JP2003194949A - Apparatus and method for radiography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a drop in a signal-to-noise ratio due to a dark current correction as far as possible and to improve a throughput and an operating efficiency by controlling the number of times of a dark current photographing operation according to a photographing purpose, a photographing object, a photographing condition or the like in a radiographic operation which performs the dark current photographing operation in a plurality of numbers of times in order to perform the dark current correction of a radiation detector. <P>SOLUTION: The radiographic apparatus is provided with a radiographic means which acquires a radiation image of a subject by using the radiation detector, a characteristic-data acquisition means which acquires characteristic data expressing a characteristic of the radiation detector, a number-of-times decision means which decides the number of times for acquiring the characteristic data and a correction means which acquires a correction image by correcting the radiation image by using the characteristic data. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation imaging apparatus and a radiation imaging method using a radiation detector.

[0002]

2. Description of the Related Art Conventionally, a screen film system (S / F system) in which an intensifying screen for converting radiation into fluorescence and a film sensitive to fluorescence are closely attached to each other as a radiation imaging apparatus for photographing a radiation image transmitted through a subject. ) Has been used. Also, phosphor and image intensifier (I.
I.) is combined to multiply the radiographic image, and the magnified image is taken by an image pickup tube through an optical system, II-T
V-cameras have also been used. The former has been mainly used for still image shooting called general shooting, and the latter has been mainly used for perspective shooting and video shooting called angio shooting.

Recently, due to the demand for image digitization, digital photographing devices having a digital image output have begun to be used. In general photography, an imaging plate that accumulates a radiation image as a latent image is used instead of the screen film system.The imaging plate is laser-scanned to excite the latent image, and the generated fluorescence is emitted by a photomultiplier tube. Reading, computed radiography devices have also been used. Also, in moving image shooting, II-DR shooting devices that use a solid-state image sensor such as a CCD instead of a pickup tube are also used. Both the Computed Radiography Equipment and the II-DR Imaging Equipment have digital image output and are beginning to contribute to the digitization of medical images.

More recently, a radiation flat panel detector (FPD) in which a phosphor and a large area amorphous silicon sensor are closely attached is used, and a radiation image is directly digitized without using an optical system or the like. Imaging devices have been put to practical use. The amorphous selenium, use iodide lead (PbI ₂₎ and iodide mercury (HgI ₂₎ or the like to convert the radiation into electronic, FPD be practically similar to detect the electronic large area amorphous silicon sensor There is. In principle, these FPDs are capable of capturing not only still images but also moving images, and are therefore expected as next-generation digital image capturing devices.

A radiation imaging system using an FPD will be briefly described with reference to FIG. In FIG. 4, reference numeral 40 is a radiographic system, 41 is an X-ray tube that emits radiation, 42 is a patient as a subject, 43 is an FPD, and 44 is a radiographic system 40.
Control PC to control the operation of, 45 is a bus line, 46
Is a capture board for temporarily storing the image output from the FPD, 47 is an image processing device for generating an image suitable for diagnosis, 48 is a display device for displaying a radiation image, 49 is a radiation image and its accompanying information It is a storage device for storing.

When the technician orients the patient and presses a radiation exposure button (not shown), the control PC 44 sends a preparation command to the FPD 43, and when the FPD 43 is ready, the X-ray tube
Irradiate from 41 to patient 42. The image obtained by the FPD 43 is transferred at high speed to the capture board 46 via the bus line 45, and basic correction processing is performed on the capture board. The processed image is transferred to the control PC 44, stored in the storage device 49, and subjected to more complicated image processing in the image processing device 47, and at the same time, the image is displayed on the display device 48. The image subjected to the image processing is stored in the storage device 49. Also, if necessary, the image is transmitted to a laser imager and a diagnostic monitor via a network (not shown) for diagnostic purposes.

Here, the principle of FPD will be briefly described with reference to FIGS. 7, 8 and 9. FIG. 7 is a diagram for explaining the principle of sensor reading operation, and shows a sensor consisting of 9 pixels for simplification. In FIG. 7, 71 is a photoelectric conversion unit that converts fluorescence into electrons, and 72 is a thin film transistor (TFT) for transferring electrons generated in the photoelectric conversion unit.
stor), 73 is a bias line for applying a bias voltage to the photoelectric conversion unit 71, 74a, 74b, 74c are gate lines for transmitting a switching signal to the TFT 72, and 75a, 75b, 75c are signal lines for transferring the electrons passing through the TFT 72, 76 is a reading IC that selects one signal line from the signal lines 75a, 75b, and 75c and amplifies the signal electrons, and 77 is an analog-digital converter (A / D: Analog-) that converts the amplified analog signal into a digital signal. to-digital convert
er) and 78 are gate driving devices that control the switching operation of the TFT 72.

