JP2006158608A - Radiographic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide radiographic equipment providing a favorably radiographic image by appropriately correcting a dark current. <P>SOLUTION: This radiographic equipment corrects dark current components of a captured image, additionally corrects noise by a method different from the aforementioned correction, corrects a gain dependent on each pixel of the image, and processes the corrected image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses an X-ray detector capable of converting an X-ray image into a digital output X-ray image, and in particular, an X-ray imaging apparatus for correcting a dark current component of the X-ray detector.

  In X-ray imaging, an imaging plate in a cassette used in a film / screen system or computed radiography with a film and an intensifying screen sandwiched between a cassette and a screen is used to obtain an X-ray image of the examiner. ing.

  In recent years, an X-ray detector that can directly convert an X-ray image into a digital signal in real time has been proposed. As such an X-ray detector, for example, it is possible to manufacture a solid-state photodetector in which an amorphous semiconductor is sandwiched between substrates made of quartz glass, and solid-state photodetector elements composed of a transparent conductive film and a conductive film are arranged in a matrix. There is an X-ray detector in which this solid-state photodetector and a scintillator that converts X-rays into visible light are stacked.

  The X-ray image acquisition process when such an X-ray detector is used is as follows. First, X-rays are converted into visible light by a phosphor by irradiating the X-ray detector with X-rays that have passed through the object. And this visible light is detected as an electrical signal by the photoelectric conversion part of a solid-state light detection element. This electric signal is read out from each solid-state photodetecting element by a predetermined reading method, and this signal is A / D converted to obtain an X-ray image.

  Details of such an X-ray detector are described in Patent Document 1, for example. Many X-ray detectors that directly acquire X-rays with a solid-state photodetector without using a phosphor have been proposed.

  In general, these X-ray detectors detect the intensity of X-rays as a charge amount. Therefore, in order to acquire an X-ray image, the charges in the pixels are reset, and the charges for accumulating signal charges by the X-rays. Accumulation, charge transfer in the pixel, and constant cycle driving are required.

Since the X-ray detector simultaneously accumulates a charge that is a dark current component proportional to the accumulation time in addition to the signal charge due to the X-ray, the acquired X-ray image includes an X-ray signal component and a dark current component. Has been added. For this reason, dark current correction processing is performed in which a dark current correction image of only the proposed current component obtained without X-ray irradiation is subtracted from the X-ray image.
JP-A-8-116044

  However, since the dark current component changes depending on the accumulation time of the X-ray detector, the temperature of the X-ray detector, and the voltage applied to the X-ray detector, the X-ray image depends on the imaging conditions. The dark current component at the time of acquisition and the dark current component of the dark current correction image are different from each other, and the dark current correction process cannot be performed properly, and the dark current component remains in the processed X-ray image. There is a problem that noise is generated in an image.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an X-ray imaging apparatus capable of appropriately performing dark current correction processing and acquiring a good X-ray image.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has come up with the following aspects.

  An X-ray imaging apparatus according to the present invention includes an X-ray detector that acquires an X-ray image of a subject as an X-ray image, dark current correction processing means that corrects a dark current component of the acquired image, and the dark current. Additional correction processing means for correcting noise that cannot be corrected by the correction processing means, gain correction processing means for correcting gains depending on individual pixels of the image, image processing means for image processing of the corrected image, and correction The image processing apparatus includes a corrected image storage unit that stores an image for processing, and performs noise correction processing by subtracting the additional correction image stored in the corrected image storage unit after dark current correction processing.

  In the correction process of the dark current component of the X-ray image, the dark current component correction process that greatly depends on the temperature is acquired immediately after the X-ray image is acquired, and the dark current correction image is acquired from the X-ray image. Is a process of subtracting. The dark current component that greatly depends on the temperature has almost the same size by acquiring the dark current correction image immediately after acquiring the X-ray image. Since they have almost the same size, the dark current component that greatly depends on the temperature is appropriately corrected by subtracting the dark current correction image from the X-ray image.

  In addition, the dark current component correction process that greatly depends on the fluctuation of the voltage applied to the electrode is a process of subtracting an additional correction image acquired in advance from the X-ray image. The dark current component that greatly depends on the fluctuation of the voltage applied to the electrode has substantially the same magnitude by being acquired under exactly the same driving conditions as when the X-ray image was acquired. Since they have substantially the same size, the dark current component that greatly depends on the fluctuation of the voltage applied to the electrode is appropriately corrected by subtracting the dark current correction image from the X-ray image.

