WO2016194295A1

WO2016194295A1 - Radiation imaging apparatus, control method thereof, and program

Info

Publication number: WO2016194295A1
Application number: PCT/JP2016/002201
Authority: WO
Inventors: Katsuro Takenaka; Atsushi Iwashita; Kosuke Terui; Shinichi Takeda
Original assignee: Canon Kabushiki Kaisha
Priority date: 2015-06-01
Filing date: 2016-04-26
Publication date: 2016-12-08
Also published as: JP6546451B2; JP2016223951A

Abstract

A radiation imaging apparatus is provided. The apparatus comprises a scintillator, a sensor panel in which each including a light detector, and a processing unit. The processing unit generates signals in accordance with the light detected by the light detectors, determines whether signals generated in the same period by a pixel group, which includes one pixel of interest and at least one pixel near the pixel of interest out of the pixels, have a specific distribution, obtains a count of the number of times the pixel of interest is determined to have the specific distribution, and obtains, based on a value obtained by converting the count in accordance with a first and a second coefficient, an incident amount of a first and a second energy band out of radiation irradiating the pixel of interest, respectively.

Description

RADIATION IMAGING APPARATUS, CONTROL METHOD THEREOF, AND PROGRAM

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

There is known a radiation imaging apparatus that uses, as an imaging apparatus used for medical imaging diagnosis or non-destructive inspection by radiation (X-rays), a flat panel detector (to be referred to as FPD hereinafter) formed from a semiconductor material. Such a radiation imaging apparatus can be used, for example, in medical imaging diagnosis, as a digital imaging apparatus for obtaining a still image or a moving image.

An integral sensor and a photon counting sensor are available as FPDs. An integral sensor measures the total amount of charges generated from incident radiation. In contrast, a photon counting sensor identifies the energy (wavelength) of incident radiation and obtains the detection count of radiation for each energy level. That is, since the photon counting sensor has an energy resolution, the diagnosis capability can be improved compared to the integral sensor.

Japanese Patent Laid-Open No. 2013-501226 proposes a direct type sensor that obtains a detection count of radiation by using CdTe to directly detect radiation energy. In addition, Japanese Patent Laid-Open No. 2003-279411 proposes an indirect type sensor that detects light intensity generated in a scintillator from incident radiation and obtains a detection count of the light.

Single crystal CdTe used in a direct type sensor can only grow to about a few cm square. Therefore, it is difficult and very costly to increase the area of a direct type sensor. Although there is a method of implementing a direct type sensor with a large area by depositing amorphous Se, a sensor manufactured by this method operates slowly and requires temperature management.

In contrast, an indirect type sensor is advantageous since it is easy to increase the area and low in cost. However, Japanese Patent Laid-Open No. 2003-279411 does not disclose a method of obtaining an incident amount of radiation having a specific band of energy.

Some embodiments of the present invention provide a technique to obtain the incident amount for each energy band of incident radiation in an indirect type sensor.

According to some embodiments, a radiation imaging apparatus comprising: a scintillator configured to convert radiation into light; a sensor panel in which a plurality of pixels each including a light detector configured to detect the light is arranged; and a processing unit, wherein the processing unit: generates signals in accordance with the light detected by the light detectors; determines whether a plurality of signals generated in the same period by a pixel group, which includes one pixel of interest and at least one pixel near the pixel of interest out of the plurality of pixels, has a specific distribution; obtains a count of the number of times the pixel of interest is determined to have the specific distribution; obtains, based on a value obtained by converting the count in accordance with a first coefficient, an incident amount of a first energy band out of radiation irradiating the pixel of interest; and obtains, based on a value obtained by converting the count in accordance with a second coefficient, an incident amount of a second energy band out of the radiation irradiating the pixel of interest, is provided.

According to some other embodiments, a control method of a radiation imaging apparatus that uses a scintillator configured to convert radiation into light and a sensor panel in which a plurality of pixels each including a light detector configured to detect the light is arranged, comprising: generating signals in accordance with the light detected by the light detectors, determining whether a plurality of signals generated in the same period by a pixel group, which includes one pixel of interest and at least one pixel near the pixel of interest out of the plurality of pixels, has a specific distribution, obtaining a count of the number of times the pixel of interest is determined to have the specific distribution, obtaining, based on a value obtained by converting the count in accordance with a first coefficient, an incident amount of a first energy band out of radiation irradiating the pixel of interest, and obtaining, based on a value obtained by converting the count in accordance with a second coefficient, an incident amount of a second energy band out of the radiation irradiating the pixel of interest, is provided.

Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

Fig. 1 is a block diagram showing an example of the arrangement of a radiation imaging apparatus according to the present invention;

Fig. 2 is a block diagram showing the arrangement of a sensor panel of the radiation imaging apparatus of Fig. 1;

Fig. 3 is a block diagram showing the arrangement of the sensor unit according to the radiation imaging apparatus of Fig. 1;

Fig. 4 is a timing chart showing an irradiation period and a readout period of the sensor panel of the radiation imaging apparatus of Fig. 1;

Fig. 5 is a timing chart showing an operation of each sensor unit during the irradiation period of the radiation imaging apparatus of Fig. 1;

Fig. 6A is a view showing the spread of light emission in a scintillator of the radiation imaging apparatus of Fig. 1;

Fig. 6B is a view showing the spread of light emission in a scintillator of the radiation imaging apparatus of Fig. 1;

Fig. 6C is a view showing the spread of light emission in a scintillator of the radiation imaging apparatus of Fig. 1;

Fig. 7A is a view showing the light emission distribution, converted into digital values, of the radiation imaging apparatus of Fig. 1;

Fig. 7B is a view showing the light emission distribution, converted into digital values, of the radiation imaging apparatus of Fig. 1;

Fig. 8 is a block diagram showing a conversion unit of the radiation imaging apparatus of Fig. 1;

Fig. 9 is a table showing an example of conversion coefficients of the radiation imaging apparatus of Fig. 1;

Fig. 10 is a timing chart showing an operation of each sensor unit during the readout period of the radiation imaging apparatus Fig. 1; and

Fig. 11 is a circuit diagram showing an arrangement of a sensor unit of a radiation imaging apparatus according to a second embodiment of the present invention.

