WO2010109539A1 - Image pickup apparatus - Google Patents
Image pickup apparatus Download PDFInfo
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- WO2010109539A1 WO2010109539A1 PCT/JP2009/001388 JP2009001388W WO2010109539A1 WO 2010109539 A1 WO2010109539 A1 WO 2010109539A1 JP 2009001388 W JP2009001388 W JP 2009001388W WO 2010109539 A1 WO2010109539 A1 WO 2010109539A1
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- Prior art keywords
- approximate expression
- conversion layer
- dark signal
- temperature
- signal amount
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- 238000006243 chemical reaction Methods 0.000 claims abstract description 107
- 238000003384 imaging method Methods 0.000 claims description 48
- 230000005855 radiation Effects 0.000 claims description 17
- 238000012937 correction Methods 0.000 claims description 8
- 238000009529 body temperature measurement Methods 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 abstract description 29
- 238000001514 detection method Methods 0.000 description 26
- 239000010409 thin film Substances 0.000 description 26
- 239000003990 capacitor Substances 0.000 description 25
- 230000006870 function Effects 0.000 description 21
- 239000000969 carrier Substances 0.000 description 17
- 238000012545 processing Methods 0.000 description 13
- 238000000034 method Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 5
- 229910004613 CdTe Inorganic materials 0.000 description 4
- 239000010408 film Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 3
- 238000012886 linear function Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 238000003759 clinical diagnosis Methods 0.000 description 1
- 238000002591 computed tomography Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 238000000206 photolithography Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
- H04N25/63—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to dark current
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/30—Circuitry of solid-state image sensors [SSIS]; Control thereof for transforming X-rays into image signals
Definitions
- the present invention relates to an imaging device used in the medical field, the industrial field, and the nuclear field.
- 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.
- a CdTe film is used as the X-ray conversion layer.
- the imaging apparatus includes a circuit that accumulates and reads out carriers converted by the X-ray conversion layer.
- this circuit is composed of a plurality of gate lines G and data lines D arranged two-dimensionally, and turns on a capacitor Ca that accumulates 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.
- the detection element electrically connected to the selected gate line G is driven to generate a carrier. Is read out.
- dark current exists even when X-rays are not irradiated, and the dark current at the time of non-irradiation is read as a dark signal (also referred to as “dark current signal”).
- dark current signal there is a method of reading out and measuring a dark signal regardless of the temperature of the X-ray conversion layer and subtracting the dark signal amount (see, for example, Patent Document 1). JP 2006-305228 A
- the present invention has been made in view of such circumstances, and an object of the present invention is to provide an imaging apparatus capable of imaging without depending on the temperature of the conversion layer.
- an imaging device includes a conversion layer that converts light or radiation information into charge information upon incidence of light or radiation, and a storage / readout circuit that stores and reads out charge information converted by the conversion layer.
- An image pickup device that obtains an image based on charge information read by the storage / readout circuit, and can obtain a dark signal amount equivalent to a charge when light or radiation is not irradiated and the dark signal amount.
- Approximate expression calculating means for obtaining an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer in correspondence with the temperature of the conversion layer at the time, and the approximate expression obtained by the approximate expression calculating means has been simplified Approximate expression converting means for converting into an equation, temperature measuring means for measuring the temperature of the conversion layer, an approximate expression converted into a simplified expression obtained by the approximate expression converting means, and measured by the temperature measuring means.
- the A dark signal amount calculating means for obtaining the dark signal amount using the temperature of the conversion layer, and a correcting means for correcting charge information at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculating means. are provided.
- the dark signal amount equivalent to the charge when not irradiated with light or radiation changes according to the temperature of the conversion layer
- the dark signal amount is acquired in advance.
- the approximate expression calculating means obtains an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer by associating the dark signal amount with the temperature of the conversion layer when the dark signal amount is obtained.
- the approximate expression conversion means simplified the approximate expression obtained by the approximate expression calculation means. Convert to an expression.
- the dark signal amount calculation means obtains the dark signal amount
- the dark signal The correction unit corrects the charge information at the time of irradiation based on the dark signal amount obtained by the amount calculation unit, and performs imaging to obtain an image based on the corrected charge information. Therefore, imaging can be performed using the approximate expression without depending on the temperature of the conversion layer. Moreover, since the approximate expression is used, it is not necessary to know all the temperatures in the corresponding range. In summary, it is not necessary to know all the temperatures in the corresponding range, and imaging can be performed using the approximate expression without depending on the temperature of the conversion layer.
- the approximate expression conversion means preferably converts the approximate expression into a simplified expression when image acquisition is not being performed. Since the approximate expression is converted to a simplified expression using the free time when image acquisition is not performed, another processing is performed when the calculation burden during image acquisition (ie during imaging) is heavy. Without performing the above, the approximate expression is converted into a simplified expression when the calculation burden when the image acquisition is not performed is small.
- the approximate expression conversion means may convert the approximate expression into a simplified expression for a part of the image.
- the approximate expression calculating means obtains an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer
- the approximate expression converting means simplifies the approximate expression obtained by the approximate expression calculating means.
- the dark signal amount calculating means uses the approximate expression converted to the simplified expression and converted to the simplified expression by the approximate expression converting means, and the temperature of the conversion layer measured by the temperature measuring means, and the dark signal amount calculating means
- the correction unit corrects the charge information at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculation unit, and performs imaging to obtain an image based on the corrected charge information. As a result, it is not necessary to know all the temperatures in the corresponding range, and imaging can be performed using the approximate expression without depending on the temperature of the conversion layer.
- FIG. 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.
- 2 is a peripheral circuit diagram of a charge-voltage conversion amplifier and an A / D converter of an X-ray imaging apparatus.
- FIG. It is the graph which showed typically the approximate expression of the correlation of the dark signal amount and the temperature of a X-ray conversion layer.
- FIG. 5 is a graph in which an expression obtained by simplifying the approximate expression is written in the graph of FIG. 4.
- FIG. 5 is a graph in which an equation obtained by updating a parameter for each temperature and simplifying an approximate expression is also shown in the graph of FIG. 4.
- It is a schematic block diagram of the conventional X-ray imaging apparatus.
- FIG. 1 is a schematic block diagram of the X-ray imaging apparatus according to the embodiment
- FIG. 2 is a schematic cross-sectional view around the X-ray conversion layer of the X-ray imaging apparatus
- FIG. 3 is a charge of the X-ray imaging apparatus. It is a peripheral circuit diagram of a voltage conversion amplifier and an A / D converter.
- X-rays will be described as an example of incident radiation
- an X-ray imaging apparatus will be described as an example of an imaging apparatus.
- the X-ray imaging apparatus performs imaging by irradiating a subject with X-rays. Specifically, an X-ray image transmitted through the subject is projected onto an X-ray conversion layer (CdTe film in this embodiment), and carriers (charge information) proportional to the density of the image are generated in the layer. Is converted into a carrier.
- X-ray conversion layer CdTe film in this embodiment
- 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
- 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 section 7 An input unit 8 for setting, and a monitor 9 for displaying the processed images.
- information such as a carrier and an image is image information related to the image.
- the X-ray conversion layer 23 corresponds to the conversion layer in the present invention
- the detection element circuit 2 corresponds to the storage / readout circuit in the present invention.
- the gate drive circuit 1 is electrically connected to a plurality of gate lines 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.
- 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.
- the gate line G includes 10 gate lines G1 to G10
- the data line D includes 10 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.
- the detection elements DU are patterned on the insulating substrate 21 in a two-dimensional matrix arrangement.
- 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 or a pattern technique by a photolithography method, and the thin film transistor Tr and capacitor Ca, the carrier collection electrode 22, the X-ray conversion layer 23, and the voltage application electrode 24 are laminated in order.
- the X-ray conversion layer 23 is formed of an X-ray sensitive semiconductor thick film, and in this embodiment is formed of a CdTe film.
- 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 as long as it is an X-ray sensitive material in which carriers are generated by the incidence of X radiation.
- a radiation-sensitive material that generates carriers by the incidence of radiation may be used instead of the X-ray conversion layer 23. Good.
- 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.
- 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.
- the voltage application electrode 24 is formed over the entire surface as a common electrode of all the detection elements DU.
- 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.
- the temperature sensor 10 corresponds to the temperature measuring means in this invention.