  In this way, by changing the image acquisition method for the dark current correction process according to the nature of the dark current component, and performing the dark current component correction process, an appropriate dark current correction process can be performed. There is an effect that an X-ray image can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  The following example is a first embodiment of an X-ray imaging apparatus that includes dark current correction processing means and additional correction processing means, and performs appropriate dark current component correction processing.

  Reference numerals 105 to 155 in FIG. 1 are schematic configuration diagrams showing a preferred example of the X-ray imaging apparatus according to the first embodiment. Reference numeral 105 denotes an X-ray irradiation means for irradiating the subject with X-rays, 110 denotes an X-ray detector for detecting the irradiated X-rays, and 115 denotes an X-ray irradiation operation of the X-ray irradiation means and driving of the X-ray detector is started. Operation means for operating, 120 a drive control means for driving and controlling the X-ray detector 110, 122 an X-ray image storage means for storing the acquired X-ray image, and 125 an X-ray acquired by the X-ray detector 110 Dark current correction processing means 130 for correcting the dark current component of the image, 130 is an additional correction processing means for correcting the remainder of the dark current component that could not be corrected by the dark current correction processing means 125 from the X-ray image, and 135 is X-ray detection. Gain correction processing means for correcting sensitivity variations with respect to X-rays in individual pixels of the device 110, image processing means 150 for image processing of the corrected X-ray image, and 155 an image processed image display.

  First, in imaging, the photographer uses the operation means 115 to output an X-ray irradiation signal to the X-ray irradiation means 105. Upon receiving the irradiation signal, the drive control means 120 puts the X-ray detector 110 into an accumulation state where signal charges due to X-rays can be accumulated. The drive control unit 120 causes the X-ray irradiation unit 105 to emit X-rays as the X-ray detector 110 enters the accumulation state.

  The irradiated X-rays enter the X-ray detector 110 and are acquired as an X-ray image. The acquired X-ray image is stored in the X-ray image storage unit 122. The drive control unit 120 acquires a dark current correction image with only a dark current component in the same accumulation time as the acquired X-ray image. The acquired dark current correction image is stored in the corrected image storage unit 140. The dark current correction processing unit 125 subtracts the dark current correction image stored in the correction image storage unit 140 from the X-ray image stored in the X-ray image storage unit 122 to perform dark current correction processing of the X-ray image. .

  As will be described in detail with reference to FIGS. 2 and 3, an X-ray image that has been subjected to dark current correction processing includes a dark current component that cannot be completely corrected by simply subtracting the dark current correction image. The additional correction processing unit 130 performs additional correction processing by subtracting the additional correction image stored in the corrected image storage unit 140 from the X-ray image after the dark current correction processing. In the X-ray image subjected to the dark current component addition process, there is a variation in sensitivity to X-rays by individual pixels. The gain correction processing unit 135 divides the X-ray image subjected to the dark current component addition processing by the gain correction image reflecting the sensitivity variation stored in the correction image storage unit 140, and performs gain correction processing. Further, the gain correction processing unit 135 performs log conversion on the X-ray image on which the gain correction processing has been performed. The X-ray image subjected to gain correction and Log conversion is subjected to image processing in the image processing means 150. The X-ray image that has been subjected to image processing is stored and displayed by the image display means 155.

  In the gain correction processing unit 135, the log conversion of the X-ray image is performed after the division of the X-ray image. However, the log conversion of the X-ray image is performed first, and then the X-ray image is subtracted. The same. This example is illustrated in FIG.

  The additional correction image and the gain correction image are acquired in advance before shooting and stored in the corrected image storage unit 140. A method for acquiring the additional corrected image will be described in detail with reference to FIG. A method for acquiring a gain-corrected image is described in JP-A-10-3237317.

  FIG. 2 illustrates the configuration of the X-ray detector 110 described in FIG. 1 and discharge of accumulated charges (hereinafter referred to as refresh), accumulation of charges, reading of charges, sleep state, and ready state. Detailed description is given in Japanese Patent Laid-Open Nos. 10-3237317 and 2002-281399.

