JP6546451B2 - Radiation imaging apparatus, control method thereof and program - Google Patents

Description

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

  A radiation imaging apparatus using a flat panel detector (hereinafter referred to as FPD) made of a semiconductor material is known as an imaging apparatus used for medical image diagnosis and nondestructive inspection by radiation (X-ray). Such a radiation imaging apparatus can be used, for example, as a digital imaging apparatus such as a still image or a moving image in medical image diagnosis.

  The FPD includes an integral sensor and a photon counting sensor. Integral sensors measure the total amount of charge generated by the incidence of radiation. In contrast, photon counting sensors identify the energy (wavelength) of the incident radiation and count the number of times the radiation is detected for each of a plurality of energy levels. That is, since the photon counting sensor has energy resolution, the diagnostic capability can be improved as compared to the integral sensor.

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

Japanese Patent Application Publication No. 2013-501226 JP 2003-279411 A

  CdTe single crystals used for direct type sensors can only be grown to about several cm square. Therefore, direct type sensors are difficult to increase in area and are very expensive. In addition, there is also a method of realizing a large area direct type sensor by depositing amorphous Se, but the sensor manufactured by the method has problems such as slow operation and the need of temperature control.

  On the other hand, the indirect sensor has the advantage of being easy to increase in area and inexpensive. However, Patent Document 2 does not describe determining the amount of incident radiation having a 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; and a sensor panel in which a plurality of pixels including a light detector that detects light are disposed; A processing unit including: a processing unit, wherein the processing unit generates a signal according to light detected by the light detector, and one of a plurality of pixels and one of a target pixel and a target pixel are in proximity It is determined whether a plurality of signals generated in the same period by a pixel group including the above pixels have a specific distribution, the number of times determined to have a specific distribution is counted for the pixel of interest, and the first coefficient Based on the value obtained by converting the number, the incident amount of the first energy band among the radiation irradiated toward the pixel of interest is obtained, and obtained by converting the number according to the second coefficient. Based on the 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 an incident amount of each incident energy band in an indirect sensor.

The figure which shows the structural example of the radiation imaging device concerning this invention. FIG. 2 is a view showing a configuration of a sensor panel of the radiation imaging apparatus of FIG. 1. FIG. 2 is a view showing the configuration of a sensor unit of the radiation imaging apparatus of FIG. 1; The figure which shows the irradiation period and read-out period of the sensor panel of the radiation imaging device of FIG. FIG. 7 is a view showing an operation of each sensor unit in an irradiation period of the radiation imaging apparatus of FIG. 1. FIG. 2 is a view showing the spread of light emission of a scintillator of the radiation imaging apparatus of FIG. 1; FIG. 2 is a view showing a light emission distribution converted into digital values of the radiation imaging apparatus of FIG. 1. FIG. 2 is a view showing a conversion unit of the radiation imaging apparatus of FIG. 1; FIG. 7 is a view showing an example of conversion coefficients of the radiation imaging apparatus of FIG. 1; FIG. 7 is a view showing an operation of each sensor unit in a reading period of the radiation imaging apparatus of FIG. 1. FIG. 7 is a view showing the configuration of a sensor unit of a radiation imaging apparatus according to a second embodiment of the present invention.

  Hereinafter, specific embodiments of a radiation imaging apparatus according to the present invention will be described with reference to the attached drawings. Note that, in the following description and the drawings, the same reference numerals are given to the same configuration throughout the plurality of drawings. Therefore, the common configuration will be described with reference to a plurality of drawings, and the description of the configuration having the same reference numeral will be omitted as appropriate. The radiation in the present invention may be, for example, X-ray having a similar or higher energy, in addition to α-ray, β-ray and γ-ray which are beams produced by particles (including photons) emitted by radiation decay. It may also include rays, particle rays, cosmic rays, etc.