- the temperature sensor 10 is provided on the voltage application electrode 24 at the 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 charge-voltage conversion amplifier 3 includes an amplifier 31 electrically connected to each data line D (D1 to D10 in FIG. 3), and electrically connected to each data line D.
- the amplifier 31 and the end of the data line D of the detection element circuit 2 are electrically connected to each data line D via the switching element SW.
- the carrier read to the data line D is sent to the amplifier 31 and the amplifier capacitor 32 of the charge-voltage conversion amplifier 3 with the switching element SW turned ON.
- the supplied carrier is amplified with the amplifier 31 and the amplifier capacitor 32 converted into a voltage, and the sample hold 33 temporarily accumulates the amplified voltage value for a predetermined time.
- the voltage value once stored is sent to the A / D converter 4 with the switching element 34 turned ON, and the A / D converter 4 converts the analog value of the sent voltage into a digital value.
- the image processing unit 5 performs various signal processing on the voltage value converted into a digital value by the A / D converter 4 to obtain an image.
- 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, the memory unit 7 and the monitor 9 described later, and in this embodiment (1)
- the detection element circuit 2 which is a readout circuit is controlled
- the carrier that is, the dark current
- the dark signal amount and the dark signal amount are obtained.
- a function for obtaining an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer 23 in correspondence with the temperature of the X-ray conversion layer 23 (function for calculating the approximate expression)
- a function for calculating the approximate expression A function for converting the approximate expression obtained in step 1 into a simplified expression (function of approximate expression conversion)
- an approximate expression converted into an expression simplified by the function of the approximate expression conversion and measurement with the temperature sensor 10
- 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 approximate expression calculation means, charge information calculation means, approximate expression conversion means, and correction 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.
- ROM Read-only Memory
- RAM Random-Access Memory
- a RAM is used for writing image information.
- ROM Read-only Memory
- ROM Random-Access Memory
- a ROM is used exclusively for reading the program related to the control sequence.
- an approximate expression is obtained, the approximate expression is converted into a simplified expression, a dark signal amount is obtained, a program relating to a control sequence to be corrected is stored in the memory unit 7, and the control sequence is read by reading the program.
- the controller 6 is made to execute.
- the input unit 8 includes a pointing device represented by a mouse, keyboard, joystick, trackball, touch panel, or the like, or input means such as a button, switch, or lever.
- a pointing device represented by a mouse, keyboard, joystick, trackball, touch panel, or the like
- input means such as a button, switch, or lever.
- a control sequence of the X-ray imaging apparatus of the present embodiment will be described. While applying a bias voltage V A of the voltage application electrode 24 to a high voltage (e.g., several 10V ⁇ number about 100 V), thereby applying X-rays to be detected.
- a bias voltage V A of the voltage application electrode 24 to a high voltage (e.g., several 10V ⁇ number about 100 V), thereby applying X-rays to be detected.
- 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.
- a scanning signal that is, a gate driving signal
- 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.
- the 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.
- the amplifier 31 of 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). It is read out and amplified in a state converted into a voltage by the amplifier 31 and the amplifier capacitor 32 of the charge-voltage conversion amplifier 3.
- 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 amplifier 31 connected to the data line D.
- 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.
- 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 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 an amplifier 31 and an amplifier capacitor 32, temporarily stored in a sample hold 33, and converted from an analog value to a digital value by an A / D converter 4. Is done.
- the image processing unit 5 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.
- FIG. 4 is a graph schematically showing an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer
- FIG. 5 shows the simplified expression along with the graph of FIG.
- FIG. 6 is a graph in which an equation obtained by updating the parameter for each temperature and simplifying the approximate expression is also shown in the graph of FIG.
- the dark signal mainly includes an offset component of the amplifier 31 that does not depend on the temperature change of the X-ray conversion layer 23 and a conversion layer leak component that depends on the temperature change of the X-ray conversion layer 23.
- an offset component of the amplifier 31 that does not depend on the temperature change of the X-ray conversion layer 23
- a conversion layer leak component that depends on the temperature change of the X-ray conversion layer 23.
- the conversion layer leak component is described for the dark signal, and correction for the conversion layer leak component is described.
- correction regarding the offset component of the amplifier 31 that does not depend on the temperature change is already corrected by subtracting the offset component from the carrier at the time of irradiation.
- the carrier at the time of non-irradiation is read as a dark signal to acquire the dark signal amount.
- the dark signal at that temperature is read in correspondence with the temperature of the X-ray conversion layer 23, and the dark signal amount and the temperature of the X-ray conversion layer 23 when the dark signal amount is obtained are plotted in correspondence. To do.
- the correlation between the dark signal amount (in this case, the conversion layer leakage component) and the temperature of the conversion layer 23 is expressed by the following equation (1). .
- I ⁇ ⁇ exp ( ⁇ / T) ⁇ 1 ⁇ (1)
- I is a dark signal amount (conversion layer leak component)
- ⁇ and ⁇ are constants
- T is a temperature [K].
- Exp is an exponential function. The approximate expression (1) is shown by a solid line in FIG.
- the temperature of the environment in which the apparatus is used is constantly changing, and a clinical diagnosis problem arises due to the temperature change of the dark signal amount appearing in the image. Therefore, by obtaining the approximate expression of the expression (1) as described above, measuring the actual temperature with the temperature sensor 10, and substituting the measured temperature of the X-ray conversion layer 23 into the expression (1). The actual dark signal amount is obtained, and the dark signal amount is subtracted from the carrier at the time of irradiation to correct the carrier at the time of irradiation.
- the temperature is measured by the temperature sensor 10 and the parameters a and b are updated.
- the temperature of the X-ray conversion layer 23 is T1, T2, and T3.
- parameters a and b are updated by obtaining a linear approximation formula for each temperature.
- the approximate expression (1) is illustrated by a dotted line in FIG. 6, and an expression obtained by simplifying the approximate expression at temperatures T1 to T3 is also illustrated by a solid line in FIG.
- the parameters while taking a picture by sequentially updating the parameters of some pixels of the image instead of all the pixels for each frame.
- the parameter may be updated for every pixel as long as the calculation is not burdened.
- the dark signal amount equivalent to the electric charge when X-rays are not irradiated changes according to the temperature of the X-ray conversion layer 23.
- the function of the approximate expression calculation is an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer 23 by associating the dark signal amount with the temperature of the X-ray conversion layer 23 when the dark signal amount is obtained. (In the present embodiment, the above equation (1)) is obtained.
- the approximate expression conversion function is an approximate expression obtained by the approximate expression calculation function.
- the dark signal amount calculation function is the dark signal amount.
- the carrier (charge information) at the time of irradiation is corrected based on the dark signal amount obtained by the dark signal amount calculation function, and imaging is performed to obtain an image based on the corrected carrier. Therefore, imaging can be performed using the approximate expression without depending on the temperature of the X-ray conversion layer 23.
- the approximate expression since the approximate expression is used, it is not necessary to know all the temperatures in the corresponding range. In summary, it is not necessary to know all the temperatures in the corresponding range, and imaging can be performed using the approximate expression without depending on the temperature of the X-ray conversion layer 23.
- the approximate expression conversion function is preferably converted into a simplified expression when the image is not acquired. Since the approximate expression is converted to a simplified expression using the free time when image acquisition is not performed, another processing is performed when the calculation burden during image acquisition (ie during imaging) is heavy. Without performing the above, the approximate expression is converted into a simplified expression when the calculation burden when the image acquisition is not performed is small.
- the approximate expression conversion means may convert the approximate expression into a simplified expression for a part of the image.
- the present invention is not limited to the above embodiment, and can be modified as follows.
- the X-ray imaging apparatus as shown in FIG. 1 has been described as an example.
- 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.
- 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).
- conversion layer X-ray conversion layer
- 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.
- the detection element circuit for detecting X-rays has been described as an example.
- 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 ⁇ -rays emitted from an administered subject.
- 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.
- the simplified formula parameters are obtained and updated each time.
- the parameters are obtained in advance at every 0.1 ° C., and stored in a table in which the parameters are arranged for each temperature. May be.