  FIG. 2 is an overall circuit diagram showing the configuration of the X-ray detector 110. 2, S11 to S33 are photoelectric conversion elements, and the lower electrode side is indicated by G and the upper electrode side is indicated by D. C11 to C33 are storage capacitors, and T11 to T33 are transfer TFTs. Vs is a read power source and Vg is a refresh power source, which are connected to the G electrodes of the photoelectric conversion elements S11 to S33 via switches SWs and SWg, respectively. The switch SWs is directly connected to the refresh control circuit RF through an inverter, and is controlled so that SWg is on during the refresh period and SWs is on during the other periods. One pixel is composed of one photoelectric conversion element, a capacitor, and a TFT, and its signal output is connected to the detection integrated circuit IC by a signal wiring SIG. The two-dimensional area sensor of this embodiment divides a total of nine pixels into three blocks and simultaneously transfers the output of three pixels per block, and is sequentially converted into an output by the integrated circuit for detection through this signal wiring and output. Each pixel is arranged two-dimensionally by arranging three pixels in one block in the horizontal direction and arranging the three blocks in the vertical direction in order.

  The refresh operation will be described. First, Hi is applied to the control wirings g1 to g3 and s1 to s2 by the shift registers SR1 and SR2. Then, the transfer TFTs T11 to T33 and the switches M1 to M3 are turned on and become conductive, and the D electrodes of the photoelectric conversion elements S11 to S33 are set to the GND potential (because the input terminal of the integration detector Amp is designed to the GND potential). ). At the same time, the refresh control circuit RF outputs Hi, the switch SWg is turned on, and the G electrodes of the photoelectric conversion elements S11 to S33 are set to a positive potential by the refresh power supply Vg. Then, the photoelectric conversion elements S11 to S33 enter a refresh mode and are refreshed.

  Next, charge accumulation will be described. The refresh control circuit RF outputs Lo, the switch SWs is turned on, and the G electrodes of the photoelectric conversion elements S11 to S33 are set to a negative potential by the reading power source Vs. Then, the photoelectric conversion elements S11 to S33 are in the photoelectric conversion mode, and at the same time, the capacitors C11 to C33 are initialized. In this state, Lo is applied to the control wirings g1 to g3 and s1 to s3 by the shift registers SR1 and SR2. Then, the transfer TFTs T11 to T33 and the switches M1 to M3 are turned off, and the D electrodes of the photoelectric conversion elements S11 to S33 are opened in DC, but the potential is held by the capacitors C11 to C13. When X-rays are irradiated at this time and the X-rays are incident on the X-ray detector 110, a photocurrent flows through the photoelectric conversion elements S11 to S33, and is accumulated in the capacitors C11 to C33 as electric charges.

  The charge reading will be described. A Hi control pulse is applied to the control wiring g1 by the shift register SR1, and signals v1 to v3 are sequentially transmitted through the transfer TFTs T11 to T13 and the switches M1 to M3 by applying control pulses to the control wirings s1 to s3 of the shift register SR2. Is output. Similarly, other signals are output under the control of the shift registers SR1 and SR2. Thereby, X-ray images of the subject are obtained as signals v1 to v9.

  Finally, the sleep state and the ready state will be described. The X-ray detector 110 has a problem that its performance deteriorates when a voltage is applied to the G electrodes of the photoelectric conversion elements S11 to S33 for a long time. In the sleep state, in order to improve this, voltage is applied to the G electrodes of the photoelectric conversion elements S11 to S33 except for the time of image acquisition such as the discharge of charges, the accumulation of charges, and the reading of charges described above. This is a state in which it is stopped (set to a GND potential other than Lo or Hi). The ready state is a state in which a voltage is applied to the G electrodes of the photoelectric conversion elements S11 to S33 at the time of acquiring an image of discharging charges, storing charges, and reading charges as described above.

  Immediately after the imaging instruction, the X-ray detector 110 is changed from the sleep state to the ready state, so that the performance degradation of the X-ray detector 110 is suppressed.

  FIG. 3 is a timing chart for explaining acquisition of an X-ray image and acquisition of a dark current correction image in the ready state.

  Above and below the protrusions of g1 to g3 and s1 to s2 indicate Hi and Off of the control wiring, and above and below the protrusion of RF indicate Hi and Lo of voltage application to the G electrode by the refresh control circuit RF. The upper and lower portions of the X13 protrusion indicate the presence or absence of X-ray irradiation, and the OUT protrusion group indicates the signals v1 to v9 described with reference to FIG. P is an accumulation state at the time of acquisition of the X-ray image, and P ′ is an accumulation state at the time of acquisition of the dark current correction image. A and B indicate signals v1 to v9 in the accumulation states P and P ', respectively.

