JP2016036467A - Radiation detection device and radiographic imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology advantageous for accurate exposure control for a region to be examined.SOLUTION: A radiation detection device includes a radiation detection part having a plurality of sensors for detecting a radiation ray and a signal processing part for processing a signal detected by the plurality of sensors. The signal processing part divides the signal detected by the plurality of sensors into a plurality of classes based on the signal value so as to generate a plurality of images corresponding to each of the plurality of classes. One image is selected from the plurality of images based on the similarity between each of at least a part of the images of the plurality of images and a reference image, the sensor that detects a signal composing the selected one image is determined as a monitoring sensor, and the irradiation of the radiation ray is monitored based on the signal detected by the monitoring sensor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiation detection apparatus and a radiation imaging system.

  In recent years, radiation imaging apparatuses have been devised to appropriately manage radiation and minimize the exposure dose. For example, there is a method (automatic exposure control: auto exposure control (hereinafter referred to as AEC)) of automatically stopping the radiation when the optimal amount of radiation for diagnosis is irradiated. Appropriate diagnosis with the minimum necessary radiation dose by stopping radiation when a predetermined amount of radiation is applied to a specific part of a patient designated by a doctor or radiologist Can do. What is required of AEC is to appropriately determine how much radiation has been applied to which part of the patient.

  Patent Document 1 describes a radiation imaging apparatus that performs automatic exposure control. This radiation imaging apparatus divides an irradiation field into a blank region, an implant region, and a subject region based on a histogram. Then, the minimum value pixel and the maximum value pixel in the subject area are specified, and radiation irradiation is stopped based on the integrated value of the respective pixel values of the minimum value pixel and the maximum value pixel. Here, the blank region is a region where radiation is directly irradiated without passing through the subject, the implant region is a region where an implant exists in the subject, and the subject region is a blank region and implant from the irradiation field. It is defined as the area excluding the area.

JP 2013-176544 A

  In the radiation imaging apparatus described in Patent Literature 1, irradiation of radiation is stopped based on the integrated value of each pixel value of the minimum value pixel and the maximum value pixel in the subject region. However, since the subject region may include regions of various parts of the subject, the method of stopping radiation irradiation based on the pixel values of the minimum value pixel and the maximum value pixel in the subject region, respectively. There is a possibility that the personal exposure control for the part to be examined cannot be performed.

  The present invention has been made with the above problem recognition as an opportunity, and an object thereof is to provide a technique advantageous for accurate exposure control with respect to a region to be inspected.

  One aspect of the present invention relates to a radiation detection apparatus, which includes a radiation detection unit having a plurality of sensors that detect radiation, and a signal processing unit that processes signals detected by the plurality of sensors. The signal processing unit generates a plurality of images respectively corresponding to the plurality of classes by dividing the signals detected by the plurality of sensors into a plurality of classes based on the signal values, Based on the similarity between each of at least some of the plurality of images and the reference image, one image is selected from the plurality of images, and a sensor that detects a signal constituting the selected one image is monitored. It determines as a sensor and monitors radiation irradiation based on the signal detected by the monitoring sensor.

  The present invention provides a technique advantageous for accurate exposure control on a region to be inspected.

The flowchart which shows AEC operation | movement of embodiment of this invention. The figure which shows the structure of the radiation imaging system of embodiment of this invention. The figure which shows the specific structure of the radiation imaging system of embodiment of this invention. The figure which shows the structure of the radiation detection part of embodiment of this invention. The figure which shows operation | movement of the radiation imaging system of embodiment of this invention. The figure which illustrates the pixel (sensor) used for AEC operation. The figure which illustrates the radiographic image and reference image of a chest. The figure which illustrates operation | movement of a reading part. The figure which illustrates the sort of the data for AEC. The figure which shows the memory space in which the data for AEC were stored. The figure which shows the memory space in which the data for AEC were stored. The figure which illustrates chest imaging | photography and knee joint imaging | photography. The figure which shows the image which divided | segmented the signal detected by the sensor at the time of imaging | photography of a chest according to the class. The figure which shows the image which divided | segmented the signal detected by the sensor at the time of imaging | photography of a knee joint part according to the class. The figure which illustrates the histogram of the data for AEC (the signal detected by the sensor 212). The figure which shows the determination method of a monitoring sensor typically. The figure which shows the determination method of a monitoring sensor typically. The figure which shows the determination method of a monitoring sensor typically.

  Hereinafter, the present invention will be described through exemplary embodiments thereof with reference to the accompanying drawings.