In FIG. 7, when a phosphor (not shown) covering the entire surface of the sensor pixel is irradiated with radiation, the phosphor emits fluorescence in proportion to its intensity. The photoelectric conversion unit 71 captures this fluorescence and converts it into signal electrons. When the gate drive device 78 sets the gate line 74a to High, all the TFTs in one horizontal line connected to the gate line 74a are turned on. Then, the photoelectric conversion unit 71
The signal electrons stored in are transferred to the signal lines 75a, 75b, 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. Then, the reading IC 76 sequentially selects 75b and 75c, and the electrons transferred to the respective signal lines are sequentially read. By this operation, the signal electrons of three pixels for one horizontal line connected to the gate line 74a in FIG. 7 are read and converted into digital signals. Next, the gate lines 74b and 74c are sequentially selected,
Similarly, the signal electrons of each three pixels for one horizontal line connected to the gate lines 74b and 74c are sequentially read and converted into digital signals.

Next, the operating principle of one pixel of the sensor will be described with reference to FIGS. 8 and 9. Figure 8 shows MIS (Metal Insulator)
FIG. 9 is an energy band diagram of a photoelectric conversion element. In FIG. 7, 71 is a photoelectric conversion unit, 72 is a TFT, 73 is a bias line, and 76 is a reading I.
C, in FIG. 8 and FIG. 9, 82 is an upper electrode (D electrode) that transmits a bias voltage to the photoelectric conversion unit 71, 83 is the same potential as the upper electrode 82, and hole injection into the a-Si intrinsic semiconductor i layer 84 is performed. N + doped layer to block, 84 is a-Si intrinsic semiconductor for photoelectric conversion i
Layer, 85 is an insulating layer that blocks movement of both electrons and holes, 8
6 is a lower electrode (G electrode).

FIGS. 9 (a) and 9 (b) 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 for the D electrode and the G electrode.

In FIG. 9 (a), 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 the electric field. At the same time, the electrons indicated by white circles are injected into the i layer 84. At this time, some holes and electrons are recombined 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 i layer 84 are swept out from i layer 84.

To change from this state to the photoelectric conversion mode shown in FIG. 9B, a positive potential is applied to the D electrode with respect to the G electrode. Then, the electrons in the i layer 84 are instantly guided to the D electrode. However, holes are not guided to the i layer 84 because the n + doped layer 83 functions as an injection blocking layer. When light enters the i-layer 84 in this state, the light is absorbed and electron-hole pairs are generated. This electron is guided to the D electrode by the electric field, and the hole is i
It moves in the layer 84 and reaches 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, and a current flows from the G electrode to maintain electrical neutrality in the element. This current corresponds to the electron-hole pair generated by light and is therefore proportional to the incident light. After the photoelectric conversion mode of FIG. 9 (b) is maintained for a certain period, when the refresh mode of FIG.
The hole that stayed at is led to the D electrode as described above,
At the same time, a current corresponding to this hole flows. The amount of the 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, but since this amount is approximately constant, it may be subtracted and detected. That is, the photoelectric conversion element can output the amount of light that is incident in real time, and at the same time, can output the total amount of light that is incident during a certain period.

However, if the period of the photoelectric conversion mode becomes long for some reason or the illuminance of the incident light is strong, the current may not flow despite the incident light. This is because 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 as shown in FIG. 9C. When the light incident state changes in this state, the current may flow unstablely, but if the refresh mode is set again, the holes in the i layer 84 are swept out, and in the next photoelectric conversion mode, the current proportional to the light is again generated. Flows.

Further, in the above description, when sweeping out the holes in the i layer 84 in the refresh mode, it is ideal to sweep out all the holes, but it is also effective to pull out only some of the holes, which is the same as the above. The current is obtained and there is no problem. That is, it is sufficient if the state of FIG. 9C is not obtained at the next photoelectric conversion mode detection occasion, 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 may 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 be negative. If there are many holes in the i-layer 84, say D
This is because the electric field in the i layer 84 is applied in the direction of guiding the holes to the D electrode even if the potential of the electrode with respect to the G electrode is positive. n
Similarly, the characteristics of the injection blocking layer of the + doped layer 83 are similar to those of the i-layer 84
Is not a requirement.