  When an X-ray irradiation signal is output in the ready state, the drive control means 120 drives the X-ray detector 110 as follows. First, the X-ray detector 110 is refreshed by setting the control wirings g1 to g3 and s1 to s2 to Hi and RF to Hi.

  Next, the control wirings g1 to g3 and s1 to s2 are turned off, and RF is set to Lo, thereby bringing the X-ray detector 110 into an accumulation state. In the accumulation state, X-rays are irradiated as indicated by X13. When the accumulation state ends, the charge is read out. In the charge reading, the signals v1 to v3 are sequentially read from the X-ray detector 110 by sequentially setting the control wirings s1 and s2 to Hi while keeping the control wiring g1 at Hi. Similarly, the signals v4 to v9 are read by sequentially setting the control wirings s1 to s2 to Hi while keeping the control wirings g1 and g2 at Hi, and all the signals of the photoelectric conversion elements S11 to S33 shown in FIG. v1 to v9 are read and an X-ray image is acquired. Subsequently, as described above, a dark current correction image is acquired by performing refresh, accumulation state, and reading of charges. In the X-ray detector 110, the process up to here is performed by one X-ray imaging.

  In the accumulation state indicated by P, since X-rays are emitted, a signal A that is the sum of a signal component and a dark current component due to X-rays is output from the X-ray image. In the accumulation state indicated by P ′, X-rays are not irradiated, so that the dark current correction image is output with the signal B of only the dark current component.

  As described with reference to FIG. 1, the dark current correction processing unit 125 performs dark current correction processing by subtracting the signal B that is a dark current correction image from the signal A that is an X-ray image. In order to appropriately correct the dark current component, the accumulation time indicated by P and the accumulation time indicated by P ′ are the same.

  FIG. 4 is a diagram showing a dark current component flowing in the photoelectric conversion element.

  The horizontal axis represents the time from the end of the sleep state (start of the ready state), and the vertical axis represents the magnitude of the dark current component. The dark current component is divided into a component that greatly depends on temperature and a component that greatly depends on the time from the end of the sleep state. The component that greatly depends on the time from the end of the sleep state is a dark current component that changes in magnitude due to voltage fluctuation as a result of applying a voltage to the G electrode of the photoelectric conversion element. The component that greatly depends on the temperature is a dark current component that always flows regardless of voltage application to the G electrode of the photoelectric conversion element, and greatly depends on the temperature of the photoelectric conversion element.

  FIG. 5 is a diagram for explaining the reason why an additional correction process is necessary after the dark current correction process.

  The horizontal axis represents the time from the start of the sleep state, and the vertical axis represents the magnitude of the dark current component. A is a dark current component that greatly depends on temperature, and B is a dark current component that greatly depends on voltage fluctuation applied to the G electrode. The areas of the two hatched portions in FIG. 5 correspond to the dark current component in the X-ray image and the dark current component in the dark current corrected image, respectively.

  As can be seen from FIG. 5, since the area of the shaded portion representing the dark current component is different between the X-ray image and the dark current correction image, it cannot be completely corrected even after the dark current correction image is subtracted from the X-ray image. There is a dark current component. The additional correction process in the additional correction processing unit 130 is a process for correcting the remaining dark current component.

  Since the dark current component corresponding to A is the same in the X-ray image and the dark current correction image, there is almost no temperature-dependent dark current component after the dark current correction image is subtracted from the X-ray image. That is, the dark current correction processing means 125 is a process for correcting a dark current component largely dependent on temperature. Further, as can be seen from FIG. 5, the remaining dark current component after subtracting the dark current correction image from the X-ray image is accumulated from the accumulation time T1 (= T2) of the X-ray detector 110 and from the end of the sleep state. It turns out that it depends on the time T3 until.

  The remaining dark current components described above are corrected by subtracting the additional correction image from the X-ray image after the dark current correction processing. Hereinafter, a method of acquiring the supplementary additional corrected image stored in the corrected image storage unit 140 will be described.

(Method 1)
The additional corrected image stored in the corrected image storage unit 140 is acquired by the same drive as the normal X-ray imaging shown in FIG. That is, the signal A corresponding to the X-ray image shown in FIG. 3 is acquired without irradiating X-rays, and the signal B corresponding to the dark current correction image is acquired, whereby the additional correction image is irradiated with X-rays. It is obtained by subtracting the dark current correction image from the X-ray image that is not. The acquired additional corrected image is stored in the corrected image storage unit 140.