The configuration of the radiation imaging system 100 according to one embodiment of the present invention will be described with reference to FIG. The radiation imaging system 100 includes an exposure switch 101, a radiation source control unit 102, a radiation source 103, a radiation detection unit 105, an information processing unit 106, and an input / output device 107. The exposure switch 101 is connected to the radiation source control unit 102 by a wired cable or wirelessly, and instructs to take a radiation image (radiation of radiation 104 from the radiation source 103, imaging of a radiation image by the radiation detection unit 105). The radiation source control unit 102, which is a switch for controlling the radiation source 103, is connected to the exposure switch 101, the radiation source 103, and the information processing unit 106. The radiation source control unit 102 causes the radiation source 103 to start emitting radiation 104 (irradiation to the patient 108) in response to the signal transmitted from the exposure switch 101. The information processing unit 106 is connected to the input / output device 107 and the radiation detection unit 105, and causes the radiation source control unit 102 to stop irradiating radiation in response to a signal from the radiation detection unit 105. That is, the information processing unit 106 performs an AEC operation. Further, the information processing unit 106 causes the input / output device 107 to display a radiation image generated based on the signal from the radiation detection unit 105.

  The description will be continued with reference to FIG. The radiation source control unit 102 includes a control circuit 102 a that controls the radiation source 103. The information processing unit 106 includes a signal processing unit 106a, a monitoring unit 106b, a comparison unit 106c, an image storage unit 106d, and a memory 106e, and performs an AEC operation. The information processing unit 106a can be configured, for example, by incorporating a program into a general-purpose computer. Such a program or a memory medium storing such a program may constitute the invention.

  The monitoring unit 106b is connected to the signal processing unit 106a and the comparison unit 106c. The comparison unit 106c is connected to the image storage unit 106d. The signal processing unit 106a is connected to the memory 106e. The radiation detection unit 105 includes a pixel array 105a and a readout unit 105b. The pixel array 105a is also a device having a plurality of sensors that detect radiation. The plurality of sensors may be used as pixels for capturing a radiation image, but may be dedicated sensors for detecting radiation. The reading unit 105 b reads a signal from the pixel array 105 a and outputs the signal to the information processing unit 106. The signal processing unit 106a may include a function of sorting the signals output from the radiation detection unit 105 based on the values, for example. In FIG. 3, the comparison unit 106c and the signal processing unit 106a are not directly connected, but can transmit and receive data to and from each other through the monitoring unit 106b. Similarly, the comparison unit 106c and the memory 106e, and the monitoring unit 106b and the memory 106e can similarly transmit and receive data to and from each other.

  The configuration of the radiation detection unit 105 will be described with reference to FIG. The radiation detection unit 105 includes a pixel array 105a and a readout unit 105b. The pixel array 105a may be a direct type that directly converts radiation into an electric signal, or may be an indirect type that converts radiation into visible light and converts the visible light into an electric signal. In the indirect type, radiation is converted into visible light by a scintillator (not shown). The scintillator can typically be arranged over the entire area of the pixel array 105a. The scintillator can be composed of, for example, gadolinium oxysulfide (GOS) or cesium iodide (CsI).

  The pixel array 105a can be composed of, for example, an active matrix array 201. The active matrix array 201 has a plurality of pixels 200 arranged to form a plurality of rows and a plurality of columns. Each pixel 200 includes a conversion element 202 that outputs an electrical signal (for example, electric charge, voltage, or current) corresponding to the amount of incident radiation, and a switch 203 that connects the conversion element 202 to the column signal line 204. In the example shown in FIG. 4, some of the plurality of pixels 200 for capturing a radiation image are used as sensors for AEC, that is, for detecting radiation. A pixel to be used as a sensor among the plurality of pixels 200 can be arbitrarily determined.

  The position of the pixel 200 can be specified by a position (column number) in the x direction (row direction) and a position (row number) in the y direction (column direction), that is, coordinates. In one example, the number of pixels in the x direction and the number of pixels in the y direction are 1000 to 4000 pixels, and the total number of pixels is about 10 million. The switch 203 is a transistor having a gate 203a, a source 203b, and a drain 203c. The switch 203 is controlled by the drive unit 206 through the drive line 205 connected to the gate 203a. The drain 203 c of the switch 203 is connected to the conversion element 202, and the source 203 b of the switch is connected to the column signal line 204.

  The conversion element 202 is, for example, a PIN conversion element (PIN photodiode) in which a P-type semiconductor, an intrinsic semiconductor, and an N-type semiconductor are stacked, or an MIS conversion in which an N-type semiconductor, an intrinsic semiconductor, and an insulator are stacked. It can be an element. The conversion element 202 has electrodes on the upper part and the lower part, one electrode is fixed in potential by a bias line (not shown), and the other electrode is floated in a state where a predetermined potential is applied. As a result, an electric field is generated in the conversion element 202. In this state, a pair of electrons and holes are generated by the incidence of radiation in the case of the direct type and by the incidence of visible light in the case of the indirect type. These electrons and holes move in opposite directions according to the electric field. And the electric charge which moved to the side of the electrode made floating among electrons and holes is accumulated. The semiconductor material constituting the conversion element 202 is preferably amorphous selenium in the case of direct type, and amorphous silicon or polysilicon in the case of indirect type. The switch 203 is composed of a transistor such as a thin film transistor, for example. The thin film transistor may be, for example, a bottom-gate thin film transistor in which the drive line 205 is located below the thin film transistor, or a top-gate thin film transistor in which the drive line 205 is located above the thin film transistor. The conversion element 202 and the switch 203 can generally be formed using a CVD (Chemical Vapor Deposition) apparatus.

