WO2016194286A1

WO2016194286A1 - Radiation imaging apparatus, driving method thereof, and program

Info

Publication number: WO2016194286A1
Application number: PCT/JP2016/002091
Authority: WO
Inventors: Atsushi Iwashita; Katsuro Takenaka; Shinichi Takeda; Kosuke Terui
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2015-06-01
Filing date: 2016-04-19
Publication date: 2016-12-08
Anticipated expiration: 2017-12-01
Also published as: JP2016223950A

Abstract

A radiation imaging apparatus that comprises a plurality of sensor units each including a detection element which detects radiation, a quantization unit configured to quantize a signal value from the detection element of each sensor unit, a count unit configured to count, for each sensor unit, the number of matches between a second pattern as a reference pattern set in advance, and a first pattern which includes a quantization result by the quantization unit of the signal value from the detection element of the sensor unit and a quantization result by the quantization unit of the signal value from the detection element of another sensor unit on the periphery of the sensor unit, and a readout unit configured to read out a count value of the count unit.

Description

RADIATION IMAGING APPARATUS, DRIVING METHOD THEREOF, AND PROGRAM

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

A radiation imaging apparatus includes, for example, a scintillator which converts radiation into light and a sensor panel on which a plurality of sensor units which detect the light (scintillation light) from the scintillator are arrayed. In each sensor unit, a signal based on the amount of the scintillation light is obtained.

Some radiation imaging apparatuses are of a photon counting type. The photon counting radiation imaging apparatus counts, based on a detection result of the scintillation light, the number of photons of radiation by each sensor unit. More specifically, the photons of the scintillation light are generated upon incidence of the photons of the radiation on the scintillator and each sensor unit detects the photons of the scintillation light, thereby counting the number of photons of the radiation. According to the photon counting radiation imaging apparatus, a radiation image is formed based on the number of the counted photons of the radiation.

The scintillation light can also diffuse in the horizontal direction (a direction parallel to the upper surface of the sensor panel) in the scintillator. Therefore, signal components associated with detection of the scintillation light may be generated not only in the sensor unit corresponding to the incident position of the radiation but also in the other peripheral sensor units. This becomes a cause of lowering the quality of the radiation image.

Japanese Patent Laid-Open No. 2013-501226 discloses a radiation imaging apparatus which includes a plurality of pixels arrayed in a matrix, a counter arranged in the central portion of each pixel, and another counter arranged between the adjacent pixels. According to Japanese Patent Laid-Open No. 2013-501226, a decision is made, based on a comparison result between a pixel value of each pixel and a pixel value of another pixel adjacent to that pixel, as to which count value of the counter to increase. According to this radiation imaging apparatus, however, the above-described comparison may not be performed appropriately when a photon of irregular radiation has entered (for example, when two or more photons have entered locally at once, when radiation such as cosmic rays which is not a detection target has entered, or the like).

Japanese Patent Laid-Open No. 2003-279411 discloses a radiation imaging apparatus which calculates the barycenter of a bright spot in a scintillator by using luminance data of scintillation light. According to Japanese Patent Laid-Open No. 2003-279411, the position of the bright spot in the scintillator is found by the calculation result, making it possible to increase imaging accuracy. According to this radiation imaging apparatus, however, the above-described calculation may not be performed appropriately when the above-described photon of the irregular radiation has entered.

These become a cause of decreasing photon count accuracy.

The present invention provides a technique advantageous in increasing photon count accuracy in a photon counting radiation imaging apparatus.

One of the aspects of the present invention provides a radiation imaging apparatus comprising a plurality of sensor units each including a detection element which detects radiation, a quantization unit configured to quantize a signal value from the detection element of each sensor unit, a count unit configured to count, for each sensor unit, the number of matches between a second pattern as a reference pattern set in advance, and a first pattern which includes a quantization result by the quantization unit of the signal value from the detection element of the sensor unit and a quantization result by the quantization unit of the signal value from the detection element of another sensor unit on the periphery of the sensor unit, and a readout unit configured to read out a count value of the count unit.

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 diagram showing an example of the arrangement of a radiation imaging apparatus; Fig. 2 is a diagram showing an example of the arrangement of each unit configured to read out a signal from a sensor unit; Fig. 3 is a diagram showing an example of the arrangement the sensor unit; Fig. 4 is an example of a driving timing chart including an irradiation period and a readout period; Fig. 5 is a chart showing an example of an operation in each sensor unit in the irradiation period; Fig. 6A is a view showing an example of an intensity distribution of scintillation light; Fig. 6B is a view showing an example of an intensity distribution of scintillation light; Fig. 7 is a view showing an example of a count method of radiation photons; Fig. 8 is a chart showing an example of an operation of each sensor unit in the readout period; Fig. 9A is a view showing an example of an intensity distribution of scintillation light; Fig. 9B is a view showing an example of an intensity distribution of scintillation light; Fig. 10 is a view showing an example of a count method of radiation photons; and Fig. 11 is a diagram showing an example of the arrangement of a sensor unit.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The same reference numerals denote the same members or the same constituent elements throughout the drawings and the repetitive description will be omitted in each embodiment below.

