JP5725188B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus used in the medical field, the industrial field, the nuclear field, and the like.

  An imaging device that obtains an image based on charge information will be described taking an example in which X-rays are incident and converted into charge information. The imaging apparatus includes an X-ray sensitive X-ray conversion layer, and the X-ray conversion layer converts into carriers (charge information) by the incidence of X-rays. As the X-ray conversion layer, the “direct conversion type” that directly converts X-rays into charge information and the X-rays converted into light by a phosphor (scintillator) such as CsI are formed of a light-sensitive material. It is roughly classified into “indirect conversion type” in which the light is converted into charge information by the conversion layer. In the direct conversion type, an amorphous amorphous selenium (a-Se) film has been conventionally used as the X-ray conversion layer. However, in recent years, CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride) is used. ) Is used.

  In addition, the imaging device includes a circuit that accumulates and reads out carriers converted by the X-ray conversion layer. As shown in FIG. 6, this circuit is composed of a plurality of gate lines G and data lines D arranged two-dimensionally, and also turns on a capacitor Ca for accumulating carriers and a carrier accumulated in the capacitor Ca. Thin film transistors (TFTs) Tr that are read out by switching between / OFF are arranged in a two-dimensional manner. The gate line G controls ON / OFF switching of each thin film transistor Tr and is electrically connected to the gate of each thin film transistor Tr. The data line D is electrically connected to the reading side of the thin film transistor Tr.

  Each detection element is constituted by each capacitor Ca, each thin film transistor Tr, and the like. By selecting the gate line G, the detection element electrically connected to the selected gate line G is driven to generate a carrier. Is read out. Therefore, the gate line G serves as a drive line for driving the detection element. Before driving the gate line G, X-rays to be detected are made incident with a bias voltage applied to a voltage application electrode (not shown in FIG. 6) (see, for example, Patent Document 1).

JP 2000-349269 A

  However, in the case of the conventional example having such a configuration, a constant value is used for the bias voltage except that the bias voltage is varied according to the X-ray intensity (incident dose) as in Patent Document 1. ing. Actually, it has been found that when the bias voltage is a constant value, a higher dynamic range or spatial resolution cannot be obtained.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an imaging device capable of obtaining desired detection film characteristics.

  As a result of earnest research to solve the above problems, the inventors have obtained the following knowledge.

  In other words, in order to solve the above problem, a constant value for the bias voltage is conventionally used regardless of the detection film characteristics represented by the dynamic range and spatial resolution described above. Based on the assumption that there is a certain correlation between the characteristics and the bias voltage, the inventors have found that the bias voltage is set and controlled in accordance with the detection film characteristics to be set. FIG. 4A is a graph schematically showing the correlation between the dynamic range for each temperature and the bias voltage, and FIG. 4B schematically shows the correlation between the spatial resolution and the bias voltage. It is a graph. As is clear from each graph of FIG. 4, since it has been found that there is a certain correlation between the detection film characteristics and the bias voltage, if the bias voltage is set and controlled in accordance with the detection film characteristics to be set, As a result, it has been found that the detection film characteristic to be set becomes a desired detection film characteristic when applied with a bias voltage whose setting is controlled.

The present invention based on such knowledge has the following configuration.
In other words, an imaging apparatus according to the present invention is an imaging apparatus that includes a detector configured with a two-dimensional matrix array of detection elements that detect radiation , and obtains an image based on data detected by the detector. And a conversion layer that converts the radiation into carriers as a detection film, a voltage application electrode that applies a bias voltage, and a patterned insulation substrate, the insulation substrate, the conversion layer, and the voltage application electrode. The imaging device is further sequentially stacked, and the imaging device is further stored in a correlation storage unit that stores a correlation between a detection film characteristic of the detector and a bias voltage applied to the voltage application electrode , and the correlation storage unit. The bias voltage is set and controlled based on the correlation between the detection film characteristic and the bias voltage and the detection film characteristic to be set. It is characterized in that and a that the bias voltage setting control means.