  The reading unit 105b includes a driving unit 206, an amplification unit 207, a multiplexer 208, an ADC (AD converter) 209, a control unit 210, and a memory 211. The drive unit 206 drives the switch 203 via the drive line 205 provided in each row. The pixels 200 in which the switch 203 is connected to one drive line 205 form one row. When the drive line 205 is driven to an active level, the switch 203 connected to the drive line 205 is turned on, and the charge of the conversion element 202 connected to the switch 203 is amplified via the column signal line 204. Forwarded to

  The control unit 210 controls the amplification unit 207, the multiplexer 208, the ADC 209, and the memory 211. The amplification unit 207 converts the charge output from the conversion element 202 into a voltage. The amplification unit 207 is reset when the control unit 210 drives the reset line 214 to the active level. The multiplexer 208 sequentially selects the voltage format signals output from the plurality of amplification units 207 respectively corresponding to the plurality of columns based on a command from the control unit 210 and provides the selected signals to the ADC 209. The ADC 209 converts the voltage format signal into a digital signal and provides the digital signal to the memory 211 and the information processing unit 106. The memory 211 holds a signal provided from the ADC 209, that is, a signal read from the pixel 200 in association with the position (coordinates) of the pixel 200.

  Hereinafter, the operation of the radiation imaging system 100 will be described with reference to FIGS. In FIG. 5, the operations of the input / output device 107, the exposure switch 101, the radiation source control unit 102, the information processing unit 106, and the radiation detection unit 105 are shown in association with the steps in the flowchart of FIG. ing.

  In step S <b> 301, patient information (subject information) is provided to the information processing unit 106 through the input / output device 107 by a doctor or a radiographer. Patient information is information that characterizes a subject, such as sex, age, weight, chest circumference, abdominal circumference, and the like. More specifically, the patient information may be gender: male, weight: 70 kg, chest circumference: 100 cm, abdominal circumference: 80 cm. In step S <b> 301, imaging part information indicating an imaging part is provided through the input / output device 107 by a doctor or a radiographer. The imaging region is, for example, the head, chest, abdomen, and the like.

  In step S 301, information specifying the AEC target site used for AEC and the pixel 200 as the AEC sensor 212 is provided from the input / output device 107 to the information processing unit 106. For example, if the imaging region is the chest, the AEC target region is set as the lung field, and the pixels 200 are arranged as the sensor 212 at intervals of 1 mm to 1 cm in each of the x direction and the y direction as illustrated in FIG. Is selected. When the pixel size is about 150 μm × 150 μm, pixels arranged at intervals of 1 mm to 1 cm correspond to pixels arranged at intervals of 8 pixels to 80 pixels. Here, um means micrometer. The AEC target site and the sensor 212 may be selected by the input / output device 107 according to the imaging site, or may be selected by a doctor or a radiologist. In one example, the default AEC target region and sensor 212 may be set by the input / output device 107 according to the imaging region. The default AEC target site and sensor 212 can be changed by the physician or radiologist as needed. The information specifying the AEC target site and the sensor 212 is an example of AEC information.

  In the example shown in FIG. 6, the sensor 212 is set for each multiple of k, such as k-th row, 2 × k-th row, etc., and the interval between adjacent sensors 212 is approximately 1 mm to 1 cm. Although set, this is just an example. The sensor 212 can be arbitrarily selected from a plurality of pixels 200 constituting the pixel array 105a according to the AEC target site. For example, in imaging where the AEC target site is the lung field, it is preferable to determine the pixels 200 arranged at intervals equal to or smaller than the size of the lung field as the sensor 212. Then, at least one sensor 212 is located within the region of the AEC target site. Patient information, imaging region information, and AEC information are transmitted from the input / output device to the comparison unit 106c of the information processing unit 106.

  In step S302, the comparison unit 106c acquires a reference image corresponding to the information (patient information, imaging region information, and AEC information) provided in step S301 from the image storage unit 106d. Here, in the image storage unit 106d, one reference image is associated with each of a plurality of combinations, each combination including patient information, imaging region information, and AEC information. Therefore, by specifying the patient information, the imaging part information, and the AEC information, it is possible to specify one corresponding reference image. The format of the reference image stored in the image storage unit 106b may be arbitrary, but may be a binary image as shown in FIG. 7B, for example. The binary image can be composed of black pixels indicating the inspection target (for example, lung field) and white pixels indicating other areas. FIG. 7A is an example of a radiographic image of the chest expressed in 8-bit gray scale. FIG. 7B shows a binary image in which the lung field portion is extracted from FIG. 7A, the lung field portion is expressed by black pixels, and the other regions are expressed by white pixels.

