JP5223699B2 - Radiation detector and radiation imaging apparatus including the same - Google Patents

Description

  The present invention relates to a radiation detector for generating a two-dimensional image, which can correct a false image reflected in an image, and a radiation imaging apparatus including the radiation detector. The false image here is particularly caused by a leakage current.

  A medical institution is provided with a radiation imaging apparatus that acquires a fluoroscopic image of a subject. Such a radiographic apparatus includes a radiation source that emits radiation and a radiation detector that detects the radiation.

  A specific configuration of the radiation detector will be described. As shown in FIG. 10, the radiation detector 51 includes a surface electrode layer 52, a semiconductor layer 53, a support layer 54, and a capacitor 55. And the surface electrode layer 52, the semiconductor layer 53, and the support layer 54 are laminated | stacked in this order. The surface electrode layer 52 is electrically connected to the bias voltage supply terminal 52a. A collection electrode 54 a is embedded in the support layer 54. In the radiation detector 51, a plurality of collection electrodes 54 a are provided, and the collection electrodes 54 a are two-dimensionally arranged along the plane in which each layer 52, 53, 54 extends. The surface electrode layer 52, the semiconductor layer 53, the support layer 54, and the capacitor 55 together form an X-ray detection matrix that detects radiation. The semiconductor layer 53 corresponds to the conversion means of the present invention, and is composed of, for example, an amorphous selenium layer or a CdZnTe layer. As the conversion layer, a scintillator or the like can be employed in addition to the semiconductor layer. In this case, the light source may be converted into light once by a scintillator and then converted into a charge signal by a photodiode or the like and stored in the capacitor 55.

  The collection electrode 54 a is in contact with the semiconductor layer 53 and is electrically connected to the capacitor 55.

  The operation of the radiation detector 51 will be described. The radiation r penetrates the surface electrode layer 52 and enters the semiconductor layer 53. Here, the radiation r is converted into a carrier pair consisting of electrons and holes.

  Incidentally, a constant bias voltage is applied to the surface electrode layer 52, and the semiconductor layer 53 is in a state where a predetermined electric field is generated. That is, the carrier pair is induced by the generated electric field, and any one type of carrier is collected by the collecting electrode 54a by the collecting electrode 54a. The collected carriers are accumulated by the capacitor 55. That is, electric charges are accumulated in the capacitor 55. This accumulated amount of charge indicates the radiation irradiation intensity. As shown in FIG. 11, the capacitors 55 are two-dimensionally arranged in the same manner as the collecting electrode 54a to form a capacitor matrix.

  A specific configuration for reading the charge accumulated in the capacitor 55 will be described. As shown in FIG. 12, each capacitor 55 is provided with transistors Tr1 to Tr3 for reading accumulated charges, control electrodes G1 to G3 for controlling them, and output electrodes P1 to P3 for taking out accumulated charges of the capacitors. It has been. When the transistors Tr1 to Tr3 are turned on through the control electrodes G1 to G3, the charge accumulated in the capacitor 55 is output from the output electrode P. Therefore, no current should flow through the output electrode P when the transistors Tr1 to Tr3 are off.

  However, as shown in FIG. 13A, the leakage current L continues to flow through the output electrodes P1-2 even if the transistors Tr1-2 are turned off. Moreover, the intensity of the leak current is not constant for all the output electrodes P1 and P2. For example, in FIG. 13A, the right capacitor 55 stores more charge than the left capacitor 55. In this case, the leakage current L2 related to the right capacitor 55 is larger than the leakage current L1 related to the right side. That is, the leak current flowing through the output electrodes P1 and P2 varies depending on the amount of charge accumulated in the capacitor 55.

  In this state, when the transistors Tr1 and Tr2 are turned on, the charges accumulated in the capacitor 55 are output from the output electrodes P1 and P2, as shown in FIG. However, even in this state, the leakage currents L1-2 continue to flow toward the output electrode P as usual. That is, the total current L1 + S1 of the signal current S1 and the leakage current L1 is output from the output electrode P1, and the total current L2 + S2 of the signal current S2 and the leakage current L2 is output from the output electrode P2. As described above, the leakage currents L1 and L2 are superimposed on the currents output from the output electrodes P1 and P2, and the magnitude of the leakage currents L1 and 2 varies depending on the output electrodes P1 and P2. Therefore, when the output of each capacitor 55 is two-dimensionally arranged to generate a fluoroscopic image, unevenness due to the leakage current is reflected in the fluoroscopic image.

  Therefore, according to the conventional configuration, a measure is taken so that the unevenness of the leakage current is not reflected in the fluoroscopic image. That is, as a first process, when the transistor Tr is off [ie, in the state of FIG. 13A], the magnitude of the leakage current L is measured in advance for each output electrode P. By doing so, unevenness in the leakage current is acquired. Thereafter, as a second process, the accumulated charge is taken out to generate a two-dimensional image in which the projected image of the subject is reflected. The unevenness of the leakage current L is reflected in the fluoroscopic image, but has the same pattern as the unevenness already acquired in the first process. Therefore, the superimposed unevenness is removed by superimposing the inversion pattern of unevenness acquired in the first process on the fluoroscopic image. A radiation detector having such a configuration is described in Patent Document 1, for example.

Japanese Patent No. 3979165

However, the conventional configuration has the following problems.
That is, according to the conventional configuration, there is a problem that the reading of the capacitor 55 cannot be performed at high speed. When it is necessary to read out each capacitor 55 at a high speed, such as when a moving image is generated by combining two-dimensional images over time, it is necessary to increase the operating frequency of the radiation detector. Along with this, the operation of acquiring the leakage current unevenness is also performed at high speed. Then, when acquiring the leak current, noise accompanying the increase in clock frequency occurs. This noise is caused by, for example, electromagnetic interference between elements constituting the electric circuit of the radiation detector.

  That is, in the first process described above, even if a leak current is to be acquired from the output electrode P, a noise component is superimposed on the leak current L. In the conventional configuration, it is considered that the unevenness of the leakage current can be acquired while including this noise component, and this is superimposed on the two-dimensional image in which the fluoroscopic image of the subject is reflected. Then, the noise component is superposed on the fluoroscopic image, and eventually the noise component is superposed on the fluoroscopic image. As described above, according to the conventional configuration, it is difficult to provide an image with excellent visibility while reading a fluoroscopic image at a high speed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a radiation detector capable of obtaining a fluoroscopic image having excellent visibility while reading a fluoroscopic image at high speed, and The object is to provide a radiation imaging apparatus.

The present invention adopts the following configuration in order to achieve such an object.
That is, according to the first aspect of the present invention, each of the storage means, the conversion means for converting radiation into charges, the storage means for storing charges arranged two-dimensionally along the first direction and the second direction, and the storage means And an output electrode provided in each of the storage means and arranged two-dimensionally along the first direction and the second direction, and charges stored in each of the storage means are transferred to the output electrode. in the switching means to output to each radiation detector with and electrically connected to the charge readout electrode to each of the output electrodes arranged along a second direction, amplifies the output of the charge readout electrode the output from the amplifier and the amplifier outputs the amplified data and amplifier array formed from the AD converter for converting the digital data, the charge readout electrode by arranging the amplified data two-dimensionally Te Image generation means for generating an original image in which the leakage current unevenness and the radiation image of the subject are reflected, original image acquisition instruction means for instructing acquisition of the original image, and unevenness acquisition for acquiring the leakage current unevenness Means for instructing acquisition of unevenness of leakage current, superimposing means for superimposing unevenness of leakage current on the radiation image, operating frequency determining means for outputting operating frequencies of the amplifier array and switching means When the unevenness acquisition instructing means gives an instruction, the operating frequency determining means sets the operating frequency to be low, and when the original image acquisition instructing means gives an instruction, the operating frequency determining means sets the operating frequency to be high. It is characterized by doing.

  [Operation / Effect] The radiation detector according to the present invention includes unevenness acquisition means for acquiring unevenness of leakage current. The leakage current is a current that flows in the charge readout electrode regardless of the OFF state of the switching means. When the accumulated charge is read from the charge readout electrode, a total current of the signal current that is the flow of the accumulated charge and the leak current flows through the charge readout electrode, and this is input to the amplification means. When the outputs (amplified data) of the amplification means are two-dimensionally arranged, an original image in which a radiation image of the subject is reflected is generated. However, this original image also includes a false image (leakage current unevenness) derived from the leak current. Therefore, the present invention has a configuration in which the unevenness acquisition unit acquires unevenness in the leakage current. As a result, it is possible to know what pattern the unevenness of the leakage current appears in the original image. The radiation detector according to the present invention includes superimposing means for superimposing the leakage current unevenness on the radiographic image. Thereby, the unevenness of the leakage current is removed from the original image.

  Moreover, according to the present invention, it is possible to read out charges at high speed while faithfully acquiring the unevenness of the leakage current. In other words, the leakage current unevenness is acquired during the first time period. The first time is a long period, and unevenness in the leakage current is acquired with little noise. On the other hand, the switching means is turned on all at once during a second time period shorter than the first time. That is, the accumulated charge is read out at high speed through the charge readout electrode during the second time period (more precisely, the switching means arranged along the first direction is read out during the second time period). Therefore, the nonuniformity of the leak current superimposed on the original image is acquired with little noise and faithfully represents the pattern of the leak current appearing in the original image. That is, the leak current pattern in the original image is surely removed.

  When the arrangement of the switching means along the first direction is referred to as a “switching means array”, when the radiation detector is viewed as a whole, for example, n switching means arrays are arranged along the second direction. Will be. Since the radiation detector is configured to read out the accumulated charge for each switching means array, it takes at least a second time × n period to read out all of the storage means of the radiation detector. Become. In order to obtain the effects as described above, it is sufficient to make the first time longer than the second time, and it is not necessary to make it longer than the second time × n.

According to a second aspect of the present invention, in the radiation detector according to the first aspect, the instruction of the unevenness acquisition instruction unit is performed after the radiation is irradiated to the conversion unit.

  [Operation / Effect] According to the above-described configuration, the leakage current unevenness is acquired after the conversion means is irradiated with radiation. The leak current flowing through the charge readout electrode varies depending on the amount of charge stored in the storage means. Since the charge is accumulated in the storage means after the radiation is irradiated to the conversion means, if the unevenness of the leakage current is acquired after the radiation irradiation, the leak current pattern reflected in the original image Can know more faithfully.

According to a third aspect of the present invention, in the radiation detector according to the first or second aspect, the instruction of the unevenness acquisition instruction unit is performed before the instruction of the original image acquisition instruction unit. It is a feature.

  [Operation / Effect] According to the above-described configuration, the unevenness of the leakage current is performed before the charge is read out. In other words, the leakage current unevenness is acquired in a state where the charge is stored in the storage means. In this way, even if the leakage current changes according to the charge stored in the storage means, it is possible to obtain a pattern similar to the leakage current pattern in which the unevenness of the leakage current is reflected in the original image.

According to a fourth aspect of the present invention, in the radiation detector according to any one of the first to third aspects, the acquisition of the unevenness of the leakage current is performed every time the original image is acquired. It is a feature.

  [Operation / Effect] According to the above-described configuration, it is possible to acquire a radiographic image from which a false image is reliably removed. Each time a radiation detector detects radiation, it captures a different radioscopic image. Along with this, the pattern of leakage current superimposed on the original image also changes. According to the above-described configuration, the leakage current unevenness is updated every time the original image is acquired. Therefore, the leak current pattern reflected in the original image is more reliably removed.

A fifth aspect of the present invention is a radiographic apparatus equipped with the radiation detector according to any one of the first to fourth aspects, wherein the radiation source irradiates radiation and radiation that controls the radiation source. And a control means.

  [Operation / Effect] The above-described configuration represents that the radiation detector according to the present invention can be mounted on a radiation imaging apparatus. According to such a radiation imaging apparatus, it is possible to acquire a radiation image in which no false image is reflected.

  The radiation detector according to the present invention includes unevenness acquisition means for acquiring unevenness of leakage current. When the accumulated charge is read from the charge readout electrode, a total current of the signal current that is the flow of the accumulated charge and the leak current flows through the charge readout electrode, and this is input to the amplification means. Accordingly, the original image in which the radiation image of the subject is reflected also includes a false image (leakage current unevenness) derived from the leakage current. Therefore, the present invention has a configuration in which the unevenness acquisition unit acquires unevenness in the leakage current. Moreover, according to the present invention, it is possible to read out charges at high speed while faithfully acquiring the unevenness of the leakage current. That is, the unevenness of the leak current is acquired during the relatively long first time period. On the other hand, the switching means is turned on all at once during a second time period shorter than the first time. Therefore, the unevenness of the leak current superimposed on the original image is acquired in a state with little noise, and the pattern of the leak current in the original image is surely removed.

3 is a functional block diagram illustrating a configuration of an X-ray detector according to Embodiment 1. FIG. 3 is a schematic diagram illustrating the configuration of an X-ray detection matrix according to Embodiment 1. FIG. FIG. 3 is a schematic diagram illustrating an amplifier according to the first embodiment. 3 is a flowchart for explaining the operation of the X-ray detector according to the first embodiment. FIG. 3 is a schematic diagram for explaining the operation of the X-ray detector according to the first embodiment. FIG. 3 is a schematic diagram for explaining the operation of the X-ray detector according to the first embodiment. FIG. 3 is a schematic diagram for explaining the operation of the X-ray detector according to the first embodiment. 6 is a functional block diagram illustrating calibration of the X-ray imaging apparatus according to Embodiment 2. FIG. It is a functional block diagram explaining the structure of the X-ray detector which concerns on one modification of this invention. It is sectional drawing explaining a conventional structure. It is a top view explaining the conventional structure. It is an equivalent circuit diagram explaining a conventional configuration. It is an equivalent circuit diagram explaining a conventional configuration.

  Hereinafter, the radiation detector according to the configuration of the first embodiment will be described with reference to the drawings. The X-ray described below is an example of radiation in the present invention.

<Description of overall configuration>
First, the configuration of the first embodiment will be described. As shown in FIG. 1, the X-ray detector 1 according to the first embodiment includes an X-ray detection matrix 2 for detecting radiation, and a gate drive 3 connected to the X-ray detection matrix 2. The X-ray detector 1 includes an amplifier array 4 connected to the X-ray detection matrix 2 and an amplifier array control unit 14 that controls the amplifier array 4. The X-ray detection matrix 2 is the same as the conventional configuration. The amplifier array corresponds to the amplification means of the present invention. The amplifier array control unit corresponds to the amplification control means of the present invention.

