calculated. Moreover, the coefficient H ′ = 0.9 is multiplied, and the converted incident amount caused by the high-energy radiation among the count values of the memory 304B is calculated. Next, the respective converted incident amounts resulting from the low energy radiation are added. Further, the respective converted incident amounts resulting from high energy radiation are added. Thus, the count value of the light distribution detected by the plurality of sensor units 201 is converted into the incident amount of the radiation incident in each of the energy bands of low energy and high energy. The acquired incident amount data resulting from the low energy radiation is stored in the output unit 305R, and the acquired incident amount data resulting from the high energy radiation is stored in the output unit 305B.

  Here, the conversion coefficient is appropriately set for each specific energy band of radiation, such as the high energy and the low energy described above. A conversion coefficient is set for each reference pattern 308. Here, for example, the conversion coefficient depends on conditions such as the tube voltage, tube current, irradiation time, material and thickness of the additional filter used, the attenuation coefficient, thickness, and visible light transmittance of the scintillator 105 used. Change. By setting the conversion coefficient as a different parameter for each imaging condition, the radiation imaging apparatus 100 can have a highly accurate energy resolution. Two conversion coefficients may be set for the count value of each memory 304 as in the present embodiment, for example, only one may be set, or for example, three or more may be set. . What is necessary is just to set suitably according to the kind of energy band of the radiation to detect. In the above example, the incident amount of radiation is acquired by adding the converted incident amount for each energy band. However, the present invention is not limited to this. For example, when there is one memory 304 or when there is a strong correlation between the absorption and emission distribution of radiation, it is not necessary to use addition only by applying a conversion coefficient. Also good.

  Here, the above-described operation in the irradiation period can be performed by setting the operating frequency of the sensor unit 201 and the irradiation amount of the irradiation unit 101 to values that can measure radiation photons one by one. For example, the operating frequency of the sensor unit 201 may be set within a range of 10 kHz to several MHz (for example, about 100 kHz). For example, the irradiation amount of the irradiation unit 101 may be set as a value when the tube voltage is about 100 kV and the tube current is about 10 mA.

  Next, the operation in the readout period in the sensor unit 201 configured as shown in FIG. 3 will be described with reference to FIG. FIG. 10 is a diagram illustrating the operation of each sensor unit 201 during the readout period. The waveform in FIG. 10 indicates the supply of the signal to the signal line 205 with the horizontal axis as time, the supply of the signal to the signal line 207, and the output of the data DATA of the incident amount of radiation acquired from the column selection circuit 208. Represents each. As shown in FIG. 10, signals are sequentially supplied to the plurality of signal lines 205 and the plurality of signal lines 207. For example, when supply of a signal to the signal line 205-0R is started, data on the incident amount of radiation in a specific energy band is supplied to the column selection circuit 208 from the output unit 305R of the sensor unit 201 connected to the signal line 205-0R. Is done. Then, in the period when the signal is supplied to the signal line 205-0R, the signals are sequentially supplied to the plurality of signal lines 207, and the radiation incident amount data DATA is sequentially supplied from the plurality of column selection circuits 208 to the output line 206. To output.

  When the signal supply to the signal line 205-0R is finished and the signal supply to the signal line 205-0B is started, a specific energy band is output from the output unit 305B of the sensor unit 201 connected to the signal line 205-0B. The data on the amount of incident radiation is supplied to the column selection circuit 208. Then, in the period when the signal is supplied to the signal line 205-0B, the signal is sequentially supplied to the plurality of signal lines 207, and the data DATA of the radiation incident amount is sequentially supplied from the plurality of column selection circuits 208 to the output line 206. To output. As a result, radiation amount data DATA from a plurality of sensor units 201 in one row can be supplied to the processor 103 via the output line 206. In this way, signals are sequentially supplied to the plurality of signal lines 205 and the plurality of signal lines 207, and the radiation incident amount data DATA for each specific energy band is output from the plurality of sensor units 201 via the output line 206. The data is supplied to the processor 103 and used to generate image data.