  The pixels constituting the reference image may include the pixel 200 used as the sensor 212 or the pixel 200 in the vicinity of the pixel 200 used as the sensor 212. For example, in the case of the pixel array 105a having 3000 pixels in the x direction and 3000 pixels in the y direction, it is not necessary to configure the reference image with all of the data for 3000 × 3000 = 9 million pixels. The reference image may include at least pixels at the coordinates of all the sensors 212. Assume that the sensor 212 is a pixel in which the coordinate in the x direction is 0 and the coordinate in the y direction is 0, and all the pixels in every 10 pixels are specified in both the x direction and the y direction. In this case, the data constituting the reference image includes pixels whose coordinates in the x direction are 0 and whose coordinates in the y direction are 0, and every pixel in the x direction, every 2 pixels, every 5 pixels, or every 10 pixels, in the y direction. Can include pixel data for every pixel, every two pixels, every pixel, or every ten pixels.

  Using a binary image as a reference image is advantageous for reducing the file size. For example, in the pixel array 105a in which 3000 pixels are arranged in the x direction and 3000 pixels are arranged in the y direction, the data of each pixel is expressed as 1 bit of 8 bits, which is 3000 × 3000 × 1 = 9 million bytes. However, if the sensor 212 is specified at intervals of 10 pixels in the x direction and the y direction, and information of 8 pixels can be stored in 1-byte memory space with 1-bit information per pixel, 3000 × 3000 × 0.1 × 0.1 ÷ 8 = 11 KB (kilobytes). Precisely, since the pixel coordinate information is required, information regarding the interval width of the pixel and the coordinate information of one pixel are necessary. Such information may be described in the header portion of the image data. In addition, when the information included in the binarized image is not stored at every pixel interval, but stored at random, the file size is further increased because coordinate information is required for all output values. growing.

  There are two advantages of using a binary image with a small file size as a reference image. The first is that the part determination speed can be increased by reducing the file size of the reference pixel, and the second is the part. A specific algorithm can be easily created.

  In step S303, radiation 104 can be emitted from the radiation source 103. A doctor or a radiologist scans the exposure switch 101 to emit radiation from the radiation source 103 and irradiate the patient 108. The exposure switch 101 is generally a two-stage switch. When the first-stage switch is turned on, the radiation source 103 starts a preliminary operation. This preliminary operation is an operation necessary for stably emitting the radiation 104. When the second-stage switch is turned on, the radiation 104 is emitted from the radiation source 103. As shown in FIG. 5, when the first switch of the exposure switch 101 is turned on, information indicating that the radiation source 103 has entered a preliminary operation includes information on the monitoring unit 106b, the signal processing unit 106a, and the radiation detection unit. 105.

  The reading unit 105b of the radiation detection unit 105 causes the pixel 200 including the sensor 212 to start accumulating charges in response to the first-stage switch of the exposure switch 101 being turned on. Thereafter, when the second-stage switch of the exposure switch 101 is turned on and the radiation 104 is irradiated from the radiation source 103, the reading unit 105b of the radiation detection unit 105 performs the reading operation of the signal detected by the sensor 212. Start.

  In step S304, the signal processing unit 106a of the information processing unit 106 acquires a signal detected by the sensor 212, that is, AEC data. FIG. 8 shows a reading operation of a signal (signal detected by the sensor 212) corresponding to the electric charge accumulated in the sensor 212 of the pixel array 105a. The reading operation is performed only for the AEC sensor 212 of the pixels 200 constituting the pixel array 105a. Specifically, according to the coordinates of the sensor 212 shown in FIG. 6, the drive lines 205 in rows of multiples of k, such as k-th row, 2 × k row, 3 × k row,. Driven to active level. The potentials of the other drive lines 205 are maintained at the inactive level.

  First, a signal detected by the sensor 212 in the k-th row is read out. First, the amplifying unit 207 is reset, and then the k-th row driving line 205 is driven to an active level from the driving unit 206 to turn on the switch 203 of the k-th row sensor 212. When the switch 203 is turned on, the charge accumulated in the conversion element 202 is transferred to the amplifying unit 207. Thereafter, a signal converted from an electric charge to an analog voltage value (D1, D2, D3...) Is sampled and held by the amplification unit 207 by a sample and hold circuit (not shown). The signals detected by the sensor 212 in the k-th row are sequentially transmitted to the ADC 209 by the multiplexer 208, and the digital voltage values (D′ 1, D′ 2) from the analog voltage values (D1, D2, D3...). , D′ 3... Since the multiplexer 208 only needs to output the signal of the sensor 212, only the column in which the sensor 212 exists is selected. Referring to FIG. 6, since the sensor 212 exists for each f column, the multiplexer 208 sequentially selects the f-th column, the second × f-column, the third × f-column,.