  The X-ray detector 1 includes a map acquisition instruction unit 11, an original image acquisition instruction unit 12, an image generation unit 21 that generates an image from the output of the amplifier array 4, and a map generation unit 23 that generates a leakage current map M1. A superimposing unit 22 that performs image processing for superimposing an image and a map. The operating frequency determination unit 15 determines the operating frequency of the gate drive 3 and the amplifier array 4, and the significance of providing this will be described later. The map acquisition instruction unit corresponds to the unevenness acquisition instruction unit of the present invention, and the image generation unit corresponds to the original image generation unit of the present invention. The map generation unit corresponds to the unevenness acquisition unit of the present invention, and the overlay unit corresponds to the overlay unit of the present invention. The original image acquisition instruction unit corresponds to the original image acquisition instruction means of the present invention.

  In addition, the main acquisition part 25 which controls the map acquisition instruction | indication part 11, the original image acquisition instruction | indication part 12, the amplifier array control part 14, the image generation part 21, and the superimposition part 22 is provided. The main control unit 25 is constituted by a CPU, and realizes each unit by executing various programs. Further, each of the above-described units may be divided and executed by an arithmetic device that takes charge of them.

  A specific configuration of the X-ray detection matrix 2 will be described. As shown in FIG. 2, the X-ray detection matrix 2 includes a first region D in which capacitors D11 to D36 are two-dimensionally arranged and a second region E in which capacitors E11 to E36 are two-dimensionally arranged. And have. In the first region D, each of the capacitors D11 to D16 arranged in the horizontal direction in FIG. 2 is connected to the control electrode G1, and the control electrodes G1 to G3 are provided for each row of the capacitors. The amplifier array 4 is arranged in the horizontal direction, and the amplifiers A1 to A6 constituting the amplifier array 4 are connected to each of the output electrodes P of the capacitors that are at the same position in the vertical direction. For example, the amplifier A1 is connected to the output electrode P included in the capacitors D11, D21, and D31. That is, each of the output electrodes P arranged in the vertical direction is connected to the charge readout electrode Q1, and the charge readout electrode Q1 is electrically connected to the amplifier A1. The vertical direction corresponds to the first direction of the present invention, and the horizontal direction corresponds to the second direction of the present invention. Further, the transistor Tr (see FIG. 12 for a specific configuration) provided in each of the capacitors D11 to E36 corresponds to the switching means of the present invention, and the capacitor corresponds to the storage means of the present invention.

  The gate drive 3 is configured by arranging control elements for controlling transistors in a line in the vertical direction. The control element corresponds to the switching control means of the present invention.

  The second area E has the same configuration as the first area D. That is, for the second region E, each of the capacitors E11 to E16 arranged in the horizontal direction in FIG. 2 is connected to the control electrode H1, and the control electrodes H1 to H3 are provided for each row of the capacitors. The amplifier array 4 is arranged in the horizontal direction, and the amplifiers B1 to B6 constituting the amplifier array 4 are connected to each of the output electrodes P of the capacitor that are at the same position in the vertical direction. For example, the amplifier B1 is connected to the output electrode P included in the capacitors E11, E21, E31.

  When X-rays are irradiated to the X-ray detector 1, charges are accumulated in the capacitors D11 to E36. An operation of reading this out and generating an X-ray fluoroscopic image will be described. First, the gate drive 3 turns on the control electrode G1, and the charges accumulated in the capacitors D11 to D16 collectively pass through the charge finding electrodes Q1 to Q6 and are input to each of the amplifiers A1 to A6. Amplified data that is the output of this amplifier is sent to the image generation unit 21. When the reading related to the capacitors D11 to D16 is completed, the gate drive 3 turns on the control electrode G2, and reads the charge of the capacitor connected thereto. In this way, the gate drive 3 turns on the control electrodes G1 to G3 one after another while shifting the time, and reads the charge of the capacitor for each row. The image generation unit 21 generates the original image p0 by two-dimensionally arranging the input amplified data. Such an operation is the same in the second region E.

  Further, the gate drive 3 turns on the two control electrodes simultaneously. That is, simultaneously with turning on the control electrode G1 in the first region D, the control electrode H1 in the second region E is turned on. In this manner, the X-ray detection matrix 2 is divided into upper and lower half areas, and the X-ray fluoroscopic image reflected in each area is read out simultaneously, so that the gate drive 3 can control all the control electrodes G, H. The time to finish turning on is reduced to about half.

  The amplifier B1 has an input terminal for inputting a control signal (see FIG. 2). The amplifier B1 is configured to be turned on / off according to the input of this control signal. That is, when the current is input from the charge readout electrode R1 when the amplifier B1 is in the on state, the amplifier B1 outputs an amplified signal to the image generation unit 21. Conversely, when the amplifier B1 is in the off state, the charge readout is performed. Even if a current is input from the electrode R1, the amplifier B1 does not output an amplified signal to the image generation unit 21. In FIG. 2, the input terminal is illustrated as being provided with only the amplifier B <b> 1, but in reality, it is provided in all of the amplifiers A <b> 1 to B <b> 6 included in the X-ray detector 1.