[Operation / Effect] An imaging apparatus according to the present invention includes a conversion layer for converting radiation into a carrier as a detection film, a voltage application electrode for applying a bias voltage, and a patterned insulating substrate. The conversion layer and the voltage application electrode are sequentially laminated. According to such an imaging apparatus , the correlation storage unit that stores the correlation between the detection film characteristic and the bias voltage is provided, the correlation between the detection film characteristic and the bias voltage stored in the correlation storage unit, and to be set Bias voltage setting control means for setting and controlling the bias voltage based on the detection film characteristics is provided. By providing the correlation storage means and the bias voltage setting control means in this way, the bias is determined according to the detection film characteristics to be set using the correlation between the detection film characteristics and the bias voltage stored in the correlation storage means. If the voltage setting control means controls the setting of the bias voltage, the detection film characteristic to be set becomes a desired detection film characteristic when the bias voltage is applied with the setting-controlled bias voltage. As a result, desired detection film characteristics can be obtained.

  In the case where the above-described detection film characteristic also depends on the temperature at which the detector is used, in the imaging device according to the present invention, the correlation storage means further includes the correlation between the detection film characteristic and the bias voltage. The bias voltage setting control means preferably stores and controls the bias voltage based on the temperature at which the detector is used and the correlation with the temperature is stored. For example, the optimum bias voltage can be set and controlled for each of a plurality of environmental temperatures (for example, −5 ° C. to + 5 ° C. of the standard set temperature) where the detector is assumed to be used so that the setting can be changed according to the usage environment. To do.

  When the detection film characteristic also depends on the temperature, examples of the detection film characteristic include a leak current and a dynamic range related to the leak current. Therefore, it is preferable that the correlation storage means further stores the correlation with the temperature in addition to the correlation between the dynamic range or the leakage current and the bias voltage.

  In these imaging devices described above, an example of a detection film in the detector is a semiconductor layer formed of CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride).

An imaging apparatus according to the present invention includes a conversion layer that converts radiation into carriers as a detection film, and includes a voltage application electrode that applies a bias voltage and a patterned insulating substrate, and includes the insulating substrate, the conversion layer, and the voltage. The application electrodes are sequentially stacked. According to such an imaging apparatus , the correlation storage means for storing the correlation between the detection film characteristic and the bias voltage, the correlation between the detection film characteristic and the bias voltage stored in the correlation storage means, and the detection film to be set By providing bias voltage setting control means for setting and controlling the bias voltage based on the characteristics, desired detection film characteristics can be obtained.

1 is a schematic block diagram of an X-ray imaging apparatus according to an embodiment. 1 is a schematic cross-sectional view around an X-ray conversion layer of an X-ray imaging apparatus. (A) is a table of the correlation between the dynamic range for each temperature and the bias voltage, and (b) is a table of the correlation between the spatial resolution and the bias voltage. (A) is a graph schematically showing the correlation between the dynamic range for each temperature and the bias voltage, and (b) is a graph schematically showing the correlation between the spatial resolution and the bias voltage. It is the graph which showed roughly the correlation of the leakage current for every temperature and bias voltage which concern on a modification. It is a schematic block diagram of the conventional X-ray imaging apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic block diagram of the X-ray imaging apparatus according to the embodiment, and FIG. 2 is a schematic cross-sectional view around the X-ray conversion layer of the X-ray imaging apparatus. In the present embodiment, X-rays will be described as an example of incident radiation, and an X-ray imaging apparatus will be described as an example of an imaging apparatus.

  The X-ray imaging apparatus according to the present embodiment performs imaging by irradiating a subject with X-rays. Specifically, an X-ray image transmitted through the subject is projected on an X-ray conversion layer (CdTe or CdZnTe in this embodiment), and carriers (charge information) proportional to the density of the image are generated in the layer. Is converted into a carrier.

  As shown in FIG. 1, the X-ray imaging apparatus accumulates and reads out carriers converted by a gate drive circuit 1 that selects a gate line G, which will be described later, and an X-ray conversion layer 23 (see FIG. 2). A detection element circuit 2 that detects X-rays, a charge-voltage conversion amplifier 3 that amplifies the carrier read out by the detection element circuit 2 into a voltage, and the charge-voltage conversion amplifier 3 An A / D converter 4 for converting a voltage analog value into a digital value, and an image processing unit 5 for obtaining an image by performing signal processing on the voltage value converted into a digital value by the A / D converter 4; The controller 6 that controls the circuits 1 and 2, the charge / voltage conversion amplifier 3, the A / D converter 4, the image processing unit 5, the memory unit 7 and the monitor 9 described later, and the processed image are stored. Memory unit 7 and input An input unit 8 which performs a constant, and a monitor 9 for displaying the processed images. In this specification, information such as a carrier and an image is image information related to the image. The X-ray conversion layer 23 corresponds to the detection film in the present invention, and the detection element circuit 2 corresponds to the detector in the present invention.