  The signals (AEC data) read in this way are sequentially stored in the memory 211. Here, the memory 211 stores a signal read from the sensor 212 (a signal detected by the sensor 212) in association with the coordinate information (position information) of the sensor 212. As a specific example, about one sensor 212, about 2 bytes for each of the position information in the x direction and the y direction, and about 2 bytes for a signal read from the sensor 212 (however, the resolution of the ADC is low). If there are more than 16 bits, a total of about 6 bytes of memory space is used. After the reading of the k-th row is completed, the 2 × k-th row, the 3 × k-th row,... Are sequentially read and stored in the memory 211 together with the position information of the sensor 212.

  In step S305, the part used for AEC is recognized. When the AEC data (signal value detected by the sensor 212) read from the sensor 212 is stored in the memory 211, the signal processing unit 106a displays the signal accumulated in the memory 211 and coordinate information associated therewith. Are copied to the memory 106e. Next, as shown in FIG. 9, the signal processing unit 106a sorts the values of the signals replicated in the memory 106e in ascending order, and associates the signal values with the signal values in another area of the memory 106e. Stores paired coordinate information.

  Here, when the AEC data is 5000, the x-direction coordinate of the sensor 212 is 150, the y-direction coordinate is 300, and the first memory address of the storage destination is 001, it is expressed as (5000, 150, 300, 0x0001). . 0x means that the memory address is expressed in hexadecimal.

As an example, the information stored in the memory 106e is
(5000, 150, 300, 0x0000),
(6000, 1500, 300, 0x0006),
(5500, 2850, 300, 0x000C),
(5800, 150, 2700, 0x0012),
(6060, 1500, 2700, 0x0018),
(4800, 2850, 2700, 0x001E)
It is assumed that there are six pieces of information. Here, the signal value can be expressed by 2 bytes, the coordinates are also expressed by 2 bytes, and a memory space of 6 bytes in total is used. Since 6 bytes are used for one sensor 212, the memory address is increased by 6 per sensor 212. When these six pieces of information are arranged in ascending order of signal values and stored in another memory space,
(4800, 2850, 2700, 0x1000),
(5000, 150, 300, 0x1006),
(5500, 2850, 300, 0x100C),
(5800, 150, 2700, 0x1012),
(6000, 1500, 300, 0x1018),
(6060, 1500, 2700, 0x101E)
The storage order is as follows. This operation is performed on the signals and coordinate information obtained from all the sensors 212.

  By the way, it is expected that the signal values of the plurality of sensors 212 for one part are substantially equal to each other. For example, in the case of the lung field, the signal values are substantially equal to each other in the right lung field and the left lung field. That is, as illustrated in FIG. 10, if a plurality of adjacent AEC data in a series of AEC data sorted according to signal values and stored in the memory 106e is extracted, AEC data for a specific part of the subject is extracted. Can be obtained. Therefore, by comparing the AEC data stored in the memory 106e with the reference image illustrated in FIG. 7B, it is possible to specify which part the AEC data represents. Therefore, this means that AEC data corresponding to the site to be examined can be specified. Thereby, the exposure can be controlled with high accuracy according to the region to be inspected with high accuracy.

  Further, as illustrated in FIG. 11, the number of sensors 212 in each of the plurality of classes is obtained by equally dividing the AEC data sorted in the order of the signal values and stored in the memory 106 e into a plurality of classes. Can be equal to each other. Since the AEC data for each of the classes (region (t), region (k), region (a)) illustrated in FIG. 11 is composed of a set of pairs of signal values and coordinates, Can be treated as The AEC data of each class illustrated in FIG. 11 is generated so as to correspond to each of the plurality of classes by dividing the signals detected by the plurality of sensors 212 into a plurality of classes based on the signal values. It can be handled as an image. In other words, the signal processing unit 106a generates a plurality of images so as to correspond to the plurality of classes by dividing the signals detected by the plurality of sensors 212 into a plurality of classes based on the signal values. Can do. Here, in the generation of each image, a signal having a signal value other than 0 among the signals detected by the plurality of sensors 212 is set as a black pixel, and a signal value of 0 among the signals detected by the plurality of sensors 212 is used. The signal can be a white pixel.

  FIG. 13 shows a plurality of classes a to t by dividing signals detected by the plurality of sensors 212 at the time of photographing the chest shown in FIG. 12A into a plurality of classes a to t based on the signal values. The example which produced | generated several images (FIG. 13 (a)-(t)) corresponding to each is shown. The classes a, b, c, d... T are signal levels of 0% -5%, 5-10%, 10-15%, 15-20%, and so on.・ It is a class of 95% -100%. FIG. 13A shows a binary image in which the signal value belonging to the class a is a black pixel and the others are white pixels. The image shown in FIG. 13A is referred to as a class a image. FIG. 13B shows a binary image in which the signal value belonging to the class b is a black pixel and the others are white pixels. The image shown in FIG. 13B is referred to as a class a image. Similarly, in FIGS. 13C to 13T, binary images are shown with the signal values belonging to the classes c to t as black pixels and the other as white pixels. FIGS. 13A to 13T show an example in which the sensor 212 is selected every 10 pixels from the plurality of pixels 200 constituting the pixel array 105a in each of the x direction and the y direction.