  The amplifier array control unit 14 suspends and resumes the function of the amplifier by adjusting the supply of the control signal of each amplifier. In FIG. 2, for convenience, the amplifier array control unit 14 is connected to only one of the amplifiers. Actually, the amplifier array control unit 14 is connected to all the amplifiers constituting the amplifier array 4. Thus, the amplifiers A1 to B6 can be turned on / off in accordance with the input of the control signal.

  A specific configuration of the amplifiers A1 to B6 will be described. As shown in FIG. 3A, the amplifier A according to the first embodiment includes an amplifier a1 that amplifies a signal and an AD converter a2 that converts an output of the amplifier a1 into digital data. The output of the AD converter a2 is an amplified signal. The first terminal n1 of the amplifier A is an input terminal for the amplifier A connected to the charge readout electrode P, and the third terminal n3 is an output terminal for the amplifier A connected to the image generation unit 21. The second terminal n2 is a terminal for controlling the amplifier A connected to the amplifier array control unit 14. In the amplifier array controller 14, the second terminal n2 sends a control signal to the amplifier A. Specifically, this is a sequence in which a reset signal s1 for resetting the amplifier A to an initial state and an output instruction signal s2 for instructing output of an amplified signal are paired. The amplifier A performs reset and output according to the control signal. This is the ON state of the amplifier A.

  On the other hand, as shown in FIG. 3B, when the amplifier array control unit 14 does not send out either the reset signal s1 or the output instruction signal s2, the amplifier A is in spite of the input of the first terminal n1. No output is made to the third terminal n3. This is the off state of the amplifier A.

  Note that when the AD converter a2 is operated at high speed, noise is superimposed on the control signal. This is the main component of noise that hinders the acquisition of X-ray fluoroscopic images in the first embodiment.

  In FIG. 2, for convenience, the X-ray detection matrix 2 has capacitors arranged in a 6 × 6 matrix. In the actual X-ray detector 1, capacitors are arranged in a matrix of 1,024 × 1,024, for example.

<Description of operation>
The operation of the X-ray detector 1 having such a configuration will be described. FIG. 4 is a flowchart for explaining the operation of the X-ray detector according to the first embodiment. First, an X-ray beam is emitted to the X-ray detector 1. Thus, the X-ray detector 1 receives X-rays (step S1). This X-ray beam captures a fluoroscopic image of the subject. X-rays incident on the X-ray detector 1 are converted into electric charges and accumulated in the capacitors D11 to E36.

  Next, the leakage current map M1 is instructed in a state where charges are accumulated in the capacitors D11 to E36 (step S2). The map acquisition instructing unit 11 operates the operating frequency determining unit 15 to set the operating frequency to a low frequency for acquiring the leakage current. This frequency is lower than the frequency for charge reading described later. At this time, the accumulated charge is not read out. The operating frequency determination unit corresponds to the operating frequency determination means of the present invention.

  The amplifier array control unit 14 turns on each of the amplifiers A <b> 1 to B <b> 6 constituting the amplifier array 4 in accordance with an instruction from the map acquisition instruction unit 11. Then, the amplified data output from the amplifier array 4 is transmitted to the map generation unit 23. This amplified data is obtained by amplifying the leakage current L flowing through the charge readout electrodes Q1 to R6. Based on this, the map generation unit 23 generates a leakage current map M1 indicating the unevenness of the leakage current L in the X-ray detection matrix 2.

  Next, the original image acquisition instruction unit 12 issues an instruction to acquire the original image in which the fluoroscopic image of the subject and the unevenness of the leakage current L are reflected (step S3). The original image acquisition instruction unit 12 operates the operating frequency determination unit 15 to set the operating frequency to a high frequency for image reading. This frequency is higher than the above-described frequency for acquiring the leakage current.

  The gate drive 3 turns on the control electrodes G and H one after another based on the high operating frequency described above, and the charge accumulated in the capacitors D11 to E36 flows through the charge read electrodes Q1 to R6 and is input to the amplifier array 4. The This flow of charges is called a signal current S. The amplifiers constituting the amplifier array 4 amplify the signal current S and send the amplified data to the image generation unit 21. The amplification data at this time is obtained by amplifying the total current L + S obtained by summing the leakage current L and the signal current S. Based on this, the image generation unit 21 generates the original image p0 in which the unevenness of the leakage current L is superimposed on the X-ray fluoroscopic image captured by the X-ray detection matrix 2.

  The original image p0 is sent to the superposition unit 22. When obtaining the original image p0, the superposition unit 22 obtains the leakage current map M1 from the map generation unit 23. The superposition unit 22 superimposes the reverse pattern of the leak current map M1 on the original image p0 (step S4). As a result, the unevenness of the leakage current L superimposed on the original image p0 is cancelled.

  An operation performed in the superposition unit 22 will be described. It is assumed that the original image p0 output from the image generation unit 21 includes an elliptical perspective image as shown in FIG. This elliptical image is a photograph of a subject that easily transmits X-rays. In other words, the capacitor located in the elliptical region in the X-ray detection matrix 2 accumulates more charge than the surrounding capacitors. As the accumulated charge increases, the leakage current L also increases as described with reference to FIG. Then, in the original image p <b> 0, a band-shaped bright area appears on the oval image. This is a false image due to the unevenness of the leakage current L.

  The reason why the unevenness of the leakage current L appears in a strip shape in the original image p0 will be described. The charges accumulated in the capacitors D11 to E36 are different from each other. That is, the leakage current L flowing through the output electrode P varies depending on each capacitor. However, for example, in the case of the capacitors D11, D21, and D31 in FIG. 2, the leakage currents L output from the output electrodes P are summed and output to the single charge readout electrode Q1. This is because the output electrode P connected to the capacitors D11, D21, D31 is connected in parallel to the charge readout electrode Q1. That is, there is no difference in the magnitude of the leakage current L in the capacitors D11, D21, and D31. Rather, the magnitude of the leakage current L varies between the capacitors D11 to D16. This is because the leakage currents L related to the capacitors D11 to D16 are output from the independent charge readout electrodes Q1 to Q6, respectively. Therefore, when the x direction of the original image p0 is the amplifier arrangement direction, the magnitude of the leakage current L is constant in the y direction of the original image p0 and varies in the x direction. In this way, a strip-like false image extending in the y direction appears in the original image p0. The distribution of the leakage current L is as shown by d0 shown in FIG. That is, the leakage current L is large at the central portion of the original image p0.

  When the map acquisition instruction unit 11 reads the distribution of the leakage current L in a state where the operating frequency is high, noise is superimposed on the distribution of the leakage current L as shown by d1 in FIG. When the leakage current map M1 is generated in this state and is superimposed on the original image p0, the band-like false image that appeared in the original image p0 is erased as in the image p1 shown in FIG. However, the noise component superimposed on the leak current map M1 is transferred to the image p1, and it is reflected as a linear false image. Such a linear false image tends to be noticed by a person who has seen the image, and becomes an obstacle to visually recognizing the image p1.

  According to the configuration of the first embodiment, it is possible to suppress the appearance of a linear false image in an image. That is, according to the first embodiment, the distribution of the leakage current L is read with the operating frequency being low. The distribution of the leakage current L thus obtained does not include a noise component as indicated by d2 in FIG. 7, and is similar to the distribution d0 of the leakage current L in FIG. When the leakage current map M1 is generated using this and superimposed on the original image p0, an image in which a linear false image does not appear can be obtained like the image p2 shown in FIG. In addition, the strip-shaped false image that appeared in the original image p0 is also erased.

  Note that the X-ray detection matrix 2 has a first region D and a second region E, which are independent of control, as shown in FIG. Therefore, how the false image appears in the original image p0 is not necessarily the same in the upper half and the lower half of the original image p0. However, in FIGS. 5, 6, and 7, the X-ray detection matrix 2 is described as having only the first region D for simplicity.

  As described above, the X-ray detector 1 according to the first embodiment includes the map generation unit 23 that acquires unevenness of the leakage current L. The leak current L is a current that flows through the charge readout electrodes Q and R regardless of the off state of the transistor Tr (see FIG. 2). When accumulated charges are read out from the charge readout electrodes Q and R, a total current L + S of the signal current S, which is the flow of the accumulated charges, and the leakage current L flows through the charge readout electrodes Q and R, which flows to the amplifier array 4. Entered. When the outputs (amplified data) of the amplifier array 4 are arranged two-dimensionally, an original image p0 in which an X-ray image of the subject is reflected is generated. However, the original image p0 also includes a false image (unevenness of the leakage current L) derived from the leakage current L (see FIG. 6). Therefore, in the first embodiment, the map generation unit 23 is configured to acquire the unevenness of the leakage current L. Thereby, it is possible to know what pattern the unevenness of the leakage current L appears in the original image p0. The X-ray detector 1 according to the first embodiment includes an overlay unit 22 that overlays the unevenness of the leakage current L on the X-ray image. Thereby, the unevenness of the leakage current L is removed from the original image p0.

  Moreover, according to the first embodiment, it is possible to read out charges at high speed while faithfully acquiring the unevenness of the leakage current L. That is, the unevenness of the leakage current L is acquired during the first time period. The first time is a sufficiently long period (specifically, about 1.7 ms to 2 ms) so that noise is not generated when acquiring the leakage current L unevenness. Is acquired. On the other hand, each of the transistors Tr is turned on at once during a second time period shorter than the first time. That is, the accumulated charge is read out at high speed through the charge readout electrodes Q and R during the second time period (more precisely, the transistors Tr arranged along the first direction are collectively in the second time period. Therefore, the nonuniformity of the leakage current L superimposed on the original image p0 is acquired with little noise and faithfully represents the pattern of the leakage current L appearing in the original image p0. That is, the pattern of the leakage current L in the original image p0 is surely removed.