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Abstract
An image pickup apparatus associates a dark signal amount, which is equivalent to the charge during a non-exposure, with a temperature of an X-ray conversion layer (23) when the dark signal amount is obtained; obtains an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer (23); and converts the approximate expression to a simplified version thereof. The image pickup apparatus then uses the simplified version of the approximate expression and the temperature of the X-ray conversion layer (23) determined by a temperature sensor (10) to obtain a dark signal amount, and then corrects, based on the obtained dark signal amount, the carrier during an exposure, thereby performing an image pickup based on the corrected carrier. Since the approximate expression is used, there is no need to know all of the temperatures within the related range, and the image pickup can be performed without depending on the temperature of the X-ray conversion layer (23). Moreover, since the approximate expression has been converted to its simplified version, the arithmetic load on the calculation of the dark signal amount can be reduced.
Description
この発明は、医療分野、工業分野、さらには原子力分野などに用いられる撮像装置に関する。
The present invention relates to an imaging device used in the medical field, the industrial field, and the nuclear field.
電荷情報に基づいて画像を得る撮像装置についてX線を入射して電荷情報に変換する場合を例に採って説明する。撮像装置は、X線感応型のX線変換層を備えており、X線の入射によりX線変換層はキャリア(電荷情報)に変換する。X線変換層としてはCdTe膜が用いられる。
An imaging apparatus that obtains an image based on charge information will be described by 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. A CdTe film is used as the X-ray conversion layer.
また、撮像装置は、X線変換層で変換されたキャリアを蓄積して読み出す回路を備えている。この回路は、図7に示すように、2次元状に配列した複数のゲートラインGおよびデータラインDで構成されているとともに、キャリアを蓄積するコンデンサCaおよびそのコンデンサCaに蓄積されたキャリアをON/OFFの切り換えで読み出す薄膜トランジスタ(TFT)Trを2次元状に配列して構成されている。ゲートラインGは、各々の薄膜トランジスタTrのON/OFF切り換えを制御し、かつ各々の薄膜トランジスタTrのゲートに電気的に接続されている。データラインDは、薄膜トランジスタTrの読み出し側に電気的に接続されている。
In addition, the imaging apparatus includes a circuit that accumulates and reads out carriers converted by the X-ray conversion layer. As shown in FIG. 7, this circuit is composed of a plurality of gate lines G and data lines D arranged two-dimensionally, and turns on a capacitor Ca that accumulates 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.
各々のコンデンサCaや各々の薄膜トランジスタTrなどで各検出素子を構成しており、ゲートラインGを選択することで、その選択されたゲートラインGに電気的に接続された検出素子を駆動させてキャリアの読み出しを行う。ところで、X線の照射時とは関係なく、X線の非照射時においても暗電流は存在し、非照射時の暗電流がダーク信号(「暗電流信号」とも呼ばれる)として読み出される。従来、X線変換層の温度と関係なくダーク信号を読み出して測定して、そのダーク信号量の減算を行う手法がある(例えば、特許文献1参照)。
特開2006-305228号公報
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. By the way, regardless of the time of X-ray irradiation, dark current exists even when X-rays are not irradiated, and the dark current at the time of non-irradiation is read as a dark signal (also referred to as “dark current signal”). Conventionally, there is a method of reading out and measuring a dark signal regardless of the temperature of the X-ray conversion layer and subtracting the dark signal amount (see, for example, Patent Document 1).
JP 2006-305228 A
しかしながら、上述した従来の手法では、X線変換層に代表される変換層の温度が変化すると、次のダーク信号量の測定を行うまでにダーク信号量が変化してしまい、前のダーク信号量を用いることでダーク信号量を減算する補正がうまくいかないという問題点がある。
However, in the above-described conventional method, when the temperature of the conversion layer represented by the X-ray conversion layer changes, the dark signal amount changes until the next dark signal amount is measured, and the previous dark signal amount is changed. There is a problem that the correction for subtracting the dark signal amount does not work by using.
この発明は、このような事情に鑑みてなされたものであって、変換層の温度に依存することなく撮像を行うことができる撮像装置を提供することを目的とする。
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an imaging apparatus capable of imaging without depending on the temperature of the conversion layer.
この発明は、このような目的を達成するために、次のような構成をとる。
すなわち、この発明の撮像装置は、光または放射線の入射により前記光または放射線の情報を電荷情報に変換する変換層と、その変換層で変換された電荷情報を蓄積して読み出す蓄積・読み出し回路とを備え、その蓄積・読み出し回路で読み出された電荷情報に基づいて画像を得る撮像装置であって、光または放射線の非照射時の電荷と等価なダーク信号量とそのダーク信号量が得られたときの変換層の温度とを対応させてダーク信号量および変換層の温度の相関関係の近似式を求める近似式算出手段と、その近似式算出手段で求められた前記近似式を簡略化した式に変換する近似式変換手段と、前記変換層の温度を測定する温度測定手段と、前記近似式変換手段で求められた簡略化した式に変換された近似式と、前記温度測定手段で測定された前記変換層の温度とを用いて前記ダーク信号量を求めるダーク信号量算出手段と、そのダーク信号量算出手段で求められた前記ダーク信号量に基づいて照射時の電荷情報を補正する補正手段とを備えることを特徴とするものである。 In order to achieve such an object, the present invention has the following configuration.
That is, an imaging device according to the present invention includes a conversion layer that converts light or radiation information into charge information upon incidence of light or radiation, and a storage / readout circuit that stores and reads out charge information converted by the conversion layer. An image pickup device that obtains an image based on charge information read by the storage / readout circuit, and can obtain a dark signal amount equivalent to a charge when light or radiation is not irradiated and the dark signal amount. Approximate expression calculating means for obtaining an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer in correspondence with the temperature of the conversion layer at the time, and the approximate expression obtained by the approximate expression calculating means has been simplified Approximate expression converting means for converting into an equation, temperature measuring means for measuring the temperature of the conversion layer, an approximate expression converted into a simplified expression obtained by the approximate expression converting means, and measured by the temperature measuring means The A dark signal amount calculating means for obtaining the dark signal amount using the temperature of the conversion layer, and a correcting means for correcting charge information at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculating means. Are provided.
すなわち、この発明の撮像装置は、光または放射線の入射により前記光または放射線の情報を電荷情報に変換する変換層と、その変換層で変換された電荷情報を蓄積して読み出す蓄積・読み出し回路とを備え、その蓄積・読み出し回路で読み出された電荷情報に基づいて画像を得る撮像装置であって、光または放射線の非照射時の電荷と等価なダーク信号量とそのダーク信号量が得られたときの変換層の温度とを対応させてダーク信号量および変換層の温度の相関関係の近似式を求める近似式算出手段と、その近似式算出手段で求められた前記近似式を簡略化した式に変換する近似式変換手段と、前記変換層の温度を測定する温度測定手段と、前記近似式変換手段で求められた簡略化した式に変換された近似式と、前記温度測定手段で測定された前記変換層の温度とを用いて前記ダーク信号量を求めるダーク信号量算出手段と、そのダーク信号量算出手段で求められた前記ダーク信号量に基づいて照射時の電荷情報を補正する補正手段とを備えることを特徴とするものである。 In order to achieve such an object, the present invention has the following configuration.
That is, an imaging device according to the present invention includes a conversion layer that converts light or radiation information into charge information upon incidence of light or radiation, and a storage / readout circuit that stores and reads out charge information converted by the conversion layer. An image pickup device that obtains an image based on charge information read by the storage / readout circuit, and can obtain a dark signal amount equivalent to a charge when light or radiation is not irradiated and the dark signal amount. Approximate expression calculating means for obtaining an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer in correspondence with the temperature of the conversion layer at the time, and the approximate expression obtained by the approximate expression calculating means has been simplified Approximate expression converting means for converting into an equation, temperature measuring means for measuring the temperature of the conversion layer, an approximate expression converted into a simplified expression obtained by the approximate expression converting means, and measured by the temperature measuring means The A dark signal amount calculating means for obtaining the dark signal amount using the temperature of the conversion layer, and a correcting means for correcting charge information at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculating means. Are provided.