  As illustrated in FIG. 11, data obtained by sorting the signals detected by the sensor 212 in order of the magnitude of the signal values is advantageous for creating a histogram. FIG. 15 illustrates a histogram of AEC data (signal detected by the sensor 212). In this histogram, there are a blank area, a non-irradiation area, and a boundary area. Here, the blank area is an area where radiation enters without passing through the subject in the imaging area constituted by the pixel array 105a. The non-irradiation area is an area that is not irradiated with radiation among the imaging area constituted by the pixel array 105a. The elementary boundary area is an area between the missing area and the subject area.

  FIG. 13 (t) and FIG. 13 (s) show an image of the blank area. FIG. 13 (r) shows an image of a boundary region (here, a region corresponding to the skin part) between the unexposed region and the subject region, and this image is an image of a region having a considerably high transmittance. FIG. 13 (q) shows an image of a region excluding the ribs in the lung field. FIG. 13 (n) to FIG. 13 (p) show images of a region corresponding to a lung field portion including a rib portion. FIG. 13 (f) to FIG. 13 (c) show images corresponding to the boundary region between the lung field portion and other parts. FIG. 13A and FIG. 13B show images of the mediastinum. As described above, a specific part (for example, lung field) can be specified by dividing the signals detected by the plurality of sensors 212 into a plurality of classes.

  FIG. 14 shows a plurality of classes a by dividing the signals detected by the plurality of sensors 212 during imaging of the knee joint portion shown in FIG. 12B into a plurality of classes a to t based on the signal values. The example which produced | generated several images (FIG. 14 (a)-(t)) each corresponding to -t is shown. Similarly to FIG. 13, the classes a, b, c, d... T have signal values of 0% -5%, 5% -10%, 10% -15%, 15%- 20% class ... 95% -100% class. FIG. 14A shows a binary image in which the signal value belonging to the class a is a black pixel and the others are white pixels. The image shown in FIG. 14A is referred to as a class a image. FIG. 14B shows a binary image in which the signal value belonging to the class b is a black pixel and the others are white pixels. The image shown in FIG. 14B is referred to as a class a image. Similarly, in FIGS. 14C to 14T, binary images are shown in which the signal values belonging to the classes c to t are black pixels and the others are white pixels. FIGS. 14A to 14T show an example in which the sensor 212 is selected every 10 pixels in the x direction and the y direction from the plurality of pixels 200 constituting the pixel array 105a. FIG. 14 (r) to FIG. 14 (t) show images of the blank area. FIG. 14 (o) to FIG. 14 (q) show images of the boundary area between the subject area and the blank area. FIG. 14 (n) and FIG. 14 (g) to FIG. 14 (k) show images of bone parts. FIG. 14 (l) and FIG. 14 (m) show images of the knee joint. FIG. 14 also shows that a specific part (for example, knee joint) can be specified by dividing the signals detected by the plurality of sensors 212 into a plurality of classes.

  Further, comparing FIG. 13 (t) with FIG. 13 (s), in FIG. 13 (t), the blank regions are dense on the upper side, but in FIG. 13 (s), the blank region is on the lower side. Are dense. This is because the radiation 104 emitted from the radiation source 103 has a spatial distribution, and the signal values are different even in the same blank region. Such a spatial distribution of radiation causes a decrease in the accuracy of the conventional AEC. If the radiation 104 is uniform, there should be an untouched region equally in both FIG. 13 (t) and FIG. 13 (s). Further, when attention is paid to FIG. 13 (r), the lung field portion is slightly drawn, but the dominant region is a boundary region between the subject region and the blank region. In the conventional method, there is a spatial distribution of the radiation, and the region where the signal value is the second largest after the background region is the boundary region between the subject region and the background region. It is difficult to monitor the radiation dose with high accuracy.

  The comparison unit 106c selects one of the plurality of images based on the similarity between each of at least some of the plurality of images stored in the memory 106e and the reference image illustrated in FIG. 7B. One image is selected as the monitoring image. The monitoring sensor determination method will be described with reference to FIG. In FIG. 16, a memory space in which AEC data sorted according to signal values (in order of signal values) is stored is a memory space A. The memory space A is divided into 20 areas, for example. This is equivalent to dividing the AEC data into 20 classes according to the signal values. Further, the comparison unit 106c uses the AEC data and coordinate information (X coordinate and Y coordinate) of each divided area as an image (divided) where the coordinates where the signal value exists are black pixels and the other coordinates are white pixels. The image is compared with the reference image. Then, as a result of the comparison, the comparison unit 106c determines, as a monitoring sensor for AEC, the sensor 212 that has detected a signal constituting a class image having the highest similarity to the reference image.

  The reference image need only be comparable to the images of each class, and need not be a binary image. The number of divisions (that is, the number of classes) of the memory space A does not have to be 20, and may be 10, 30, 40, for example. Further, the division need not be equal division. Further, after selecting one area from the plurality of divided areas, the selected area is further divided into a plurality of small areas, and one small area is selected from the plurality of small areas. The division and selection may be performed multiple times.