(First Embodiment)
Fig. 1 shows an example of the arrangement of a radiation imaging apparatus 100 (or may be referred to as a "radiation imaging system") according to the first embodiment. The radiation imaging apparatus 100 includes, for example, an irradiation unit 101 that irradiates an object such as a patient with radiation, an irradiation control unit 102 that controls the irradiation unit 101, an imaging unit 104 that images the object irradiated with radiation, and a processor 103. Note that the concept of radiation includes, for example, α-rays, β-rays, and the like, in addition to X-rays generally used for radiation imaging.

The imaging unit 104 includes, for example, a scintillator 105 which converts incident radiation into light and a sensor panel 106. The scintillator 105 is arranged on the side of the radiation irradiation surface of the sensor panel 106. On the sensor panel 106, for example, a plurality of sensor units 201 each detecting light (scintillation light) from the scintillator 105 are arrayed so as to form a plurality of rows and a plurality of columns. The sensor units 201 may be referred to as "pixels". Each sensor unit 201 has an arrangement for performing radiation imaging by a photon counting method and counts the number of photons of radiation (to be referred to as "radiation photons" hereinafter) based on a detection result of the scintillation light, details of which will be described later.

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 this from the imaging unit 104. This signal includes counted values of the 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. The processor 103 may perform predetermined correction processing on the image data. The processor 103 supplies, to the irradiation control unit 102, a signal for starting or terminating radiation irradiation. The processor 103 may also function as a driving unit which drives the respective units described above and respective constituent elements thereof while controlling them synchronously. However, the driving unit may be arranged separately from the processor 103.

Note that the arrangement of the radiation imaging apparatus 100 is not limited to the above-described example. The radiation imaging apparatus 100 may be configured such that the other units have some functions of one unit or several units are integrated. For example, the arrangement has been exemplified in which the irradiation control unit 102 and the processor 103 are arranged separately from each other. However, they may be implemented as a single unit.

Fig. 2 shows an example of the arrangement of each unit on the sensor panel 106. The sensor panel 106 includes, for example, the plurality of sensor units 201, a vertical scanning circuit 202, a horizontal scanning circuit 203, and column selecting circuits 208. The arrangement has been exemplified here in which 3 (rows) × 3 (columns) sensor units 201 are arrayed, for the sake of simplicity. In practice, however, the number of sensor units 201 is larger than this number. For example, on a 17-inch sensor panel, about 2,800 (rows) × about 2,800 (columns) sensor units 201 can be arrayed.

The vertical scanning circuit 202 forms a sensor driving unit configured to drive the plurality of sensor units 201 and can be formed by, for example, a shift register. More specifically, the vertical scanning circuit 202 drives the operations of the plurality of sensor units 201 for each row by using signal lines 205 corresponding to each row. In this example, the signal lines 205 of each row include two signal lines (for example, 205-0R and 205-0B for the first row, 205-1R and 205-1B for the second row, and 205-2R and 205-2B for the third row). A signal of each sensor unit 201 is output to the corresponding column selecting circuit 208 via a corresponding column signal line 204.

The horizontal scanning circuit 203 and the column selecting circuits 208 form a readout unit configured to read out the signal from each sensor unit 201. More specifically, the horizontal scanning circuit 203, formed by a shift register for example, controls the column selecting circuit 208 by using a signal line 207 (such as 207-0) corresponding to each column, and reads out the signal from the sensor unit 201 of the corresponding column. The readout signal undergoes horizontal transferring via an output line 206 and is output as output data DATA.

Fig. 3 shows an example of the arrangement of the unit sensor unit 201. One sensor unit 201 receives attention here and the sensor unit 201 will be referred to as a "sensor unit 201₁" so as to be distinguished from the other sensor units 201. The sensor unit 201₁ includes, for example, a quantization unit U₁ which includes a detection element 301, a monitor unit 302, and comparison units 303, a count unit U₂ which includes determination units 307 and memories 304, and output units 305.

The detection element 301 detects scintillation light from the scintillator 105 exposed to radiation. More specifically, the detection element 301 converts the scintillation light into an electrical signal corresponding to the amount of that light. A well-known photoelectric conversion element (for example, a photodiode) can be used for the detection element 301.

The quantization unit U₁ quantizes the intensity (or a signal value corresponding to it) of the light detected by the detection element 301. Note that "quantization" includes conversion of the intensity of the light into a numerical value based on a predetermined criterion, calculation of a numerical value corresponding to the intensity of the light, or the like and can be interpreted broadly. More specifically, in the quantization unit U₁, the monitor unit 302 monitors the change amount of a potential of the detection element 301. For example, a differentiating circuit can be used for the monitor unit 302. Each comparison unit 303 compares the magnitude relationship between a predetermined reference value (reference voltage) and a monitoring result (a voltage corresponding to the change amount of the potential of the detection element 301) by the monitor unit 302, and outputs the comparison result to a corresponding signal line out of a group 309 of signal lines.