First Embodiment
A radiation imaging apparatus 100 (or may be referred to as 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 radiation to an object, an irradiation control unit 102 that controls the irradiation unit 101, and an imaging unit 104 that images an object irradiated with radiation. And a processor 103. Each of the irradiation control unit 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 separately configured. However, the present invention is not limited thereto, and may be integrally configured. 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 of which detects light converted from radiation by the scintillator 105 is arranged 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 radiation imaging of a photon counting method, and measures the number of photons of incident radiation based on the detection result of light.

  The processor 103 exchanges signals or data with the imaging unit 104. Specifically, the processor 103 controls the imaging unit 104 to perform radiation imaging, and receives a signal obtained thereby from the imaging unit 104. This signal includes a measurement value of radiation photons, and 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 predetermined correction processing on the image data. Also, the processor 103 supplies the irradiation control unit 102 with a signal for starting or ending the irradiation.

  Next, the configuration of the sensor panel 106 will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the sensor panel 106. As shown in FIG. 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 by the scintillator 105. Then, it may be configured to count the number of times of detecting a specific distribution among the acquired light distributions. Each sensor unit 201 converts data of the number of times of detection according to one or more distributions into an incident amount for each energy band of radiation emitted toward each sensor unit 201. When a signal is supplied through the signal line 205, each sensor unit 201 outputs data of the incident amount to the column selection circuit 208 through the column signal line 204.

  The vertical scanning circuit 202 switches the signal lines 205 for supplying signals in order so that data of the incident amount is output from each sensor unit 201. When a signal is supplied via the signal line 207, the column selection circuit 208 outputs data of the incident amount 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 lines 207 for supplying signals so that the operation of outputting the data of the incident amount to the output line 206 is sequentially performed in the plurality of column selection circuits 208. Here, FIG. 2 shows the sensor panel 106 in which the sensor units 201 of 3 rows × 3 columns are arrayed to simplify the description, but the sensor panel 106 in which more sensor units 201 are arrayed is used. It may be done. For example, in a 17-inch sensor panel 106 (FPD), about 2800 rows × about 2800 columns of sensor units 201 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 one dimension. .

  Next, the configuration of the sensor unit 201 will be described with reference to FIG. FIG. 3 is a diagram showing the configuration of the sensor unit 201. As shown in FIG. Each sensor unit 201 of the sensor panel 106 can include, for example, a detection element 301 that is a light detector, 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. For 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 differential circuit, converts the signal generated by the detection element 301 into a pulse signal of voltage, and outputs the 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 according to the comparison result. When the voltage value of the pulse signal output from the voltage conversion unit 302 is equal to or higher than the voltage value of the reference voltage 306, the comparison unit 303 outputs a digital value "1" as a signal according 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 according to the comparison result. The reference voltage 306 supplied to the comparison unit 303 can be set to a value common to all the sensor units 201 in the sensor panel 106. When radiation is incident on the scintillator 105 and converted into light, the comparison unit 303 generates a binary digital value signal via the voltage conversion unit 302 according to the light detected by the detection element 301.

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

  Next, the determination unit 307 determines whether the signal pattern 309 has a specific distribution. When determining 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. When it is determined that the signal pattern 309 and the reference pattern 308 match, the determination unit 307 determines that the distribution corresponding to the reference pattern 308 is detected, and outputs a distribution detection signal that adds 1 to the count value of the memory 304. Do. If 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 has been 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 of detection in which the signal pattern 309 and the reference pattern 308 match 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 provided from the outside of the determination unit 307.

  Here, the determination of the detection of the distribution 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, using the addition circuit that adds the output of the comparison unit 303 of the adjacent sensor unit 201, the determination unit 307 may count the memory 304 according to the total value of the digital values output from the comparison unit 303. . For example, when the output from the comparing unit 303 of the sensor unit 201 is “1”, the sum of the outputs from the comparing unit 303 of the sensor unit 201 and the four sensor units 201 adjacent to the top, bottom, left, and right of the sensor unit 201 is “ 2 or more. In this case, the determination unit 307 may add 1 to the count value of the memory 304 on the assumption that the specific distribution is detected. In the determination unit 307, 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 by the scintillator 105 is spread and detected by the plurality of sensor units 201. Can be determined.