  Hereinafter, with reference to FIG. 17, the memory space A is divided into 20 areas (classes), and one area from the 20 areas (classes) is divided using the reference image shown in FIG. An example of determination will be described. First, the reference image illustrated in FIG. 17B is written in the memory space B of the memory 106e. Information to be written is a signal of a pixel having coordinates in the x direction and coordinates in the y direction equal to those of the AEC sensor 212 among the pixels (black pixel and white pixel) constituting the reference image. Value, x-direction coordinates, and y-direction coordinates. The pixels constituting the reference image include pixels having the same coordinates as all the AEC sensors 212. The signal value of the reference image is composed of 1-bit information per pixel. In addition, when the x-direction and y-direction coordinates of the pixels constituting the reference image are periodic values, the coordinate information itself may not be directly included in the reference image data. However, when writing to the memory 106e, the signal value and the coordinate information can be written in pairs. The determination value as the comparison result is stored in the memory space C of the memory 106e. In FIG. 17, AEC data (memory space A), reference image data (memory space B) sorted according to the magnitude of the signal value, x-direction coordinates, y-direction coordinates, and determination values (memory space) of the comparison result. All of C) are represented by 2 bytes.

  The storage order of the coordinate information stored in the memory space C is the same as that of the memory space A. In the memory space A, (250, 320), (230, 1240), (1570, 780), as the in-memory address increases every 6 bytes, such as (0x100,000), (0x100006), (0x10000C). .. The coordinates are stored. Even in the memory space C, the coordinates (250, 320), (230, 1240), (1570, 780),... Is stored.

  When the reference image data is stored in the memory space B, the comparison unit 106 c searches the memory space B for coordinate information that matches the coordinates of the data stored in the memory space A. When the matching coordinate information is obtained, the comparison unit 106c examines a signal value associated with the coordinate information in the memory space B, determines a determination value (comparison result) based on the signal value, Corresponding to the same coordinate information in the memory space C, it is stored as a judgment value. Here, if the signal value in the memory space B is 1, the determination value is 1, and if the signal value is 0, the determination value is 0. That the signal value of the coordinate to be compared in the memory space B is 1 indicates that the signal value of the coordinate of the AEC data stored in the memory space A and the signal of the coordinate in the reference image stored in the memory space B Means that the value matches. On the other hand, if the signal value of the comparison target coordinate in the memory space B is 0, the signal value of the coordinate of the AEC data stored in the memory space A and the coordinate in the reference image stored in the memory space B This means that the signal value does not match. Therefore, storing 1 as the determination value means that the signal value of the AEC data stored in the memory space A matches the signal value of the reference image. In addition, storing 0 as the determination value means that the signal value of the AEC data stored in the memory space A does not match the signal value of the reference image.

  For example, in the example shown in FIG. 17, coordinate information in which the coordinate in the x direction is 250 and the coordinate in the y direction is 320 is searched in the memory space B, and the signal value associated with the coordinate information is 0. is there. Further, 0 is stored as a determination value corresponding to coordinate information in which the coordinate in the x direction is 250 and the coordinate in the y direction is 320 in the memory space C. Further, since the signal value corresponding to the coordinate information in which the coordinate in the x direction is 3000 and the coordinate in the y direction is 2980 is 1 in the memory space B, 1 is stored in the memory space C as the determination value corresponding to the coordinate information. Is done.

  The comparison as described above may be performed for all of the 20 regions (a) to (t) or may be performed for a part. Specifically, the 20 areas (a) to (t) can include at least one of an image of a blank area and an image of a non-irradiated area. Since the image of the unexposed area and the non-irradiated area cannot be used for AEC, it is efficient to exclude these from the comparison target. It is also efficient to exclude the above-mentioned boundary area (class image adjacent to the class of the image in the unexposed area and class image adjacent to the class of the image in the non-irradiated area) from the comparison target. It is. Therefore, the signal processing unit 106a includes a reference image and each of at least some of the plurality of images generated by dividing the signals detected by the plurality of sensors 212 into a plurality of classes based on the signal values. It can be configured to compare similarities.

  At the coordinates where the determination value of the data stored in the memory space C is 1, the signal value of the reference image stored in the memory space B is 1. Therefore, the coordinates where the determination value of the data stored in the memory space C is 1 indicate the coordinates of the part for AEC represented by the reference image.

  Next, the comparison unit 106c calculates the sum of the determination values of the memory space C in each of the regions (classes) that have been compared. This sum is an index for evaluating the similarity between the image of each region (class) and the reference image. The comparison unit 106c determines an area (class) having the highest sum of determination values, that is, an area (class) having the highest similarity to the reference image as a part to be used for AEC, and indicates the area (class). Is transmitted to the monitoring unit 106b.