In this example, two comparison units 303 are arranged (they are denoted by 303-R and 303-B, respectively). Reference voltages 306-R and 306-B having different voltage values are supplied to the two comparison units 303-R and 303-B, respectively. The reference voltages 306-R and 306-B can be supplied to the plurality of sensor units 201 in common. For example, when a voltage corresponding to the change amount of the potential of the detection element 301 is higher than the reference voltage 306-B, the comparison unit 303-B outputs, as the output value of the quantization unit U₁, a digital value "1" to the corresponding signal line out of the group 309 of signal lines. On the other hand, when the voltage corresponding to the change amount of the potential of the detection element 301 is lower than the reference voltage 306-B, the comparison unit 303-B outputs, as the output value of the quantization unit U₁, a digital value "0" to the corresponding signal line.

Note that the group 309 of signal lines includes, in addition to the signal line which transmits the output value of the quantization unit U₁ in the sensor unit 201₁, signal lines which transmit the output values of the quantization units U₁ in the other sensor units 201 on the periphery of the sensor unit 201₁.

The count unit U₂ counts the number of radiation photons by using, for example, the output value of the quantization unit U₁. More specifically, in the count unit U₂, the determination units 307 receive, from the group 309 of signal lines, patterns 310 (first patterns) including the output value of the quantization unit U₁ in the sensor unit 201₁ and the output values of the quantization units U₁ in the other sensor units 201. Reference patterns 308 (second pattern) set in advance are supplied to the determination units 307. The determination units 307 determine whether the patterns 310 received from the group 309 of signal lines and the reference patterns 308 match. The determination units 307 may be referred to as checking units which check the patterns 310 with the reference patterns 308. Then, if they match, the values of the memories 304 are added. That is, the memories 304 hold, as count values of the count unit U₂, counted values of the number of matches between the patterns 310 and the reference patterns 308. The values of the memories 304 indicate a count result of the number of radiation photons.

In this example, two determination units 307 are arranged (they are denoted by 307-R and 307-B, respectively). Reference patterns 308-R and 308-B having different contents are supplied to the two determination units 307-R and 307-B, respectively. Two memories 304 are arranged so as to correspond to the two determination units 307-R and 307-B (the memories are denoted by 304-R and 304-B, respectively). For example, if the patterns 310 received from the group 309 of signal lines and the reference pattern 308-B match, the determination unit 307-B adds "1" to the value of the memory 304-B. On the other hand, if the patterns 310 and the reference pattern 308-B do not match, the determination unit 307-B leaves the value of the memory 304-B as it is (does not add "1" to the value of the memory 304-B). Note that the above-described determination can be performed by predetermined arithmetic processing such as an exclusive OR operation, and the determination units 307-R and 307-B can be formed by relatively simple circuits.

Two output units 305 are arranged so as to correspond to the above-described two memories 304-R and 304-B (the output units are denoted by 305-R and 305-B, respectively). For example, based on a control signal supplied via the signal line 205-0B, the output unit 305-B outputs that value from the corresponding memory 304-B via the column signal line 204. The same also applies to the output unit 305-R.

According to the above-described arrangement example, in each sensor unit 201, the quantization unit U₁ quantizes the intensity of the light detected by the detection element 301. Then, the count unit U₂ counts, based on the output value of the quantization unit U₁ and the output values of the quantization units U₁ other than this (of the other sensor units 201 on the periphery of the sensor unit 201 to which the quantization unit U₁ belongs), the number of radiation photons. A more detailed count method will be described later.

Fig. 4 exemplifies the outline of a driving timing chart of the radiation imaging apparatus 100. In this example, a moving image mode is shown. In Fig. 4, the abscissa indicates a time axis, and the ordinate indicates the operation of the apparatus 100, a radiation dose (high level indicates an irradiation state and low level indicates a non-irradiation state), and the output data DATA output via the output line 206. In the moving image mode, the radiation imaging apparatus 100 alternately performs a count operation (first operation) of counting the number of radiation photons and a readout operation (second operation) of reading out a count result of the count operation. Radiation irradiation is performed in a period during which the above-described count operation is performed (in Fig. 4, this period will be referred to as an "irradiation period A"). Radiation irradiation is stopped in a period during which the above-described readout operation is performed (in Fig. 4, this period will be referred to as a "readout period B"). Then, the processor 103 generates image data of one frame (third operation) by using the count result of the number of radiation photons obtained by the above-described readout operation. In the moving image mode, a series of these operations can be performed a plurality of times. A moving image can be played back by outputting image data of one frame obtained by one series of operations to the display unit sequentially. The moving image mode has been exemplified here. However, the same operation can also be performed in a continuous shooting mode. In a still image mode, it is only necessary to perform the above-described one series of operations.

A count method of the radiation photons in the irradiation period A will be described below with reference to Figs. 5 to 7. Fig. 5 is a timing chart for explaining the operation of the sensor unit 201₁ in the irradiation period A. In Fig. 5, the abscissa indicates a time axis, and the ordinate indicates the output of the monitor unit 302, the outputs of the comparison units 303-R and 303-B, and the values of the memories 304-R and 304-B while indicating the incident radiation photons by arrows.