A detailed embodiment of a radiation imaging apparatus according to the present invention will now be described with reference to the accompanying drawings. Note that in the following description and drawings, common reference numerals denote common components throughout a plurality of drawings. Hence, the common components will be described by cross-referring to the plurality of drawings, and a description of components denoted by common reference numerals will appropriately be omitted. Note that radiation according to the present invention can include not only α-rays, β-rays, and γ-rays, which are beams generated by particles (including photons) emitted by radioactive decay, but also beams having energy equal to or higher than the energy of these beams, for example, X-rays, particle beams, and cosmic rays.

A radiation imaging apparatus 100 (also referred to as a "radiation imaging system") according to a first embodiment of the present invention will be described. Fig. 1 shows an example of the arrangement of the radiation imaging apparatus 100 according to the first embodiment. The radiation imaging apparatus 100 of the first embodiment includes, for example, an irradiating unit 101 that irradiates an object with radiation, an irradiation control unit 102 that controls the irradiating unit 101, an imaging unit 104 for imaging the object irradiated with radiation, and a processor 103. Each of the irradiation control unit 102 and the processor 103 may be formed by a computer which includes a CPU, a memory, and the like. Although the irradiation control unit 102 and the processor 103 are formed separately in this embodiment, the present invention is not limited to this, and they may be formed integrally. That is, the irradiation control unit 102 and the processor 103 can be formed by one computer that includes 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 is arranged so as to form a plurality of rows and a plurality of columns. Each sensor unit 201 can be referred to as a "pixel". Each sensor unit 201 (to be described in detail later) has an arrangement for performing photon counting radiation imaging and counts the number of photons of incident radiation based on each light detection result.

The processor 103 exchanges a signal and data with the imaging unit 104. More specifically, the processor 103 controls the imaging unit 104 to perform radiation imaging and receives a signal obtained by the operation from the imaging unit 104. The signal includes counted values of radiation photons. For example, the processor 103 generates, based on the counted values, image data for displaying a radiation image on a display unit (not shown) such as a display or the like. At this time, the processor 103 can perform predetermined correction processing on the image data. In addition, the processor 103 supplies, to the irradiation control unit 102, a signal to start or end radiation irradiation.

Next, the arrangement of the sensor panel 106 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the arrangement of the sensor panel 106. The sensor panel 106 may include, for example, the plurality of sensor units 201, a vertical scanning circuit 202, a horizontal scanning circuit 203, column signal lines 204, signal lines 205, an output line 206, signal lines 207, and column selection circuits 208. Each of the plurality of sensor units 201 obtains a light distribution generated by the scintillator 105. Each sensor unit 201 can be arranged to subsequently obtain the detection count of each specific distribution which has been detected out of the obtained light distributions. Each sensor unit 201 converts the detection count data corresponding to at least one distribution into an incident amount for each energy band of radiation irradiating each sensor unit 201. When a signal is supplied to each sensor unit 201 via a corresponding signal line 205, incident amount data is output from each sensor unit 201 to the corresponding column selection circuit 208 via a corresponding column signal line 204.

The vertical scanning circuit 202 sequentially switches the signal lines 205 which supply signals so that the incident amount data will be output from each sensor unit 201. When a signal is supplied to each column selection circuit 208 via a corresponding signal line 207, the incident amount data output from each corresponding sensor unit 201 is output as output data DATA from each column selection circuit 208 to the output line 206. In addition, the horizontal scanning circuit 203 sequentially switches the signal lines 207 which supply signals so that the operation to output incidence data to the output line 206 will be sequentially performed by the plurality of column selection circuits 208. Although the sensor panel 106 arranged with 3 rows × 3 columns of sensor units has been shown for the sake of descriptive convenience in Fig. 2, a sensor panel 106 arranged with a larger number of sensor units 201 can be used as well. For example, in a 17 inch sensor panel 106 (FPD), approximately 2,800 rows × 2,800 columns of sensor units 201 can be arranged. Also, for example, the sensor panel 106 is not limited to an arrangement in which the sensor units 201 are arranged in a two-dimensional array, and may be a linear sensor panel 106 in which the sensor units 201 are arranged one-dimensionally.

The arrangement of each sensor unit 201 will be described next with reference to Fig. 3. Fig. 3 is a block diagram showing the arrangement of the sensor unit 201. Each sensor unit 201 of the sensor panel 106 may include, for example, a detecting element 301 serving as a light detector, a processing unit 330, output units 305, and a reference voltage unit that supplies a reference voltage 306. The processing unit 330 may also include a voltage conversion unit 302, a comparison unit 303, memories 304, determination units 307, and a conversion unit 130. The detecting element 301 is a photoelectric converter that generates a signal by detecting light generated in the scintillator 105 when the radiation enters the scintillator 105. A known photoelectric conversion element such as a photodiode or the like can be used as the detecting element 301. For example, a differential circuit is used as the voltage conversion unit 302. The voltage conversion unit 302 converts the signal generated by the detecting element 301 into a pulse signal of a voltage and outputs the converted 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 in accordance with the comparison result. If the voltage value of the pulse signal output from the voltage conversion unit 302 is equal to or more than the voltage value of the reference voltage 306, the comparison unit 303 outputs a digital value "1" as the signal according to the comparison result. Meanwhile, if the voltage value of the pulse signal output from the voltage conversion unit 302 is less than the reference voltage 306, the comparison unit 303 outputs a digital value "0" as the signal according to the comparison result. The reference voltage 306 which is supplied to the comparison unit 303 may be set to be a common value for all of the sensor units 201 in the sensor panel 106. When radiation enters the scintillator 105 and is converted into light, the comparison unit 303 generates a binary digital value signal, via the voltage conversion unit 302, in accordance with the light detected by the detecting element 301.