この発明の撮像装置によれば、光または放射線の非照射時の電荷と等価なダーク信号量は、変換層の温度に応じて変化するので、ダーク信号量を予め取得する。ダーク信号量とそのダーク信号量が得られたときの変換層の温度とを対応させて、近似式算出手段はダーク信号量および変換層の温度の相関関係の近似式を求める。さらに、近似式算出手段の後段のダーク信号量算出手段によるダーク信号量の算出に関する演算の負担を低減させるために、近似式変換手段は、近似式算出手段で求められた近似式を簡略化した式に変換する。そして、その近似式変換手段で簡略化した式に変換された近似式と、温度測定手段で測定された変換層の温度とを用いて、ダーク信号量算出手段はダーク信号量を求め、ダーク信号量算出手段で求められたダーク信号量に基づいて補正手段は照射時の電荷情報を補正することで、補正された電荷情報に基づいて画像を得る撮像を行う。したがって、近似式を用いて変換層の温度に依存することなく撮像を行うことができる。また、近似式を用いているので、該当する範囲中の温度を全部知る必要がない。以上をまとめると、該当する範囲中の温度を全部知る必要がなく、近似式を用いて変換層の温度に依存することなく撮像を行うことができる。
According to the imaging apparatus of the present invention, since the dark signal amount equivalent to the charge when not irradiated with light or radiation changes according to the temperature of the conversion layer, the dark signal amount is acquired in advance. The approximate expression calculating means obtains an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer by associating the dark signal amount with the temperature of the conversion layer when the dark signal amount is obtained. Furthermore, in order to reduce the burden of calculation related to the calculation of the dark signal amount by the dark signal amount calculation means subsequent to the approximate expression calculation means, the approximate expression conversion means simplified the approximate expression obtained by the approximate expression calculation means. Convert to an expression. Then, using the approximate expression converted to the simplified expression by the approximate expression conversion means and the temperature of the conversion layer measured by the temperature measurement means, the dark signal amount calculation means obtains the dark signal amount, and the dark signal The correction unit corrects the charge information at the time of irradiation based on the dark signal amount obtained by the amount calculation unit, and performs imaging to obtain an image based on the corrected charge information. Therefore, imaging can be performed using the approximate expression without depending on the temperature of the conversion layer. Moreover, since the approximate expression is used, it is not necessary to know all the temperatures in the corresponding range. In summary, it is not necessary to know all the temperatures in the corresponding range, and imaging can be performed using the approximate expression without depending on the temperature of the conversion layer.
上述した発明の撮像装置において、以下のようにするのが好ましい。すなわち、近似式変換手段は、画像取得を行っていないときに、近似式を簡略化した式に変換するのが好ましい。画像取得を行っていないときの空いている時間を利用して、近似式を簡略化した式に変換しているので、画像取得中(すなわち撮像中)の演算の負担が大きいときに別の処理を行うことなく、画像取得を行っていないときにおける演算の負担が小さいときに近似式を簡略化した式に変換することになる。
In the imaging device of the invention described above, it is preferable to do the following. That is, the approximate expression conversion means preferably converts the approximate expression into a simplified expression when image acquisition is not being performed. Since the approximate expression is converted to a simplified expression using the free time when image acquisition is not performed, another processing is performed when the calculation burden during image acquisition (ie during imaging) is heavy. Without performing the above, the approximate expression is converted into a simplified expression when the calculation burden when the image acquisition is not performed is small.
上述した近似式を簡略化した式に変換する場合において、必ずしも画像の全領域に対して行わなくてもよい。すなわち、近似式変換手段は、画像の一部に対して、近似式を簡略化した式に変換してもよい。
In the case of converting the above approximate expression into a simplified expression, it is not necessarily performed for the entire area of the image. That is, the approximate expression conversion means may convert the approximate expression into a simplified expression for a part of the image.
この発明に係る撮像装置によれば、近似式算出手段はダーク信号量および変換層の温度の相関関係の近似式を求め、近似式変換手段は、近似式算出手段で求められた近似式を簡略化した式に変換し、その近似式変換手段で簡略化した式に変換された近似式と、温度測定手段で測定された変換層の温度とを用いて、ダーク信号量算出手段はダーク信号量を求め、ダーク信号量算出手段で求められたダーク信号量に基づいて補正手段は照射時の電荷情報を補正することで、補正された電荷情報に基づいて画像を得る撮像を行う。その結果、該当する範囲中の温度を全部知る必要がなく、近似式を用いて変換層の温度に依存することなく撮像を行うことができる。
According to the imaging apparatus of the present invention, the approximate expression calculating means obtains an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer, and the approximate expression converting means simplifies the approximate expression obtained by the approximate expression calculating means. The dark signal amount calculating means uses the approximate expression converted to the simplified expression and converted to the simplified expression by the approximate expression converting means, and the temperature of the conversion layer measured by the temperature measuring means, and the dark signal amount calculating means The correction unit corrects the charge information at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculation unit, and performs imaging to obtain an image based on the corrected charge information. As a result, it is not necessary to know all the temperatures in the corresponding range, and imaging can be performed using the approximate expression without depending on the temperature of the conversion layer.
10 … 温度センサ
2 … 検出素子用回路
23 … X線変換層
6 … コントローラ
I … ダーク信号量(変換層リーク成分)
T … 温度 DESCRIPTION OFSYMBOLS 10 ... Temperature sensor 2 ... Detection element circuit 23 ... X-ray conversion layer 6 ... Controller I ... Dark signal amount (conversion layer leak component)
T… temperature
2 … 検出素子用回路
23 … X線変換層
6 … コントローラ
I … ダーク信号量(変換層リーク成分)
T … 温度 DESCRIPTION OF
T… temperature
以下、図面を参照してこの発明の実施例を説明する。図1は、実施例に係るX線撮影装置の概略ブロック図であり、図2は、X線撮影装置のX線変換層周辺の概略断面図であり、図3は、X線撮影装置の電荷電圧変換アンプやA/D変換器の周辺回路図である。本実施例では、入射する放射線としてX線を例に採って説明するとともに、撮像装置としてX線撮影装置を例に採って説明する。
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, FIG. 2 is a schematic cross-sectional view around the X-ray conversion layer of the X-ray imaging apparatus, and FIG. 3 is a charge of the X-ray imaging apparatus. It is a peripheral circuit diagram of a voltage conversion amplifier and an A / D converter. 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.
本実施例に係るX線撮影装置は、被検体にX線を照射して撮像を行う。具体的には、被検体を透過したX線像がX線変換層(本実施例ではCdTe膜)上に投影されて、像の濃淡に比例したキャリア(電荷情報)が層内に発生することでキャリアに変換される。
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 onto an X-ray conversion layer (CdTe film in this embodiment), and carriers (charge information) proportional to the density of the image are generated in the layer. Is converted into a carrier.
X線撮影装置は、図1に示すように、後述するゲートラインGを選択するゲート駆動回路1と、X線変換層23(図2を参照)で変換されたキャリアを蓄積して読み出すことでX線を検出する検出素子用回路2と、その検出素子用回路2で読み出されたキャリアを電圧に変換した状態で増幅する電荷電圧変換アンプ3と、その電荷電圧変換アンプ3で増幅された電圧のアナログ値からディジタル値に変換するA/D変換器4と、そのA/D変換器4でディジタル値に変換された電圧値に対して信号処理を行って画像を得る画像処理部5と、これらの回路1,2や電荷電圧変換アンプ3やA/D変換器4や画像処理部5や後述するメモリ部7やモニタ9などを統括制御するコントローラ6と、処理された画像などを記憶するメモリ部7と、入力設定を行う入力部8と、処理された画像などを表示するモニタ9とを備えている。本明細書では、キャリアや画像などの情報を、画像に関する画像情報とする。X線変換層23は、この発明における変換層に相当し、検出素子用回路2は、この発明における蓄積・読み出し回路に相当する。
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 section 7 An input unit 8 for setting, 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 conversion layer in the present invention, and the detection element circuit 2 corresponds to the storage / readout circuit in the present invention.
ゲート駆動回路1は複数のゲートラインGに電気的に接続されている。ゲート駆動回路1から各ゲートラインGに電圧を印加することで、後述する薄膜トランジスタ(TFT)TrをONにして後述するコンデンサCaに蓄積されたキャリアの読み出しを開放し、各ゲートラインGへの電圧を停止する(電圧を-10Vにする)ことで、薄膜トランジスタTrをOFFにしてキャリアの読み出しを遮断する。なお、各ゲートラインGに電圧を印加することでOFFにしてキャリアの読み出しを遮断し、各ゲートラインGへの電圧を停止することでONにしてキャリアの読み出しを開放するように、薄膜トランジスタTrを構成してもよい。
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.
検出素子用回路2は、2次元状に配列した複数のゲートラインGおよびデータラインDで構成されているとともに、キャリアを蓄積するコンデンサCaおよびそのコンデンサCaに蓄積されたキャリアをON/OFFの切り換えで読み出す薄膜トランジスタTrを2次元状に配列して構成されている。ゲートラインGは、各々の薄膜トランジスタTrのON/OFF切り換えを制御し、かつ各々の薄膜トランジスタTrのゲートに電気的に接続されている。データラインDは、薄膜トランジスタTrの読み出し側に電気的に接続されている。
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.