(Method 2)
As described with reference to FIG. 5, the remaining dark current component is an offset component with respect to a signal by X-rays. Therefore, the additional correction process is effective even for a uniform constant image having an average value of the additional correction images acquired by the method 1. Therefore, the additional corrected image can be a uniform constant image having the same average value as in Method 1. A uniform constant image is stored in the corrected image storage unit 140.

  As described above, since there is a dark current component that greatly depends on voltage fluctuation applied to the electrodes, a difference occurs between the amount of dark current indicated by T1 and the amount of dark current indicated by T2. As can be seen from FIG. 5, the longer the time T3 from the end of the sleep state to the start of accumulation, the smaller the fluctuation of the dark current component, and the difference between the amount of dark current shown in T1 and the amount of dark current shown in T2. , Get smaller. However, in actual imaging, the inspection efficiency is deteriorated, so the value of T3 must be short. This is the reason why additional correction processing is necessary.

  The acquisition of the gain correction image does not affect the inspection efficiency as in the case of actual shooting, and therefore, the T3 value at the time of acquisition of the gain correction image is set to T1 by making it longer than the T3 value at the time of actual shooting. A difference between the amount of dark current and the amount of dark current indicated by T2 is reduced as much as possible, and a good gain-corrected image reflecting only variations in sensitivity to X-rays can be acquired.

  Further, when acquiring a gain-corrected image, the shorter T1 (= T2) is, the smaller the difference between the amount of dark current shown in T1 and the amount of dark current shown in T2 can be reduced as much as possible, reflecting only variations in sensitivity to X-rays. A good gain-corrected image can be acquired.

  FIG. 6 shows an imaging flow in the X-ray imaging apparatus having the configuration shown in FIG.

  In step S <b> 605, an imaging condition such as a patient name or an imaging region is input from the operation unit 115. In step S605, the X-ray detector 110 is changed from the sleep state to the ready state. In step S <b> 610, an X-ray irradiation signal for the X-ray irradiation unit 105 by the photographer is received from the operation unit 115. Upon reception of the X-ray irradiation signal, S615 causes the X-ray detector 110 to perform the driving shown in the first half of FIG. 3 to acquire an X-ray image and store it in the X-ray image storage unit 122. In S620, the driving shown in the second half of FIG. 3 is performed, a dark current correction image is acquired, and stored in the correction image storage unit 140.

  In S625, dark current correction processing is performed by subtracting the dark current correction image from the X-ray image. The dark current correction processing in S625 is mainly intended to correct dark current components that greatly depend on temperature. In S630, an additional correction process is performed by subtracting the additional correction image stored in the corrected image storage unit 140 from the X-ray image after the dark current correction process. The additional correction processing in S630 is mainly intended to correct the dark current component that greatly depends on the voltage fluctuation of the electrode.

  In step S635, the gain correction process is performed by dividing the X-ray image after the dark current correction process and the additional correction process by a gain correction image reflecting the sensitivity variation of each pixel with respect to the X-ray. Further, Log conversion is performed on the X-ray image after gain correction processing for image processing. In step S640, image processing is performed on the X-ray image after gain correction processing and log conversion. In step S645, the X-ray image after the image processing is output to a printer or a monitor. As described above, the imaging flow of X-ray imaging is performed.

  FIG. 7 is a diagram illustrating specific calculations of the dark current correction process, the additional correction process, and the gain correction process.

  First, an additional correction image and a gain correction image are acquired and stored in the correction image storage unit 140 in advance before shooting. At the time of imaging, an X-ray image is acquired from the X-ray detector 110 and stored in the X-ray image storage unit 122. Next, a dark current correction image is acquired from the X-ray detector 110 and stored in the corrected image storage unit 140. The dark current correction process is performed by subtracting the dark current correction image stored in the correction image storage unit 140 from the X-ray image stored in the X-ray image storage unit 122. After the dark current correction process, the additional correction process is performed by subtracting the additional correction image stored in the corrected image storage unit 140 from the X-ray image after the dark current correction process. After the additional correction process, the X-ray image subjected to the additional correction process is subjected to log conversion.

  In addition, the gain image reflecting the sensitivity of each pixel to the X-ray is also Log-transformed. The gain correction process is performed by subtracting the log-corrected gain correction image from the log-converted X-ray image. The X-ray image after log conversion and gain correction processing is subjected to image processing by the image processing means 150.