Each determination unit 307 obtains a signal pattern 309 that includes a plurality of digital value signals output from the comparison units 303 of the plurality of sensor units 201 (pixel group) in the same period. By obtaining the signal pattern 309 formed from the plurality of signals output from the sensor units 201 in the same period, each determination unit 307 can obtain the spread of light distribution converted by the scintillator 105 from one radiation photon of incident radiation.

Subsequently, each determination unit 307 determines whether the signal pattern 309 has a specific distribution. If it is determined that the signal pattern 309 has a specific distribution, the determination unit 307 obtains the detection count of the specific distribution during a predetermined period. More specifically, each determination unit 307 compares the obtained signal pattern 309 with a corresponding one of the reference patterns 308 each 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 to add 1 to the count value of a corresponding memory 304. If the signal pattern 309 and the reference pattern 308 do not match, the determination unit 307 does not output the distribution detection signal indicating that a distribution was detected, and the count value of the corresponding memory 304 is not changed. The signal pattern 309 and a reference pattern 308 are matched, and the detection count of the number of times a specific distribution is determined to be detected is obtained by each determination unit 307 and the corresponding memory 304. The reference patterns 308 can be, for example, recorded in memories in the respective determination units 307 or can be provided from outside the determination units 307.

The determination of distribution detection to add 1 to the count value of each memory 304 is not limited to the comparison of the signal pattern 309 and the reference pattern 308. For example, using an adding circuit that adds the outputs from the comparison units 303 of adjacent sensor units 201, each determination unit 307 can cause a corresponding memory 304 to count in accordance with the total value of digital values output from the comparison units 303. For example, if an output from the comparison unit 303 of a sensor unit 201 is "1", the total of the outputs from this sensor unit 201 and the comparison units 303 of the respective four sensor units 201 adjacent to the top, bottom, left, and right of this sensor unit 201 becomes "2" or more. In this case, each determination unit 307 can add 1 to the count value of the corresponding memory 304 to indicate that a specific distribution has been detected. Each determination unit 307 can determine that light has been detected in not only one sensor unit 201 but also in the plurality of sensor units 201 adjacent to the sensor unit 201 and that light emitted from the scintillator 105 has been detected spread out over the plurality of sensor units 201.

The signal pattern 309 may be a multi-bit digital value formed from the output of the comparison unit 303 of one sensor unit 201 and the outputs of the comparison units 303 of four sensor units 201 adjacent to the top, bottom, left, and right of this one sensor unit 201. That is, the signal pattern 309 is a digital value of a plurality of signals that reflect a light emission distribution at the time when radiation photons are converted into light in the scintillator 105. In the arrangement shown in Fig. 3, since one comparison unit 303 is arranged for each sensor unit 201, each signal pattern 309 is a 5-bit digital value. However, this embodiment is not limited to this. For example, a plurality of comparison units 303 each having a different reference voltage 306 can be arranged for each sensor unit 201 and a determination can be made using multiple values. By arranging a plurality of comparison units 303, each sensor unit 201 can obtain the detection count for a plurality of levels of light emission distributions related to the light intensity.

A description of the conversion unit 130 that converts the count value stored in the memories 304 into an incident amount for each energy band of incident radiation will be given later. When a signal is supplied from the vertical scanning circuit 202 via each signal line 205 connected to the corresponding output unit 305, each output unit 305 supplies data DATA of the incident amount for each energy band of radiation converted by the conversion unit 130 to the corresponding column selection circuit 208 via the corresponding column signal line 204. Subsequently, when a signal is supplied to each column selection circuit 208 via a corresponding signal line 207, data DATA of the incident amount for each energy band of incident radiation is output to the processor 103.

In the arrangement shown in Fig. 3, two determination units 307, a determination unit 307R and a determination unit 307B, are arranged in each sensor unit 201. The determination unit 307R and the determination unit 307B each use a different reference pattern 308 to determine the signal pattern 309. A reference pattern 308R and a reference pattern 308B are provided to the determination unit 307R and the determination unit 307B, respectively. The two memories 304, which are constituted by a memory 304R connected to the determination unit 307R and a memory 304B connected to the determination unit 307B, are arranged. If it is determined that the signal pattern 309 and the reference pattern 308R match in the determination unit 307R, the determination unit 307R adds 1 to the count value of the memory 304R. If it is determined that the signal pattern 309 and the reference pattern 308B match in the determination unit 307B, the determination unit 307B adds 1 to the count value of the memory 304B. In this embodiment, by arranging a plurality of determination units 307 and memories 304, the incident amounts of radiation photons having a plurality of specific energy bands can be obtained.