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

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

  In the configuration illustrated in FIG. 3, two determination units 307 of determination unit 307R and determination unit 307B are disposed 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. The reference pattern 308R is provided to the determination unit 307R, and the reference pattern 308B is provided to the determination unit 307B. In the memory 304, two memories, a memory 304R connected to the determination unit 307R and a memory 304B connected to the determination unit 307B, are arranged. If the determination unit 307R determines that the signal pattern 309 and the reference pattern 308R coincide with each other, the determination unit 307 adds 1 to the count value of the memory 304R. In addition, when 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, by arranging the plurality of determination units 307 and the memory 304, the incident amount of radiation photons having a plurality of specific energies is acquired.

  Although the example which arranges two determination parts 307 in one sensor part 201 is shown in this embodiment, it is not restricted to it, for example, you may arrange only one determination part 307. FIG. Further, for example, three or more determination units 307 may be arranged, and it may be determined whether or not different reference patterns 308 and signal patterns 309 coincide with each other. Further, although the example shown in FIG. 3 shows an example in which two memories 304 are arranged, the present invention is not limited to this. For example, only one memory 304 may be arranged according to the number of judgment units 307 arranged. And three or more memories 304 may be arranged. Further, the signal pattern 309 is configured by the output of the comparison unit 303 of the five sensor units of the sensor unit 201 and four sensor units adjacent to the sensor unit 201 vertically and horizontally in this embodiment. However, for example, from the output of the two sensor units 201 adjacent to each other, the four sensor units 201 obliquely adjacent to the sensor unit 201, and the comparison unit 303 of the sensor units 201 separated by two or more, for example, the signal pattern 309 It may be configured. In addition, the signal pattern 309 may be configured by, for example, an 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 due to the incidence of radiation, and is generated in the same period by the sensor unit 201 which is one pixel of interest among the plurality of sensor units 201 and one or more sensor units close to the sensor unit 201 to be noted. Any configuration may be used as long as the spread of the light emission distribution is acquired. Then, the determination unit 307 acquires, for each of the sensor units 201 to be focused on, the distribution of light emission generated in the same period, and determines whether the distribution of light emission has a specific distribution.

  Next, driving of the radiation imaging system in the present embodiment will be described. FIG. 4 is a diagram showing the drive timing of the sensor panel 106 of the imaging unit 104. As shown in FIG. The waveform in FIG. 4 represents the irradiation period of radiation and the period of readout of the data DATA, with the horizontal axis representing 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, and the spread of the light distribution is acquired. It is a period in which the number of times of coincidence is counted. The readout period is a period in which the sensor panel 106 outputs data DATA obtained by converting the number of times of detection obtained in the radiation irradiation period into an incident amount for each energy band of the incident radiation. As shown in FIG. 4, the sensor panel 106 can acquire a moving image by alternately performing a radiation irradiation period and a readout period. Further, for example, the still image may be acquired by performing the radiation irradiation period and the readout 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. The waveforms in FIG. 5 represent the output of the voltage conversion unit 302, the output of the comparison unit 303, and the count value of the memory 304, where the horizontal axis represents time. Radiation photons enter the imaging unit 104 and are converted to light by the scintillator 105. The electric signal resulting from the light detected in the detection element 301 is converted into a pulse of voltage in the voltage conversion unit 302. When the pulse of the voltage 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 is present between the comparison unit 303 and the memory 304. If both 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), and the reference pattern 308R match, the determination unit 307R determines that the count value of the memory 304R is 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 and the reference pattern 308 match is counted as the number of times of detection of detecting a specific distribution, and is stored in the memory 304.