First, a case will be described in which the first radiation photon in Fig. 5 enters the scintillator 105. Upon incidence of the first radiation photon, the potential of the detection element 301 changes and thus the output of the monitor unit 302 changes. In this example, the output of the monitor unit 302 is higher than the reference voltage 306-R and lower than the reference voltage 306-B. In this case, the output of the comparison unit 303-R becomes "1" while the output of the comparison unit 303-B becomes "0". Via the group 309 of signal lines, the determination unit 307-R receives a comparison result between the comparison units 303-R and 303-B in this sensor unit 201₁, and further receives comparison results between the comparison units 303-R and 303-B in the other peripheral sensor units 201.

As described above, the comparison result between the comparison units 303-R and 303-B in the sensor unit 201₁ corresponds to the output value of the quantization unit U₁ in the sensor unit 201₁. Similarly, the comparison results between the comparison units 303-R and 303-B in the other peripheral sensor units 201 correspond to the output values of the quantization units U₁ in the other sensor units 201. The determination unit 307-R in the sensor unit 201₁ receives these output values as the aforementioned patterns 310. The determination unit 307-R checks the patterns 310 with the reference pattern 308-R and determines whether they match. If they match, the determination unit 307-R adds "1" to the value of the memory 304-R. If they do not match, no addition is performed. The same also applies to the determination unit 307-B. In this example, "1" is added to the value of the memory 304-R but is not added to the value of the memory 304-B (the value of the memory 304-R becomes "1" and the value of the memory 304-B remains "0").

Next, a case will be described in which the second radiation photon enters the scintillator 105 and the output of the monitor unit 302 changes. In this example, the output of the monitor unit 302 is higher than both the reference voltages 306-R and 306-B. In this case, the outputs of both the comparison units 303-R and 303-B become "1". Each of the determination units 307-R and 307-B performs determination in the same procedure. As a result, in this example, "1" is added to the values of both the memories 304-R and 304-B (the value of the memory 304-R becomes "2" and the value of the memory 304-B becomes "1").

In a case in which the third radiation photon enters the scintillator 105, the third radiation photon has energy almost equal to that of the first radiation photon and the same operation as in the case in which the first radiation photon enters is performed. As a result, in this example, "1" is added to the value of the memory 304-R but is not added to the value of the memory 304-B (the value of the memory 304-R becomes "3" and the value of the memory 304-B remains "1").

For example, when one radiation photon enters the sensor unit 201₁, scintillation light generated in the scintillator 105 by that incidence can also diffuse in the horizontal direction (a direction parallel to the upper surface of the sensor panel 106).

Fig. 6A shows an intensity distribution (luminance distribution) of scintillation light and a distribution obtained by converting it into a value corresponding to the output of the monitor unit 302 in a case in which a radiation photon having relatively large energy enters. The conversion distribution shows the reference voltages 306-R and 306-B for comparison. As in Fig. 6A, Fig. 6B shows a case in which a radiation photon having relatively small energy enters.

In Fig. 6A, the intensity of light in the sensor unit 201₁ in the center of the view is higher than a value corresponding to the reference voltage 306-B. In addition, in Fig. 6A, the intensities of light in the other adjacent sensor units 201 can be higher than a value corresponding to the reference voltage 306-R. On the other hand, in Fig. 6B, the intensity of light in the sensor unit 201₁ in the center of the view is higher than the value corresponding to the reference voltage 306-R and lower than the value corresponding to the reference voltage 306-B. In addition, in Fig. 6B, the intensities of light in the other adjacent sensor units 201 are lower than the value corresponding to the reference voltage 306-R.

Fig. 7 is a view obtained by digitizing the intensity distribution of the scintillation light in Fig. 6A described above. Each value is a value quantized by the aforementioned quantization unit U₁. An expression "intensity of light" will be used (or a simple expression "intensity" may be used) hereinafter for the sake of simplicity. More specifically, the intensity of the light in the sensor unit 201₁ in the center of the view is indicated as "2", the intensities of light in the other sensor units 201 adjacent to it in an opposite side direction and a diagonal direction are indicated as "1", and the intensities of light in the other sensor units 201 outside of them are indicated as "0". These values can be given by the comparison results between the comparison units 303-R and 303-B, and can be read out from the group 309 of signal lines. More specifically, for example, if the outputs of both the comparison units 303-R and 303-B are "1", the intensity of the light is set to "2". If the output of the comparison unit 303-R is "1" and the output of the comparison unit 303-B is "0", the intensity of the light is set to "1". Further, if the outputs of both the comparison units 303-R and 303-B are "0", the intensity of the light is set to "0".

Note that in the sensor unit 201₁ in the center of the table, the determination units 307 of the count unit U₂ receive, from the group 309 of signal lines, the intensity "2" of the light in the sensor unit 201₁ and the intensities of the light in the other peripheral sensor units 201. Note that the other sensor units 201 include two sensor units 201 adjacent to the sensor unit 201₁ in the row direction and two sensor units 201 adjacent to the sensor unit 201₁ in the column direction (the intensities of the light in any of these sensor units 201 are "1"). That is, the determination units 307 receive the intensities of the light in five sensor units 201 in total, namely, the sensor unit 201₁ and four sensor units 201 adjacent to it in the row direction and the column direction, respectively. In this example, the patterns 310 of the intensities of the light in the above-described five sensor units 201 and the reference patterns 308 match, and the determination units 307 add "1" to the values of the memories 304 in accordance to it.