In this embodiment, although an example in which two determination units 307 are arranged in one sensor unit 201 is shown, the present invention is not limited to this. For example, only one determination unit 307 can be arranged. Alternatively, for example, three or more determination units 307 can be arranged to determine whether the signal pattern 309 matches the different reference patterns 308. In addition, although 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 can be arranged or three or more memories 304 may be arranged depending on the number of determination units 307 to be arranged. The signal pattern 309 is formed from the outputs of the comparison units 303 of five sensor units, that is, one sensor unit 201 and the four sensor units 201 adjacent to the top, bottom, left, and right of the sensor unit 201. However, the signal pattern 309 can be formed from the outputs of the comparison units 303 of two sensor units 201 adjacent to each other, four sensor units 201 diagonally adjacent to the one sensor unit 201, or from the sensor units 201 located two or more pixels apart. The signal pattern 309 can be formed from the outputs of comparison units 303 of 9 sensor units 201, that is, one sensor unit 201 and 8 adjacent sensor units 201 surrounding the one sensor unit 201. It is sufficient to have an arrangement in which the scintillator 105 emits light when radiation enters and the spread of each light emission distribution generated during the same period can be obtained by one sensor unit 201 serving as a pixel of interest and one or more sensor units near the sensor unit 201 of interest out of the plurality of sensor units. Subsequently, the determination units 307 obtain the light emission distribution generated in the same period for each sensor unit 201 of interest and determine whether each light emission distribution has a specific distribution.

Driving of the radiation imaging system according to this embodiment will be described next. Fig. 4 is a timing chart showing the timing of driving the sensor panel 106 of the imaging unit 104. The waveforms in Fig. 4 represent the radiation irradiation period and the readout period of data DATA with respect to the abscissa representing the time. In Fig. 4, the radiation irradiation period is a period in which the object is irradiated with radiation by the irradiating unit 101, the radiation that entered the sensor panel 106 is converted into light by the scintillator 105, the spread of each light distribution is obtained, and the number of times each obtained distribution matches the reference patterns 308 is counted. The readout period is a period in which data DATA, which is obtained by converting the detection count obtained during the radiation irradiation period into an incident amount for each energy band of incident radiation, is output from the sensor panel 106. As shown in Fig. 4, the sensor panel 106 can obtain a moving image by alternately performing the radiation irradiation period and the readout period. In addition, for example, a still image can be obtained by performing the radiation irradiation period and the readout period once.

The operation performed during the radiation irradiation period in the sensor unit 201 arranged as shown in Fig. 3 will be described next with reference to Fig. 5. Fig. 5 shows the timings when the voltage conversion unit 302, the comparison unit 303, and the memories 304 are driven during a radiation irradiation operation. The waveforms in Fig. 5 represent the outputs of the voltage conversion unit 302, the outputs of the comparison unit 303, and the count values of the respective memories 304 with respect to the abscissa representing the time. The radiation photons enter the imaging unit 104 and are converted into light by the scintillator 105. The electrical signal arising from light detected by the detecting element 301 is converted into a voltage pulse in the voltage conversion unit 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 this embodiment, as described above, the determination units 307 that compare the signal pattern 309 with the reference patterns 308 are present between the comparison unit 303 and the memories 304. If the signal patterns 309 which are a plurality of signals output by the comparison units 303 of the plurality of sensor units 201 (pixel group) and the reference pattern 308R match, the determination unit 307R adds 1 to the count value of the memory 304R. In the same manner, if 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 the signal pattern 309 and each reference pattern 308 have been determined to match in the corresponding determination unit 307 is obtained as the detection count of a specific distribution and is stored in the corresponding memory 304.

The method of converting the detection count obtained during the radiation irradiation period into the incident amount of radiation having specific energy will be described next with reference to Figs. 6A to 6C, 7, 8, and 9. Figs. 6A to 6C are views showing the relationship between the energy of incident radiation and the light emission distribution of the scintillator 105. In the arrangements shown in Figs. 6A to 6C, the radiation enters from the upper side of each view, and the scintillator 105 and the sensor panel 106 (detecting elements 301) are arranged in this order from the side that the radiation enters the imaging unit 104. The plurality of radiation photons that forms the radiation has various levels of energy. As shown in Fig. 6A, a low-energy radiation photon is distant from the detecting elements 301 and has a high possibility of being absorbed near the radiation incident side. In this case, since the light converted from radiation by the scintillator 105 is widely diffused within the scintillator 105, the light is detected by the detecting elements 301 of many sensor units 201. Meanwhile, it is more difficult for a high-energy radiation photon to be absorbed by the scintillator 105 than a low-energy radiation photon. Hence, there can be a case in which a radiation photon is absorbed in the radiation incident face side as in Fig. 6A and a case in which a radiation photon is absorbed near the detecting elements 301 as shown in Fig. 6B. If a radiation photon is absorbed near the detecting elements 301 as shown in Fig. 6B, the light converted from radiation by the scintillator 105 is not diffused compared to the case of Fig. 6A and is detected in the detecting element 301 of one sensor unit 201.

In this manner, the depth where the radiation is absorbed in the scintillator 105 varies in accordance with the different levels of energy of the incident radiation photons. If the depth at which each radiation photon is converted into light in the scintillator varies, the spread of light emission distribution also varies accordingly. As a result, the radiation imaging apparatus 100 has an energy resolution for incident radiation and can detect the incident amount for each specific energy band of radiation out of the rays of radiation that irradiate each sensor unit 201.

In this case, the greater the difference in the spread of light emission distribution arising from the difference in the levels of energy of the radiation, the more the energy resolution is improved. The spread of the light emission distribution may greatly change due to a thickness 702 of the scintillator 105. The larger the thickness 702 of the scintillator 105, the more detecting elements 301 of the sensor units 201 to which the light emitted by the radiation absorbed near the radiation incident face will spread. In order to diffuse the light emitted by the radiation photons absorbed near the radiation incident face to a wider range, it is preferable, for example, for the thickness 702 of the scintillator 105 to be greater than the pitch of each sensor unit 201 on which the detecting element 301 is arranged.