The above is the description of the operation in the MIS type sensor, but other types of sensors used in FPD, such as P
In the sensor using the IN photodiode, almost the same operation is performed although it is partially different. JP 10
An example is the FPD sensor disclosed in -170657.
In addition to the method using a phosphor, instead of the phosphor, amorphous selenium that directly converts radiation into electrons,
Even in sensors that use gallium arsenide (GaAs), cadmium telluride (CdTe), lead iodide (PbI ₂ ), mercury iodide (HgI ₂ ), etc., the operation of reading electrons accumulated in pixels and the refresh operation are extremely difficult. Is similar.

By the way, the sensor used in the FPD has several million pixels, but the characteristics of each pixel are slightly different. Particularly important characteristics as an image sensor are dark current characteristics and sensitivity characteristics. Therefore, in FPD, the process 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 process is also common to systems using amorphous selenium or the like. The method of correcting the dark current characteristic and the sensitivity characteristic will be described below.

First, the terms used below will be briefly described. First, irradiating a radiation detector with radiation for imaging is called radiation imaging, and the image obtained here is called a radiation image. Next, the measurement of the dark current characteristic is the same as the radiography except that no input is given to the sensor. Therefore, the measurement of the dark current characteristic is called dark current photography, and the image obtained here is called a dark current image. An image that has been dark current-corrected by using dark current images N times may be referred to as an N-order dark current-corrected image.
Furthermore, an image subjected to sensitivity correction on the (Nth) dark current corrected image is an (Nth) corrected image, and an image subjected to image processing such as gradation processing suitable for image diagnosis on the (Nth) corrected image. May be referred to as (Nth order) diagnostic image.

A method of 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, subtraction of the image when no signal is input to the sensor from the image when a signal is input to the sensor makes it possible to correct offset components that differ for each pixel. If the radiographic image when a signal is input to the sensor is X ₀ (x, y) and the dark current image measured immediately after that is D ₁ (x, y), the primary dark current corrected image after dark current correction C _1X (x, y) is expressed by the following equation.
However, x and y are the addresses of the two-dimensionally arrayed pixels. The random component is R (x, y), and the stationary offset component is
It is assumed to be F (x, y).

[0019]

[Equation 1]

By the way, since the offset component F (x, y) in the dark current image is constant regardless of the input to the sensor when the photographing conditions are the same, the offset correction shown in the equation (3) is performed. Therefore, it can be completely removed. However
Since R ₀ (x, y) appearing in equation (1) and R ₁ (x, y) appearing in equation (3) are different, the random component R (x, y) is removed by the offset correction shown in equation (3). It is impossible. 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 has a random component R (x, y) in the radiation image X (x, y)
If the size is sufficiently smaller than that of, the radiographic image X (x, y), which is a signal, such as in low-dose radiography, will be small. is there.

Therefore, by utilizing the property shown in the equation (5), the dark current image is photographed many times and the average value thereof is taken, so that the random component R (x, y) contained in the dark current image is substantially ignored. It is possible to make it as small as possible. If the random component R (x, y) is normally distributed, measure the random component R (x, y)
The standard deviation σ ₀ per measurement and the standard deviation σ _n of the average value of the measurement times n times have the following relationship.

[0022]

[Equation 2]

A dark current correction method using this property is disclosed in JP Moy, B. Bosset, "How does real offset and ga.
in correction affect the DQE in images from X-ray
Flat detector ", SPIE proceedings Vol.3659, 90-97 (1
999). Using this method, the dark current image D _X can be obtained by using the average value of 4 dark current images.
The random component R (x, y) included in (x, y) is halved, and good dark current correction can be performed. The ratio of the standard deviations of the random components R (x, y) remaining in the first-order dark current correction image and the fourth-order dark current correction image is shown in equation (7). However, both the random component superimposed on the radiation image itself and the random component of the four-time average dark current image are considered.

[0024]

[Equation 3]

From the equation (7), in low-dose radiography in which random noise is dominant, by performing dark-current radiography four times, the signal noise ratio is improved by about 20% as compared with one dark-current radiography. It turns out that is expected.