説明の便宜上、本実施例では、縦・横式2次元マトリックス状配列で10×10個の薄膜トランジスタTrおよびコンデンサCaが形成されているとする。すなわち、ゲートラインGは、10本のゲートラインG1~G10からなり、データラインDは、10本のデータラインD1~D10からなる。各ゲートラインG1~G10は、図1中のX方向に並設された10個の薄膜トランジスタTrのゲートにそれぞれ接続され、各データラインD1~D10は、図1中のY方向に並設された10個の薄膜トランジスタTrの読み出し側にそれぞれ接続されている。薄膜トランジスタTrの読み出し側とは逆側にはコンデンサCaが電気的に接続されており、薄膜トランジスタTrとコンデンサCaとの個数が一対一に対応する。
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 includes 10 gate lines G1 to G10, and the data line D includes 10 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.
また、検出素子用回路2は、図2に示すように、検出素子DUが2次元マトリックス状配列で絶縁基板21にパターン形成されている。すなわち、絶縁基板21の表面に、各種真空蒸着法による薄膜形成技術やフォトリソグラフィ法によるパターン技術を利用して、上述したゲートラインG1~G10およびデータラインD1~D10を配線し、薄膜トランジスタTr,コンデンサCa,キャリア収集電極22,X線変換層23および電圧印加電極24を順に積層形成することで構成されている。
Further, 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. In other words, 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 or a pattern technique by a photolithography method, and the thin film transistor Tr and capacitor Ca, the carrier collection electrode 22, the X-ray conversion layer 23, and the voltage application electrode 24 are laminated in order.
X線変換層23は、X線感応型の半導体厚膜で形成されており、本実施例では、CdTe膜で形成されている。X線変換層23は、X線の入射によりX線の情報を電荷情報であるキャリアに変換する。なお、X線変換層23は、X放射線の入射によりキャリアが生成されるX線感応型の物質であれば、CdTeに限定されない。また、X線以外の放射線(γ線など)を入射して撮像を行う場合には、X線変換層23の替わりに、放射線の入射によりキャリアが生成される放射線感応型の物質を用いてもよい。また、光を入射して撮像を行う場合には、X線変換層23の替わりに、光の入射によりキャリアが生成される光感応型の物質を用いてもよい。
The X-ray conversion layer 23 is formed of an X-ray sensitive semiconductor thick film, and in this embodiment is formed of a CdTe film. 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 as long as it is an X-ray sensitive material in which carriers are generated 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.
キャリア収集電極22は、コンデンサCaに電気的に接続されており、X線変換層23で変換されたキャリアを収集してコンデンサCaに蓄積する。このキャリア収集電極22も、薄膜トランジスタTrおよびコンデンサCaと同様に、縦・横式2次元マトリックス状配列で多数個(本実施例では10×10個)形成されている。それらキャリア収集電極22,コンデンサCaおよび薄膜トランジスタTrが各検出素子DUとしてそれぞれ分離形成されている。また、電圧印加電極24は、全検出素子DUの共通電極として全面にわたって形成されている。
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.
本実施例では、その他に、X線変換層23の温度を測定する温度センサ10を備えている。温度センサ10による測定結果をコントローラ6に送り込む。温度センサ10は、この発明における温度測定手段に相当する。
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. The temperature sensor 10 corresponds to the temperature measuring means in this invention.
X線変換層23の温度を測定するには、図2に示すように検出有効エリア(図示省略)から外れた端部において電圧印加電極24に温度センサ10を設ける。具体的には、図2(a)に示すように電圧印加電極24中に温度センサ10を埋め込んでもよいし、図2(b)に示すように電圧印加電極24上に温度センサ10を積層してもよい。なお、X線変換層23中に温度センサを埋め込む、あるいはX線変換層23上に温度センサ10を積層してもよい。
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 the 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.
電荷電圧変換アンプ3は、図3に示すように、各々のデータラインD(図3ではD1~D10)に電気的に接続されたアンプ31と、各々のデータラインDに電気的に接続されたアンプ用コンデンサ32と、データラインD毎のアンプ31およびアンプ用コンデンサ32に電気的に並列に接続されたサンプルホールド33と、データラインD毎のサンプルホールド33に電気的に接続されたスイッチング素子34とを備えている。また、アンプ31と検出素子用回路2のデータラインDの端部とは、スイッチング素子SWを介して、データラインD毎に電気的に接続されている。データラインDに読みだされたキャリアを、スイッチング素子SWがONにして電荷電圧変換アンプ3のアンプ31およびアンプ用コンデンサ32に送り込む。送り込まれたキャリアを、アンプ31およびアンプ用コンデンサ32が電圧に変換した状態で増幅し、増幅された電圧値をサンプルホールド33は所定時間だけ一旦蓄積する。一旦蓄積された電圧値を、スイッチング素子34をONにしてA/D変換器4に送り込み、送り込まれた電圧のアナログ値からディジタル値にA/D変換器4は変換する。
As shown in FIG. 3, the charge-voltage conversion amplifier 3 includes an amplifier 31 electrically connected to each data line D (D1 to D10 in FIG. 3), and electrically connected to each data line D. Amplifier capacitor 32, amplifier 31 for each data line D, sample hold 33 electrically connected in parallel to amplifier capacitor 32, and switching element 34 electrically connected to sample hold 33 for each data line D And. The amplifier 31 and the end of the data line D of the detection element circuit 2 are electrically connected to each data line D via the switching element SW. The carrier read to the data line D is sent to the amplifier 31 and the amplifier capacitor 32 of the charge-voltage conversion amplifier 3 with the switching element SW turned ON. The supplied carrier is amplified with the amplifier 31 and the amplifier capacitor 32 converted into a voltage, and the sample hold 33 temporarily accumulates the amplified voltage value for a predetermined time. The voltage value once stored is sent to the A / D converter 4 with the switching element 34 turned ON, and the A / D converter 4 converts the analog value of the sent voltage into a digital value.
図1の説明に戻って、画像処理部5は、A/D変換器4でディジタル値に変換された電圧値に対して各種の信号処理を行って画像を求める。コントローラ6は、回路1,2や電荷電圧変換アンプ3やA/D変換器4や画像処理部5や後述するメモリ部7やモニタ9などを統括制御し、本実施例では(1)蓄積・読み出し回路である検出素子用回路2を制御して、X線の非照射時のキャリア(すなわち暗電流)をダーク信号量として取得し、そのダーク信号量とそのダーク信号量が得られたときのX線変換層23の温度とを対応させて、ダーク信号量およびX線変換層23の温度の相関関係の近似式を求める機能(近似式算出の機能)、(2)その近似式算出の機能で求められた近似式を簡略化した式に変換する機能(近似式変換の機能)、(3)その近似式変換の機能で簡略化した式に変換された近似式と、温度センサ10で測定されたX線変換層23の温度とを用いてダーク信号量を求める機能(ダーク信号量算出の機能)および(4)そのダーク信号量算出の機能で求められたダーク信号量に基づいて照射時のキャリア(電荷情報)を補正する機能(補正の機能)をも備えている。画像処理部5およびコントローラ6は、中央演算処理装置(CPU)や、プログラマブルロジックデバイス(FPGA)などの組み合わせで構成されている。コントローラ6は、この発明における近似式算出手段,電荷情報算出手段,近似式変換手段および補正手段に相当する。
Returning to the description of FIG. 1, the image processing unit 5 performs various signal processing on the voltage value converted into a digital value by the A / D converter 4 to obtain an image. 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, the memory unit 7 and the monitor 9 described later, and in this embodiment (1) When the detection element circuit 2 which is a readout circuit is controlled, the carrier (that is, the dark current) when X-rays are not irradiated is acquired as the dark signal amount, and the dark signal amount and the dark signal amount are obtained. A function for obtaining an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer 23 in correspondence with the temperature of the X-ray conversion layer 23 (function for calculating the approximate expression), (2) a function for calculating the approximate expression A function for converting the approximate expression obtained in step 1 into a simplified expression (function of approximate expression conversion), (3) an approximate expression converted into an expression simplified by the function of the approximate expression conversion, and measurement with the temperature sensor 10 For determining the dark signal amount using the temperature of the X-ray conversion layer 23 (Dark signal amount calculation function) and (4) A function (correction function) for correcting the carrier (charge information) at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculation function Yes. 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 approximate expression calculation means, charge information calculation means, approximate expression conversion means, and correction means in this invention.