  Next, a method of converting the number of times of detection obtained in the radiation irradiation period into an incident amount of radiation having a 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 distribution of light emission of the scintillator 105. As shown in FIG. In the configuration shown in FIG. 6, radiation is incident from the upper side of the drawing, and in the imaging unit 104, the scintillator 105 and the sensor panel 106 (detection element 301) are disposed in this order from the radiation incident side. The radiation photons that make up the radiation have different energies. As shown in FIG. 6A, radiation photons having low energy are likely to be absorbed far from the detection element 301 and near the radiation incident side. In this case, the light converted from the radiation by the scintillator 105 is widely diffused in the scintillator 105, and is thus detected by the detection elements 301 of the many sensor units 201. On the other hand, radiation photons having high energy are less absorbed by the scintillator 105 than radiation photons having low energy. Therefore, as shown in FIG. 6A, the radiation may be absorbed on the incident surface side, or as shown in FIG. 6B, the radiation may be absorbed in the vicinity of the detection element 301. When absorbed in the vicinity of the detection element 301 as shown in FIG. 6B, for example, one sensor does not diffuse the light converted from the radiation by the scintillator 105 as compared to 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 depths in the scintillator where the radiation photons are converted to light are different, the spread of the distribution of the light emission will be different accordingly. Thus, the radiation imaging apparatus 100 has a resolution of energy with respect to the incident radiation, and among the radiation emitted toward each of the sensor units 201, the amount of incident light for each specific energy band of the radiation is It can be detected.

  Here, the energy resolution can be improved as the difference in the spread of light emission distribution caused by the difference in the energy of the radiation is larger. The spread of the light emission distribution can be largely changed by the thickness 702 of the scintillator 105. As the thickness 702 of the scintillator 105 is thicker, light emission by radiation absorbed near the radiation incident surface spreads to more detection elements 301 of the sensor unit 201. 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 disposed, in order to diffuse the emission of radiation photons absorbed in the vicinity of the radiation incident surface to a wider range. Good.

  Further, in order to enhance the accuracy of energy resolution, the absorbing layer 701 may be disposed on the side of the scintillator 105 opposite to the side facing the detection element 301, in the case of the configuration shown in FIG. The light emitted by the scintillator 105 can be diffused in various directions. Even when light is emitted in a region close to the detection element 301, light can be diffused to directions other than the direction to the detection element 301 as shown in FIG. 6C. When the light reflectance is high on the surface of the scintillator 105, this diffused light may be reflected on the surface and be incident on the detection element 301. The reflected light emits light in the vicinity of the detection element 301 and can spread to the detection elements 301 of the plurality of sensor units 201 as compared with the light directly incident on the detection element 301. For this reason, a difference with the light emission distribution of the light emitted at the position away from the detection element 301 may not easily occur. An absorption layer 701 may be disposed to prevent the diffusion of light due to this reflection. For example, when 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.

  Further, in the present embodiment, as shown in FIG. 6, in the imaging unit 104, the scintillator 105 and the sensor panel 106 are disposed in order from the radiation incident side. However, the arrangement of the scintillator 105 and the detection element 301 is not limited to this. Radiation may be incident from the side of the sensor panel 106 and may be incident on the scintillator 105 after 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 being widely diffused in the scintillator 105. On the other hand, radiation photons having high energy are less absorbed by the scintillator 105 than radiation photons having low energy. For this reason, for example, the light emission due to the radiation absorbed by the scintillator at a place away from the detection element 301 is widely diffused in the scintillator 105 and detected by the detection elements 301 of the many sensor units 201. As described above, even when radiation is incident from the side of the sensor panel 106, the spread of the light emission distribution differs depending on the difference in the light emission depth. Thus, the radiation imaging apparatus 100 can detect the energy of the incident radiation and the amount of the incident radiation among the radiation irradiated toward the sensor units 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 is a sensor panel 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 position away from the detection element 301 of the scintillator 105, light is diffused in the scintillator 105 because the light is emitted at a position away from the detection element 301. The light emission distribution spreads to a plurality of sensor units 201. In this case, as shown in FIG. 7A, the digital value from the comparison unit 303 of each sensor unit 201 indicates that light is detected also in the sensor unit 201 adjacent to the sensor unit 201A that is the pixel of interest. It can be a signal pattern 309R. The signal pattern 309R matches the reference pattern 308R for identifying that the light is detected by the sensor unit 201A and a plurality of sensor units 201 close to the sensor unit 201A. Therefore, the determination unit 307R determines that the signal pattern 309A and the reference pattern 308R match, and adds 1 to the count value of the memory 304R.