Next, the correction of the sensitivity characteristic will be described. The sensitivity characteristic correction is sometimes called calibration. Sensitivity correction is a step of correcting variations in sensitivity characteristics of pixels that form the sensor. Assuming that the sensitivity characteristic is stationary, dividing the image when a signal is input to the sensor by the image when a uniform input is applied to the sensor enables correction of different sensitivity characteristics for each pixel. . The image when a uniform input is given to the sensor is C _W (x, y), and the radiation image component and dark current image component contained in C _W (x, y) are W (x, y) and
If D _W (x, y), the corrected image C ₁ (x, y) after sensitivity correction is expressed by the following equation.

[0027]

[Equation 4]

In a radiation imaging apparatus, it is common to irradiate uniform radiation for the purpose of correcting the sensitivity characteristic. However, at the dose level used for radiation image diagnosis, quantum noise proportional to the square root of the radiation quantum number is superimposed on the radiation image. This noise is inevitable in principle, so naturally
Quantum noise is also superimposed on C _W (x, y). So C _W (x, y)
There is concern that the accuracy of sensitivity characteristic correction may deteriorate due to the noise superimposed on. Therefore, in general, for sensitivity characteristic correction,
C _W (x, y) with multiple radiographs and averaging of the images
The accuracy of sensitivity characteristic correction is improved by increasing the effective number of radiation quantum contained in the.

By the way, in order to correct the sensitivity characteristic, radiographing a plurality of times and averaging the images are performed. In addition to the reduction of the quantum noise, the random component of the dark current image included in C _W (x, y) is removed. It also contributes to reduction. The reason is D _W (x,
This is because the effect shown in Eq. (6) occurs by averaging y).

A method of driving the FPD sensor for performing the above-described radiation imaging and dark current imaging will be described with reference to FIG. 2 which is a sensor driving flowchart. In FIG. 2, 21 is idling drive, 22 is initialization drive for radiography, 23 is photography drive for radiography, 24 is initialization drive for dark current photography, and 25 is photography for dark current photography. Driving, 26 is radiation exposure. As shown in Figure 2, FPD
The drive state of the sensor is roughly divided into idling drive 21,
There are three types: initialization drive 22 and 24 and shooting drive 23 and 25. When a bias voltage is applied to the FPD sensor, dark current generated by a trap of the photoelectric conversion layer and 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 process which is intermittently performed from the time when a bias voltage is applied to the sensor to the time immediately before photographing. The pseudo read cycle at this time is relatively long. The reason is to suppress the increase in power consumption and the sensor temperature increase due to the reading operation to the minimum. Next, the initialization drives 22 and 24 are steps in which a pseudo reading operation is performed to sweep out the dark current and prepare for radiation exposure. The read cycle performed by the initialization drives 22 and 24 is faster than the idling drive 21. The reason is that the radiation exposure command cannot be accepted during the reading period, and the read cycle is shortened to shorten the delay time from the radiation irradiation command to the actual radiation exposure. Then, after the radiation exposure, the reading drive 23 is performed to capture a radiation image.

Dark current imaging is performed subsequent to radiation imaging. When radiography is performed as shown in FIG. 2, the sensor immediately starts the initialization drive 24, and performs dark current photography 25 at the same timing as the radiography. This timing will be described in some detail with reference to FIG.

FIG. 3 is a timing chart for explaining the timing of radiation exposure and sensor driving. 3 in Figure 3
1 is the radiation exposure request signal from the radiation exposure switch, 32
Is a radiation exposure permission signal, 33 is radiation exposure, and 34 is a driving method
1 is a drive signal, and 35 is a drive signal of drive method 2. Also R
Is refresh, X is radiography, D is dark current photography, T _e1
And T _e2 is the storage time, and T _i is the time required for one read cycle.

First, the driving method 1 will be described. When the radiation exposure request signal 31 is turned on, the sensor switches from idling drive to initialization drive. Then, the sensor performs a refresh operation to sweep 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 stops the accumulation and reads the radiation image (8). The storage time of the sensor at this time is T _e1 . The sensor immediately performs a refresh operation, then repeats the read cycle, and when the fourth read cycle ends, dark current imaging (D) is performed at the accumulation time T _e1 .