  In steps S306 and S307, the monitoring unit 106b monitors the irradiation of radiation based on the signal detected by the monitoring sensor determined in step S305. Specifically, in step S306, the monitoring unit 106b determines an evaluation value such as an average value of signal values belonging to the area (class) stored in the memory space A, which is specified according to the information transmitted from the comparison unit 106c. (A value for evaluating the irradiated radiation dose) is calculated. Here, the signal value belonging to the region (class) stored in the memory space A, specified according to the information transmitted from the comparison unit 106c, is a signal value detected by the monitoring sensor. In step S307, the monitoring unit 106b determines whether or not the evaluation value calculated in step S205 exceeds a threshold value. If it is determined that the evaluation value exceeds the threshold value, in step S308, the monitoring unit 106b determines to the radiation source control unit 102a. Order to stop radiation exposure. In response to this, the radiation source control unit 102a controls the radiation source 103 so as to stop the radiation irradiation. On the other hand, if the monitoring unit 106b determines that the evaluation value does not exceed the threshold value, the process returns to step S306.

  In the above-described embodiment, an example in which there is an unexposed region and a non-irradiated region such as an implant portion is described, but the present invention also holds when there is no unexposed region and / or non-irradiated region. For example, even when there is no blank area, AEC should not be monitored using a sensor that outputs the maximum signal value. If there is no unexposed area, the sensor that outputs the maximum signal value is considered to indicate a specific part, but in reality, the radiation source has an initial distribution, and radiation with very high output in some areas. May occur. A sensor that outputs the maximum signal value due to various causes including such a case may indicate a region different from a region targeted by a doctor or a radiologist. Similarly, when there is no non-irradiated area such as an implant part, AEC should not be monitored using a sensor in a specific range including the sensor that outputs the lowest signal value. In that case, it is difficult to specify the site by the output of the sensor that has output the lowest signal value due to the influence of the noise component, and it is difficult to make an accurate AEC determination.

  In this embodiment, since the class for AEC (sensor 212 used for AEC) is determined by comparing each class image with the reference image (that is, by pattern matching), the noise resistance is high. Therefore, a site for AEC (that is, a sensor used for AEC) can be determined with high accuracy.

  In the above embodiment, means for supplying a program to a computer, for example, a computer-readable memory medium storing the program or a transmission medium such as the Internet for transmitting the program can also be applied as an embodiment of the present invention. . The above program can also be applied as an embodiment of the present invention. The above program, recording medium, transmission medium, and program product are included in the scope of the present invention. In addition, an invention that can be easily imagined from the embodiments is also included in the scope of the present invention.

105: Radiation detection unit, 106: Signal processing unit, 200: Pixel, 212: Sensor

Claims (8)

A radiation detection unit having a plurality of sensors for detecting radiation;
A signal processing unit for processing signals detected by the plurality of sensors,
The signal processing unit generates a plurality of images respectively corresponding to the plurality of classes by dividing the signals detected by the plurality of sensors into a plurality of classes based on the signal values, and One image is selected from the plurality of images based on the similarity between at least some of the images and the reference image, and a sensor that detects a signal constituting the selected image is determined as a monitoring sensor. Monitoring radiation exposure based on a signal detected by the monitoring sensor;
A radiation detector characterized by that. In each of the plurality of images, a signal having a signal value other than 0 among the signals detected by the plurality of sensors is a black pixel, and a signal having a signal value of 0 among the signals detected by the plurality of sensors Is a binary image with white pixels, and the reference image is a binary image composed of black pixels and white pixels,
The signal processing unit evaluates the similarity based on the number of matching black pixels in each of the plurality of images and black pixels in the reference image;
The radiation detection apparatus according to claim 1. The plurality of images are at least one of an image generated by a signal detected by a sensor that is irradiated with radiation without passing through the subject and an image generated by a signal detected by a sensor that is not irradiated with radiation. Including
The at least part of the image includes an image generated by a signal detected by a sensor that is irradiated with radiation without passing through the subject, and an image generated by a signal detected by a sensor that is not irradiated with radiation. Not decided,
The radiation detection apparatus according to claim 1, wherein: The at least part of the image is detected by an image of a class adjacent to a class of images generated by a signal detected by a sensor that is irradiated with radiation without passing through the subject, and a sensor that is not irradiated with radiation. Determined not to include images of a class adjacent to the class of images generated by the signal,
The radiation detection apparatus according to claim 3. The signal processing unit selects the reference image from a plurality of reference images according to information set for capturing a radiographic image.
The radiation detection apparatus according to any one of claims 1 to 4, wherein the radiation detection apparatus is characterized in that: The signal processing unit stops radiation irradiation based on a signal detected by the monitoring sensor;
The radiation detection apparatus according to any one of claims 1 to 5, wherein the radiation detection apparatus includes: Each of the plurality of sensors is also used as a pixel for capturing a radiation image.
The radiation detection apparatus according to claim 1, wherein A radiation source that emits radiation; and
The radiation detection apparatus according to any one of claims 1 to 7,
A radiation imaging system comprising: