JP6041856B2 - Radiation imaging system, control method, recording medium, and program - Google Patents

Description

  The present invention relates to a radiation imaging apparatus, a radiation imaging method, a recording medium, and a program, and more particularly to an apparatus and method for correcting a dark current of a radiation plane detector using a radiation plane detector (flat panel detector) as a solid radiation detector. About.

  As a radiation imaging device that captures a radiation image that has passed through a subject, conventionally, a screen film system (S / F system) is used in which an intensifying screen that converts radiation into fluorescence and a film that is sensitive to fluorescence are brought into close contact with each other. The device has been used. In addition, a radiographic image is multiplied by combining a phosphor and an image intensifier (II), and the multiplied image is photographed with an imaging tube via an optical system. Imaging devices have also been used. The former has been mainly used for still image shooting called general shooting, and the latter is mainly used for moving image shooting called fluoroscopic shooting or angio shooting.

  Recently, a digital photographing apparatus having a digital image output has begun to be used due to a demand for image digitization. In general photography, an imaging plate that accumulates a radiation image as a latent image is used in place of the screen / film system. The imaging plate is scanned with a laser to excite the latent image, and the generated fluorescence is emitted by a photomultiplier tube. Read, computed radiography devices are also used. In moving image shooting, an II-DR imaging apparatus that uses a solid-state imaging device such as a CCD instead of the imaging tube is also used. Both the computed radiography apparatus and the II-DR imaging apparatus have digital image output and are beginning to contribute to the digitization of medical images.

More recently, there has been a digital imaging device that directly digitizes a radiation image without using an optical system or the like, using a radiation flat panel detector (FPD) in which a phosphor and a large area amorphous silicon sensor are in close contact. It has been put into practical use. An FPD that uses amorphous selenium, lead iodide (PbI ₂ ), mercury iodide (HgI ₂ ), etc. to convert radiation into electrons and detects the electrons with a large-area amorphous silicon sensor has also been put to practical use. Yes. These FPDs are expected as next-generation digital photographing devices because they can shoot not only still images but also moving images in principle.

  Here, the principle of the FPD will be briefly described with reference to FIGS. FIG. 6 is a diagram for explaining the principle of sensor reading operation, and shows a sensor composed of nine pixels for simplicity. In FIG. 6, 71 is a photoelectric conversion unit that converts fluorescence into electrons, 72 is a thin film transistor (TFT) for transferring electrons generated in the photoelectric conversion unit, and 73 is a bias voltage applied to the photoelectric conversion unit 71. Bias lines, 74a, 74b, and 74c are gate lines that transmit a switching signal to the TFT 72, 75a, 75b, and 75c are signal lines that transfer electrons that have passed through the TFT 72, and 76 is one signal line from the signal lines 75a, 75b, and 75c. IC for selecting and amplifying signal electrons, 77 is an analog-to-digital converter (A / D) that converts the amplified analog signal into a digital signal, 78 is controlling the switching operation of the TFT 72 This is a gate driving device.

  In FIG. 7, when radiation is applied to a phosphor (not shown) that covers the entire surface of the sensor pixel, the phosphor emits fluorescence proportional to its intensity. The photoelectric conversion unit 71 captures this fluorescence and converts it into signal electrons. When the gate driving device 78 sets the gate line 74a to High, all the TFTs in the horizontal row connected to the gate line 74a are turned on. Then, the signal electrons accumulated in the photoelectric conversion unit 71 are transferred to the signal lines 75a, 75b, and 75c. When the reading IC 76 selects the signal line 75a, the electrons transferred to the signal line 75a are amplified and read, and converted into a digital signal by the A / D 77. Subsequently, the reading IC 76 sequentially selects 75b and 75c, and the electrons transferred to the respective signal lines are sequentially read. By this operation, signal electrons of three pixels for one horizontal row connected to the gate line 74a in FIG. 6 are read and converted into digital signals. Next, the gate lines 74b and 74c are sequentially selected, and similarly, the signal electrons of the respective three pixels for one horizontal row connected to the gate lines 74b and 74c are sequentially read and converted into digital signals.

  Next, the operation principle of one pixel of the sensor will be described with reference to FIGS. FIG. 7 is a configuration diagram of a MIS (Metal Insulator Semiconductor) type sensor, and FIG. 8 is an energy band diagram of a photoelectric conversion element. 7 and 8, 71 is a photoelectric conversion unit, 72 is a TFT, 73 is a bias line, 76 is a reading IC, 82 is an upper electrode (D electrode) for transmitting a bias voltage to the photoelectric conversion unit 71, and 83 is an upper electrode. The n + doped layer has the same potential as that of 82 and prevents hole injection into the a-Si intrinsic semiconductor i layer 84, 84 is an a-Si intrinsic semiconductor i layer that performs photoelectric conversion, and 85 is the movement of both electrons and holes. The blocking insulating layer 86 is a lower electrode (G electrode).

  FIGS. 8A and 8B are energy band diagrams of the photoelectric conversion element showing operations in the refresh (or reset) and photoelectric conversion modes, respectively, and show the state of each layer in the thickness direction. This photoelectric conversion element has two types of operations, a refresh mode and a photoelectric conversion mode, depending on the voltage application method of the D electrode and the G electrode.

  In FIG. 8A, the D electrode is given a negative potential with respect to the G electrode, and the holes indicated by black circles in the i layer 84 are guided to the D electrode by an electric field. At the same time, electrons indicated by white circles are injected into the i layer 84. At this time, some holes and electrons recombine and disappear in the n + doped layer 83 and the i layer 84. If this state continues for a sufficiently long time, the holes in the i layer 84 are swept out of the i layer 84.

  From this state, to make the photoelectric conversion mode of FIG. 8B, a positive potential is applied to the D electrode with respect to the G electrode. Then, the electrons in the i layer 84 are instantaneously guided to the D electrode. However, holes are not led to the i layer 84 because the n + doped layer 83 serves as an injection blocking layer. When light enters the i layer 84 in this state, the light is absorbed and an electron / hole pair is generated. The electrons are guided to the D electrode by the electric field, and the holes move in the i layer 84 and reach the interface between the i layer 84 and the insulating layer 85.

  However, since it cannot move into the insulating layer 85, it moves to the interface of the insulating layer 85 in the i layer 84, so that a current flows from the G electrode in order to maintain electrical neutrality in the element. Since this current corresponds to the electron-hole pair generated by light, it is proportional to the incident light. After maintaining the photoelectric conversion mode of FIG. 8B for a certain period and then entering the state of FIG. 8A of the refresh mode again, the holes remaining in the i layer 84 are guided to the D electrode as described above, At the same time, a current corresponding to this hole flows. The amount of holes corresponds to the total amount of light incident during the photoelectric conversion mode period. At this time, a current corresponding to the amount of electrons injected into the i layer 84 also flows. However, since this amount is approximately constant, it may be detected by subtracting. In other words, this photoelectric conversion element can output the amount of light incident in real time and simultaneously output the total amount of light incident in a certain period.

  However, when the period of the photoelectric conversion mode becomes long for some reason, or when the illuminance of incident light is strong, current may not flow even though light is incident. This is because, as shown in FIG. 8C, a large number of holes remain in the i layer 84 and recombine with the holes in the i layer 84 due to the holes. If the light incident state changes in this state, the current may flow in an unstable manner. However, if the refresh mode is set again, the holes in the i layer 84 are swept away, and in the next photoelectric conversion mode, the current is proportional to the light again. Flows.

  In the above description, when holes in the i layer 84 are swept out in the refresh mode, it is ideal that all holes be swept out, but it is effective to pull out only some of the holes, and a current equal to that described above can be obtained. There is no problem. That is, the detection opportunity in the next photoelectric conversion mode does not have to be in the state of FIG. 8C, the potential of the D electrode with respect to the G electrode in the refresh mode, the period of the refresh mode, and the implantation of the n + doped layer 83 The characteristics of the blocking layer can be determined. Further, in the refresh mode, injection of electrons into the i layer 84 is not a necessary condition, and the potential of the D electrode with respect to the G electrode is not limited to negative. This is because when many holes remain in the i layer 84, even if the potential of the D electrode with respect to the G electrode is positive, the electric field in the i layer 84 is applied in the direction leading the holes to the D electrode. Similarly, the characteristics of the injection blocking layer of the n + doped layer 83 are not necessarily required to be able to inject electrons into the i layer 84.

The above is the description of the operation in the MIS type sensor, but other types of sensors used in the FPD, for example, a sensor using a PIN type photodiode, perform almost the same operation although partially different. An example is the FPD sensor disclosed in Patent Document 1. In addition to a method using a phosphor, amorphous selenium, gallium arsenide (GaAs), cadmium telluride (CdTe), lead iodide (PbI ₂ ), iodide, which directly converts radiation into electrons instead of the phosphor Even in a sensor using mercury (HgI ₂ ) or the like, an operation for reading electrons accumulated in a pixel and a refresh operation are very similar.

  By the way, although the sensor used for FPD consists of several million pixels, the characteristic of each pixel differs slightly. Particularly important characteristics as an image sensor are dark current characteristics and sensitivity characteristics. Therefore, in the FPD, a step of correcting these characteristics is performed, and it is used as a sensor in which the characteristics of each pixel are substantially uniform. This correction step is common to a method using amorphous selenium or the like. A method for correcting dark current characteristics and sensitivity characteristics will be described below.

  First, terms used below are briefly described. First, imaging by irradiating a radiation detector with radiation is referred to as radiation imaging, and an image obtained here is referred to as a radiation image. Next, since the measurement of dark current characteristics is the same as that of radiography except that no input is given to the sensor, the measurement of dark current characteristics is called dark current imaging, and the image obtained here is called a dark current image. In addition, an image obtained by correcting dark current using N times of dark current images may be referred to as an Nth-order dark current corrected image. Further, an image obtained by applying sensitivity correction to the (Nth) dark current corrected image is an (Nth) corrected image, and an image obtained by performing image processing such as gradation processing suitable for image diagnosis on the (Nth) corrected image. May be referred to as an (Nth order) diagnostic image.

A method for correcting the dark current characteristic will be described. Here, the dark current is a current measured when there is no input to the sensor, and is assumed to be composed of a random component and a steady offset component. Assuming that the dark current does not depend on the sensor input, it is possible to correct an offset component different for each pixel by subtracting an image when no signal is input to the sensor from an image when the signal is input to the sensor. When a radiographic image when a signal is input to the sensor is X _n (x, y) and a dark current image measured immediately after that is D ₁ (x, y), a primary dark current corrected image after dark current correction is performed. C _1X (x, y) is expressed by the following equation. However, x and y are addresses of pixels arranged two-dimensionally. The random component is R (x, y), and the stationary offset component is F (x, y).

Next, correction of sensitivity characteristics will be described. Sensitivity correction is a step of correcting variations in sensitivity characteristics of pixels constituting the sensor. Assuming that the sensitivity characteristics are stationary, it is possible to correct different sensitivity characteristics for each pixel by dividing the image when a signal is input to the sensor by the image when a uniform input is given to the sensor. . If the output is W (x, y) when uniform input is given to the sensor, the corrected image C ₁ (x, y) after the sensitivity correction is expressed by the following equation.

By the way, F (x, y), which is an offset component in the dark current image, is constant regardless of the input to the sensor when the imaging conditions are the same. Can be removed. However, since R ₀ (x, y) appearing in the equation (1) and R ₁ (x, y) appearing in the equation (3) are different, the random component R (x, y) is not corrected by the offset correction shown in the equation (3). It cannot be removed. As a result, even if the image is subjected to both dark current correction and sensitivity correction, finite random noise derived from the sensor remains in the image. This random noise is not a problem if the random component R (x, y) is sufficiently smaller than the radiation image X (x, y), but the radiation image X (x, y), which is a signal as in low-dose imaging. In the case of shooting with a small image quality, there is a possibility that deterioration of image quality due to a decrease in signal-to-noise ratio is pointed out.