Next, the driving method 2 will be described. Similarly, when the radiation exposure request signal 31 is turned on, the sensor switches from idling drive to initialization drive. Then, the sensor performs a refresh operation to sweep out the holes accumulated in the sensor. And 4 of read cycle in initialization drive
When the radiation exposure permission signal 32 is turned ON for the second time, the sensor stops the reading cycle, the radiation exposure 33 is turned ON, and the sensor accumulates a signal by radiation. When the predetermined time T _e2 has elapsed, the sensor ends the accumulation and reads the radiation image (8).
The sensor immediately performs a refresh operation, then repeats the read cycle, and when the fourth read cycle ends, dark current imaging (D) is performed at the accumulation time T _e2 . Storage time T
_{The e2} is set to a time of 1 to 2 seconds so that it can be used for long-term shooting. For this driving method, see John MB
oudry, "Operation of AmorphousSilicon Detectors fo
r Chest Radiography Within System Latency Requirem
ent ", SPIE proceedings Vol. 3659, 336-344 (1999).

As is 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.
In the driving method 2, the accumulation time T _e2 is fixed. Since the driving method 1 can minimize the accumulation time, it has an advantage that the accumulation of dark current can be reduced as compared with the driving method 2 which adopts the accumulation time corresponding to the longest expected exposure time. Moreover, since the actual radiation exposure time is about 20 msec for general chest imaging, there is an advantage that sensor driving can be completed in a short time and an image can be displayed early. On the other hand, drive method 2 has a constant storage time,
It may be possible to perform dark current photography before radiation exposure.

It should be noted that both methods perform the same dark current imaging immediately after radiation imaging, and the same refresh cycle of the initialization drive performed before radiation imaging and dark current imaging, and the number of read cycles. Furthermore, the accumulation times of radiography and dark current photography are the same. This is (1)
The offset component F (x, y) shown in Eqs. (2) and (2) is a function of storage time and drive timing, and the amount of dark current has a high correlation with the storage time, and due to the transient characteristics of the sensor, This is because the drive timing and the dark current have a high correlation. If for 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 the formula is performed, a part of the offset component F (x, y) remains, and an unexpected sensor-specific pattern (artifact) may appear.

In FIGS. 2 and 3, the case of one dark current photographing is shown for simplicity of explanation. However, as described above, by performing dark current imaging a plurality of times, it is possible to reduce the random component included in the dark current image and improve the signal noise ratio. Therefore, in actuality, following radiography, dark current photography is performed once to several times as necessary.

However, when dark current imaging is performed a plurality of times, it takes a long time to obtain an image after radiation imaging. For example, in the driving method 2, one refresh operation for initialization drive, four read cycles, one refresh operation for one time, and the read cycle required time T _i are 0.2.
Second, the accumulation time T _e2 is 2 seconds, and dark current imaging is performed four times. In this case, the time T required from the end of radiation exposure to the end of the fourth dark current imaging and the display of an image on the monitor
_display is the total of image transfer time and image processing time T
It is expressed by the following formula, where _process is 0.5 seconds.

[0039]

[Equation 5]

Since the FPD can quickly display an image 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 shorten the waiting time of the patient for reimaging. However, if it takes more than 10 seconds to display an image, the technician cannot wait until the image is displayed, and improvement of the technician's workflow cannot be expected. This also makes it difficult to reduce patient waiting time.

To solve this problem, driving method 2
Then, by utilizing the fact that the accumulation time T _e2 is fixed, dark current imaging may be performed (a plurality of times) prior to radiation imaging, and dark current correction may be performed using this dark current image. However, due to the transient nature of the sensor, the correlation between the dark current image in dark current imaging and the dark current image superimposed on the radiographic image is lost when dark current imaging and radiography are temporally separated. It is possible that artifacts will occur. Therefore, it is practically impossible to perform dark current imaging before requesting radiation exposure. In addition, a method of performing dark current imaging in the period from the radiation exposure request to the radiation exposure by using the radiation exposure request as a trigger can be considered. However, in this method, the time from the radiation exposure request to the actual radiation exposure becomes long, and the patient's movement and respiratory arrest are forced during this long time, which is not practical. Therefore, even in the driving method in which the accumulation time T _e2 is constant, it is desirable to perform dark current imaging immediately after radiation imaging as shown in driving method 2. In the driving method 1, since the actual radiation exposure time cannot be predicted in the photo timer photography or the like, dark current photography cannot be performed prior to the radiography.