  In addition, according to Example 1, the nonuniformity of the leakage current L can be acquired more reliably. That is, in order to acquire the unevenness of the leakage current L, it is necessary to output only this from the amplifier array 4, and it is not convenient if the signal current S flows through the charge readout electrodes Q and R during the first time period. . According to the above-described configuration, the signal current S does not flow through the charge readout electrodes Q and R while the map acquisition instruction unit 11 gives an instruction. Therefore, according to the above-described configuration, it is ensured that the unevenness of the leakage current L is reliably acquired.

  According to the first embodiment, the unevenness of the leakage current L is acquired after the semiconductor layer is irradiated with the X-rays. The leak current L flowing through the charge readout electrodes Q and R varies depending on the amount of charge accumulated in the capacitors D11 to E36. Since the charges are accumulated in the capacitors D11 to E36 after the X-rays are irradiated on the semiconductor layer, if the unevenness of the leakage current L is acquired after the X-ray irradiation, it is reflected in the original image p0. It is possible to know the pattern of the leak current L more faithfully.

  According to the first embodiment, the unevenness of the leakage current L is performed before the charge is read out. That is, the unevenness of the leakage current L is acquired in a state where the charges are stored in the capacitors D11 to E36. Even if the leakage current L changes according to the charges accumulated in the capacitors D11 to E36, it is possible to obtain a pattern similar to the pattern of the leakage current L in which the unevenness of the leakage current L is reflected in the original image p0.

  Further, the amplifier array 4 that operates according to the first time according to the first embodiment and the gate drive 3 that operates according to the second time operate at different operating frequencies. Moreover, the operating frequency is changed by the operating frequency determination unit 15 in an integrated manner. Therefore, according to the above-described configuration, the control of the X-ray detector 1 can be simplified.

  Next, a radiation imaging apparatus according to the second embodiment will be described. This radiation imaging apparatus includes the X-ray detector 1 according to the first embodiment.

  First, the configuration of the X-ray imaging apparatus 31 according to the second embodiment will be described. FIG. 8 is a functional block diagram illustrating the configuration of the X-ray imaging apparatus 31 according to the second embodiment. As shown in FIG. 8, the X-ray imaging apparatus 31 according to the second embodiment includes a top plate 32 on which the subject M is placed, and a pulsed X-ray beam provided on the top plate 32. An X-ray tube 33 for irradiation, an X-ray detector 10 for detecting X-rays transmitted through the subject M, and an X-ray grid 35 for removing scattered X-rays incident on the X-ray detector 10 are provided. . Further, the configuration of the second embodiment includes an X-ray tube controller 36 that controls the tube voltage, tube current, and time pulse width of the X-ray beam of the X-ray tube 33, and an X-ray tube that moves the X-ray tube 33. A moving mechanism 37 and an X-ray tube movement control unit 38 for controlling the moving mechanism 37 are provided. The X-ray imaging apparatus 31 according to the second embodiment includes a detector moving mechanism 39 that moves the X-ray detector 10 and a detector movement control unit 34 that controls the detector moving mechanism 39.

  In FIG. 8, the image generation unit 21 and the superposition unit 22 described in the first embodiment are shown again. The X-ray tube corresponds to the radiation source of the present invention.

  The X-ray imaging apparatus 31 includes an operation console 43 that receives an operator's instruction and a display unit 44 that displays an X-ray fluoroscopic image or a moving image.

  Furthermore, the X-ray imaging apparatus 31 includes an X-ray tube control unit 36, an X-ray tube movement control unit 38, an image generation unit 21, and a main control unit 45 that comprehensively controls the superposition unit 22. The main control unit 45 is constituted by a CPU and realizes each unit by executing various programs. Further, each of the above-described units may be divided and executed by an arithmetic device that takes charge of them. The main control unit 25 in the first embodiment is integrated with the main control unit 45 in the second embodiment.

  The X-ray tube 33 is irradiated with X-rays toward the subject at a predetermined tube current, tube voltage, and irradiation time in accordance with the control of the X-ray tube control unit 36.

  The operation of the X-ray imaging apparatus 31 having such a configuration will be described. First, the subject M is placed on the top board 32. The operator controls the X-ray tube 33 through the X-ray tube control unit 36 to irradiate the subject M with X-rays. X-rays that have passed through the subject M are detected by the X-ray detector 10, detection data (amplified data) is sent to the image generation unit 21, and a leak current map M1 and a fluoroscopic image of the subject M are captured. An original image p0 is generated. Then, the superimposing unit 22 generates an X-ray fluoroscopic image in which the unevenness of the leakage current L is not reflected as shown in FIG. The X-ray fluoroscopic image is displayed on the display unit 44, and the acquisition of the X-ray fluoroscopic image by the X-ray imaging apparatus 31 according to the second embodiment is finished.