  On the other hand, as shown in FIG. 6B, when radiation is absorbed and emitted near the detection element 301 of the scintillator 105, light is emitted at a position near the detection element 301. For this reason, the distribution of light emission does not spread to 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. The signal pattern 309B detects light only by the sensor unit 201A, and matches the reference pattern 308B for identifying that light is not detected by the adjacent sensor unit 201. Therefore, the determining unit 307B determines that the signal pattern 309B and the reference pattern 308B match, and adds 1 to the count value of the memory 304B. As described above, the signal pattern 309 and the reference pattern 308 match each other by the determination unit 307 and the memory 304, and the number of times of detection determined that 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 the incident radiation from the count value of the number of times of detection obtained for each sensor unit 201 will be described. FIG. 8 shows a conversion unit 130 for converting the number of detections into an incident amount of radiation, and FIG. In the following example, the case where the energy of radiation is divided into two energy bands with a certain threshold (for example, 60 keV) as a boundary, and the amount of incident radiation is acquired for each energy band will be described. Energy below this threshold is called low energy and energy above this threshold is called high energy.

  Radiation having low energy is necessarily absorbed on the incident surface side of the scintillator 105 to broaden the distribution of light emission, and radiation having high energy is necessarily absorbed at a location away from the incident surface side of the scintillator 105 to have narrow emission distribution 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. Therefore, each count value of the memory 304R and the memory 304B, which is the number of times of detection of the signal pattern 309 coincident with each reference pattern 308, is converted into the 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 radiation photons and the possibility that the signal pattern 309 obtained by converting radiation photons into light and the reference pattern 308 may coincide. For example, each count value is converted by multiplying the count value of the memory 304R by the coefficient L, the coefficient H, and the count value of the memory 304B by the coefficient L 'and the coefficient H'. In the configuration of the conversion unit 130 illustrated in FIG. 8, the count value of the memory 304R that has detected that the distribution of light detection in the signal pattern 309 is wide is multiplied by a coefficient L = 0.6. As a result, the conversion incident amount caused by the low energy radiation in the count value of the memory 304R is calculated. Further, the count value of the memory 304R is multiplied by the coefficient H = 0.4 to calculate the converted incident amount caused by the high energy radiation among the count values of the memory 304R. Similarly, the count value of the memory 304B, which detects that the distribution for detecting the light of the signal pattern 309 is narrow, is multiplied by the coefficient L ′ = 0.1, and the low energy radiation among the count values of the memory 304B is multiplied. The resulting converted incident amount is calculated. Further, by multiplying the coefficient H ′ = 0.9, the converted incident amount caused by the high energy radiation among the count values of the memory 304 B is calculated. Then, the respective converted incident amounts resulting from the low energy radiation are added. In addition, the respective converted incident amounts resulting from the high energy radiation are added. As a result, the count value of the distribution of light detected by the plurality of sensor units 201 is converted into the incident amount of radiation incident in each energy band of low energy and high energy. Data of the amount of incidence due to the acquired low energy radiation is stored in the output unit 305R, and data of the amount of incidence due to the acquired high energy radiation are stored in the output unit 305B.