Also, without using the radiation exposure request as a trigger,
A driving method in which image reading is continuously repeated is also conceivable. For example, in JP 2000-070250, this driving method is used,
Moreover, a proposal is disclosed in which dark current correction is performed using a single dark current image captured immediately before radiography. However, in this method, since a large number of reading operations are required for one radiographic imaging of unknown timing, there is a possibility that power consumption and heat generation may occur. Further, since the dark current radiography and the radiography cannot be synchronized in principle, there is a problem in that the timings of the two overlap. In order to solve the latter problem, in the modified implementation of the first embodiment of the proposal,
When the timings of both dark current radiography and radiography overlap, multiple radiographic images covering the entire radiation exposure period are stored, and the dark current image immediately before radiography is multiplied by multiple times from the radiographic images. A proposal is disclosed for dividing the resulting image. However, the coefficient multiplication image division operation only increases the random component R (x, y) even if the stationary offset component F (x, y) may be corrected, and the random component R (x It cannot be expected to reduce x, y). The reason is explained as follows.

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

[0044]

[Equation 6]

The ratio of the random component remaining in this calculation to the random component remaining in the normal dark current correction method is expressed by equation (14). As shown in Eq. (14), when this method is used, the averaging effect of the random component R (x, y) shown in Eq. (6) cannot be used, so the noise component increases. Therefore, in this method, there is a concern that the signal-to-noise ratio may deteriorate.

Further, since the reading operation actually requires a long time, there is a possibility that the radiation information exposed during the reading period cannot be accurately converted into electrons, and the radiation information during the reading period becomes invalid, resulting in increased patient exposure. there's a possibility that.
On the other hand, in the second example of the proposal, in addition to one dark current imaging immediately before radiography, one radiography immediately after radiography is performed to create a dark current image in which the two are associated with each other. A proposal for performing dark current correction using an image is disclosed. Also in this method, the disclosed correlation is only the coefficient multiplication operation, and the same offset component
Even if F (x, y) can be corrected, the random component R (x, y) only increases, and the reduction effect due to averaging cannot be expected. In addition, the dark current image immediately after radiography contains an afterimage component that could not be swept out by the refresh operation. It is not practical to combine this image and the dark current image immediately before radiography that does not include the afterimage component because the correlation between the two is insufficient. In other words, the dark current correction intended by JP 2000-070250 is only the correction of the steady offset component F (x, y), and the random component based on the average of multiple dark current images shown in equation (6) is used. No consideration is given to the reduction of R (x, y), ie the improvement of the signal to noise ratio.

[0047]

By the way, when performing dark current photographing a plurality of times, how many dark current photographings are necessary, or how many dark current photographings are optimal for the purpose of photographing. The question is whether it is unclear. Further, as described above, as time elapses after radiation imaging, the correlation between the dark current image at the time of radiographic imaging and the dark current image after elapse of time gradually disappears. When it is unknown how the correlation is lost, it is unclear how many dark current images are effective after the radiographic image capturing. Furthermore, since the dark current image is composed of extremely weak signals, there is a problem that it is easily affected by disturbance. For example, when a device that generates a strong noise operates during dark current imaging, the influence thereof may cause an artifact to be mixed in the dark current image. The problem is that this possibility increases as the number of dark current imaging increases.

Since there are various cases in which the signal level of the radiographic image obtained by radiography can be considered, it is conceivable that the optimum number of dark current radiography changes depending on this signal level. For example, when the signal level is low, it is necessary to use an imaging method that minimizes noise, that is, dark current imaging that is frequently performed. Of course, automatic exposure control (Auto Expo
By using sure control (AEC), a method for keeping the signal level constant without depending on the patient's body thickness has been put into practical use. However, even if the AEC is used, the passing radiation dose near the AEC detector can be made constant, but the passing radiation dose may be insufficient in other portions. As described above, when it is necessary to determine the number of times of dark current imaging according to the signal level, it is a problem that the number of times of dark current imaging required before imaging is unknown.

The present invention controls the number of times of dark current imaging in radiation imaging in which dark current imaging is performed a plurality of times to correct the dark current of the radiation detector, according to the purpose of imaging, the object to be imaged, the imaging conditions, and the like. Therefore, it is an object of the present invention to reduce the signal noise ratio reduction due to the dark current correction as much as possible, and at the same time, improve the throughput and the work efficiency.

[0050]

According to one aspect of the present invention, a radiation image pickup means for obtaining a radiation image of a subject using a radiation detector, and a characteristic for obtaining characteristic data representing the characteristic of the radiation detector. Radiation imaging, comprising: a data acquisition unit; a number determination unit that determines the number of times the characteristic data is acquired; and a correction unit that acquires a corrected image obtained by correcting the radiation image using the characteristic data. A device is provided.