  The gate drive circuit 1 is electrically connected to a plurality of gate lines G. By applying a voltage from the gate driving circuit 1 to each gate line G, a thin film transistor (TFT) Tr described later is turned on to release reading of carriers accumulated in a capacitor Ca described later, and the voltage applied to each gate line G Is stopped (the voltage is set to −10 V), and the thin film transistor Tr is turned off to block carrier reading. Note that the thin film transistor Tr is turned off by applying a voltage to each gate line G to cut off carrier reading and stopping the voltage to each gate line G to turn on and release carrier reading. It may be configured.

  The detection element circuit 2 includes a plurality of gate lines G and data lines D arranged in a two-dimensional manner, and switches the capacitor Ca that accumulates carriers and the carriers accumulated in the capacitor Ca to ON / OFF. The thin film transistors Tr to be read out are arranged in a two-dimensional manner. The gate line G controls ON / OFF switching of each thin film transistor Tr and is electrically connected to the gate of each thin film transistor Tr. The data line D is electrically connected to the reading side of the thin film transistor Tr.

  For convenience of explanation, in this embodiment, it is assumed that 10 × 10 thin film transistors Tr and capacitors Ca are formed in a vertical and horizontal two-dimensional matrix arrangement. That is, the gate line G is composed of ten gate lines G1 to G10, and the data line D is composed of ten data lines D1 to D10. The gate lines G1 to G10 are respectively connected to the gates of ten thin film transistors Tr arranged in parallel in the X direction in FIG. 1, and the data lines D1 to D10 are arranged in parallel in the Y direction in FIG. Each of the ten thin film transistors Tr is connected to the reading side. A capacitor Ca is electrically connected to the side opposite to the reading side of the thin film transistor Tr, and the number of the thin film transistor Tr and the capacitor Ca corresponds one to one.

  In the detection element circuit 2, as shown in FIG. 2, the detection elements DU are patterned on the insulating substrate 21 in a two-dimensional matrix arrangement. That is, the gate lines G1 to G10 and the data lines D1 to D10 described above are wired on the surface of the insulating substrate 21 by using a thin film forming technique by various vacuum deposition methods and a pattern technique by a photolithography method. Ca, the carrier collection electrode 22, the X-ray conversion layer 23, and the voltage application electrode 24 are laminated in order. The detection element DU corresponds to the detection element in the present invention.

  The X-ray conversion layer 23 is formed of an X-ray sensitive semiconductor thick film (detection film). In this embodiment, the semiconductor layer is formed of CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride). It is formed with. The X-ray conversion layer 23 converts X-ray information into carriers as charge information by the incidence of X-rays. The X-ray conversion layer 23 is not limited to CdTe or CdZnTe as long as it is an X-ray sensitive material that generates carriers by the incidence of X radiation. In addition, when imaging is performed by injecting radiation other than X-rays (such as γ-rays), a radiation-sensitive material that generates carriers by the incidence of radiation may be used instead of the X-ray conversion layer 23. Good. Further, when imaging is performed with light incident, instead of the X-ray conversion layer 23, a photosensitive material that generates carriers by the incidence of light may be used.

  The carrier collection electrode 22 is electrically connected to the capacitor Ca, collects the carrier converted by the X-ray conversion layer 23 and accumulates it in the capacitor Ca. Similarly to the thin film transistor Tr and the capacitor Ca, a large number (10 × 10 in this embodiment) of the carrier collection electrodes 22 are formed in a vertical / horizontal two-dimensional matrix arrangement. The carrier collecting electrode 22, the capacitor Ca, and the thin film transistor Tr are separately formed as each detecting element DU. Further, the voltage application electrode 24 is formed over the entire surface as a common electrode of all the detection elements DU.

  In this way, the insulating substrate 21, the X-ray conversion layer 23, and the voltage application electrode 24 in which the detection elements DU and the like are patterned in a two-dimensional matrix arrangement are sequentially stacked. The detection element circuit 2 including these X-ray conversion layers 23 is also called a flat panel X-ray detector (FPD).