Second Embodiment
A radiation imaging apparatus (radiation imaging system) according to a second embodiment of the present invention will be described. Although the radiation photon measurement method according to the first embodiment described above uses the processing unit 330 disposed in the sensor unit 201, these functions are realized on a program or software in the processor 103, for example. May be. That is, the sensor unit 201 may be configured by a circuit for outputting a signal corresponding to the light converted by the scintillator 105, and the number of radiation photons may be measured outside the sensor unit 201.

  FIG. 11 shows a configuration example of the sensor unit 201 ′ according to the second embodiment. In addition to the detection element 301, the sensor unit 201 'includes, for example, a reset unit 510, a signal amplification unit 520, a photosensitivity selection unit 530, a clamp unit 540, a first sampling unit 550, and a second sampling unit 560. The reset unit 510 includes a transistor M1, and resets the potential of the detection element 301 by turning on the transistor M1. Signal amplifier 520 includes transistors M2-M3 connected to a current source. By turning on the transistor M2, the transistor M3 performs a source follower operation, whereby a signal corresponding to the amount of charge generated and accumulated in the detection element 301 is amplified.

  Photosensitivity selection unit 530 includes transistors M4 to M7 and capacitors C4 to C5. For example, when the transistor M4 is turned on, the capacitor C4 is connected to the gate of the transistor M3, and when the transistor M6 is turned on, the transistor M7 performs a source follower operation. Thereby, the signal amplification factor of the signal according to the charge amount generated in the detection element 301 can be changed. Further, by making the transistor M5 conductive, the capacitor C4 is connected to the gate of the transistor M3, and the signal amplification factor can be further changed.

  Clamp unit 540 includes transistors M8 to M10 and a capacitor C1. The output from the signal amplifying unit 520 when the detection element 301 is reset is supplied to one terminal n1 of the capacitor C1, and the other terminal n2 of the capacitor C1 is supplied with power by turning on the transistor M8. Voltage is supplied. Thereby, the voltage when the detection element 301 is reset is clamped as a noise component between the terminals n1 and n2. After that, the transistor M8 is turned off and the transistor M9 is turned on, so that the transistor M10 performs a source follower operation. A signal corresponding to a change in voltage at the terminal n2 due to detection of light by the detection element 301 is amplified by the source follower operation of the transistor M10 and output to the sampling unit 550 or 560.

  The sampling unit 550 includes transistors M11 to M13, a capacitor C2, and an analog switch SW2, and samples a signal (S signal) corresponding to the amount of light detected by the detection element 301. Specifically, the signal from the clamp unit 540 can be sampled and held in the capacitor C2 by controlling the transistor M11. The signal is amplified by the transistor M12 that performs the source follower operation, and is output to the column signal line 204 via the analog switch SW2. The transistor M13 can be disposed, for example, between the capacitor C2 and the capacitor C2 of another sensor unit around the sensor unit 201 '. By making the transistor M13 conductive, an average of the S signal of the sensor unit 201 'and the S signals of other sensor units in the vicinity thereof can be acquired, and noise components can be reduced. The sampling unit 560 may sample the signal (N signal) corresponding to the noise component and be configured in the same manner as the sampling unit 550.

  The sensor unit 201 ′ is not limited to the configuration example of FIG. 11, and other configurations for detecting radiation may be taken.

  The output from the sensor unit 201 ′ as described above is converted into a digital value by an AD converter (not shown) and then supplied to the processor 103. In the processor 103, processing corresponding to the voltage conversion unit 302, the comparison unit 303, the memory 304, the determination unit 307, and the conversion unit 130 is performed on software.