According to another aspect of the present invention, radiation imaging means for acquiring a radiation image of an object using a radiation detector, characteristic data acquisition means for acquiring characteristic data representing characteristics of the radiation detector, A radiation imaging apparatus is provided, comprising: a selection unit that selects the characteristic data and a correction unit that acquires a corrected image obtained by correcting the radiation image using the characteristic data.

According to still another aspect of the present invention, a radiation imaging step of acquiring a radiation image of a subject using a radiation detector, and a characteristic data acquisition step of acquiring characteristic data representing characteristics of the radiation detector. A radiation imaging method comprising: a number-of-times determination step of determining the number of times of acquiring the characteristic data; and a correction step of acquiring a corrected image obtained by correcting the radiation image using the characteristic data. It

According to still another aspect of the present invention, a radiation imaging step of acquiring a radiation image of a subject using a radiation detector, and a characteristic data acquisition step of acquiring characteristic data representing characteristics of the radiation detector. There is provided a radiation imaging method, comprising: a selection step of selecting the characteristic data; and a correction step of acquiring a corrected image obtained by correcting the radiation image using the characteristic data.

According to the present invention, by determining the number of times of acquisition of the characteristic data, good image quality can be obtained and the throughput of radiation imaging can be optimized.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) In the first embodiment of the present invention, the number of times characteristic data is acquired for a single radiography is optimized in advance according to the purpose of radiography, etc. Stores the number of times characteristic data is acquired in association with
This is a radiographic imaging method in which the optimum number of characteristic data acquisitions is automatically set by selecting the imaging purpose and the like. A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flowchart explaining the radiation imaging method of the first embodiment.

In FIG. 1, 101 is a step of determining the number of times the characteristic data of the radiation detector is acquired, 102 is a radiation imaging step of irradiating radiation and driving the radiation detector to perform radiation imaging, and 103 is radiation A characteristic data acquisition process for acquiring the characteristic data of the detector, 104 is an output (N
Based on the number of times), the judgment branch step of judging whether or not the number of times of characteristic data acquisition has reached N times, and changing the processing flow according to the judgment result, 105 is an arithmetic step of performing an operation on the characteristic data acquired N times, Reference numeral 106 is a correction step of creating a correction image using the radiation image and the calculated characteristic data. In the present embodiment, the radiation detector is an FPD (FIGS. 4, 7, and 8), and the characteristic data will be described as a dark current image of the FPD.

First, the number determination step 101 will be described.
The number-of-times determination step 101 is a step of determining the number of times the dark current image of the FPD is captured. As an example of the number-of-times determination step 101, an example in which the number of times of dark current imaging is determined according to the selection of the imaging menu will be described with reference to FIG.

FIG. 5 is a flow chart for explaining a work menu which is the number of times determining step and the operator selects an operation to be performed, and 120 is a number of times determining step and a job menu which the operator selects an operation to be performed, 121 is an imaging menu, 122 is patient imaging, 123 is calibration imaging, 124 is an imaging region menu, and 125 is various imaging region buttons.

The radiation imaging apparatus displays an imaging menu 121. The operator takes a patient image 1 in the imaging menu 121.
If 22 is selected, then the radiation imaging apparatus displays the imaging region menu 124 and prompts the operator to select the imaging region. The operator selects the desired imaging region button from the imaging region buttons 125, and the preparation for radiation imaging is completed.

By the series of input operations by the operator, the number-of-times determining step 120 determines the number of times of capturing the dark current image which is the characteristic data. The imaging region button 125 stores the optimal number of dark current imagings in addition to the imaging conditions and image processing conditions according to the imaging region. For example, the chest screening radiographing button stores a setting such that the number of dark current radiography is one. This is because the chest screening radiographing is intended for mass screening, and it is necessary to radiograph a patient with a low morbidity at a high throughput. By setting dark current photography to once, the chest screening radiography button enables high throughput radiography. On the other hand, the baby shooting button stores a setting such that the dark current shooting count is four times. This is because it is necessary for infants to reduce the exposure dose as much as possible, and for infants, because it is difficult to orient the patient, it is possible to satisfy the radiographing request and the radiographing reality that there is no problem even if the radiographing interval is long.