On the other hand, in the sensor unit 201 (to be referred to as a "sensor unit 201₂" for distinction) adjacent to the sensor unit 201₁ in the diagonal direction, the determination units 307 of the count unit U₂ receive, from the group 309 of signal lines, the intensity "1" of the light in the sensor unit 201₂ and the intensities of the light in the other peripheral sensor units 201. Note that the other sensor units 201 include two sensor units 201 adjacent to the sensor unit 201₂ in the row direction (the intensity of the light in one sensor unit 201 is "1" and the intensity of the light in the other sensor unit 201 is "0") and two sensor units 201 adjacent to the sensor unit 201₂ in the column direction (the intensity of the light in one sensor unit 201 is "1" and the intensity of the light in the other sensor unit 201 is "0"). For the sensor unit 201₂, the patterns 310 of the intensities of the light in the total of these five sensor units 201 and the reference patterns 308 do not match. Therefore, the determination unit 307-B does not add "1" to the values of the memories 304.

As described above, when one radiation photon enters the sensor unit 201₁, the scintillation light generated in the scintillator 105 by that incidence can also diffuse in the horizontal direction. That is, while a part (substantially a large part) of the scintillation light enters the sensor unit 201₁, another part of the light can enter the other sensor units 201 on the periphery of the sensor unit 201₁. As a result, not only a signal from the sensor unit 201₁ but also signals from the other sensor units 201 have signal components associated with detection of the scintillation light. For this reason, image quality may be lowered if these signals are used as a part of image data.

According to this arrangement example, the count unit U₂ of the sensor unit 201₁ receives the patterns 310 including the output value from the quantization unit U₁ of the sensor unit 201₁ (that is, a quantization result of the intensity of the light in the sensor unit 201₁) and the output values from the quantization units U₁ of the other sensor units 201 on the periphery of the sensor unit 201₁ (that is, quantization results of the intensities of the light in the other sensor units 201). Then, in the count unit U₂, the determination units 307 determine whether the patterns 310 and the reference patterns 308 match. If the above-described patterns 310 and reference patterns 308 match, "1" is added to the values of the memories 304 of the count unit U₂, assuming that the radiation photon has entered the sensor unit 201₁. On the other hand, if the above-described patterns 310 and reference patterns 308 do not match, the values of the memories 304 of the count unit U₂ are not changed ("1" is not added), assuming that the radiation photon has not entered the sensor unit 201₁. That is, the reference patterns 308 can also be regarded as predictive patterns indicating the intensity distribution of the light estimated from light diffusion in the scintillator 105 (light diffusion from immediately above the sensor unit 201₁ to the peripheral sensor units 201).

In another expression, the sensor unit 201₁ shares a detection value of the scintillation light with the other peripheral sensor units 201. Then, the sensor unit 201₁ determines, based on a detection value in the sensor unit 201₁ itself and detection values in the other peripheral sensor units 201, whether the radiation photon has entered the sensor unit 201₁ with reference to the reference patterns 308.

In the above-described example, two sensor units 201 adjacent to the sensor unit 201₁ in the row direction and two sensor units 201 adjacent to the sensor unit 201₁ in the column direction have been exemplified as the above-described other sensor units 201. However, the other sensor units 201 can be arranged on the periphery of or in proximity to the sensor unit 201₁, and may be adjacent to the sensor unit 201₁ in the row direction or the column direction. However, the other sensor units 201 may be other than these. For example, the other sensor units 201 may include sensor units adjacent to the sensor unit 201₁ in the diagonal direction or may include sensor units not adjacent to the sensor unit 201₁, or may include combinations of them. In this example, as the reference patterns 308, the patterns have been exemplified which include the total of five values, that is, a value ("2" in this example) associated with the sensor unit 201₁, values ("1" in this example) associated with two sensor units 201 adjacent to the sensor unit 201₁ in the row direction, and values ("1" in this example) associated with two sensor units 201 adjacent to the sensor unit 201₁ in the column direction. However, the reference patterns 308 are not limited to the patterns in this example and may include more values.

According to this arrangement example, in the sensor unit 201₁, the count unit U₂ counts the number of radiation photons with respect to the respective intensities "1" and "2" of the light detected by the detection element 301. More specifically, the intensity "0" is obtained when the output of the monitor unit 302 is lower than the reference voltage 306-R by using two comparison units 303-R and 303-B. In this case, it can be determined that the radiation photon has not entered the sensor unit 201₁. When the output is higher than the reference voltage 306-R and lower than the reference voltage 306-B, the intensity "1" is obtained. In this case, it can be determined that the radiation photon having energy corresponding to the intensity "1" has entered the sensor unit 201₁. The intensity "2" is obtained when the output is higher than the reference voltage 306-B. In this case, it can be determined that the radiation photon having energy corresponding to the intensity "2" has entered the sensor unit 201₁. The count unit U₂ can count the radiation photons for each intensity described above. In other words, the count unit U₂ can perform count the radiation photons for each energy of the radiation photons.