  First, as a process corresponding to the voltage conversion unit 302, the processor 103 calculates a differential value of the output of the sensor unit circuit. Next, the processor 103 compares the calculated differential value with a digital value corresponding to the reference voltage 306 as processing corresponding to the comparison unit 303. The processor 103 sets the digital value “1” when the differential value is greater than or equal to the digital value corresponding to the reference voltage 306, and sets the digital value “0” when the differential value is smaller than the digital value corresponding to the reference voltage 306. To do. Then, as a process corresponding to the determination unit 307 and the memory 304, the digital value signal pattern 309 is compared with a reference pattern 308 of a distribution indicating that a preset light is detected, and detection is performed when it is determined that they match. 1 is added to the count value corresponding to the number of times. Similarly to the first embodiment, the signal pattern 309 includes, for example, one sensor unit 201 and a plurality of processing outputs corresponding to the comparison unit 303 of one or more sensor units 201 adjacent to the sensor unit 201. A digital value of bits. As a result, the processor 103 can obtain the number of times that the signal pattern 309 and the reference pattern 308 coincide with each other. Next, the processor 103 performs processing corresponding to the conversion unit 130. Conversion set for each reference pattern 308 for a specific energy band of radiation for converting the number of detections determined that the signal pattern 309 and the reference pattern 308 coincide with each other into an incident amount for each energy band of the incident radiation Conversion is performed according to the coefficient. Then, the processor 103 generates an image based on the converted number of detections. These processes can be executed by the CPU of the processor 103, for example. A storage area for storing the number of detections is secured in the memory of the processor 103. There may be a plurality of digital values corresponding to the reference voltage 306 and functions for performing processing corresponding to the comparison unit 303 and the determination unit 307 in accordance with the level relating to the light intensity and the reference pattern 308.

<Other embodiments>
Each function of the processing unit 330 including the voltage conversion unit 302, the comparison unit 303, the memory 304, the determination unit 307, and the conversion unit 130 in the present invention is arranged in each sensor unit of the sensor panel as in the first embodiment. It may be. Moreover, the form which performs all on software like 2nd Embodiment may be sufficient. However, it is not limited to these embodiments. At least part of the processing performed by the processing unit 330, for example, the voltage conversion unit 302 and the comparison unit 303 are arranged in each sensor unit of the sensor panel 106, and the processing corresponding to the memory 304, the determination unit 307, and the conversion unit 130 is performed on software. You may make it the form performed by. Further, instead of software, a circuit provided outside the sensor panel 106 may be used. In this case, for example, the circuit may be configured with an FPGA.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  As mentioned above, although embodiment which concerns on this invention was shown, it cannot be overemphasized that this invention is not limited to these embodiment, In the range which does not deviate from the summary of this invention, each embodiment mentioned above is changed and combined suitably. Is possible.

DESCRIPTION OF SYMBOLS 100 Radiation imaging device, 105 Scintillator, 106 Sensor panel, 130 Conversion part, 201 Sensor part, 301 Detection element, 330 Processing part

Claims (16)