  Here, the conversion factor is appropriately set for each specific energy band of radiation, such as the high energy and low energy described above. The conversion coefficient is set for each reference pattern 308. Here, for example, the conversion factor depends on conditions such as the tube voltage, tube current, irradiation time, material and thickness of the additional filter, and 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 energy resolution with high accuracy. Further, two conversion coefficients may be set to the count value of each memory 304 as in the present embodiment, for example, only one may be set, or three or more may be set, for example. . It may be set appropriately according to the type of energy band of the radiation to be detected. Moreover, in the above-mentioned example, the incident amount of radiation was acquired by adding the conversion incident amount for every 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 of radiation and the distribution of emission, etc., conversion coefficients are only applied and addition is not used. It is 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). Further, for example, the irradiation amount of the irradiation unit 101 may be set to a value when the tube voltage is about 100 kV and the tube current is about 10 mA.

  Next, the operation in the reading period in the sensor unit 201 configured as shown in FIG. 3 will be described with reference to FIG. FIG. 10 is a diagram showing an operation of each sensor unit 201 in the reading period. The waveforms in FIG. 10 indicate the supply of signals to the signal line 205 with time on the horizontal axis, the supply of signals to the signal line 207, and the output of data DATA of the amount of incident radiation acquired from the column selection circuit 208. It represents each. As shown in FIG. 10, signals are supplied to the plurality of signal lines 205 and the plurality of signal lines 207 in order. For example, when signal supply to the signal line 205-0R is started, data of the amount of incident radiation of 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. Be done. Then, in a period in which signals are supplied to the signal lines 205-0R, signals are sequentially supplied to the plurality of signal lines 207, and the data DATA of the incident amount of radiation is sequentially output to the output lines 206 from the plurality of column selection circuits 208. Make it output.

  Further, when the supply of the signal to the signal line 205-0R is ended and the supply of the signal 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 of the amount of incident radiation is supplied to the column selection circuit 208. Then, in a period in which a signal is supplied to the signal line 205-0 B, the signals are sequentially supplied to the plurality of signal lines 207, and the data DATA of the incident amount of radiation is sequentially output to the output line 206 from the plurality of column selection circuits 208. Make it output. Thereby, data DATA of the incident amount of radiation can be supplied to the processor 103 through the output line 206 from the plurality of sensor units 201 in one row. In this manner, signals are sequentially supplied to the plurality of signal lines 205 and the plurality of signal lines 207, and the data DATA of the incident amount of radiation for each specific energy band is output from the plurality of sensor units 201 via the output line 206. It 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. The radiation photon measurement method according to the first embodiment described above uses the processing unit 330 disposed in the sensor unit 201, but these functions are realized, for example, on a program or software in the processor 103. 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 a sensor unit 201 'according to the second embodiment. The sensor unit 201 ′ includes, for example, a reset unit 510, a signal amplification unit 520, a light sensitivity selection unit 530, a clamp unit 540, a first sampling unit 550, and a second sampling unit 560 in addition to the detection element 301. The reset unit 510 includes a transistor M1, and resets the potential of the detection element 301 by turning on the transistor M1. The signal amplification unit 520 includes transistors M2 to 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.

  The light sensitivity selection unit 530 includes transistors M4 to M7 and capacitors C4 to C5. For example, the capacitor C4 is connected to the gate of the transistor M3 by turning on the transistor M4, and the transistor M7 performs a source follower operation by turning on the transistor M6. Thereby, it is possible to change the signal amplification factor of the signal according to the charge amount generated in the detection element 301. Further, by turning on the transistor M5, 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 amplification 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 turned on by turning on the transistor M8. A voltage is supplied. As a result, the voltage when the detection element 301 is reset is clamped as a noise component between the terminals n1 and n2. Thereafter, the transistor M8 performs a source follower operation by rendering the transistor M8 non-conductive and the transistor M9 conductive. A signal corresponding to a change in voltage of the terminal n2 accompanying detection of light by the detection element 301 is amplified by the source follower operation of the transistor M10, and is 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 light amount of light detected by the detection element 301. Specifically, by controlling the transistor M11, the signal from the clamp unit 540 can be sampled and held in the capacitor C2. The signal is amplified by the transistor M12 that performs a source follower operation, and is output to the column signal line 204 via the analog switch SW2. The transistor M13 may be disposed, for example, between the capacitor C2 and a capacitor C2 of another sensor unit around the sensor unit 201 '. By turning on the transistor M13, it is possible to obtain an average of the S signal of the sensor unit 201 'and the S signals of other sensor units in the vicinity thereof, and to reduce noise components. The sampling unit 560 may be configured in the same manner as the sampling unit 550 by sampling a signal (N signal) corresponding to a noise component.