  FIG. 8 is a diagram illustrating an additional correction image acquisition flow. First, in step S805, it is confirmed whether the X-ray imaging apparatus is turned on. If it is confirmed that the power is turned on, S810 acquires an additional corrected image. In step S815, the acquired additional corrected image is stored in the corrected image storage unit 140. If the additional corrected image is already stored in the corrected image storage unit 140, the additional corrected image is updated and stored. In step S820, the flow of the additional correction image is waited for a predetermined time in the acquisition flow of the additional correction image. In step S825, it is determined whether an image is being input to the operation unit 115 and whether the X-ray detector 110 is being driven during imaging. If shooting is in progress, the process returns to S820. If it is not during shooting, it is determined whether the time since the last shooting is Ta or more. If it is less than Ta, the process returns to S820. If it is greater than or equal to Ta, it is determined whether or not the time since the additional correction image has been updated is greater than or equal to Tb. If it is equal to or greater than Tb, the process returns to S810 to acquire an additional corrected image. If it is less than Tb and the power source is not lowered, the process returns to S820 again. If the power is dropped, the flow ends.

  Acquisition of the gain correction image is the same as the method of acquiring a normal X-ray image without a subject. The gain-corrected image is an X-ray image without a subject before image processing. When the gain correction process is divided, the gain correction image is stored in the corrected image storage unit 140 without log conversion. When the gain correction process is subtraction, the gain correction image is subjected to log conversion and stored in the corrected image storage unit 140.

  As described above in the embodiment of the X-ray imaging apparatus, in the correction process of the dark current component of the X-ray image, the correction process of the dark current component that greatly depends on the temperature is performed immediately after the X-ray image is acquired. This is a process of acquiring a dark current correction image and subtracting the dark current correction image from the X-ray image. The dark current component that greatly depends on the temperature has almost the same size by acquiring the dark current correction image immediately after acquiring the X-ray image. In addition, the dark current component correction process that greatly depends on the fluctuation of the voltage applied to the electrode is a process of subtracting an additional correction image acquired in advance from the X-ray image. The dark current component, which greatly depends on the fluctuation of the voltage applied to the electrodes, is acquired by using the same driving conditions (T1 and T3 shown in FIG. 3) as those at the time of acquiring the X-ray image. have. In this way, by changing the image acquisition method for the dark current correction process according to the nature of the dark current component, and performing the dark current component correction process, an appropriate dark current correction process can be performed. There is an effect that an X-ray image can be obtained.

  The following example is a second embodiment of an X-ray imaging apparatus that includes dark current correction processing means and additional correction processing means, and performs appropriate dark current component correction processing.

  Reference numerals 105 to 155 and 905 in FIG. 9 are schematic configuration diagrams showing a preferred example of the X-ray imaging apparatus according to the second embodiment. Reference numerals 105 to 155 in FIG. 9 are the same as the configuration described in FIG. 1 of the first embodiment. The difference from the configuration described in FIG. 1 is that a plurality of additional correction images are acquired by changing the driving conditions. For this reason, it is necessary to record each driving condition of the additional corrected image. Reference numeral 905 denotes drive time acquisition means for recording drive conditions (T1 and T3 shown in FIG. 3) for each additional correction image and associating them with each additional correction image stored in the correction image storage means 140. Further, the driving time acquisition unit 905 records the driving conditions (T1 and T3 shown in FIG. 3) also at the time of acquiring the X-ray image, and associates it with the X-ray image stored in the X-ray image storage unit 122.

  First, an additional corrected image is acquired before shooting. In the additional correction image acquisition flow illustrated in FIG. 8, in the second embodiment, S810 acquires a plurality of additional correction images by changing drive conditions (T1 and T3 illustrated in FIG. 3). In S815, each driving condition (T1 and T3 shown in FIG. 3) is stored in association with each additional correction image. Of course, a gain-corrected image is also acquired before shooting.

  First, in imaging, the photographer uses the operation means 115 to output an X-ray irradiation signal to the X-ray irradiation means 105. Upon receiving the irradiation signal, the drive control means 120 puts the X-ray detector 110 into an accumulation state where signal charges due to X-rays can be accumulated. The drive control unit 120 causes the X-ray irradiation unit 105 to emit X-rays as the X-ray detector 110 enters the accumulation state. The irradiated X-rays enter the X-ray detector 110 and are acquired as an X-ray image.