Additionally, in order to have higher energy resolution, an absorption layer 701 can be arranged on the radiation incident side, that is, the side opposite to the side facing the detecting elements 301 of the scintillator 105 in the case of each arrangement shown in Figs. 6A to 6C. The light emitted in the scintillator 105 can be diffused in various directions. Even when the light is emitted in a region near the detecting elements 301, the light can be diffused not only toward the detecting elements 301 but also in other directions, as shown in Fig. 6C. If the surface of the scintillator 105 has a high reflectance, the diffused light can be reflected by the surface and enter the detecting elements 301. Compared to the light that was emitted near the detecting elements 301 and had directly entered a detecting element 301, this reflected light can spread to the detecting elements 301 of the plurality of sensors 201. Therefore, it may be difficult to generate a difference between the light emission distribution in this case and the light emission distribution of light emitted at a distant position from the detecting element 301. It is preferable to arrange the absorption layer 701 to prevent this diffusion of light due to reflection. For example, when the light emitted by the scintillator 105 enters the absorption layer 701, it is preferable for the absorption layer 701 to absorb at least 10% of the light.

In addition, in this embodiment, the scintillator 105 and the sensor panel 106 are arranged in this order from the radiation incident side in the imaging unit 104 as shown in Figs. 6A to 6C. However, the arrangement of the scintillator 105 and the detecting elements 301 is not limited to this. The radiation can enter from the side of the sensor panel 106 and enter the scintillator 105 after passing through the sensor panel 106. In this case, the low-energy radiation photons are absorbed near the detecting elements 301 of the scintillator 105. The light converted from the radiation by the scintillator 105 is, for example, detected by the detecting element 301 of one sensor unit 201 instead of being diffused widely in the scintillator 105. In contrast, it is more difficult for the high-energy radiation photons to be absorbed by the scintillator 105 than the low-energy radiation photons. Hence, for example, light emission from the radiation absorbed by the scintillator in a location away from the detecting elements 301 is greatly diffused within the scintillator 105 and is detected by the detecting elements 301 of many sensor units 201. In this manner, even in a case in which the radiation enters from the side of the sensor panel 106, the spread of light emission distribution can vary in accordance with the difference in the depths of light emission. Therefore, the radiation imaging apparatus 100 can detect the energy of the incident radiation and the amount of incident radiation out of the rays of radiation that irradiate each sensor unit 201.

Figs. 7A and 7B are views each showing the signal pattern 309 obtained by detecting light emission by the detecting elements 301 of the sensor units 201 and converting the detected light into digital values by the comparison units 303. The sensor panel 106 arranged as shown in Fig. 2 has X rows × Y columns of sensor units 201 arranged in a two-dimensional array. Figs. 7A and 7B show the digital values from the comparison units 303 of the sensor units 201 arranged in a 5 × 5 (rows × columns) matrix.

As shown in Fig. 6A, when radiation is absorbed and light is emitted, in the scintillator 105, at a location distant from the detecting elements 301, the light is diffused inside the scintillator 105 since light is emitted in a location distant from the detecting elements 301 and the light emission distribution is spread out over the plurality of sensor units 201. In this case, as shown in Fig. 7A, the digital values from the comparison units 303 of the sensor units 201 can become a signal pattern 309R which shows that light has been detected by a center sensor unit 201A serving as a pixel of interest and its adjacent sensor units 201. This signal pattern 309R matches the reference pattern 308R for identifying that light has been detected by the sensor unit 201A and the plurality of sensor units 201 near the sensor unit 201A. Hence, the determination unit 307R determines that the signal pattern 309R matches the reference pattern 308R and adds 1 to the count value of the memory 304R.

In contrast, as shown in Fig. 6B, when radiation is absorbed and light is emitted, in the scintillator 105, at a location near the detecting elements 301, light is emitted in a location near a detecting element 301. Accordingly, the light emission distribution is not spread out over the plurality of sensor units 201 and the light is, for example, detected only by the one sensor unit 201A. In this case, the digital values from the comparison units 303 of the sensor units 201 can change to a signal pattern 309B in which light has been detected only in the sensor unit 201A as shown in Fig. 7B. This signal pattern 309B matches the reference pattern 308B for identifying that light is detected only by the sensor unit 201A and that sensor units 201 nearby do not detect light. 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. In this manner, by the determination units 307 and the memories 304, the signal patterns 309 and the reference patterns 308 are matched and the detection count of a specific distribution that has been detected and determined is obtained for each sensor unit 201.

A method of obtaining the incident amount for each specific energy band of incident radiation from the count value of the detection count obtained for each sensor unit 201 will be described next. Fig. 8 shows an example of the conversion unit 130 that converts each detection count into an incident amount of radiation, and Fig. 9 is a table showing an example of conversion coefficients which are coefficients to convert each detection count into an incident amount of radiation. In the following example, a case in which an incident amount of radiation is obtained for each energy band by using a given threshold (for example, 60 keV) as a boundary to divide the energy of the radiation into two energy bands will be described. Energy lower than this threshold will be called low energy and energy higher than this threshold will be called high energy.