A radiation imaging apparatus comprising: a scintillator that converts radiation into light; a sensor panel that includes a plurality of pixels including a photodetector that detects the light; and a processing unit.
The processor is
Generating a signal according to the light detected by the photodetector;
Determining whether a plurality of signals generated in the same period by a pixel group including one target pixel and one or more pixels close to the target pixel among the plurality of pixels have a specific distribution;
Count the number of times determined to have the specific distribution for the pixel of interest,
Based on the value obtained by converting the number of times according to the first coefficient, obtaining the incident amount of the first energy band of the radiation irradiated toward the target pixel,
Radiation imaging characterized in that, based on a value obtained by converting the number of times according to a second coefficient, an incident amount of a second energy band is acquired from radiation irradiated toward the pixel of interest. apparatus. The processor is
Determining whether a signal pattern including the plurality of signals generated by the pixel group matches a preset reference pattern representing the specific distribution;
The radiation imaging apparatus according to claim 1, wherein when it is determined that the signal pattern matches the reference pattern, it is determined that the plurality of signals have a distribution corresponding to the reference pattern. The processor is
Determining whether a signal pattern including the plurality of signals generated by the pixel group matches a preset first reference pattern or second reference pattern;
Counting the first number of times that the signal pattern and the first reference pattern are determined to match, and the second number of times that the signal pattern and the second reference pattern are determined to match,
Based on a value obtained by converting the first number of times according to the first coefficient and a value obtained by converting the second number of times according to a third coefficient, the first number Get the incident amount of energy band,
Based on the value obtained by converting the first number of times according to the second coefficient and the value obtained by converting the second number of times according to a fourth coefficient, the second number The radiation imaging apparatus according to claim 2, wherein an incident amount of an energy band is acquired.   4. The radiation imaging apparatus according to claim 1, wherein the processing unit generates a binary signal according to the intensity of light detected for each of the photodetectors. The processing unit is
A voltage converter that converts a signal output from the photodetector into a voltage value;
A comparison unit that compares the voltage value with a predetermined voltage value and generates a comparison result signal indicating a comparison result;
The plurality of comparison result signals generated in the same period by each comparison unit of the pixel group including the one pixel of interest and one or more pixels adjacent to the pixel of interest among the plurality of pixels. A determination unit that determines whether the distribution has the specific distribution;
A memory for storing the number of times the distribution is determined to be the specific distribution by the determination unit;
In order to obtain a value based on the incident amount of the first energy band among the radiation irradiated to the pixel of interest, the number of times is converted according to the first coefficient, and among the radiation irradiated to the pixel of interest A conversion unit that converts the number of times according to a second coefficient to obtain a value based on an incident amount of the second energy band;
The radiation imaging apparatus according to claim 1, comprising:   The comparison result signal includes a binary signal of a signal when the voltage value is equal to or higher than the predetermined voltage value and a signal when the voltage value is smaller than the predetermined voltage value. The radiation imaging apparatus according to claim 5. The determination unit is
The signal pattern including the distribution output from the comparison unit of each of the pixel groups in the same period matches the first reference pattern or the second reference pattern representing the specific distribution set in advance. Determine whether
If it is determined that the signal pattern and the first reference pattern match, it is determined that the plurality of signals have a distribution corresponding to the first reference pattern, and a first distribution detection signal is output,
When it is determined that the signal pattern and the second reference pattern match, it is determined that the plurality of signals have a distribution corresponding to the second reference pattern, and a second distribution detection signal is output,
The memory stores a first number of times that the first distribution detection signal is output and a second number of times that the second distribution detection signal is output;
The conversion unit is
Based on the sum of the value obtained by converting the first number of times according to the first coefficient and the value obtained by converting the second number of times according to a third coefficient, the first number Obtain the incident amount of 1 energy band,
Based on the sum of the value obtained by converting the first number of times according to the second coefficient and the value obtained by converting the second number of times according to a fourth coefficient, the first number The radiation imaging apparatus according to claim 5, wherein an incident amount in an energy band of 2 is acquired.   The radiation imaging apparatus according to claim 1, wherein the plurality of pixels are arranged in a two-dimensional array.   9. The radiation imaging apparatus according to claim 1, wherein the light detector converts the light into an electric charge, and detects the intensity of the light based on an accumulated amount of the electric charge.   The radiation imaging apparatus according to claim 1, wherein a thickness of the scintillator is thicker than a pitch at which the plurality of pixels are arranged.   The radiation imaging apparatus according to any one of claims 1 to 10, wherein the scintillator and the sensor panel are arranged in this order from a radiation irradiation side.   The radiation imaging apparatus according to claim 1, wherein the sensor panel and the scintillator are arranged in this order from the side irradiated with radiation.   13. The scintillator according to claim 1, wherein the scintillator includes an absorption layer that absorbs light converted by the scintillator on a side opposite to a side facing the sensor panel. Radiation imaging device.   The radiation imaging apparatus according to claim 1, wherein at least a part of the processing unit is arranged in each pixel of the plurality of pixels. A method for controlling a radiation imaging apparatus using a scintillator that converts radiation into light and a sensor panel that includes a plurality of pixels that include a photodetector that detects the light,
Generating a signal according to the light detected by the photodetector;
Determining whether a plurality of signals generated in the same period by a pixel group including one target pixel and one or more pixels close to the target pixel among the plurality of pixels have a specific distribution;
Counting the number of times determined to have the specific distribution for the pixel of interest;
Based on the value obtained by converting the number of times according to the first coefficient, the incident amount of the first energy band is acquired among the radiation irradiated toward the target pixel, and the incident amount of the first energy band is acquired according to the second coefficient. Acquiring the incident amount of the second energy band of the radiation irradiated toward the pixel of interest based on the value obtained by converting the number of times;
The control method characterized by including.   A program causing a computer to execute each step of the control method according to claim 15.

Images