  The driving time acquisition unit 905 acquires driving conditions (T1 and T3 shown in FIG. 3) at the time of acquiring the X-ray image. The acquired X-ray image is stored in the X-ray image storage unit 122 in association with driving conditions (T1 and T3 shown in FIG. 3). The drive control unit 120 acquires a dark current correction image with only a dark current component in the same accumulation time as the acquired X-ray image. The acquired dark current correction image is stored in the corrected image storage unit 140. The dark current correction processing unit 125 subtracts the dark current correction image stored in the correction image storage unit 140 from the X-ray image stored in the X-ray image storage unit 122 to perform dark current correction processing of the X-ray image. . As described with reference to FIGS. 2 and 3, the X-ray image that has been subjected to the dark current correction process includes a dark current component that cannot be completely corrected only by subtracting the dark current correction image. The additional correction processing unit 130 performs additional correction processing by subtracting the additional correction image stored in the corrected image storage unit 140 from the X-ray image after the dark current correction processing. Here, a plurality of additional corrected images are stored in the corrected image storage unit 140 in association with driving conditions (T1 and T3 shown in FIG. 3). An additional correction image having the same driving condition (T1 and T3 shown in FIG. 3) as the driving condition of the X-ray image (T1 and T3 shown in FIG. 3) is selected, and an additional correction process is performed. If there is no additional correction image having the same driving conditions (T1 and T3 shown in FIG. 3), an additional correction image close to the X-ray image and the driving conditions (T1 and T3 shown in FIG. 3) is created and added. Correction processing is performed. A method of creating an additional corrected image having a driving condition (T1 and T3 shown in FIG. 3) close to the driving condition of the X-ray image (T1 and T3 shown in FIG. 3) is described in FIG.

  In the X-ray image subjected to the dark current component addition process, there is a variation in sensitivity to X-rays by individual pixels. The gain correction processing unit 135 divides the X-ray image subjected to the dark current component addition processing by the gain correction image reflecting the sensitivity variation stored in the correction image storage unit 140, and performs gain correction processing. Further, the gain correction processing unit 135 performs log conversion on the X-ray image on which the gain correction processing has been performed. The X-ray image subjected to gain correction and Log conversion is subjected to image processing in the image processing means 150. The X-ray image that has been subjected to image processing is stored and displayed by the image display means 155.

  As described in the second embodiment, an additional correction image having the same or close driving conditions (T1 and T3 shown in FIG. 3) as the X-ray image and the driving conditions (T1 and T3 shown in FIG. 3) are added. By performing the correction process, there is an effect that the correction process of the dark current component that greatly depends on the fluctuation of the voltage applied to the electrode can be appropriately performed. Further, as described in the first embodiment, when there is only one additional correction image, an X-ray image driving condition (T1 and T3 shown in FIG. 3) is also used in order to perform appropriate additional correction processing. , Fixed to one. Therefore, when there are a plurality of additional corrected images, the driving conditions for the X-ray image (T1 and T3 shown in FIG. 3) are not fixed to one, but the driving conditions suitable for each imaging (T1 shown in FIG. 3). There is an effect that the photographing of T3) can be performed. For example, in chest imaging with a large amount of X-ray transmission, T1 of the driving condition (T1 and T3 shown in FIG. 3) is short, but in lumbar imaging with a small amount of X-ray transmission, the driving condition (T1 shown in FIG. 3). For example, T1 in T3) is long, so that it is possible to select shooting under driving conditions (T1 and T3 shown in FIG. 3) suitable for each shooting.

  On the contrary, in the first embodiment, the driving conditions (T1 and T3 shown in FIG. 3) of the X-ray image are fixed. As a result, only one additional correction image needs to be acquired and stored, and the time required for acquisition and the processing time are fast.

  Further, when the additional correction image is a uniform constant image, there is an effect that it is not necessary to acquire the additional correction image and it does not take time for acquisition.

  FIG. 10 is a diagram illustrating a method of creating an additional corrected image having a driving condition (T1 and T3 shown in FIG. 3) close to the driving condition of the X-ray image (T1 and T3 shown in FIG. 3).

  A to D images in 10-1 indicate additional corrected images having different driving conditions (T1 and T3 shown in FIG. 3). The time on the horizontal axis corresponds to T1 (or T3) of the driving conditions of the A to D images. That is, the A to D images have different driving conditions of T1 (or T3). 10-2 shows a graph in which pixel values of the same coordinates of each additional corrected image having the driving conditions of each T1 (or T3) are plotted.