This can be performed by setting the reference patterns 308 for each intensity described above. In the arrangement of this example, the reference pattern 308-R can be set so as to correspond to the intensity "1" and the reference pattern 308-B can be set so as to correspond to the intensity "2". Then, the number radiation photons corresponding to the intensity "1" is counted in the determination unit 307-R which receives the reference pattern 308-R and the number radiation photons corresponding to the intensity "2" is counted in the determination unit 307-B which receives the reference pattern 308-B. Note that, for example, the reference patterns 308 exemplified in Fig. 7 correspond to patterns for counting the number of times the radiation photons corresponding to the intensity "2" have entered. This also makes it possible, in the count unit U₂, to specify to what extent of energy the radiation photons have entered the sensor unit 201₁. The number of respective units described above such as comparison units 303-R and 303-B is two in this example. However, the number may be three or more.

The method of counting the number of radiation photons has been described above by paying attention to one sensor unit 201₁. The same also applies to each sensor unit other than this. The count unit U₂ counts the number of radiation photons in each of the plurality of sensor units 201. Then, their count results (that is, the count values of the count units U₂) are output to the processor 103 by the output units 305 and used to generate the image data.

Note that the above-described count operation in the irradiation period A can be performed by setting the operating frequency of the sensor unit 201₁ (mainly the quantization unit U₁ and the count unit U₂) and the irradiation amount of the irradiation unit 101 to a value capable of counting the radiation photons one by one. For example, the operating frequency of the sensor unit 201₁ may be set within a range of 10 [kHz] to several [MHz] (for example, about 100 [kHz]). For example, the irradiation amount of the irradiation unit 101 may be set to a value obtained when a tube voltage is about 100 [kV] and a tube current is about 10 [mA].

Fig. 8 shows an example of the operation in each sensor unit 201 in the readout period B as an example of a readout method of the count results obtained by the above-described count method. In Fig. 8, the abscissa indicates a time axis, and the ordinate indicates the waveforms of control signals which propagate through the signal lines 205 (such as 205-0R) and the signal lines 207 (such as 207-0) described with reference to Fig. 2, and the output data DATA which propagates through the output line 206. In the readout period B, the respective signals of the signal lines 205-0R, 205-0B, 205-1R, 205-1B, 205-2R, and 205-2B are activated sequentially. The respective signals of the signal line 207-0 and signal lines 207-1 and 207-2 are also activated sequentially while the respective signals are activated.

For example, first, the signal of the signal line 205-0R is activated, and during that time, the respective signals of the signal lines 207-0, 207-1, and 207-2 are activated sequentially. Consequently, the values of the memories 304-R in the respective sensor units 201 of the first row are read out via the column signal lines 204 by the output units 305-R, and sequentially output to the first column, the second column, and the third column, respectively, via the output line 206. Then, likewise, the signal of the signal line 205-0B is activated, and during that time, the respective signals of the signal lines 207-0, 207-1, and 207-2 are activated sequentially. Consequently, the values of the memories 304-B in the respective sensor units 201 of the first row are read out via the column signal lines 204 by the output units 305-B, and sequentially output to the first column, the second column, and the third column, respectively, via the output line 206. Consequently, a readout operation of the count value of the count unit U₂ in each sensor unit 201 of the first row is completed. Then, readout operations of the count values of the count units U₂ in the respective sensor units 201 of the second row and the third row are performed sequentially as in the above-described readout operation for the first row. Consequently, the readout operations of the count values of the count units U₂ in all the sensor units 201 are completed.

The processor 103 generates the image data of one frame by using the count values of the count units U₂ (that is, the count results of the number of radiation photons) read out as described above. Note that the number of radiation photons can be counted for each energy of the radiation photons as described above, and thus the radiation image based on the image data may be displayed on the display unit such as the display with a color corresponding to its energy level being applied.

As described above, according to this embodiment, even if the detection element 301 of each sensor unit 201 has detected light, the number of radiation photons is not counted when the patterns 310 and the reference patterns 308 do not match, assuming that the radiation photons have not entered the sensor unit 201. Therefore, for example, in a case in which irregular radiation photons have entered, it is possible to prevent miscount of the radiation photons that may be caused by this. Note that the case in which the irregular radiation photons have entered refers to, for example, a case in which two or more photons have entered locally at once, a case in which photons of radiation of a type different from radiation to be detected (cosmic rays or the like can be taken as an example), or a case in which the radiation photons have entered the detection element 301 directly (without being converted into light by the scintillator 105). Therefore, according to this embodiment, it is possible to increase photon count accuracy. This is particularly effective in a case in which the incident radiation has relatively large energy, a case in which the diffusion amount of scintillation light is large in the horizontal direction, or the like.

Note that the number of irregular radiation photons described above can also be counted by adding patterns for detecting the irregular radiation photons to the reference patterns 308. In addition to this, the other comparison units 303 configured to detect the irregular radiation photons may be added to the sensor units 201.