It is not always the case that the light emission distribution will be wide because low-energy radiation is absorbed in the incident face side of the scintillator 105 nor is it always the case that the light emission distribution will be narrow because high energy radiation is absorbed in a distant location from the incident face side of the scintillator 105. Low-energy radiation has a high possibility of being absorbed in the incident face side of the scintillator 105 and high-energy radiation has a high possibility of being absorbed almost uniformly in the scintillator 105. Therefore, the count value of each of the

memories

304R and 304B, which is the detection count of the signal pattern 309 that has matched a corresponding one of the reference patterns 308, is converted into an incident amount of radiation for each energy band in accordance with a conversion coefficient shown in Fig. 9. Each conversion coefficient is a coefficient expressing the relationship between the energy of radiation photons and the possibility that the signal pattern 309 obtained by converting the radiation photons into light will match a corresponding one of the reference patterns 308. For example, each count value is converted by multiplying each count value of the memory 304R using a corresponding one of a coefficient L and a coefficient H and multiplying each count value of the memory 304B using a corresponding one of a coefficient L' and a coefficient H'. In the arrangement of the conversion unit 130 shown in Fig. 8, a count value of the memory 304R which has detected a wide light detection distribution of the signal pattern 309 is multiplied by the coefficient L = 0.6. As a result, a converted incident amount arising from low-energy radiation is calculated out of the count values of the memory 304R. In addition, a count value of the memory 304R is multiplied by the coefficient H = 0.4 and a converted incident amount arising from high-energy radiation is calculated out of the count values of the memory 304R. In the same manner, a count value of the memory 304B which has detected a narrow light detection distribution of the signal patterns 309 is multiplied by the coefficient L'= 0.1 and a converted incident amount arising from low-energy radiation is calculated out of the count values of the memory 304B. A count value of the memory 304B is multiplied by the coefficient H' = 0.9 and a converted incident amount arising from high-energy radiation is calculated from the count values of the memory 304B. Subsequently, the converted incident amounts arising from low-energy radiation are added. The converted incident amounts arising from high-energy radiation are also added. In this manner, the count values of light distributions detected by the plurality of sensor units 201 are converted into incident amounts of radiation that have entered through the respective high-energy and low-energy bands. The data of the obtained incident amount arising from low-energy radiation is stored in an output unit 305R and data of the obtained incident amount arising from high-energy radiation is stored in an output unit 305B.

Assume that the conversion coefficient is appropriately set for each specific energy band of radiation such as the above described high energy band and low energy band. In addition, assume that the conversion coefficient is set for each reference pattern 308. For example, assume that the conversion coefficient changes in accordance with conditions such as the tube voltage, the tube current, the irradiation time, the material and thickness of the added filter of the irradiating unit 101 to be used and the attenuation coefficient, thickness, and visible light transmission rate of the scintillator 105 to be used. By setting the conversion coefficient as a parameter that differs for each imaging condition, the radiation imaging apparatus 100 can have a high energy resolution. Two conversion coefficients can be set for the count values of each memory 304 as in this embodiment or, for example, only one conversion coefficient can be set. Alternatively, for example, three or more conversion coefficients may be set for the count values of each memory 304. The conversion coefficients can be appropriately set in accordance with the type of energy band of radiation to be detected. In addition, in the above-described example, the incident amount of radiation was obtained by adding the converted incident amount for each energy band. However, the present invention is not limited to this. For example, if there is only one memory 304 or if there is a strong correlation between the absorption of the radiation and the light emission distribution, addition is unnecessary and the conversion coefficients need only be applied.

Assume that the above-described operation during an irradiation period may be performed by setting the operating frequency of each sensor unit 201 and the irradiation amount of the irradiating unit 101 to be values that can count radiation photons one by one. For example, the operating frequency of each sensor unit 201 can be set in the range of 10 kHz to a few MHz (for example, about 100 kHz). Alternatively, the irradiation amount of the irradiating unit 101 can be set to a value obtained when the tube voltage is about 100 kV and the tube current is about 10 mA.

The operation during a readout period of each sensor unit 201 arranged as shown in Fig. 3 will be described with reference to Fig. 10. Fig. 10 is a timing chart showing the operation of each sensor unit 201 during a readout period. The waveforms in Fig. 10 represent the signal supply to each signal line 205, the signal supply to each signal line 207, and the output of data DATA of the incident amount of radiation obtained from each column selection circuit 208 with respect to the abscissa representing the time. 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 a signal supply operation to the signal line 205-0R is started, data of the incident amount of radiation for a specific energy band is supplied from the output unit 305R of each sensor unit 201 connected to the signal line 205-0R to a corresponding one of the column selection circuits 208. Then, during the signal supply period of the signal line 205-0R, signals are sequentially supplied to the plurality of signal lines 207, and pieces of data DATA of the incident amount of radiation are sequentially output from the plurality of column selection circuits 208 to the output line 206.

When the signal supply operation to the signal line 205-0R ends and a signal supply operation to the signal line 205-0B starts, data DATA of the incident amount of radiation for a specific energy band is output from the output unit 305B of each sensor unit 201 connected to the signal line 205-0B to the corresponding one of the column selection circuits 208. Then, during the signal supply period of the signal line 205-0B, signals are sequentially supplied to the plurality of signal lines 207 and data DATA of the incident amount of radiation are sequentially output from the plurality of column selection circuits 208 to the output line 206. This allows data DATA of the incident amount of radiation from the plurality of sensor units 201 of one row to be supplied to the processor 103 via the output line 206. In this manner, signals are sequentially supplied to the plurality of signal lines 205 and the plurality of signal lines 207, and data DATA of the incident amount of radiation for each specific energy band are supplied from the plurality of sensor units 201 to the processor 103 via the output line 206 to generate image data.

A radiation imaging apparatus (radiation imaging system) according to a second embodiment of the present invention will be described. Although the radiation photon counting method according to the aforementioned first embodiment used the processing unit 330 arranged in each sensor unit 201, these functions can be implemented by, for example, a program or software in the processor 103. That is, each sensor unit 201 can be formed by a circuit to output a signal corresponding to the light converted by the scintillator 105 and the number of radiation photons can be counted outside each sensor unit 201.