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

  The output from the sensor unit 201 ′ as described above is supplied to the processor 103 after being converted into a digital value by an AD converter (not shown). Then, 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, the processor 103 calculates a differential value of the output of the sensor unit circuit as a process corresponding to the voltage conversion unit 302. Next, the processor 103 compares the calculated differential value with the 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. Do. Then, as processing corresponding to the determination unit 307 and the memory 304, the signal pattern 309 of the digital value is compared with the reference pattern 308 of the distribution indicating that the light set in advance is detected, and it is determined that they match. Add 1 to the count value corresponding to the number. Similar to the first embodiment, the signal pattern 309 includes, for example, a plurality of outputs of processing corresponding to one sensor unit 201 and a comparison unit 303 of one or more sensor units 201 close to the sensor unit 201. It is a digital value of bits. By this, the processor 103 can obtain the number of matched detections of the signal pattern 309 and the reference pattern 308. Next, the processor 103 performs a process corresponding to the conversion unit 130. A conversion set for each reference pattern 308 with respect to a specific energy band of radiation for converting the number of times of detection determined that the signal pattern 309 and the reference pattern 308 match to an incident amount for each energy band of incident radiation Convert according to the coefficients. Then, the processor 103 generates an image based on the converted number of times of detection. These processes may be executed, for example, in the CPU of the processor 103. In addition, a storage area for storing the number of times of detection 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, depending on the level of the light intensity and the reference pattern 308.

<Other Embodiments>
The respective functions 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 are disposed in each sensor unit of the sensor panel as in the first embodiment. It may be Further, as in the second embodiment, all may be performed on software. However, it is not limited to these embodiments. At least a 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 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 by an FPGA.

  The present invention is also realized by executing the following processing. That is, software (program) for realizing 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 execute.

  Although the embodiments according to the present invention have been described above, it goes without saying that the present invention is not limited to these embodiments, and the above-described embodiments can be appropriately modified or combined without departing from the scope of the present invention. Is possible.

Reference Signs List 100 radiation imaging apparatus, 105 scintillator, 106 sensor panel, 130 conversion unit, 201 sensor unit, 301 detection element, 330 processing unit

Claims (16)

A radiation imaging apparatus comprising: a scintillator that converts radiation into light; a sensor panel in which a plurality of pixels having a light detector for detecting the light are disposed; and a processing unit,
The processing unit is
Generating a signal in response to the light detected by the light detector,
It is determined whether a plurality of signals generated in the same period by a pixel group including one target pixel among the plurality of pixels and one or more pixels close to the target pixel have a specific distribution.
Counting the number of times determined to have the specific distribution for the pixel of interest;
Acquiring an incident amount of a first energy band among the radiation irradiated toward the pixel of interest based on a value obtained by converting the number of times according to a first coefficient;
Radiation imaging characterized in that an incident amount of a second energy band among radiation irradiated toward the target pixel is acquired based on a value obtained by converting the number of times according to a second coefficient. apparatus. The processing unit is
It is determined whether a signal pattern including the plurality of signals generated by the pixel group matches a reference pattern representing the predetermined distribution set in advance.
The radiation imaging apparatus according to claim 1, wherein when it is determined that the signal pattern and the reference pattern match, it is determined that the plurality of signals have a distribution corresponding to the reference pattern. The processing unit is
It is determined whether a signal pattern including the plurality of signals generated by the pixel group matches a preset first reference pattern or a second reference pattern.
Counting a first number of times that the signal pattern and the first reference pattern are determined to match, and a second number of times that the signal pattern and the second reference pattern are determined to match;
The first method is based on a value obtained by converting the first number according to the first coefficient and a value obtained by converting the second number according to a third coefficient. Get the amount of incident energy band,
The second based on the value obtained by converting the first number according to the second coefficient and the value obtained by converting the second number according to a fourth coefficient The radiation imaging apparatus according to claim 2, wherein an incident amount of an energy band is acquired.   The radiation processing apparatus according to any one of claims 1 to 3, wherein the processing unit generates a binary signal according to the intensity of light detected for each of the light detectors. The processing unit
A voltage conversion unit that converts a signal output from the light detector 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 of the comparison units of the pixel group including one target pixel among the plurality of pixels and one or more pixels close to the target pixel A determination unit that determines whether the distribution has the specific distribution;
A memory that stores the number of times that the distribution is determined to have 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 target pixel, the number of times is converted according to the first coefficient, and of the radiation irradiated to the target pixel A converter for converting the number according to a second coefficient to obtain a value based on the incident amount of the second energy band;
The radiation imaging apparatus according to claim 1, further comprising:   The comparison result signal has 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 device according to claim 5. The determination unit
A signal pattern including the distribution output from the comparison unit of each of the pixel groups during the same period matches a first reference pattern or a second reference pattern representing the specific distribution set in advance. To determine
When 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 matches the second reference pattern, 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 the first distribution detection signal is output and a second number of times the second distribution detection signal is output;
The conversion unit
The first based on a sum of a value obtained by converting the first number according to the first coefficient and a value obtained by converting the second number according to a third coefficient; Get the amount of incident in the energy range of 1,
The first one is based on the sum of a value obtained by converting the first number according to the second coefficient and a value obtained by converting the second number according to a fourth coefficient. The radiation imaging device according to claim 5 or 6, wherein an incident amount in an energy band of 2 is acquired.   The radiation imaging apparatus according to any one of claims 1 to 7, wherein the plurality of pixels are arranged in a two-dimensional array.   The radiation imaging apparatus according to any one of claims 1 to 8, wherein the light detector converts the light into an electric charge, and detects the intensity of the light based on the accumulated amount of the electric charge.   The radiation imaging apparatus according to any one of claims 1 to 9, wherein a thickness of the scintillator is larger 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 disposed in this order from the side irradiated with radiation.   The radiation imaging apparatus according to any one of claims 1 to 10, wherein the sensor panel and the scintillator are arranged in this order from the side irradiated with radiation.   The said scintillator includes the absorption layer which absorbs the light converted with the said scintillator on the opposite side to the side facing the said sensor panel, The any one of the Claims 1-12 characterized by the above-mentioned. Radiation imaging device.   The radiation imaging apparatus according to any one of claims 1 to 13, wherein at least a part of the processing unit is disposed in each of the plurality of pixels. A control method of a radiation imaging apparatus using a scintillator that converts radiation into light, and a sensor panel in which a plurality of pixels having a light detector that detects the light are disposed,
Generating a signal in response to the light detected by the light detector;
Determining whether a plurality of signals generated in the same period by a pixel group including one target pixel among the plurality of pixels and one or more pixels close to the target pixel have a specific distribution;
Counting the number of times determined to have the specific distribution for the target pixel;
Based on a value obtained by converting the number of times according to a first coefficient, an incident amount of a first energy band among the radiation irradiated toward the target pixel is obtained, and according to a second coefficient Acquiring an incident amount of a second energy band of radiation irradiated toward the target pixel based on a value obtained by converting the number of times;
A control method characterized by including.   A program causing a computer to execute each step of the control method according to claim 15.

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