  The leakage current map M1 is generated every time X-ray fluoroscopic imaging is performed (that is, every time X-rays are irradiated). If the image reflected in the fluoroscopic image is different, the distribution pattern of the leakage current L also changes. Therefore, the generation of the leakage current map M1 is executed every time an X-ray fluoroscopic image is acquired in order to surely remove the unevenness of the leakage current L.

  As described above, according to the configuration of the second embodiment, the X-ray detector 1 according to the first embodiment can be mounted on the X-ray imaging apparatus 31. According to such an X-ray imaging apparatus 31, it is possible to acquire an X-ray image in which no false image is reflected.

  The present invention is not limited to the above-described configuration and can be modified as follows.

  (1) In the configuration of the first embodiment, the map generation unit 23 is provided. However, the present invention is not limited to this configuration. As shown in FIG. 9, a leak current distribution acquisition unit 24 and a distribution data acquisition instruction unit 11 a may be provided instead of the map generation unit 23 and the map acquisition instruction unit 11. According to this modification, the same configuration as that of the first embodiment can be realized without creating the leakage current map M1. The leak current distribution acquisition unit 24 receives the amplified data obtained by amplifying the leak current L from the amplifier array 4, and generates a leak current array in which the intensity of the leak current L is one-dimensionally arranged based on the amplified data. The leakage current array represents unevenness of the leakage current L in the X-ray detection matrix 2 as in the leakage current map M1. The superimposing unit 22 refers to the leakage current arrangement and erases the unevenness of the leakage current L reflected in the original image p0 output from the image generation unit 21. With this configuration, the present modification has the same effect as that of the first embodiment without generating the leakage current map M1. The distribution data acquisition instruction unit 11a instructs the leakage current distribution acquisition unit 24 to start acquisition of distribution data, and the details of the operation are the same as those of the map acquisition instruction unit 11. In FIG. 9, each part related to the gate drive 3 is omitted.

  (2) Each embodiment described above is a medical device, but the present invention can also be applied to industrial and nuclear devices.

  (3) The X-rays referred to in the above embodiments are an example of radiation in the present invention. Therefore, the present invention can be applied to radiation other than X-rays.

D11 to E36 Capacitor (accumulating means)
P output electrode Q, R charge readout electrode Tr transistor (switching means)
1,10 X-ray detector (radiation detector)
3 Gate drive (switching control means)
4 Amplifier array (amplification means)
11 Map acquisition instruction section (unevenness acquisition instruction means)
12 Original image acquisition instruction unit (original image acquisition instruction means)
14 Amplifier array control unit (amplification control means)
15 Operating frequency determining unit (operating frequency determining means)
21 Image generator (original image generator)
22 Superposition part (superposition means)
23 Map generator (unevenness acquisition means)
31 X-ray equipment (radiography equipment)
33 X-ray tube (radiation source)
36 X-ray tube control unit (radiation source control unit)
53 Semiconductor layer (conversion means)

Claims (5)

Conversion means for converting radiation into charges; storage means for storing charges arranged two-dimensionally in the first direction and the second direction; output electrodes provided in each of the storage means; Switching that is provided in each of the storage means and is arranged two-dimensionally along the first direction and the second direction, and outputs the charge stored in each of the storage means to each of the output electrodes Means and a radiation detector electrically connected to each of the output electrodes arranged along the second direction, wherein the output of the charge readout electrode is amplified to obtain amplified data and amplifier array configured to output from the output to the amplifier and the amplifier from the AD converter for converting the digital data, the charge readout electrode by arranging the amplified data two-dimensionally An original image generating means for generating an original image in which a leakage current unevenness and a radiation image of a subject are reflected, an original image acquisition instruction means for instructing acquisition of the original image, and acquiring the leakage current unevenness The operating frequency of the unevenness acquisition means, the unevenness acquisition instruction means for instructing acquisition of the unevenness of the leakage current, the superimposing means for superimposing the unevenness of the leak current on the radiation image, the amplifier array, and the switching means Operating frequency determining means for outputting, when the unevenness acquisition instructing means gives an instruction, the operating frequency determining means has a low operating frequency, and when the original image acquisition instructing means gives an instruction, the operating frequency The radiation detector according to claim 1, wherein the determining means has a high operating frequency. The radiation detector according to claim 1 .
The radiation detector is characterized in that the instruction of the unevenness acquisition instruction unit is performed after radiation is irradiated on the conversion unit. In the radiation detector in any one of Claim 1 or Claim 2 ,
The radiation detector according to claim 1, wherein the instruction of the unevenness acquisition instruction means is performed before the instruction of the original image acquisition instruction means. The radiation detector according to any one of claims 1 to 3 ,
The radiation detector is characterized in that the acquisition of the leakage current unevenness is performed every time the original image is acquired. A radiographic apparatus equipped with the radiation detector according to any one of claims 1 to 4 , comprising a radiation source for irradiating radiation and a radiation control means for controlling the radiation source. Radiography equipment.

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