Fig. 11 shows an example of the arrangement of a sensor unit 201' according to the second embodiment. In addition to a detecting element 301, the sensor unit 201' includes, for example, a reset unit 510, a signal amplification unit 520, a light sensitivity selecting 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 detecting element 301 by turning on the transistor M1. The signal amplification unit 520 includes transistors M2 and M3 connected to a current source. The transistor M3 performs a source follower operation by turning on the transistor M2, thereby amplifying a signal corresponding to the amount of charges generated and accumulated in the detecting element 301.

The light sensitivity selecting unit 530 includes transistors M4 to M7 and capacitors C4 and 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. This makes it possible to change the signal amplification factor of the signal corresponding to the amount of the charges generated in the above-described detecting element 301. The capacitor C4 is further connected to the gate of the transistor M3 by turning on the transistor M5, making it possible to further change the signal amplification factor.

The clamp unit 540 includes transistors M8 to M10 and a capacitor C1. An output from the signal amplification unit 520 obtained when the detecting element 301 has been reset is supplied to one terminal n1 of the capacitor C1. A power supply voltage is supplied to the other terminal n2 of the capacitor C1 by turning on the transistor M8. Consequently, a voltage obtained when the detecting element 301 has been reset is clamped, as a noise component, between the terminals n1 and n2. Then, the transistor M10 performs a source follower operation by turning off the transistor M8 and turning on the transistor M9. A signal corresponding to a change in the voltage of the terminal n2 associated with detection of light by the detecting 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 amount of the light detected by the detecting element 301. More specifically, the sampling unit 550 can control the transistor M11 to sample a signal from the clamp unit 540 and hold it in the capacitor C2. The signal is amplified by the transistor M12 which performs a source follower operation and is output to column signal lines 204 via the analog switch SW2. Note that the transistor M13 can be arranged between the capacitor C2 and the capacitor C2 of another sensor unit in the periphery of the sensor unit 201'. It is also possible, by turning on the transistor M13, to obtain an average between the S signal of the sensor unit 201' and the S signal of the other peripheral sensor unit, and to reduce the noise component. The sampling unit 560 can sample a signal (N signal) corresponding to the noise component and have the same arrangement as the sampling unit 550.

The sensor unit 201' is not limited to the example of the arrangement in Fig. 11 and can have another arrangement for detecting radiation.

The output from such an above-described sensor unit 201' is converted into a digital value by an A/D converter (not shown) and supplied to a processor 103. Then, processes corresponding to the operations of a voltage conversion unit 302, a comparison unit 303, memories 304, determination units 307, and a conversion unit 130 are performed by software in the processor 103.

First, the processor 103 calculates a differential value of the output of the sensor unit circuit as the processing corresponding to the voltage conversion unit 302. Next, the processor 103 compares the calculated differential value with a digital value corresponding to a reference voltage 306 as the processing corresponding to the comparison unit 303. The processor 103 sets a digital value "1" if the differential value is equal to or more than the digital value corresponding to the reference voltage 306 and sets a digital value "0" if the differential value is less than the digital value corresponding to the reference voltage 306. Then, as processing corresponding to the determination units 307 and the memories 304, a signal pattern 309 of the digital value and a reference pattern 308 of a distribution indicating that a preset light has been detected are compared and 1 is added to the count value corresponding to the detection count if they match. In the same manner as the first embodiment, the signal pattern 309 is, for example, a multi-bit digital value formed by the outputs from processing corresponding to the comparison units 303 of one sensor unit 201 and the one or more sensor units 201 near the one sensor unit 201. This allows the processor 103 to obtain the detection count of the number of times the signal pattern 309 and one of the reference pattern 308 have matched. Next, the processor 103 performs processing corresponding to the conversion unit 130. Each detection count of the number of times the signal pattern 309 and the reference pattern 308 were determined to match is converted according to conversion coefficients set for each reference pattern 308 for a specific energy band of radiation to convert the detection count into the incident amount for each energy band of incident radiation. Then, the processor 103 generates an image based on the converted detection count. These processes are, for example, executed by the CPU of the processor 103. The storage region that stores the detection count is allocated in the memory of the processor 103. There can be a plurality of digital values corresponding to the reference voltage 306 and functions that perform processing corresponding to the comparison unit 303 and the determination units 307 in accordance with the levels of light intensity and the reference patterns 308.

The functions of the processing unit 330 including the voltage conversion unit 302, the comparison unit 303, the memories 304, the determination units 307, and the conversion unit 130 according to the present invention can be arranged in each sensor unit of the sensor panel as in the first embodiment. Alternatively, all the processes can be performed by software as in the second embodiment. However, the present invention is not limited to these embodiments. At least some of the processes, such as the voltage conversion unit 302 and the comparison unit 303, performed in the processing unit 330 can be arranged in each sensor unit of a sensor panel 106 and the remaining processes corresponding to the memories 304, the determination units 307, and the conversion unit 130 can be performed by software. Furthermore, the functions can be performed not by software but by a circuit provided outside the sensor panel 106. In this case, the circuit is formed preferably by, for example, an FPGA.

Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a 'non-transitory computer-readable storage medium') to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)^TM), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2015-111677, filed June 1, 2015, which is hereby incorporated by reference wherein in its entirety.