メモリ部7は、画像情報などを書き込んで記憶し、コントローラ6からの読み出し指令に応じて画像情報などがメモリ部7から読み出される。メモリ部7は、ROM(Read-only Memory)やRAM(Random-Access Memory)などに代表される記憶媒体などで構成されている。なお、画像情報の書き込みにはRAMが用いられ、例えば制御シーケンスに関するプログラムの読み出しによって制御シーケンスをコントローラ6に実行させる場合には、制御シーケンスに関するプログラムの読み出し専用にはROMが用いられる。本実施例では、近似式を求め、その近似式を簡略化した式に変換し、ダーク信号量を求め、補正する制御シーケンスに関するプログラムをメモリ部7に記憶させ、そのプログラムの読み出しによって制御シーケンスをコントローラ6に実行させる。
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 this embodiment, an approximate expression is obtained, the approximate expression is converted into a simplified expression, a dark signal amount is obtained, a program relating to a control sequence to be corrected is stored in the memory unit 7, and the control sequence is read by reading the program. The controller 6 is made to execute.
入力部8は、マウスやキーボードやジョイスティックやトラックボールやタッチパネルなどに代表されるポインティングデバイス、あるいはボタンやスイッチやレバーなどの入力手段で構成されている。入力部8に入力設定すると、入力設定データがコントローラ6に送り込まれ、入力設定データに基づいて回路1,2や電荷電圧変換アンプ3やA/D変換器4や画像処理部5やメモリ部7やモニタ9などが制御される。
The input unit 8 includes a pointing device represented by a mouse, keyboard, joystick, trackball, touch panel, or the like, or input means such as a button, switch, or 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.
続いて、本実施例のX線撮影装置の制御シーケンスについて説明する。電圧印加電極24に高電圧(例えば数10V~数100V程度)のバイアス電圧VAを印加した状態で、検出対象であるX線を入射させる。
Subsequently, a control sequence of the X-ray imaging apparatus of the present embodiment will be described. While applying a bias voltage V A of the voltage application electrode 24 to a high voltage (e.g., several 10V ~ number about 100 V), thereby applying X-rays to be detected.
X線の入射によってX線変換層23でキャリアが生成されて、そのキャリアが電荷情報としてキャリア収集電極22を介してコンデンサCaに蓄積される。ゲート駆動回路1の信号(ここではキャリア)読み出し用の走査信号(すなわちゲート駆動信号)によって、対象となるゲートラインGが選択される。本実施例では、ゲートラインG1,G2,G3,…,G9,G10の順に1つずつ選択されるものとして説明する。また、ゲート駆動回路1からの信号読み出し用の走査信号は、ゲートラインGに電圧(例えば15V程度)を印加する信号である。
The carriers are generated in the X-ray conversion layer 23 by the incidence of X-rays, and the carriers are accumulated as charge information in the capacitor Ca via the carrier collecting electrode 22. 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.
ゲート駆動回路1から対象となるゲートラインGを選択して、選択されたゲートラインGに接続されている各薄膜トランジスタTrが選択指定される。この選択指定で選択指定された薄膜トランジスタTrのゲートに電圧が印加されてON状態となる。その選択指定された各薄膜トランジスタTrに接続されているコンデンサCaから蓄積されたキャリアが、選択指定されてON状態に移行した薄膜トランジスタTrを経由して、データラインDに読み出される。すなわち、選択されたゲートラインGに関する検出素子DUが選択指定されて、その選択指定された検出素子DUのコンデンサCaに蓄積されたキャリアが、データラインDに読み出される。
The 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.
具体的には、データラインDに接続されている電荷電圧変換アンプ3のアンプ31がリセットされて、さらに薄膜トランジスタTrがON状態(すなわちゲートがON)に移行することで、キャリアがデータラインDに読み出され、電荷電圧変換アンプ3のアンプ31およびアンプ用コンデンサ32にて電圧に変換された状態で増幅される。
Specifically, the amplifier 31 of 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). It is read out and amplified in a state converted into a voltage by the amplifier 31 and the amplifier capacitor 32 of the charge-voltage conversion amplifier 3.
つまり、各検出素子DUのアドレス(番地)指定は、ゲート駆動回路1からの信号読み出し用の走査信号と、データラインDに接続されているアンプ31の選択とに基づいて行われる。
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 amplifier 31 connected to the data line D.
先ず、ゲート駆動回路1からゲートラインG1を選択して、選択されたゲートラインG1に関する検出素子DUが選択指定されて、その選択指定された検出素子DUのコンデンサCaに蓄積されたキャリアが、全データラインD同時に読み出されて、サンプルホールド後にデータラインD1~D10の順にA/D変換器4にてディジタル値に変換される。次に、ゲート駆動回路1からゲートラインG2を選択して、同様の手順で、選択されたゲートラインG2に関する検出素子DUが選択指定されて、その選択指定された検出素子DUのコンデンサCaに蓄積されたキャリアが、全データラインD同時に読み出されて、サンプルホールド後にデータラインD1~D10の順にA/D変換器4にてディジタル値に変換される。残りのゲートラインGについても同様に順に選択することで、2次元状のキャリアを読み出す。
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 order. Similarly, the remaining gate lines G are sequentially selected to read out a two-dimensional carrier.
読みだされた各キャリアはアンプ31およびアンプ用コンデンサ32で電圧に変換された状態でそれぞれ増幅されて、サンプルホールド33で一旦蓄積されて、A/D変換器4でアナログ値からディジタル値に変換される。このディジタル値に変換された電圧値に基づいて、画像処理部5は各種の信号処理を行って、2次元状の画像を得る。得られた2次元状の画像やキャリアなどに代表される画像情報は、コントローラ6を介してメモリ部7に書き込まれて記憶され、必要に応じてコントローラ6を介してメモリ部7から読み出される。また、画像情報は、コントローラ6を介してモニタ9に表示される。
Each read carrier is amplified in a state of being converted into a voltage by an amplifier 31 and an amplifier capacitor 32, temporarily stored in a sample hold 33, and converted from an analog value to a digital value by an A / D converter 4. Is done. 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.
次に、一連の制御シーケンスについて、図4~図6を参照して説明する。図4は、ダーク信号量およびX線変換層の温度の相関関係の近似式を模式的に示したグラフであって、図5は、近似式を簡略化した式を図4のグラフに併記したグラフであって、図6は、温度毎にパラメータを更新して近似式を簡略化した式を図4のグラフに併記したグラフである。
Next, a series of control sequences will be described with reference to FIGS. FIG. 4 is a graph schematically showing an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer, and FIG. 5 shows the simplified expression along with the graph of FIG. FIG. 6 is a graph in which an equation obtained by updating the parameter for each temperature and simplifying the approximate expression is also shown in the graph of FIG.
主にダーク信号は、X線変換層23の温度変化に依存しないアンプ31のオフセット成分と、X線変換層23の温度変化に依存する変換層リーク成分とで構成される。以下の説明では、ダーク信号については変換層リーク成分のみについて記述するとともに、変換層リーク成分に関する補正について記述する。その他、温度変化に依存しないアンプ31のオフセット成分等に関する補正については、照射時のキャリアからオフセット成分を減算することで既に補正されているものとする。
The dark signal mainly includes an offset component of the amplifier 31 that does not depend on the temperature change of the X-ray conversion layer 23 and a conversion layer leak component that depends on the temperature change of the X-ray conversion layer 23. In the following description, only the conversion layer leak component is described for the dark signal, and correction for the conversion layer leak component is described. In addition, correction regarding the offset component of the amplifier 31 that does not depend on the temperature change is already corrected by subtracting the offset component from the carrier at the time of irradiation.