(Second Embodiment)
The second embodiment will be described with reference to Figs. 9A to 10. In the aforementioned first embodiment, the case has been exemplified in which the scintillation light generated upon incidence of the radiation photons diffuses uniformly in the horizontal direction. However, some radiation photons, for example, change their traveling directions when passing through an object and enter the upper surface of the sensor panel 106 obliquely. In this case, the diffusion direction of the scintillation light may be biased. This embodiment is different from the aforementioned first embodiment in that the incident angles of the radiation photons are specified based on the bias of the diffusion direction of the scintillation light.

Fig. 9A shows an intensity distribution of scintillation light and a distribution obtained by converting it into a value corresponding to an output of a monitor unit 302 in a case in which a radiation photon enters the upper surface of a sensor panel 106 obliquely (in a direction from the upper left to the lower right in Fig. 9A). Fig. 9B shows a case in which a radiation photon enters in a direction crossing the direction in the example of Fig. 9A (from the upper right to the lower left in Fig. 9B). According to Figs. 9A and 9B, when the scintillation light enters obliquely, the diffusion amount of the scintillation light in a direction parallel to the incident direction can be larger than the diffusion amount of the scintillation light in the direction crossing it.

Fig. 10 is a view obtained by digitizing the intensity distribution of the scintillation light in Fig. 9B described above. This example is different from the example (refer to Fig. 7) of the first embodiment in that the intensity of light in another sensor unit 201 adjacent to a sensor unit 201₁ in one of opposite side directions is indicated as "0".

In each sensor unit 201, a count unit U₂ determines whether corresponding patterns 310 and reference patterns 308 match in the same procedure as in the first embodiment. Note that in this example, a plurality of reference patterns 308 (to be denoted as 308₁ to 308₅, respectively) are prepared and each of the plurality of reference patterns 308₁ to 308₅ corresponds to the bias of the diffusion direction of the scintillation light. For example, in this example, the pattern 308₁ (the same pattern as in the first embodiment) corresponds to a case in which there is no bias in the diffusion direction of the scintillation light. The pattern 308₂ corresponds to a case in which the bias is in the row direction. The pattern 308₃ corresponds to a case in which the bias is in the column direction. The pattern 308₄ corresponds to a case in which the bias is in one of diagonal directions. The pattern 308₅ corresponds to a case in which the bias is in the other of the diagonal directions.

For example, for the sensor unit 201₁, the patterns 310 match the pattern 308₅ out of the plurality of reference patterns 308, and thus "1" is added to values of memories 304. In this case, the count unit U₂ may further include a specifying unit which specifies the incident direction of the scintillation light, and the specifying unit may specify the incident direction based on whether the patterns 310 match any one of the plurality of reference patterns 308. Then, information indicating the specified incident direction can be read out together with a count value of the count unit U₂. A processor 103 generates image data of one frame by using the read out count value of the count unit U₂ and the specified incident direction.

Note that for a sensor unit 201₂, the patterns 310 match none of the plurality of reference patterns 308, and thus "1" is not added to the values of the memories 304.

According to this embodiment, in addition to obtaining the same effect as in the first embodiment, it is also possible to specify the incident angle of the radiation photon, to calculate object information three-dimensionally based on the specified incident angle, and then to display a radiation image three-dimensionally.

(Third Embodiment)
The count methods of the radiation photons according to the aforementioned first and second embodiments use the quantization unit U₁ and the count unit U₂. However, their functions may be implemented, for example, on a program or software in the processor 103. That is, each sensor unit 201 may be formed by a circuit configured to output a signal corresponding to the amount of scintillation light, and quantization of the intensity of the light and count of the number of radiation photons based on this may be performed outside the sensor units 201.

Fig. 11 shows an example of the arrangement of a sensor unit 201' according to the third embodiment. In addition to a detection 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 detection 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 in the detection element 301.

The light sensitivity selecting unit 530 includes transistors M4 to M7 and capacities C4 and C5. For example, the capacity 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 detection element 301. The capacity 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 capacity C1. An output from the signal amplification unit 520 obtained when the detection element 301 has been reset is supplied to one terminal n1 of the capacity C1. A power supply voltage is supplied to other terminal n2 of the capacity C1 by turning on the transistor M8. Consequently, a voltage obtained when the detection 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 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 capacity C2, and an analog switch SW2 and samples a signal (S signal) corresponding to the amount of the light detected by the detection 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 capacity C2. The signal is amplified by the transistor M12 which performs a source follower operation and output to column signal lines 204 via the analog switch SW2. Note that the transistor M13 can be arranged in an electrical path between the capacity C2 and the capacity C2 of another sensor unit on 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 difference of the noise component between them. 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 value of the signal read out from each sensor unit 201' as described above indicates the intensity of the light detected by the detection element 301. This allows a processor 103 to quantize, based on the value of the signal, the intensity of the light in each sensor unit 201'. That is, the processor 103 can achieve the function of the aforementioned quantization unit U₁. The processor 103 can also obtain the aforementioned patterns 310 based on the quantization result, determine whether patterns 310 and reference patterns 308 match, and count the number of the matches. That is, the processor 103 can achieve the function of the aforementioned count unit U₂.