Therefore, by using the property shown in the equation (5), the dark current image is taken many times and an average value thereof is taken so that the random component R (x, y) included in the dark current image can be substantially ignored. It is conceivable to make it even smaller. When the random component R (x, y) has a normal distribution, the standard deviation σ ₀ per measurement of the random component R (x, y) and the standard deviation σ _n of the average value n times of measurement have the following relationship. .

A dark current correction method using this property is described in Non-Patent Document 1. If this method is used, the random component R (x, y) included in the dark current image D _X (x, y) is halved by using the average value of the four times of dark current imaging, which is good. Dark current correction can be performed. The ratio of the standard deviation of the random component R (x, y) remaining in each of the primary dark current corrected image and the quaternary dark current corrected image is shown in equation (8). However, both the random component superimposed on the radiation image itself and the random component of the four-time average dark current image are taken into consideration.

  From the equation (8), in low-dose imaging where the random noise is dominant, it is expected that the signal-to-noise ratio will be improved by about 20% compared to the single dark current imaging by performing the dark current imaging 4 times. I understand that

  A method of driving the FPD sensor for performing the radiography and dark current imaging described above will be described with reference to FIG. 9 which is a sensor driving flowchart. In FIG. 9, 21 is an idling drive, 22 is an initialization drive for radiography, 23 is an imaging drive for radiography, 24 is an initialization drive for dark current imaging, and 25 is for dark current imaging. The imaging drive 26 is radiation exposure.

  As shown in FIG. 9, the driving state of the FPD sensor is roughly divided into three types: idling driving 21, initialization driving 22 and 24, and imaging driving 23 and 25. When the bias voltage starts to be applied to the FPD sensor, dark current generated by a trap of the photoelectric conversion layer or the like continues to be accumulated. The idling drive 21 is an operation for sweeping out this dark current by a pseudo reading operation, and is a sensor preparation step which is intermittently performed from the time when a bias voltage is applied to the sensor to just before photographing. The pseudo reading cycle at this time is relatively long. The reason is to suppress an increase in power consumption and a sensor temperature rise due to the reading operation to a minimum.

  Next, the initialization drives 22 and 24 are steps for performing a pseudo reading operation to sweep out the dark current and prepare for radiation exposure at the same time. The read cycle performed by the initialization drives 22 and 24 is faster than the idling drive 21. The reason is that a radiation exposure command cannot be accepted during the reading period, and the delay time from the radiation exposure command to the actual radiation exposure is shortened by increasing the reading cycle. Then, after the radiation exposure, the reading drive 23 is performed to capture a radiation image.

  Dark current imaging is performed following radiography. When radiography is performed as shown in FIG. 8, the sensor immediately starts the initialization drive 24, and performs dark current imaging 25 at the same timing as radiography. This timing will be described in detail with reference to FIG.

FIG. 10 is a timing chart for explaining the timing of radiation exposure and sensor driving. In FIG. 10, 31 is a radiation exposure request signal by a radiation exposure switch, 32 is a radiation exposure permission signal, 33 is radiation exposure, 34 is a driving signal of driving method 1, and 35 is a driving signal of driving method 2. . R is refresh, X is radiography, D is dark current imaging, T _e1 and T _e2 are accumulation times, and T _i is the time required for one reading cycle.

First, the driving method 1 will be described. When the radiation exposure request signal 31 is turned on, the sensor is switched from idling driving to initialization driving. Then, the sensor performs a refresh operation and sweeps out the holes accumulated in the sensor. When the fourth read cycle in the initialization drive is completed, the radiation exposure permission signal 32 is turned on, the sensor stops the read cycle, the radiation exposure 33 is turned on, and the sensor accumulates the radiation signal. When the radiation exposure 33 is turned off, the sensor immediately ends the accumulation and reads the radiation image (X). The sensor accumulation time at this time is _Te1 . The sensor immediately performs a refresh operation, and then repeats the reading cycle. When the fourth reading cycle is completed, dark current imaging (D) is performed at the accumulation time _Te1 .

Next, the driving method 2 will be described. Similarly, when the radiation exposure request signal 31 is turned on, the sensor is switched from idling driving to initialization driving. Then, the sensor performs a refresh operation and sweeps out the holes accumulated in the sensor. When the radiation exposure permission signal 32 is turned on at the fourth reading cycle in the initialization drive, the sensor stops the reading cycle, the radiation exposure 33 is turned on, and the sensor accumulates a signal due to radiation. When the predetermined time _Te2 elapses, the sensor ends the accumulation and reads the radiation image (X). The sensor immediately performs a refresh operation, and then repeats the reading cycle. When the fourth reading cycle is completed, dark current imaging (D) is performed at the accumulation time _Te2 . The accumulation time _Te2 is set to a time of 1 second to 2 seconds so as to be able to cope with long-time shooting. This driving method is described in Non-Patent Document 2.

As apparent from the above, the difference between the driving method 1 and the driving method 2 is that the driving method 1 can freely change the accumulation time T _e1 according to the radiation exposure time, whereas the driving method 2 is the accumulation. Time T _e2 is fixed. Since the driving method 1 can minimize the accumulation time, there is an advantage that dark current accumulation can be reduced as compared with the driving method 2 that employs the accumulation time corresponding to the longest expected exposure time. In addition, since the actual radiation exposure time is about 20 msec for general chest imaging, there is an advantage that the sensor driving can be completed in a short time and an image can be displayed at an early stage. On the other hand, since the accumulation time is always constant in the driving method 2, there is a possibility that dark current imaging can be performed before radiation exposure.

It should be noted here that both methods perform dark current imaging immediately after radiation imaging, and the refresh operation of the initialization drive performed before radiation imaging and dark current imaging is the same as the number of read cycles, and further The accumulation time for photographing and dark current photographing is also the same. This is because the offset component F (x, y) shown in equations (1) and (2) is a function of the accumulation time and drive timing, the dark current amount has a high correlation with the accumulation time, and the transient of the sensor This is because the correlation between the drive timing and the dark current is high due to the characteristic characteristics. If, because Without such a drive, a dark current image D is superimposed on the radiation image ₀ (x, y) and the dark due to dark current shot current image D ₁ (x, y) is the correlation of the loss, (3 Even if the subtraction operation shown in equation (4) is performed, a part of the offset component F (x, y) may remain and an unexpected sensor-specific pattern (artifact) may appear.

  In FIG. 9 and FIG. 10, for the sake of simplicity of explanation, the case of one dark current imaging is shown. However, as already described, by performing dark current imaging a plurality of times, random components included in the dark current image can be reduced and the signal-to-noise ratio can be improved. Therefore, actually, the radiographic imaging is followed by one to several dark current imaging as required.

JP-A-10-170657 JP 2000-070250 A

J.P.Moy, B.Bosset, "How does real offset and gain correction affect the DQE in images from X-ray Flat detector", SPIE proceedings Vol.3659, 90-97 (1999) John M. Boudry, "Operation of Amorphous Silicon Detectors for Chest Radiography Within System Latency Requirement", SPIE proceedings Vol. 3659, 336-344 (1999)

However, when dark current imaging is performed a plurality of times, there is a problem that it takes a long time until an image is obtained after radiation imaging. For example, in the driving method 2, the initialization drive refresh operation is performed once, the read cycle is performed four times, the refresh operation for one time and the read cycle required time T _i are 0.2 seconds, the accumulation time _{Te 2} is 2 seconds, the dark current Consider an example in which shooting is performed four times. In this case, the time T _display required from the end of the radiation exposure to the end of the fourth dark current imaging and the display of the image on the monitor is calculated by the following equation, assuming that the total T _process of the image transfer time and the image processing time is 0.5 seconds. It is represented by

  Since FPD can display an image quickly after photographing, it is expected that a diagnostic image can be confirmed immediately after photographing. In particular, when a diagnostic image is displayed within a few seconds after radiation exposure, it is expected to improve the workflow of the radiologist and reduce the waiting time of the patient for re-imaging. However, if 10 seconds or more are required for image display, the engineer cannot wait until the image is displayed, and improvement of the engineer's workflow cannot be expected. This also makes it difficult to reduce patient waiting time.

In order to solve this problem, in the driving method 2, taking advantage of the fact that the accumulation time _Te2 is fixed, dark current imaging is performed (multiple times) prior to radiation imaging, and this dark current image is used. It is conceivable to perform dark current correction. However, due to the transient nature of the sensor, when dark current imaging and radiography are separated in time, the correlation between the dark current image in dark current imaging and the dark current image superimposed on the radiation image is lost. Artifacts may occur. For this reason, it is virtually impossible to perform dark current imaging before a radiation exposure request. In addition, a method of performing dark current imaging during a period from a radiation exposure request to a radiation exposure using a radiation exposure request as a trigger can be considered.

However, this method is not practical because it takes a long time from the radiation exposure request to the actual radiation exposure, forcing the patient to move and stop breathing over this long period. Therefore, it is desirable to perform dark current imaging immediately after radiography as shown in driving method 2 even in a driving method in which the accumulation time _Te2 is constant. In the driving method 1, since the actual radiation exposure time cannot be predicted in phototimer imaging or the like, dark current imaging cannot be performed prior to radiation imaging.

  In addition, a driving method in which image reading is continuously repeated without using a radiation exposure request as a trigger is also conceivable. For example, Patent Document 2 discloses a proposal for performing dark current correction using this driving method and using a single dark current image taken immediately before radiography. However, in this method, a large number of reading operations are required for one radiography at an unknown timing, which may cause problems of power consumption and heat generation. In addition, since dark current imaging and radiation imaging cannot be synchronized in principle, there arises a problem that the timings of the both overlap.

  In order to solve the latter problem, in the modified embodiment of the first embodiment of Patent Document 2, when the timings of both dark current imaging and radiation imaging overlap, a plurality of sheets covering the entire radiation exposure period are provided. A proposal is disclosed in which a radiation image is stored, and an image obtained by multiplying the plurality of radiation images by a plurality of times a dark current image immediately before radiation imaging is divided. However, the division operation of the coefficient-multiplied image only increases the random component R (x, y) even if there is a possibility of correcting the stationary offset component F (x, y). The effect of reducing R (x, y) cannot be expected. The reason is explained as follows.

The dark current image immediately before radiography is D ₋₁ (x, y), and the first and second radiographic images during radiation exposure are X ₀ (x, y) and X ₁ (x, y), respectively. Then, the calculation performed here is expressed as follows.

  The ratio of the random component remaining by this calculation to the random component remaining by the normal dark current correction method is expressed by equation (14). As shown in the equation (14), when this method is used, the noise component increases because the averaging effect of the random component R (x, y) shown in the equation (7) cannot be used. Therefore, there is a concern that the signal-to-noise ratio is deteriorated by this method.

  Furthermore, in fact, since the reading operation takes time, there is a possibility that the radiation information exposed during the reading period cannot be accurately converted to electrons, and the radiation information during the reading period becomes invalid and patient exposure may increase. There is sex. On the other hand, in the second embodiment of Patent Document 2, in addition to one dark current imaging immediately before radiation imaging, one radiation imaging is performed immediately after radiation imaging to create a dark current image associating both, and this dark current imaging is performed. A proposal for performing dark current correction using a current image is disclosed.

  The association disclosed in this method is only coefficient multiplication, and even if the stationary offset component can be corrected for F (x, y), the random component R (x, y) is only increased. The reduction effect due to averaging cannot be expected. In addition, the dark current image immediately after radiography includes an afterimage component that could not be swept out by the refresh operation. Combining this image with a dark current image immediately before radiography that does not contain an afterimage component is impractical because the correlation between the two is insufficient. That is, the dark current correction intended by Patent Document 2 is only the correction of the stationary offset component F (x, y), and the random component R based on the average of a plurality of dark current images shown in equation (7). No consideration is given to the reduction of (x, y), that is, the improvement of the signal to noise ratio.

  The present invention has been made in view of the above problems, and prior to obtaining a final image, an image that has been subjected to some correction immediately after radiography can be obtained, and can be confirmed. An object of the present invention is to provide a radiation imaging apparatus and method capable of improving the workflow and significantly reducing the waiting time required for re-imaging.

The radiation imaging system of the present invention includes a radiation detector that obtains a radiation image by detecting radiation generated from a radiation generation unit, and performs dark current imaging on the radiation detector in a state in which radiation from the radiation generation unit is not irradiated. An acquisition unit that acquires dark current data obtained by executing, a correction unit that obtains a corrected image by correcting the radiation image based on the dark current data, and a corrected image corrected by the correction unit Display control means for displaying an image based on the display unit, detection means for detecting whether or not the radiation detector is executing dark current imaging, and the radiation detector is executing dark current imaging And a control means for controlling to prohibit radiation exposure by the radiation generator when the detection means detects .

The method of the present invention, that a first step of obtaining a radiographic image by detecting radiation generated from the radiation generating unit, the detected radiation is to execute dark current shot ray detector release in a state of not irradiated A second step of acquiring dark current data obtained by the above, a third step of obtaining a corrected image by correcting the radiation image based on the dark current data, and a post-correction corrected by the correcting means A fourth step of displaying an image based on the image on the display unit, a fifth step of detecting whether or not the radiation detector is performing dark current imaging, and dark current imaging in the fifth step And a sixth step of performing a control for prohibiting radiation exposure when it is detected that is being executed.

  According to the present invention, prior to obtaining a final image, it is possible to obtain an image that has undergone some correction immediately after radiography, enabling confirmation, improving the user workflow, and re-imaging. The waiting time can be greatly reduced.

  In addition, according to the present invention, it is possible to display the simplified correction image immediately after shooting the subject image and to display the correction image with high accuracy later, so that the accuracy of the shot image can be confirmed.

  Furthermore, according to the present invention, a simplified correction image can be displayed immediately after the subject image is captured, a highly accurate correction image can be displayed later, and a method for updating the display can be selected. This makes it possible to operate without waste.

  Furthermore, according to the present invention, a simple correction image can be displayed immediately after the subject image is captured, and a highly accurate correction image can be displayed later, and the user can know the image processing status. Is prevented.

It is a flowchart explaining the radiography method of 1st Embodiment. It is a schematic diagram which shows schematic structure of the radiography apparatus of this invention. It is a flowchart explaining the radiography method of 2nd Embodiment. It is a flowchart explaining the radiography method of 3rd Embodiment. It is a schematic diagram which shows the internal structure of a personal user terminal device. It is a schematic diagram explaining the sensor reading operation principle. It is a block diagram of an MIS type sensor. It is an energy band figure of a photoelectric conversion element. It is a flowchart which shows a sensor drive. It is a timing chart explaining the timing of radiation exposure and sensor drive.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a flowchart for explaining a radiation imaging method of the first embodiment, and FIG. 2 is a schematic diagram showing a radiation imaging apparatus of the present invention.

  In FIG. 1, 1 is a radiation exposure request step, 2 is a step of initializing a radiation detector in preparation for radiography, 3 is a step of exposing radiation, 4 is a step of reading a radiation image, and 5 is a first step. Initializing the radiation detector in preparation for the second dark current imaging, 6 reading the first dark current image, and 7 initializing the radiation detector in preparation for the second dark current imaging. , 8 is a step of reading the second dark current image, 9 is a step of initializing the radiation detector in preparation for the third dark current image shooting, and 10 is a step of reading the third dark current image, 11 Is the step of initializing the radiation detector in preparation for the fourth dark current image capturing, 12 is the step of reading the fourth dark current image, and 13 is the dark current correction using the first dark current image. Picture A step of displaying an image, 14 a step of averaging the dark current images from the first time to the fourth time, and 15 a dark current correction of the radiation image using an average of the dark current images from the first time to the fourth time This is a step of saving the image that has been subjected to.

  In FIG. 2, 40 is a radiation imaging system, 41 is a radiation generator, 42 is a patient, 43 is a radiation detector, 44 is a control PC for controlling the radiation imaging system 40, and 45 is a component constituting the radiation imaging system 40. The connecting bus line, 46 is a capture board that temporarily stores an image transmitted from the radiation detector 43, 47 is an image processing device that performs image processing (including correction processing) of the radiation image, and 48 is a display device that displays the radiation image. 49 are storage devices for storing radiographic images.

  When the radiologist positions the patient 42 and turns on the radiation exposure switch (step 1), the radiation detector initialization drive is started and the reading cycle is repeated (step 2). When preparation of the radiation generator 41 and the radiation detector 43 is completed, a radiation exposure command is issued. In response to this command, the radiation detector 43 starts accumulation, and in synchronization with this, the radiation generator 41 starts radiation exposure (step 3). When the radiation exposure ends, the radiation detector 43 immediately ends the accumulation and reads the accumulated radiation image (step 4). Subsequently, the radiation detector 43 starts the initialization drive (step 5), and starts accumulation after repeating the reading cycle as many times as the radiation imaging. When the same accumulation time as that for radiography is completed, the radiation detector reads the accumulated dark current image (step 6).

The radiation image and dark current image obtained in the steps so far are transmitted to the capture board 46, and the primary dark current correction shown in the equation (3) is performed in the image processing device 47. Further, the image processing device 47 performs sensitivity correction, trimming processing, gradation processing, sharpening processing and the like shown in the equation (6) for the primary dark current correction image, and the obtained primary diagnostic image is immediately displayed on the display device. 48 is displayed (step 13). If these image processes require time, the display time can be shortened by performing image processing on a reduced image obtained by performing low-pass filter processing and thinning sampling on the primary dark current corrected image. good. At this time, since the stored image is processed in the background using a full-size image that is not reduced, there is no problem that the image quality deteriorates. The time T _display from the radiation exposure until the image is displayed on the display device 48 is calculated as the following equation under the same conditions as the equation (9).

If the driving method 1 in FIG. 10 is adopted and the radiation exposure time is 20 msec and the sensor accumulation time is 30 msec, T _display can be about 3 seconds.

  In parallel with the display step 13, the radiation detector 43 performs dark current imaging shown in steps 7 to 12 and transfers each image to the capture board 46. When the four dark current imaging operations are completed, the image processing device 47 averages the four dark current images (step 14), performs a subtraction process with the radiation image and sensitivity correction, and stores the obtained fourth-order corrected image. It is stored in the device 49 (step 15). Further, the image processing device 47 performs trimming processing, gradation processing, sharpening processing, and the like on the quaternary corrected image to create a quaternary diagnostic image.

  Since these steps are performed as a background process of the display step 13, the radiologist uses the primary diagnostic image displayed on the display device 48 immediately after the radiation exposure to determine whether the patient is sufficiently positioned. You can check if there is no problem with the image quality. The image provided for diagnosis is excellent in image quality because four dark current images are used.

  In this embodiment, the number of times of dark current imaging for displaying on the display device 48 is set to 1 and the total number of times of dark current imaging is set to 4. However, the setting of the number of times does not limit the scope of the present invention. The number of dark current imaging times and the total number of dark current imaging times to be displayed on the display device 48 can be arbitrarily set. If the number of dark current imaging times to be displayed on the display device 48 is less than the total number of dark current imaging times, the present invention. The effect of can be obtained. Therefore, the number of times of dark current imaging for display on the display device 48 is 0 or more, and the total number of times of dark current imaging is 1 or more.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a flowchart for explaining the radiation imaging method of the second embodiment. In FIG. 3, the steps common to FIG. 1 use the same reference numerals as those in FIG.

  In FIG. 3, 1 is a radiation exposure request step, 2 is a step of initializing a radiation detector in preparation for radiography, 3 is a step of radiation exposure, 4 is a step of reading a radiation image, and 5 is a first step. Initializing the radiation detector in preparation for the second dark current imaging, 6 reading the first dark current image, and 7 initializing the radiation detector in preparation for the second dark current imaging. , 8 is a step of reading the second dark current image, 9 is a step of initializing the radiation detector in preparation for the third dark current image shooting, and 10 is a step of reading the third dark current image, 11 Is the step of initializing the radiation detector in preparation for the fourth dark current image capturing, 12 is the step of reading the fourth dark current image, and 13 is the dark current correction using the first dark current image. A step of displaying an image, 14 a step of averaging the dark current images from the first time to the fourth time, and 15 a dark current correction of the radiation image using an average of the dark current images from the first time to the fourth time This is a step of saving the image that has been subjected to. 16 is a step of displaying an image obtained by performing dark current correction of a radiographic image using an average of dark current images from the first to the fourth time, 51 is a step of selecting an image update method, and 52 is a step of selecting a radiation detector 43. The step 53 for confirming the operation status is a step for confirming the image processing status.

  When the radiologist positions the patient 42 and turns on the radiation exposure switch (step 1), the radiation detector initialization drive is started and the reading cycle is repeated (step 2). When preparation of the radiation generator 41 and the radiation detector 43 is completed, a radiation exposure command is issued. In response to this command, the radiation detector 43 starts accumulation, and in synchronization with this, the radiation generator 41 starts radiation exposure (step 3). When the radiation exposure ends, the radiation detector 43 immediately ends the accumulation and reads the accumulated radiation image (step 4). Subsequently, the radiation detector 43 starts the initialization drive (step 5), and starts accumulation after repeating the reading cycle as many times as the radiation imaging. When the same accumulation time as that for radiography is completed, the radiation detector reads the accumulated dark current image (step 6).

  The radiation image and dark current image obtained in the steps so far are transmitted to the capture board 46, and the primary dark current correction shown in the equation (3) is performed in the image processing device 47. Further, the image processing device 47 performs sensitivity correction, trimming processing, gradation processing, sharpening processing and the like shown in the equation (6) for the primary dark current correction image, and the obtained primary diagnostic image is immediately displayed on the display device. 48 is displayed (step 13). The image processing status confirmation step 53 that operates at an arbitrary timing confirms that the image displayed on the display device 48 is generated based on the first dark current imaging, and displays the information on the display device 48. .

  In parallel with the display step 13, the radiation detector 43 performs dark current imaging shown in steps 7 to 12 and transfers each image to the capture board 46. When the four plan current imaging is completed, the image processing device 47 averages the images by the four plan currents (step 14), and performs a subtraction process with the radiation image. The fourth-order corrected image corrected with the dark current image for four times and subjected to sensitivity correction is stored in the storage device 49 (step 15). Further, the image processing device 47 performs trimming processing, gradation processing, sharpening processing, and the like on the quaternary corrected image to create a quaternary diagnostic image, and this quaternary diagnostic image is displayed by the display device 48 (steps). 16).

  The display method of the quaternary diagnostic image can be selected by the user in the display update method selection step 51. The first display method is a method in which the fourth diagnostic image is immediately displayed on the display device 48 as soon as the fourth diagnostic image is created. The second display method is a method of updating the primary diagnostic image in step 13 with the fourth diagnostic image in step 16 only when the primary diagnostic image displayed in step 13 is displayed on the display device 48. It is. This is because when the display device 48 has both an image display function and an operation function of the radiation imaging system 40 like a touch panel, it does not interfere with the system operation performed by the radiologist for preparation of the next imaging. . In the second display method, when the display device 48 is displaying the system operation screen, the next diagnostic image is completed by using the image processing confirmation step 53 instead of displaying the fourth diagnostic image. You may display the icon etc. which conveys. Further, the progress of image correction and image processing may be displayed on the photographed image list with icons or the like.

  Further, the radiation detector status confirmation step 52 that operates at an arbitrary timing can confirm whether the radiation detector is in the dark current imaging state or is in a pause state. Based on the confirmed radiation detector status, the status of the radiation detector 43 is displayed on the display device 48. If the radiation detector 43 is executing dark current imaging, the control PC 44 issues an exposure prohibition command to the radiation generator. As a result, radiation is not exposed during dark current imaging in the background, so that the radiation imaging system 40 can safely perform dark current imaging. In addition, the patient is not accidentally given invalid radiation exposure. It should be noted that prohibiting radiation exposure during imaging of a plurality of dark current images is an effective method whether or not dark current imaging is performed before or after radiation exposure.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a flowchart for explaining the radiation imaging method of the third embodiment. In FIG. 4, the steps common to FIG. 1 use the same reference numerals as those in FIG.

  In FIG. 4, 1 is a radiation exposure request step, 2 is a step of initializing a radiation detector in preparation for radiography, 3 is a step of exposing radiation, 4 is a step of reading a radiation image, and 5 is a first step. Initializing the radiation detector in preparation for the second dark current imaging, 6 reading the first dark current image, and 7 initializing the radiation detector in preparation for the second dark current imaging. , 8 is a step of reading the second dark current image, 9 is a step of initializing the radiation detector in preparation for the third dark current image shooting, and 10 is a step of reading the third dark current image, 11 Is the step of initializing the radiation detector in preparation for the fourth dark current image capturing, 12 is the step of reading the fourth dark current image, and 13 is the dark current correction using the first dark current image. A step of displaying an image, 14 a step of averaging the dark current images from the first time to the fourth time, and 15 a dark current correction of the radiation image using an average of the dark current images from the first time to the fourth time This is a step of saving the image that has been subjected to. 16 is a step of displaying an image obtained by performing dark current correction of a radiographic image using an average of dark current images from the first to fourth times, and 17 is a first dark current image and a second dark current. A step of calculating an average value of the image, 18 is a step of displaying an image obtained by performing dark current correction of the radiation image using an average value of the first dark current image and the second dark current image, and 19 is a first step. The step of calculating the average value of the dark current image from the first time to the third time, 20 displays an image obtained by correcting the dark current of the radiation image using the average value of the first to third dark current images It is a step to do.

  When the radiologist positions the patient 42 and turns on the radiation exposure switch (step 1), the radiation detector initialization drive is started and the reading cycle is repeated (step 2). When preparation of the radiation generator 41 and the radiation detector 43 is completed, a radiation exposure command is issued. In response to this command, the radiation detector 43 starts accumulation, and in synchronization with this, the radiation generator 41 starts radiation exposure (step 3). When the radiation exposure ends, the radiation detector 43 immediately ends the accumulation and reads the accumulated radiation image (step 4). Subsequently, the radiation detector 43 starts the initialization drive (step 5), and starts accumulation after repeating the reading cycle as many times as the radiation imaging. When the same accumulation time as that for radiography is completed, the radiation detector reads the accumulated dark current image (step 6).

  The radiation image and the dark current image obtained in the steps so far are respectively transmitted to the capture board 46, and the primary dark current correction shown in the equation (3) is performed in the image processing device 47. Further, the image processing device 47 performs sensitivity correction, trimming processing, gradation processing, sharpening processing and the like shown in the equation (6) for the primary dark current correction image, and the obtained primary diagnostic image is immediately displayed on the display device. 48 is displayed (step 13). If these image processes require time, a reduced image obtained by performing low-pass filter processing and thinning sampling on the primary dark current correction image may be used.

  In parallel with the display step 13, the radiation detector 43 performs the initialization drive shown in step 7 and the second dark current imaging step shown in step 8. Then, the average of the first dark current image and the second dark current image is calculated (step 17), and the subtraction process, the sensitivity correction, and the diagnostic image process are performed on the radiation image, and the obtained secondary diagnosis is performed. The image is displayed on the display device 48 (step 18). Further, the radiation detector 43 executes the initialization drive shown in step 9 and the third dark current imaging step shown in step 10. Then, the average calculation of the first to third dark current images is performed (step 19), the subtraction process with the radiation image, the sensitivity correction, and the diagnostic image process are performed, and the obtained tertiary diagnosis image is displayed on the display device. 48 (step 20). Further, the radiation detector 43 performs the initialization drive shown in step 11 and the fourth dark current imaging step shown in step 12. Then, the average calculation of the dark current images from the first time to the fourth time is performed (step 14), and the subtraction process and sensitivity correction with respect to the radiation image are performed. The fourth-order corrected image corrected with the dark current image for four times is stored in the storage device 49 (step 15). Further, the image processing device 47 performs trimming processing, gradation processing, sharpening processing, and the like on the quaternary corrected image to create a quaternary diagnostic image. The fourth diagnostic image is displayed as a final image by the display device 48 (step 16).

  The display method of the N-th diagnostic image in the display step 18, the display step 20, and the display step 16 can be selected by the user using the display update method selection step 51. The first display method is a method of immediately displaying the latest diagnostic image on the display device 48 as soon as the latest diagnostic image is created. The second display method is a method of updating with the N-order image only when the (N-1) next diagnosis image displayed on the display device 48 is displayed. This is because when the display device 48 has both an image display function and an operation function of the radiation imaging system 40 like a touch panel, it does not hinder the system operation performed by the radiologist for preparation for the next imaging. The third display method is a method that does not update. In the second display method, when the display device 48 displays the system operation screen, and in the third display method, instead of displaying the latest diagnostic image, an icon or the like indicating that the diagnostic image has been completed is displayed. May be performed. Further, the progress of image correction and image processing may be displayed on the photographed image list with icons or the like.

  The contents of the image processing for obtaining the Nth order diagnostic image and the image processing for obtaining the M (≠ N) th order diagnostic image (N and M are natural numbers) can be changed. For example, consider the case where N = 1 and M = 4. Since the primary diagnostic image is an image based on one dark current imaging, there is more noise than the fourth diagnostic image based on four dark current imaging. Therefore, the image processing performed on the primary diagnostic image is different from the image processing performed on the fourth diagnostic image by changing the contents of the image processing such as increasing the noise smoothing processing and weakening the sharpening processing. And a method of providing an image suitable for diagnosis while reducing the difference between the first and fourth-order diagnostic images.

  In addition, each function which comprises the radiation imaging device by the 1st-3rd this embodiment mentioned above, and each step which comprises the radiation imaging method operate | move by the program memorize | stored in RAM, ROM, etc. of computer. realizable. This program and a computer-readable recording medium recording the program are included in the embodiment of the present invention.

  Specifically, the program is recorded on a recording medium such as a CD-ROM or provided to a computer via various transmission media. As a recording medium for recording the program, besides a CD-ROM, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, a nonvolatile memory card, or the like can be used. On the other hand, as the transmission medium of the program, a communication medium (wired line such as an optical fiber, etc.) in a computer network (LAN, WAN such as the Internet, wireless communication network, etc.) system for propagating and supplying program information as a carrier wave A wireless line or the like.

  In addition, the functions of the above-described embodiments are realized by executing a program supplied by a computer, and the program is used in cooperation with an OS (operating system) or other application software running on the computer. When the functions of the above-described embodiment are realized, or when all or part of the processing of the supplied program is performed by a function expansion board or a function expansion unit of the computer, the function of the above-described embodiment is realized. Such a program is included in the embodiment of the present invention.

  FIG. 5 is a schematic diagram showing an internal configuration of a general personal user terminal device. In FIG. 5, reference numeral 1200 denotes a computer PC. The PC 1200 includes a CPU 1201, executes device control software stored in the ROM 1202 or the hard disk (HD) 1211, or supplied from the flexible disk drive (FD) 1212, and collects all devices connected to the system bus 1204. To control.

40 Radiation Imaging System 41 Radiation Generator 42 Patient 43 Radiation Detector 44 Control PC
45 Bus Line 46 Capture Board 47 Image Processing Device 48 Display Device 49 Storage Device 71 Photoelectric Conversion Unit 72 Thin Film Transistor (TFT)
73 Bias line 74 Gate line 75 Signal line 76 Reading IC
77 Analog-to-digital converter (A / D)
78 Gate drive device 82 Upper electrode (D electrode)
83 n + doped layer 84 a-Si intrinsic semiconductor i layer 85 insulating layer 86 lower electrode (G electrode)

Claims (15)

A radiation detector that detects radiation generated from the radiation generator and obtains a radiation image;
An acquisition means for acquiring dark current data obtained by causing the radiation detector to execute dark current imaging in a state in which radiation from the radiation generation unit is not irradiated;
Correction means for obtaining a corrected image by correcting the radiation image based on the dark current data;
Display control means for displaying an image based on the corrected image corrected by the correction means on the display unit;
Detecting means for detecting whether or not the radiation detector is performing dark current imaging;
Control means for performing control to prohibit exposure of radiation by the radiation generation unit when the detection means detects that the radiation detector is performing dark current imaging. system. A transmission means for transmitting a reduced image of the subject image captured by the radiation detector before the image of the subject image;
The radiation imaging system according to claim 1, wherein the display unit displays the image of the subject image after displaying the reduced image. The correction means includes a first correction process using first correction data in the middle of acquiring second correction data obtained after the image data of the subject image is captured by the radiation detector, and the second correction data. A second correction process using the correction data is applied to the image data of the subject image,
The radiographic system according to claim 1, wherein the display unit displays an image based on the second correction process after displaying an image based on the first correction process.   The radiation imaging system according to claim 3, wherein the first and second correction data are predetermined characteristics of the imaging unit.   The radiation imaging system according to claim 4, wherein the predetermined characteristic is a dark current characteristic.   6. The radiation imaging system according to claim 5, wherein the second correction data is obtained based on a measurement having a larger number of times than the first correction data. The correction means includes a first correction process based on first correction data obtained after the image data of the subject image is captured by the radiation detector, and the first correction process used for the first correction process. A second correction process based on the second correction data acquired more times than the number of correction data acquisition times is performed on the image data of the subject image;
The radiographic system according to claim 1, wherein the display control unit displays an image based on the second correction process on the display unit after displaying the image based on the first correction process.   The radiation imaging system according to claim 3, wherein the first correction process is performed on a reduced image of the image data of the subject image. The radiation imaging system according to claim 1, wherein the display control unit causes the display unit to display a status of the radiation detector detected by the detection unit. A method for controlling radiography,
A first step of obtaining radiation images by detecting radiation generated from the radiation generation unit;
A second step of the detected radiation to obtain a dark current data obtained by executing dark current shot ray detector release in a state of not irradiated,
A third step of obtaining a corrected image by correcting the radiation image based on the dark current data;
A fourth step of causing the display unit to display an image based on the corrected image corrected by the correcting unit;
A fifth step of detecting whether the radiation detector is performing dark current imaging;
And a sixth step of controlling to prohibit radiation exposure when it is detected that dark current imaging is being executed in the fifth step . In the third step, the first correction process using the first correction data in the middle of acquiring the second correction data obtained after capturing the image data of the subject image, and the first correction data And subjecting the image data of the subject image to a second correction process with the second correction data configured based on
The control method according to claim 10 , wherein, in the fourth step, an image based on the second correction process is displayed on the display unit after an image based on the first correction process is displayed. In the third step, a first correction process based on the first correction data obtained after capturing the image data of the subject image, and the first correction data used for the first correction process A second correction process based on the second correction data acquired after imaging at a number of times greater than the number of acquisitions of the subject image,
The control method according to claim 10 , wherein, in the fourth step, an image based on the second correction process is displayed on the display unit after an image based on the first correction process is displayed. The control method according to any one of claims 10 to 12, wherein the state of the radiation detector detected in the fifth step is displayed on the display unit. A computer-readable recording medium on which a program for causing a computer to execute each step of the control method according to any one of claims 10 to 13 is recorded. Program for executing the respective steps of the control method according to the computer in any one of claims 10-13.

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