予め、温度センサ10でX線変換層23の温度を測定しつつ、非照射時のキャリアをダーク信号として読み出して、ダーク信号量を取得する。X線変換層23の温度に対応させて、その温度のときのダーク信号を読み出して、ダーク信号量とそのダーク信号量が得られたときのX線変換層23の温度とを対応させてプロットする。そのプロットされたグラフから例えば最小自乗法などで近似すると、ダーク信号量(この場合には変換層リーク成分)と変換層23の温度との相関関係は、下記(1)式のように表わされる。
In advance, while measuring the temperature of the X-ray conversion layer 23 with the temperature sensor 10, the carrier at the time of non-irradiation is read as a dark signal to acquire the dark signal amount. The dark signal at that temperature is read in correspondence with the temperature of the X-ray conversion layer 23, and the dark signal amount and the temperature of the X-ray conversion layer 23 when the dark signal amount is obtained are plotted in correspondence. To do. When the plotted graph is approximated by, for example, the method of least squares, the correlation between the dark signal amount (in this case, the conversion layer leakage component) and the temperature of the conversion layer 23 is expressed by the following equation (1). .
I=α{exp(β/T)-1} …(1)
ただし、Iはダーク信号量(変換層リーク成分)、α,βは定数、Tは温度[K]である。また、expは指数関数である。上記(1)式の近似式を図4では実線で図示する。 I = α {exp (β / T) −1} (1)
However, I is a dark signal amount (conversion layer leak component), α and β are constants, and T is a temperature [K]. Exp is an exponential function. The approximate expression (1) is shown by a solid line in FIG.
ただし、Iはダーク信号量(変換層リーク成分)、α,βは定数、Tは温度[K]である。また、expは指数関数である。上記(1)式の近似式を図4では実線で図示する。 I = α {exp (β / T) −1} (1)
However, I is a dark signal amount (conversion layer leak component), α and β are constants, and T is a temperature [K]. Exp is an exponential function. The approximate expression (1) is shown by a solid line in FIG.
一般的に、装置使用環境の温度は常に変化しており、ダーク信号量の温度変化が画像に現れることにより臨床診断上の問題が生じる。そこで、上述したような(1)式の近似式を求めて、実際の温度を温度センサ10で測定して、その測定されたX線変換層23の温度を(1)式に代入することにより、実際のダーク信号量を求めて、そのダーク信号量を照射時のキャリアから減算することで照射時のキャリアを補正する。
Generally, the temperature of the environment in which the apparatus is used is constantly changing, and a clinical diagnosis problem arises due to the temperature change of the dark signal amount appearing in the image. Therefore, by obtaining the approximate expression of the expression (1) as described above, measuring the actual temperature with the temperature sensor 10, and substituting the measured temperature of the X-ray conversion layer 23 into the expression (1). The actual dark signal amount is obtained, and the dark signal amount is subtracted from the carrier at the time of irradiation to correct the carrier at the time of irradiation.
しかし、実際には、X線撮影装置にて人体の透視画像を撮影する場合、例えば1024×1024画素からなる画像を、30フレーム/秒程度のフレームレートで撮影する必要があるので、コントローラ6等の負担を考慮すると、上記(1)式を用いたダーク信号量の算出に関する演算を低減させる。そこで、上記(1)式を簡略化する。例えば、下記(2)式のような一次関数(直線)で近似して簡略化する。
However, in reality, when a fluoroscopic image of a human body is captured by an X-ray imaging apparatus, for example, an image composed of 1024 × 1024 pixels needs to be captured at a frame rate of about 30 frames / second. In consideration of this burden, the calculation related to the calculation of the dark signal amount using the above equation (1) is reduced. Therefore, the above equation (1) is simplified. For example, it is simplified by approximating with a linear function (straight line) like the following formula (2).
I=aT+b …(2)
ただし、a,bは定数である。上記(1)式の近似式を図5では点線で図示するとともに、上記(1)式を簡略化した上記(2)式を図5では実線で併記する。図5では、温度T2での上記(1)式の接線を上記(2)式としたが、上記(1)式の近似曲線上の温度(T2+k),温度(T2-k)(kは例えば1℃)を結ぶ直線を、近似式を簡略化した式としてもよい。 I = aT + b (2)
However, a and b are constants. The approximate expression (1) is shown by a dotted line in FIG. 5, and the expression (2) obtained by simplifying the expression (1) is also shown by a solid line in FIG. In FIG. 5, the tangent line of the above equation (1) at the temperature T2 is the above equation (2). However, the temperature (T2 + k) and the temperature (T2-k) (k on the approximate curve of the above equation (1) are The straight line connecting 1 ° C.) may be an expression obtained by simplifying the approximate expression.
ただし、a,bは定数である。上記(1)式の近似式を図5では点線で図示するとともに、上記(1)式を簡略化した上記(2)式を図5では実線で併記する。図5では、温度T2での上記(1)式の接線を上記(2)式としたが、上記(1)式の近似曲線上の温度(T2+k),温度(T2-k)(kは例えば1℃)を結ぶ直線を、近似式を簡略化した式としてもよい。 I = aT + b (2)
However, a and b are constants. The approximate expression (1) is shown by a dotted line in FIG. 5, and the expression (2) obtained by simplifying the expression (1) is also shown by a solid line in FIG. In FIG. 5, the tangent line of the above equation (1) at the temperature T2 is the above equation (2). However, the temperature (T2 + k) and the temperature (T2-k) (k on the approximate curve of the above equation (1) are The straight line connecting 1 ° C.) may be an expression obtained by simplifying the approximate expression.
上記(2)式では、上述した演算が低減するが、上述したように温度T2で最適になるように直線で近似することで上記(1)式の近似式を簡略化して(2)式に変換すると、温度T1,T3では実際のダーク信号量との誤差が大きくなる。理想的に、フレーム毎に温度を測定して、上述したパラメータa,bを求めて誤差を減らすのが可能だが、パラメータa,bが画素(ピクセル)毎に異なる場合には、フレーム毎に温度を測定してパラメータa,bを更新するとピクセル数の分だけコントローラ6の負担が大きくなる。
In the above formula (2), the above-described calculation is reduced, but as described above, the approximation formula of the above formula (1) is simplified to the formula (2) by approximating with a straight line so as to be optimal at the temperature T2. When converted, an error from the actual dark signal amount increases at temperatures T1 and T3. Ideally, it is possible to measure the temperature for each frame and obtain the parameters a and b described above to reduce the error. However, if the parameters a and b are different for each pixel, the temperature is determined for each frame. When the parameters a and b are updated, the burden on the controller 6 increases by the number of pixels.
そこで、画像取得(撮像)を行っていないときに温度を温度センサ10で測定して、パラメータa,bを更新する。図5および図6の例では、画像取得(撮像)を行っていないタイミングが3回あり、X線変換層23の温度がT1,T2,T3であったとする。図6に示すように、それぞれの温度毎に直線の近似式を求めてパラメータa,bを更新する。上記(1)式の近似式を図6では点線で図示するとともに、温度T1~T3のときに近似式を簡略化した式を図6では実線で併記する。このようなタイミングでパラメータa,bを更新することで、画像取得を行っていないときに近似式を簡略化した式に変換する。そして、パラメータa,bの更新により、誤差を減らすことが可能である。
Therefore, when the image acquisition (imaging) is not performed, the temperature is measured by the temperature sensor 10 and the parameters a and b are updated. In the example of FIGS. 5 and 6, it is assumed that there are three timings when image acquisition (imaging) is not performed and the temperature of the X-ray conversion layer 23 is T1, T2, and T3. As shown in FIG. 6, parameters a and b are updated by obtaining a linear approximation formula for each temperature. The approximate expression (1) is illustrated by a dotted line in FIG. 6, and an expression obtained by simplifying the approximate expression at temperatures T1 to T3 is also illustrated by a solid line in FIG. By updating the parameters a and b at such timing, the approximate expression is converted into a simplified expression when the image is not acquired. The error can be reduced by updating the parameters a and b.
また、全画素でなく画像の一部の画素のパラメータをフレーム毎に順次に更新することで、撮影を行いながらパラメータの更新を行うことも可能である。もちろん、演算の負担にならなければ、全画素毎にパラメータの更新を行ってもよい。
Also, it is possible to update the parameters while taking a picture by sequentially updating the parameters of some pixels of the image instead of all the pixels for each frame. Of course, the parameter may be updated for every pixel as long as the calculation is not burdened.
上述した本実施例に係るX線撮影装置によれば、X線の非照射時の電荷と等価なダーク信号量は、X線変換層23の温度に応じて変化するので、ダーク信号量を予め取得する。ダーク信号量とそのダーク信号量が得られたときのX線変換層23の温度とを対応させて、近似式算出の機能はダーク信号量およびX線変換層23の温度の相関関係の近似式(本実施例では上記(1)式)を求める。さらに、近似式算出の機能の後段のダーク信号量算出の機能によるダーク信号量の算出に関する演算の負担を低減させるために、近似式変換の機能は、近似式算出の機能で求められた近似式を簡略化した式(本実施例では上記(2)式)に変換する。そして、その近似式変換の機能で簡略化した式に変換された近似式と、温度センサ10で測定されたX線変換層23の温度とを用いて、ダーク信号量算出の機能はダーク信号量を求め、ダーク信号量算出の機能で求められたダーク信号量に基づいて照射時のキャリア(電荷情報)を補正することで、補正されたキャリアに基づいて画像を得る撮像を行う。したがって、近似式を用いてX線変換層23の温度に依存することなく撮像を行うことができる。また、近似式を用いているので、該当する範囲中の温度を全部知る必要がない。以上をまとめると、該当する範囲中の温度を全部知る必要がなく、近似式を用いてX線変換層23の温度に依存することなく撮像を行うことができる。
According to the above-described X-ray imaging apparatus according to the present embodiment, the dark signal amount equivalent to the electric charge when X-rays are not irradiated changes according to the temperature of the X-ray conversion layer 23. get. The function of the approximate expression calculation is an approximate expression of the correlation between the dark signal amount and the temperature of the X-ray conversion layer 23 by associating the dark signal amount with the temperature of the X-ray conversion layer 23 when the dark signal amount is obtained. (In the present embodiment, the above equation (1)) is obtained. Furthermore, in order to reduce the burden of calculation related to the dark signal amount calculation by the dark signal amount calculation function at the latter stage of the approximate expression calculation function, the approximate expression conversion function is an approximate expression obtained by the approximate expression calculation function. Is converted into a simplified expression (the above expression (2) in this embodiment). Then, using the approximate expression converted into the simplified expression by the approximate expression conversion function and the temperature of the X-ray conversion layer 23 measured by the temperature sensor 10, the dark signal amount calculation function is the dark signal amount. Then, the carrier (charge information) at the time of irradiation is corrected based on the dark signal amount obtained by the dark signal amount calculation function, and imaging is performed to obtain an image based on the corrected carrier. Therefore, imaging can be performed using the approximate expression without depending on the temperature of the X-ray conversion layer 23. Moreover, since the approximate expression is used, it is not necessary to know all the temperatures in the corresponding range. In summary, it is not necessary to know all the temperatures in the corresponding range, and imaging can be performed using the approximate expression without depending on the temperature of the X-ray conversion layer 23.
上述したように、近似式変換の機能は、画像取得を行っていないときに、近似式を簡略化した式に変換するのが好ましい。画像取得を行っていないときの空いている時間を利用して、近似式を簡略化した式に変換しているので、画像取得中(すなわち撮像中)の演算の負担が大きいときに別の処理を行うことなく、画像取得を行っていないときにおける演算の負担が小さいときに近似式を簡略化した式に変換することになる。
As described above, the approximate expression conversion function is preferably converted into a simplified expression when the image is not acquired. Since the approximate expression is converted to a simplified expression using the free time when image acquisition is not performed, another processing is performed when the calculation burden during image acquisition (ie during imaging) is heavy. Without performing the above, the approximate expression is converted into a simplified expression when the calculation burden when the image acquisition is not performed is small.
上述したように、近似式を簡略化した式に変換する場合において、必ずしも画像の全領域(すなわち全画素)に対して行わなくてもよい。すなわち、近似式変換手段は、画像の一部に対して、近似式を簡略化した式に変換してもよい。
As described above, in the case of converting the approximate expression to a simplified expression, it is not necessarily performed for the entire area (that is, all pixels) of the image. That is, the approximate expression conversion means may convert the approximate expression into a simplified expression for a part of the image.
この発明は、上記実施形態に限られることはなく、下記のように変形実施することができる。
The present invention is not limited to the above embodiment, and can be modified as follows.
(1)上述した実施例では、図1に示すようなX線撮影装置を例に採って説明したが、この発明は、例えばC型アームに配設されたX線透視撮影装置にも適用してもよい。また、この発明は、X線CT装置にも適用してもよい。
(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)上述した実施例では、入射したX線に代表される放射線をX線変換層(変換層)によって電荷情報に直接に変換した、「直接変換型」の検出素子用回路をこの発明は適用したが、入射した放射線をシンチレータなどの変換層によって光に変換し、光感応型の物質で形成された変換層によってその光を電荷情報に変換する「間接変換型」の検出素子用回路をこの発明は適用してもよい。
(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)上述した実施例では、X線を検出するための検出素子用回路を例に採って説明したが、この発明は、ECT(Emission Computed Tomography)装置のように放射性同位元素(RI)を投与された被検体から放射されるγ線を検出するための検出素子用回路に例示されるように、放射線を検出する検出素子用回路であれば特に限定されない。同様に、この発明は、上述したECT装置に例示されるように、放射線の入射により撮像を行う装置であれば特に限定されない。
(3) In the above-described embodiments, 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)上述した実施例では、X線などに代表される放射線撮像を例に採って説明したが、この発明は、光の入射により撮像を行う装置にも適用することができる。
(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)上述した実施例では、一次関数(直線)で近似して簡略化したが、上記(1)式が曲線であることを考慮して、二次曲線等で近似して簡略化してもよい。
(5) In the above-described embodiment, the function is approximated and simplified by a linear function (straight line). Good.
(6)上述した実施例では、簡略化した式のパラメータをその都度計算で求めて更新したが、例えば0.1℃毎にパラメータを予め求めて、温度毎にパラメータを並べたテーブルして記憶してもよい。
(6) In the above-described embodiment, the simplified formula parameters are obtained and updated each time. For example, the parameters are obtained in advance at every 0.1 ° C., and stored in a table in which the parameters are arranged for each temperature. May be.
Claims (3)
- 光または放射線の入射により前記光または放射線の情報を電荷情報に変換する変換層と、その変換層で変換された電荷情報を蓄積して読み出す蓄積・読み出し回路とを備え、その蓄積・読み出し回路で読み出された電荷情報に基づいて画像を得る撮像装置であって、光または放射線の非照射時の電荷と等価なダーク信号量とそのダーク信号量が得られたときの変換層の温度とを対応させてダーク信号量および変換層の温度の相関関係の近似式を求める近似式算出手段と、その近似式算出手段で求められた前記近似式を簡略化した式に変換する近似式変換手段と、前記変換層の温度を測定する温度測定手段と、前記近似式変換手段で簡略化した式に変換された近似式と、前記温度測定手段で測定された前記変換層の温度とを用いて前記ダーク信号量を求めるダーク信号量算出手段と、そのダーク信号量算出手段で求められた前記ダーク信号量に基づいて照射時の電荷情報を補正する補正手段とを備えることを特徴とする撮像装置。 A conversion layer that converts light or radiation information into charge information by the incidence of light or radiation; and a storage / readout circuit that stores and reads out the charge information converted by the conversion layer. An imaging device that obtains an image based on read charge information, the amount of dark signal equivalent to the charge when light or radiation is not irradiated, and the temperature of the conversion layer when the dark signal amount is obtained Corresponding approximate expression calculating means for obtaining an approximate expression of the correlation between the dark signal amount and the temperature of the conversion layer, and an approximate expression converting means for converting the approximate expression obtained by the approximate expression calculating means into a simplified expression; The temperature measurement means for measuring the temperature of the conversion layer, the approximate expression converted into a simplified expression by the approximate expression conversion means, and the temperature of the conversion layer measured by the temperature measurement means dark And dark signal amount calculating means for calculating the issue amount, an imaging apparatus characterized by comprising a correction means for correcting the charge information at the time of irradiation based on the dark signal amount obtained by the dark signal amount calculating means.
- 請求項1に記載の撮像装置において、前記近似式変換手段は、画像取得を行っていないときに、前記近似式を簡略化した式に変換することを特徴とする撮像装置。 2. The imaging apparatus according to claim 1, wherein the approximate expression conversion unit converts the approximate expression into a simplified expression when image acquisition is not performed.
- 請求項1または請求項2に記載の撮像装置において、前記近似式変換手段は、画像の一部に対して、前記近似式を簡略化した式に変換することを特徴とする撮像装置。 3. The imaging apparatus according to claim 1, wherein the approximate expression converting unit converts the approximate expression into a simplified expression for a part of an image.
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