Note that the sensor unit 201' exemplified in this embodiment is not limited to an arrangement example of Fig. 11 but may have another arrangement for detecting radiation. For example, the sensor unit 201' may be configured such that the sensor unit has the function of a quantization unit U₁ and the processor 103 has the function of a count unit U₂.

As described above, according to this embodiment, it is also possible, while using a sensor unit having a well-known arrangement, to count radiation photons by implementing the respective functions of the quantization unit U₁ and the count unit U₂ outside the sensor unit. Consequently, the same effect as in the first embodiment is obtained.

(Others)
Some preferred embodiments have been exemplified above. However, the present invention is not limited to these examples. A part of each example may be modified without departing from the scope of the present invention. In the example above, reference has been made to a so-called "indirect conversion type" arrangement in which the scintillator 105 converts radiation into light and the detection element 301 converts the light into an electrical signal. However, the present invention may be applied to a so-called "direct conversion type" arrangement in which radiation is converted into the electrical signal directly.

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. 2015-111676, filed June 1, 2015, which is hereby incorporated by reference herein in its entirety.

Claims

A radiation imaging apparatus comprising:
a plurality of sensor units each including a detection element which detects radiation;
a quantization unit configured to quantize a signal value from the detection element of each sensor unit;
a count unit configured to count, for each sensor unit, the number of matches between a second pattern as a reference pattern set in advance, and a first pattern which includes a quantization result by the quantization unit of the signal value from the detection element of the sensor unit and a quantization result by the quantization unit of the signal value from the detection element of another sensor unit on the periphery of the sensor unit; and
a readout unit configured to read out a count value of the count unit.
The apparatus according to claim 1, wherein the quantization unit and the count unit are arranged in each of the plurality of sensor units, and the count unit of each sensor unit counts, by setting a pattern including an output value from the quantization unit of the sensor unit and an output value from the quantization unit of the other senor unit on the periphery of the sensor unit as the first pattern, the number of matches between the first pattern and the second pattern.
The apparatus according to claim 1 or 2, further comprising a scintillator which converts radiation into light,
wherein the detection element detects light from the scintillator.
The apparatus according to any one of claims 1 to 3, wherein the quantization unit includes a monitor unit configured to monitor a change amount of a potential of the detection element, and a comparison unit configured to compare a magnitude relationship between the monitored change amount and each of reference values of not less than two.
The apparatus according to any one of claims 1 to 4, wherein the count unit includes a determination unit configured to determine whether the first pattern and the second pattern match, and a memory configured to store the number of matches when the first pattern and the second pattern match.
The apparatus according to claim 5, wherein in the count by the count unit for each sensor unit, the determination unit determines that a photon of the radiation has entered the sensor unit and the sensor unit out of the other peripheral sensor units when the first pattern and the second pattern match.
The apparatus according to any one of claims 1 to 6, wherein the count unit
receives the plurality of second patterns, and
counts when the first pattern and one of the plurality of second patterns match.
The apparatus according to claim 7, wherein the count unit counts the number of the matches with respect to each of the plurality of second patterns.
The apparatus according to claim 7 or 8, wherein the count unit includes a specifying unit configured to specify an incident direction of the photon of the radiation based on whether the first pattern matches any of the plurality of second patterns, and
the readout unit further reads out information indicating the specified incident direction.
The apparatus according to any one of claims 1 to 9, wherein the plurality of sensor units are arrayed so as to form a plurality of rows and a plurality of columns, and
the first pattern used by the count unit includes
the quantization result by the quantization unit of the signal value from the detection element of each sensor unit,
a quantization result by the quantization unit of signal values of the respective detection elements of the two sensor units adjacent to the sensor unit in a row direction, and
a quantization result by the quantization unit of signal values of the respective detection elements of the two sensor units adjacent to the sensor unit in a column direction.
The apparatus according to any one of claims 1 to 9, wherein the plurality of sensor units are arrayed so as to form a plurality of rows and a plurality of columns, and
the first pattern used by the count unit includes
the quantization result by the quantization unit of the signal value from the detection element of each sensor unit, and
a quantization result by the quantization unit of signal values of respective detection elements of eight sensor units arranged around the sensor unit so as to surround the sensor unit.
The apparatus according to any one of claims 1 to 11, further comprising a processor configured to generate image data based on the count value of the count unit read out from the readout unit.
The apparatus according to claim 12, wherein the processor performs
a first operation of performing, on each sensor unit, the quantization by the quantization unit and the count by the count unit, and
a second operation of generating the image data of one frame based on the count value of the count unit obtained in the first operation.
The apparatus according to claim 13, wherein the processor plays back a moving image by performing a series of operations including the first operation and the second operation a plurality of times.
A driving method of a radiation imaging apparatus that includes a plurality of sensor units each including a detection element which detects radiation, the method comprising:
quantizing a signal value from the detection element of each sensor unit;
counting, for each sensor unit, the number of matches between a second pattern as a reference pattern set in advance, and a first pattern which includes the quantization result of the signal value from the detection element of the sensor unit and the quantization result of the signal value from the detection element of another sensor unit on the periphery of the sensor unit; and
reading out a count value for each sensor unit obtained in the counting.
A program that causes a computer to perform quantizing, counting, and reading out, respectively, defined in claim 15.