Claims

A radiation imaging apparatus comprising: a scintillator configured to convert radiation into light; a sensor panel in which a plurality of pixels each including a light detector configured to detect the light is arranged; and a processing unit,
wherein the processing unit:
generates signals in accordance with the light detected by the light detectors;
determines whether a plurality of signals generated in the same period by a pixel group, which includes one pixel of interest and at least one pixel near the pixel of interest out of the plurality of pixels, has a specific distribution;
obtains a count of the number of times the pixel of interest is determined to have the specific distribution;
obtains, based on a value obtained by converting the count in accordance with a first coefficient, an incident amount of a first energy band out of radiation irradiating the pixel of interest; and
obtains, based on a value obtained by converting the count in accordance with a second coefficient, an incident amount of a second energy band out of the radiation irradiating the pixel of interest.
The apparatus according to claim 1, wherein the processing unit
determines whether a signal pattern including the plurality of signals generated by the pixel group matches a reference pattern representing the specific distribution set in advance, and
determines that the plurality of signals has a distribution corresponding to the reference pattern if the signal pattern is determined to match the reference pattern.
The apparatus according to claim 2, wherein the processing unit
determines whether the signal pattern including the plurality of signals generated by the pixel group matches one of a first reference pattern and a second reference pattern set in advance,
obtains a first count of the number of times the signal pattern is determined to match the first reference pattern and a second count of the number of times the signal pattern is determined to match the second reference pattern,
obtains the incident amount of the first energy band based on a value obtained by converting the first count in accordance with the first coefficient and a value obtained by converting the second count in accordance with a third coefficient, and
obtains the incident amount of the second energy band based on a value obtained by converting the first count in accordance with the second coefficient and a value obtained by converting the second count in accordance with a fourth coefficient.
The apparatus according to any of claims 1 - 3, wherein the processing unit generates a binary signal in accordance with a light intensity detected for each light detector.
The apparatus according to claim 1, wherein the processing unit comprises
a voltage conversion unit configured to convert a signal output from each light detector into a voltage value,
a comparison unit configured to compare the voltage value with a predetermined voltage value and generate a comparison result signal indicating a comparison result,
a determination unit configured to determine whether a distribution formed from a plurality of comparison result signals generated in the same period by comparison units of the pixel group, which includes the one pixel of interest and the at least one pixel near the pixel of interest out of the plurality of pixels, has the specific distribution,
a memory configured to store a count of the number of times the determination unit determines that the distribution has the specific distribution, and
a conversion unit configured to convert the count in accordance with the first coefficient to obtain a value based on the incident amount of the first energy band out of the radiation irradiating the pixel of interest and convert the count in accordance with the second coefficient to obtain a value based on an incident amount of the second energy band out of the radiation irradiating the pixel of interest.
The apparatus according to claim 5, wherein the comparison result signal has a binary signal formed from a signal of a case in which the voltage value is equal to or more than the predetermined voltage value and a signal of a case in which the voltage value is less than the predetermined voltage value.
The apparatus according to claim 5 or 6, wherein the determination unit
determines whether a signal pattern that includes the distribution output in the same period from the comparison units of the pixel group matches one of a first reference pattern and a second reference pattern representing the specific distribution set in advance,
outputs a first distribution detection signal, if the signal pattern is determined to match the first reference pattern, by determining that the plurality of signals has a distribution corresponding to the first reference pattern, and
outputs a second distribution detection signal, if the signal pattern is determined to match the second reference pattern, by determining that the plurality of signals has a distribution corresponding to the second reference pattern, and
the memory stores a first count of the number of the times the first distribution detection signal is output and a second count of the number of times the second distribution signal is output, and
the conversion unit
obtains the incident amount of the first energy band based on a sum of a value obtained by converting the first count in accordance with the first coefficient and a value obtained by converting the second count in accordance with a third coefficient, and
obtains the incident amount of the second energy band based on a sum of a value obtained by converting the first count in accordance with the second coefficient and a value obtained by converting the second count in accordance with a fourth coefficient.
The apparatus according to any of claims 1 - 7, wherein the plurality of pixels is arranged in a two-dimensional array.
The apparatus according to any of claims 1 - 8, wherein each light detector converts the light into charges and detects a light intensity in accordance with the amount of accumulated charges.
The apparatus according to any of claims 1 - 9, wherein the thickness of the scintillator is not less than an arrangement pitch of the plurality of pixels.
The apparatus according to any of claims 1 - 10, wherein the scintillator and the sensor panel are arranged in this order from a radiation irradiation side.
The apparatus according to any of claims 1 - 10, wherein the sensor panel and the scintillator are arranged in this order from a radiation irradiation side.
The apparatus according to any of claims 1 - 12, wherein the scintillator comprises an absorption layer that absorbs light converted by the scintillator and that is arranged on a side opposite to a side facing the sensor panel.
The apparatus according to any of claims 1 - 13, wherein at least a part of the processing unit is arranged on each pixel of the plurality of pixels.
A control method of a radiation imaging apparatus that uses a scintillator configured to convert radiation into light and a sensor panel in which a plurality of pixels each including a light detector configured to detect the light is arranged, comprising:
generating signals in accordance with the light detected by the light detectors,
determining whether a plurality of signals generated in the same period by a pixel group, which includes one pixel of interest and at least one pixel near the pixel of interest out of the plurality of pixels, has a specific distribution,
obtaining a count of the number of times the pixel of interest is determined to have the specific distribution,
obtaining, based on a value obtained by converting the count in accordance with a first coefficient, an incident amount of a first energy band out of radiation irradiating the pixel of interest, and
obtaining, based on a value obtained by converting the count in accordance with a second coefficient, an incident amount of a second energy band out of the radiation irradiating the pixel of interest.
A program for causing a computer to execute each step of a control method defined in claim 15.