  In this embodiment, in addition, a temperature sensor 10 for measuring the temperature of the X-ray conversion layer 23 is provided. The measurement result by the temperature sensor 10 is sent to the controller 6. By providing the temperature sensor 10, the temperature at which the detection element circuit 2 is used, and hence the environmental temperature, is measured.

  In order to measure the temperature of the X-ray conversion layer 23, as shown in FIG. 2, the temperature sensor 10 is provided on the voltage application electrode 24 at an end portion outside the effective detection area (not shown). Specifically, the temperature sensor 10 may be embedded in the voltage application electrode 24 as shown in FIG. 2A, or the temperature sensor 10 is laminated on the voltage application electrode 24 as shown in FIG. May be. Note that the temperature sensor may be embedded in the X-ray conversion layer 23 or the temperature sensor 10 may be stacked on the X-ray conversion layer 23.

  The image processing unit 5 obtains an image by performing various signal processing on the voltage value converted into a digital value by the A / D converter 4. The controller 6 comprehensively controls the circuits 1 and 2, the charge / voltage conversion amplifier 3, the A / D converter 4, the image processing unit 5, a memory unit 7 and a monitor 9 described later, and in this embodiment, a detection film characteristic described later. And a function of setting and controlling the bias voltage (function of bias voltage setting control) based on the correlation between the bias voltage and the detection film characteristic to be set. The image processing unit 5 and the controller 6 are configured by a combination of a central processing unit (CPU) and a programmable logic device (FPGA). The controller 6 corresponds to the bias voltage setting control means in this invention.

  The memory unit 7 writes and stores image information and the like, and the image information and the like are read from the memory unit 7 in response to a read command from the controller 6. The memory unit 7 includes a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Note that a RAM is used for writing image information. For example, when the controller 6 executes the control sequence by reading a program related to the control sequence, a ROM is used exclusively for reading the program related to the control sequence. In the present embodiment, a program relating to a control sequence for setting and controlling the bias voltage is stored in the memory unit 7 based on the above-described correlation and the detection film characteristics to be set, and the control sequence is stored in the controller 6 by reading the program. Let it run.

  In addition, the memory unit 7 includes a correlation memory unit 7a that stores the above-described correlation in advance. The correlation memory unit 7a corresponds to the correlation storage means in this invention.

  The input unit 8 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, or the like, or an input means such as a button, a switch, or a lever. When input is set in the input unit 8, input setting data is sent to the controller 6, and based on the input setting data, the circuits 1, 2, the charge / voltage conversion amplifier 3, the A / D converter 4, the image processing unit 5 and the memory unit 7. And the monitor 9 are controlled.

Subsequently, a control sequence of the X-ray imaging apparatus of the present embodiment will be described. X-rays to be detected are incident on the voltage application electrode 24 with a high voltage (for example, several tens of volts to several hundreds of volts) bias voltage _VA applied thereto. Note that the bias voltage V _A is not a fixed value but is selected and controlled by the controller 6 as will be apparent from the description below.

  Carriers are generated in the X-ray conversion layer 23 by the incidence of X-rays, and the carriers are accumulated in the capacitor Ca through the carrier collection electrode 22 as charge information. A target gate line G is selected by a scanning signal (that is, a gate driving signal) for reading a signal (here, carrier) of the gate driving circuit 1. In the present embodiment, description will be made assuming that gate lines G1, G2, G3,..., G9, G10 are selected one by one in order. The scanning signal for reading signals from the gate driving circuit 1 is a signal for applying a voltage (for example, about 15 V) to the gate line G.

  A target gate line G is selected from the gate drive circuit 1, and each thin film transistor Tr connected to the selected gate line G is selected and designated. A voltage is applied to the gate of the thin film transistor Tr selected and designated by this selection designation to turn on. Carriers accumulated from the capacitors Ca connected to the selected and designated thin film transistors Tr are read out to the data line D via the thin film transistors Tr that have been designated and designated to be turned on. That is, the detection element DU related to the selected gate line G is selected and designated, and carriers accumulated in the capacitor Ca of the selected and designated detection element DU are read out to the data line D.

  Specifically, the charge-voltage conversion amplifier 3 connected to the data line D is reset, and the thin film transistor Tr is turned on (that is, the gate is turned on), whereby the carrier is read out to the data line D. Then, it is amplified in a state converted into a voltage by the charge-voltage conversion amplifier 3.

  That is, the address (address) designation of each detection element DU is performed based on the scanning signal for signal reading from the gate drive circuit 1 and the selection of the charge voltage conversion amplifier 3 connected to the data line D.

  First, the gate line G1 is selected from the gate drive circuit 1, the detection element DU related to the selected gate line G1 is selected and specified, and the carriers accumulated in the capacitor Ca of the selected and specified detection element DU are all stored. Data line D is read out simultaneously, and after sample hold, data lines D1 to D10 are converted into digital values by A / D converter 4 in this order. Next, the gate line G2 is selected from the gate drive circuit 1, and the detection element DU related to the selected gate line G2 is selected and specified in the same procedure, and is stored in the capacitor Ca of the selected detection element DU. All the data lines D are read out simultaneously, and after sample-holding, the data lines D1 to D10 are converted into digital values by the A / D converter 4 in this order. Similarly, the remaining gate lines G are sequentially selected to read out a two-dimensional carrier.

  Each read carrier is amplified in a state of being converted into a voltage by the charge-voltage conversion amplifier 3 and converted from an analog value to a digital value by the A / D converter 4. Based on the voltage value converted into the digital value, the image processing unit 5 performs various signal processing to obtain a two-dimensional image. The obtained two-dimensional image and image information represented by a carrier are written and stored in the memory unit 7 via the controller 6 and are read from the memory unit 7 via the controller 6 as necessary. Further, the image information is displayed on the monitor 9 via the controller 6.

  Next, the correlation between the detection film characteristic and the bias voltage and the function of the bias voltage setting control will be described with reference to FIGS. 3A is a table showing the correlation between the dynamic range for each temperature and the bias voltage, and FIG. 3B is a table showing the correlation between the spatial resolution and the bias voltage. FIG. 4 is a graph schematically showing the correlation between the dynamic range and the bias voltage for each temperature, and FIG. 4B is a graph schematically showing the correlation between the spatial resolution and the bias voltage.

  Correlates the correlation between the detection film characteristics in the detection element circuit 2 (see FIGS. 1 and 2) and the bias voltage applied to the detection element circuit 2 (voltage application electrode 24 (see FIG. 2)). The data is written and stored in the related memory unit 7a (see FIG. 1). The detection film characteristics are not particularly limited as long as the characteristics depend on the X-ray conversion layer 23 (see FIG. 2) corresponding to the detection film, and in this embodiment, the dynamic range (DR: dynamic range) and spatial resolution ( An explanation will be given by taking MTF: Modulation Transfer Function) as an example.

  In this embodiment, when an X-ray imaging apparatus including the detection element circuit 2 is shipped, the optimum value of the bias voltage to be applied is associated with the dynamic range and spatial resolution of an image acquired by each apparatus. The correlation between the dynamic range and the bias voltage is written and stored in the correlation memory unit 7a, and the correlation between the spatial resolution and the bias voltage is written and stored in the correlation memory unit 7a. When writing and storing in the correlation memory unit 7a, it may be stored in the table format shown in FIG. 3, for example, or may be stored as an approximate expression program shown in FIG.

In the case of storing in the table format shown in FIG. 3, when the correlation between the dynamic range for each temperature and the bias voltage is written and stored in the correlation memory unit 7a, the correlation is performed as shown in FIG. Specifically, as shown in FIG. 3 (a), associates the bias voltage _{V 1} and the dynamic range _{DR 11} at ambient temperatures _{T 1,} and a bias voltage _{V 2} and the dynamic range _{DR 12} at ambient temperatures _{T 1} correspondence, following similar manner by associating at ambient temperatures T ₁ and the bias voltage and the dynamic range, respectively, stores a correlation between the dynamic range and the bias voltage for each environmental temperature T ₁ of a table format. Similarly, as shown in FIG. 3 (a), associates the bias voltage _{V 1} and the dynamic range _{DR 21} at environmental temperature _{T 2,} associates the bias voltage _{V 2} and the dynamic range _{DR 22} at environmental temperature _{T 2} , following a similar manner by associating the environmental temperature T ₂ and the bias voltage and the dynamic range, respectively, it stores a correlation between the dynamic range and the bias voltage for each environmental temperature T ₂ in a table format. Similarly, as shown in FIG. 3 (a), associates the bias voltage _{V 1} and the dynamic range _{DR 31} at ambient temperature _{T 3,} associates the bias voltage _{V 2} and the dynamic range _{DR 32} at ambient temperature _{T 3} , following a similar manner by associating at ambient temperature T ₃ and the bias voltage and the dynamic range, respectively, stores a correlation between the dynamic range and the bias voltage for each environmental temperature T ₃ in the form of a table.

On the other hand, when storing in the table format shown in FIG. 3, the correlation between the spatial resolution and the bias voltage is written and stored in the correlation memory unit 7a as shown in FIG. 3B. Specifically, as shown in FIG. 3B, the bias voltage V ₁ and the spatial resolution MTF ₁₁ are associated, the bias voltage V ₂ and the spatial resolution MTF ₁₂ are associated, and so on. Is correlated with each spatial resolution, and the correlation between the spatial resolution and the bias voltage is stored in a table format.

When the bias voltage is set and controlled with reference to the detection film characteristics (dynamic range and spatial resolution) other than the table format shown in FIG. 3, the bias voltage is set and controlled with reference to the closest detection film characteristics. To do. Alternatively, the bias voltage may be interpolated from the correlation stored in the table format. For example, when the correlation is expressed by a linear relationship as shown in FIG. 4, the bias voltage is set and controlled from the dynamic range (DR ₁₁ + DR ₁₂ ) / 2 of the intermediate value between the dynamic ranges DR ₁₁ and DR _12. In this case, an intermediate value (V ₁ + V ₂ ) / 2 between the bias voltages V ₁ and V ₂ corresponding to the dynamic ranges DR ₁₁ and DR ₁₂ is obtained as a bias voltage, and the obtained bias voltage (V _{It is} only necessary to perform setting control to a value of ₁ + V ₂ ) / 2.

  Since the table format shown in FIG. 3 is a set of discrete values, it may be approximated by a function as shown in FIG. 4, and the program of the approximate expression may be written and stored in the correlation memory unit 7a. By storing the approximate expression program in this way, it is possible to set and control the bias voltage with a continuous value. The approximate expression may be obtained by using the least square method. Further, the approximation formula is not limited to the linear relationship shown in FIG. 4, and may be a polynomial of a quadratic formula or higher, and partially approximated by an exponential function, a trigonometric function, a logarithmic function, or the like. May be.

As shown in FIG. 4A, when the bias voltage V increases, the dynamic range DR decreases. However, as shown in FIG. 4B, the spatial resolution MTF increases, and an image with good spatial resolution is captured and acquired. can do. Further, when the environmental temperature is T ₁ <T ₂ <T ₃ , as shown in FIG. 4A, the environmental temperature is relatively high as compared with the case where the environmental temperature is relatively low (eg, T ₁ ). (For example, T ₃ ), the leak current decreases at the same bias voltage V, and the dynamic range DR increases.

As described above, the higher the bias voltage V, the higher the spatial resolution MTF and the better the spatial resolution characteristics, but considering the value of the dynamic range DR that should be kept to a minimum (DR _{bottom in} FIG. 4A). , a plurality of environmental temperature T _1, T 2, _T 3 _(e.g., -5 ℃ ~ + 5 ℃ standard set temperature) optimum bias voltage in each use of X-ray imaging device and the detection device circuit 2 is assumed (e.g. In FIG. 4A, by calculating V ₁ , V ₂ , V ₃ ), the bias voltage can be changed according to the use environment. It should be noted that the bias voltage _{V 1,} V 2, _{V 3} and the bias voltages _V 1 in FIG. _4, V 2, _{V 3} in FIG. 3 is a separate value.

In this way, using the correlation shown in FIG. 3 or FIG. 4, the controller 6 (see FIG. 4) according to the detection film characteristic to be set (for example, DR _bottom in FIG. 4A) at the time of use after shipment. 1) set and control the bias voltage. When DR _bottom is set as the value of the dynamic range DR to be kept to the minimum, the value of V ₁ is selected as the bias voltage and controlled at the environmental temperature T ₁ as shown in FIG. Similarly, to set control values for V ₂ when the environmental temperature T ₂ is selected as a bias voltage. Similarly, when the environmental temperature is T ₃ , the value of V ₃ is selected as the bias voltage and set and controlled.

When the environmental temperature is unknown, the temperature of the X-ray conversion layer 23 may be measured by the temperature sensor 10 (see FIG. 2). When the environmental temperature is known, the value of the environmental temperature may be input by the input unit 8 (see FIG. 1). In this way, if the controller 6 controls the setting of the bias voltage, the dynamic range DR _bottom to be set becomes the desired dynamic range when the bias voltage is applied with the setting controlled. The method for setting and controlling the bias voltage in accordance with the spatial resolution to be set is the same as the method for setting and controlling the bias voltage in accordance with the dynamic range, and thus the description thereof is omitted.

  The X-ray imaging apparatus according to the present embodiment described above includes the correlation memory unit 7a that stores the correlation between the detection film characteristics (dynamic range and spatial resolution in the present embodiment) and the bias voltage, and includes a correlation memory. Bias voltage for setting and controlling the bias voltage based on the correlation between the detection film characteristic (dynamic range and spatial resolution) stored in the unit 7a and the bias voltage and the detection film characteristic (dynamic range and spatial resolution) to be set The controller 6 has a setting control function. By providing the correlation memory unit 7a and the bias voltage setting control function in this way, the correlation between the detection film characteristics (dynamic range and spatial resolution) stored in the correlation memory unit 7a and the bias voltage is used. If the bias voltage setting control function controls the bias voltage according to the detection film characteristics to be set (dynamic range and spatial resolution), when the bias voltage is applied with the setting controlled bias, the detection film characteristics to be set (dynamic Range and spatial resolution) are the desired detection film properties (dynamic range and spatial resolution). As a result, desired detection film characteristics (dynamic range and spatial resolution) can be obtained.

  In the case where the detection film characteristic (for example, dynamic range) also depends on the temperature (for example, environmental temperature) at which the detector (detection element circuit 2) is used as in the present embodiment, preferably, the correlation memory unit In addition to the correlation between the detection film characteristic (dynamic range) and the bias voltage, 7a further stores the correlation with the temperature as shown in FIG. 3A or FIG. Based on the temperature at which the detection element circuit 2) is used, the bias voltage setting control function sets and controls the bias voltage. For example, the optimum bias voltage is set and controlled for each of a plurality of environmental temperatures (for example, the standard set temperature of −5 ° C. to + 5 ° C.) where the detector (detection element circuit 2) is assumed to be used. The setting can be changed accordingly.

  In the present embodiment, the case where the detection film characteristic also depends on the temperature is described by taking a dynamic range related to the leakage current as an example. Therefore, in the present embodiment, preferably, the correlation memory unit 7a is further connected to the temperature as shown in FIG. 3A or FIG. 4A in addition to the correlation between the dynamic range and the bias voltage. The correlation is memorized.

  In this embodiment, a semiconductor layer formed of CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride) as a detection film (X-ray conversion layer 23 in this embodiment) in the detector (detection element circuit 2). Is taken as an example.

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

  (1) In the above-described embodiment, the X-ray imaging apparatus as shown in FIG. 1 has been described as an example. However, the present invention is also applicable to an X-ray fluoroscopic imaging apparatus disposed on a C-type arm, for example. May be. The present invention may also be applied to an X-ray CT apparatus.

  (2) In the embodiment described above, the present invention provides a “direct conversion type” detection element circuit in which radiation represented by incident X-rays is directly converted into charge information by an X-ray conversion layer (conversion layer). Although applied, an indirect conversion type detection element circuit that converts incident radiation into light by a conversion layer such as a scintillator and converts the light into charge information by a conversion layer formed of a photosensitive material The present invention may be applied.

  (3) In the above-described embodiment, the detection element circuit for detecting X-rays has been described as an example. However, the present invention uses a radioisotope (RI) as in an ECT (Emission Computed Tomography) apparatus. The detection element circuit is not particularly limited as long as it is a detection element circuit for detecting radiation, as exemplified by a detection element circuit for detecting γ-rays emitted from an administered subject. Similarly, the present invention is not particularly limited as long as it is an apparatus that performs imaging by incidence of radiation, as exemplified by the above-described ECT apparatus.

  (4) In the above-described embodiments, radiation imaging represented by X-rays and the like has been described as an example, but the present invention can also be applied to an apparatus that performs imaging by incidence of light.

  (5) In the above-described embodiment, the voltage application electrode 24 has a structure as shown in FIG. 2, but the present invention is also applied to a structure having a graphite substrate that also serves as a support substrate and a voltage application electrode, for example. be able to.

(6) In the above-described embodiments, the dynamic range and the spatial resolution have been described as examples of the detection film characteristics. However, the characteristics are not particularly limited as long as the characteristics depend on the detection film as described above. For example, in addition to these, the detection film characteristics may be leakage current, sensitivity (related to charge), response (in time), and the like. In particular, when the detection film characteristic is a leakage current, as in the dynamic range, in addition to the correlation between the leakage current and the bias voltage, as shown in FIG. Good. In the case of FIG. 5, the leakage current L increases as the bias voltage V increases. Further, compared with a case where the environmental temperature is relatively low (for example, T ₁ ), the leakage current L increases at the same bias voltage V when the environmental temperature is relatively high (for example, T ₃ ).

  (7) In the above-described embodiment, the correlation between the detection film characteristic and the bias voltage is written and stored in the correlation memory unit 7a at the time of shipment. However, the correlation between the detection film characteristic and the bias voltage is used at the time of use after shipment. The correlation memory unit 7a may be configured to be rewritable to the correlation at the time of use after shipment. Therefore, even when the correlation changes over time, it is possible to cope with it.

2 ... Detection element circuit 6 ... Controller 7a ... Correlation memory unit 23 ... X-ray conversion layer DU ... Detection element T ... Temperature V ... Bias voltage DR ... Dynamic range MTF ... Spatial resolution L ... Leakage current

Claims (11)

An imaging apparatus comprising a detector configured with a two-dimensional matrix array of detection elements for detecting radiation , and obtaining an image based on data detected by the detector,
With a conversion layer that converts the radiation into carriers as a detection film,
A voltage application electrode for applying a bias voltage;
Patterned insulating substrate and
With
The insulating substrate, the conversion layer, and the voltage application electrode are sequentially laminated,
The imaging device further includes correlation storage means for storing a correlation between a detection film characteristic in the detector and a bias voltage applied to the voltage application electrode ;
Bias voltage setting control means for setting and controlling the bias voltage based on the correlation between the detection film characteristic stored in the correlation storage means and the bias voltage, and the detection film characteristic to be set. An imaging apparatus characterized by that. The imaging device according to claim 1,
In addition to the correlation between the detection film characteristic and the bias voltage, the correlation storage unit further stores a correlation with temperature,
2. The imaging apparatus according to claim 1, wherein the bias voltage setting control means sets and controls the bias voltage based on a temperature at which the detector is used. The imaging device according to claim 2,
The detection film characteristic is a dynamic range,
In addition to the correlation between the dynamic range and the bias voltage, the correlation storage unit further stores a correlation with temperature. The imaging device according to claim 2,
The detection film characteristic is a leakage current,
In addition to the correlation between the leakage current and the bias voltage, the correlation storage unit further stores a correlation with temperature. The imaging apparatus according to any one of claims 2 to 4 ,
A temperature sensor for measuring the temperature of the conversion layer;
An image pickup apparatus that measures the temperature at which the detector is used by providing the temperature sensor. The imaging apparatus according to claim 5 ,
An image pickup apparatus, wherein the temperature sensor is provided on the voltage application electrode or the conversion layer . The imaging device according to claim 1,
The correlation storage unit stores each bias voltage and each detection film characteristic in association with each other in a table format. The imaging apparatus according to claim 7 ,
An image pickup apparatus that interpolates a bias voltage from a correlation stored in a table format when the bias voltage is set and controlled with reference to a detection film characteristic other than the table format. The imaging device according to claim 1,
An imaging apparatus, wherein the correlation storage unit stores an approximate expression program by approximating the bias voltage and the detection film characteristic with a function. In the imaging device in any one of Claims 1-9 ,
The detection film characteristic is spatial resolution,
The correlation storage unit stores a correlation between the spatial resolution and the bias voltage. In the imaging device in any one of Claims 1-10 ,
An imaging device, wherein the detection film in the detector is a semiconductor layer formed of CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride).

Images