  When an additional corrected image having T1 (or T3) between the B image and the C image is created, an additional corrected image having a pixel value at the midpoint between points B and C of the graph 10-2 in each coordinate. Create Here, 10-2 shows an example of linear interpolation, but the creation of an additional corrected image does not depend on the interpolation method.

  As described above, by creating an additional correction image close to the X-ray image driving conditions (T1 and T3 shown in FIG. 3), the correction processing of the dark current component that greatly depends on the fluctuation of the voltage applied to the electrode is appropriate. There is an effect that can be done.

It is a schematic block diagram which shows a suitable example of the X-ray imaging apparatus which is 1st Embodiment. It is the figure explaining the structure and drive of the X-ray detector 110 demonstrated in FIG. 1 in detail. It is a timing diagram explaining acquisition of an X-ray image and acquisition of a dark current correction image. It is the figure which showed the dark current component which flows into a photoelectric conversion element. It is a figure explaining the reason why additional correction processing is necessary after dark current correction processing. 2 shows an imaging flow in an X-ray imaging apparatus having the configuration shown in FIG. It is the figure which showed the specific calculation of the dark current correction process, the additional correction process, and the gain correction process. It is a figure explaining the acquisition flow of the additional correction image. It is a schematic block diagram which shows a suitable example of the X-ray imaging apparatus which is 2nd Embodiment. It is a figure explaining the method of producing the additional correction image with the drive condition close | similar to the drive condition of a X-ray image.

Explanation of symbols

105 X-ray irradiation means 110 X-ray detector 115 Operation means 120 Drive control means 122 X-ray image storage means 125 Dark current correction processing means 130 Additional correction processing means 135 Gain correction processing means 140 Correction image storage means 150 Image processing means 155 Image Display means 905 Driving time acquisition means

Claims (13)

An X-ray detector for acquiring an X-ray image of a subject as an X-ray image;
Dark current correction processing means for correcting the dark current component of the acquired image;
Additional correction processing means for correcting noise that cannot be corrected by the dark current correction processing means;
Gain correction processing means for correcting sensitivity depending on individual pixels of the image;
Image processing means for image processing of the corrected image;
In an X-ray imaging apparatus provided with corrected image storage means for storing an image for correction processing,
Subtract the additional correction image stored in the correction image storage means after dark current correction processing,
An X-ray imaging apparatus characterized by performing noise correction processing. The X-ray imaging apparatus according to claim 1,
2. The X-ray imaging apparatus according to claim 1, wherein the X-ray detector enters a ready state from a sleep state immediately before signal accumulation. The X-ray imaging apparatus according to claim 1,
The X-ray imaging apparatus according to claim 1, wherein the additional correction image is determined according to an accumulation time of the X-ray image. The X-ray imaging apparatus according to claim 1,
The X-ray detector is characterized in that an X-ray image is acquired at a constant accumulation time. The X-ray imaging apparatus according to claim 1,
The X-ray imaging apparatus according to claim 1, wherein the additional correction image is a uniform constant image. The X-ray imaging apparatus according to claim 2,
The X-ray imaging apparatus according to claim 1, wherein the additional correction image is determined according to a time from the end of the sleep state to the start of the accumulation state. The X-ray imaging apparatus according to claim 1,
The X-ray imaging apparatus characterized in that the additional correction image is acquired immediately after the X-ray detector is powered on. The X-ray imaging apparatus according to claim 1,
The X-ray imaging apparatus according to claim 1, wherein the additional correction image is acquired when acquisition of an X-ray image is not performed for a predetermined time. The X-ray imaging apparatus according to claim 4.
The X-ray imaging apparatus characterized in that the gain correction processing means uses a gain correction image acquired with an accumulation time shorter than a certain accumulation time for acquiring an X-ray image. The X-ray imaging apparatus according to claim 4.
The X-ray imaging apparatus characterized in that the gain correction processing means uses a gain correction image acquired in a longer time from the end of the sleep state to the start of the accumulation state than at the time of examination. The X-ray imaging apparatus according to claim 3 or 6,
An X-ray imaging apparatus, wherein a plurality of the additional corrected images are acquired by changing driving conditions. The X-ray imaging apparatus according to claim 1,
The X-ray imaging apparatus according to claim 1, wherein the additional correction image is acquired when a predetermined time or more has elapsed since the update. The X-ray imaging apparatus according to claim 3, 6 or 11,
The X-ray imaging apparatus, wherein the additional correction image is created from a plurality of additional correction images having different driving conditions.