Returning to FIG. 1, the radiation imaging apparatus executes the radiation imaging step 102 according to the operator's radiation exposure request.
Next, the radiation imaging apparatus executes the characteristic data acquisition step 103, that is, dark current imaging. The number of times of dark current imaging is determined according to the output of the number determination step 101. Judgment branch process 1
04 determines whether the number of times of dark current photography has reached N times, and when it is less than N times, dark current photography 103 is executed. When the number of times reaches N times, the process shifts to the calculation step 105 and the dark current image averaging is executed. Finally, in the correction step 106, the dark current correction shown in the equation (3) is executed, and the series of processing is completed.

By storing the number of times of dark current photographing in the photographing region button 125 in this way, it is possible to set the number of times of dark current photographing suitable for the purpose of photographing and the demand for photographing without the operator having to intend each time. . As a result, good image quality is obtained and the throughput of the radiation imaging apparatus is optimized.

On the other hand, the flow when the operator selects the calibration photographing 123 in the photographing menu 121 of FIG. 5 will be described with reference to FIG. In FIG. 6, 130 is a calibration shooting menu, 131 is an operator inputting the number of calibration shootings (N times), 132 is a branch process corresponding to the input of the number of calibration shootings, and 133 is the number of calibration shootings of 4 or more. The number of dark current photographing times is set, and 134 is the number of dark current photographing times when the number of times of calibration photographing is less than 4.

In FIG. 6, the operator inputs the number of times of calibration photographing (131). The branching process 132 branches the process according to the input of the number of times of calibration imaging (N times). If N is 4 or more, set the number of dark current photography performed at each calibration photography to 1. Once again N is 4
If it is less than, set the dark current photography to be performed at the time of each calibration photography to the number of times of rounding up the decimal point of the quotient of 4 / N. With this setting, the dark current image included in the sensitivity characteristic image C _W (x, y) shown in the equation (8) becomes an average value for at least four times of photographing. As a result, the random component of the dark current image included in C _W (x, y) is reduced to 1/2 or less, so that good sensitivity correction can be guaranteed. At the same time, especially N
When 4 is set to 4 or more, the dark current photography accompanying one calibration photography is completed once, so that the calibration photography can be executed quickly.

As described above, a unique dark current photographing number setting algorithm is prepared for calibration photographing, which is one of the photographing purposes, and the optimum dark current photographing number is set based on the algorithm. Thus, it is possible to minimize the decrease in the signal noise ratio due to the dark current correction and improve the throughput of calibration imaging.

(Second Embodiment) In the second embodiment of the present invention, the number of times characteristic data is acquired for one radiography is
This is a radiation imaging method that optimizes while acquiring characteristic data. A second embodiment of the present invention will be described with reference to FIG. FIG. 10 is a flowchart of the present embodiment, 141 is a radiographic imaging step, 142 is a characteristic data acquisition step of acquiring characteristic data, 143 is an evaluation step of evaluating characteristic data, 144
Is a judgment branching step of judging whether the output of the evaluation step 143 satisfies a predetermined condition and branching the flow according to the judgment result, 145 is a calculation step of calculating characteristic data, and 146 is a radiation image corrected by the characteristic data. This is a correction step. In this embodiment, the radiation detector is an FPD, and the characteristic data is a dark current image of the FPD.

The radiation imaging apparatus carries out the radiation imaging step 141 in response to the radiation exposure request issued by the operator. Subsequently, the radiation imaging apparatus performs the characteristic data acquisition step 142 to capture a dark current image. Further, the radiation imaging apparatus carries out the evaluation step 143. The evaluation step 143 is a step of evaluating the amount of noise and artifacts included in the dark current image.

First, the evaluation of the amount of noise included in the dark current image will be described. The amount of noise included in the dark current image of the FPD is a function of temperature, and the amount of noise changes when the FPD temperature changes. Similarly, the noise amount included in the FPD dark current image is a function of the FPD drive timing, and the noise amount also changes when the radiation exposure timing shown in FIG. 3 changes depending on the imaging purpose, for example, the imaging time. Since the amount of noise included in the dark current image varies from one image to another as described above, it may be difficult to determine how many times the dark current image is averaged to have a noise amount that is less than the specified value or if the dark current image is not captured. Therefore, the evaluation step 143 evaluates the noise amount included in the dark current image for each dark current photographing and the noise amount of the average value of the dark current images photographed so far. As a method of evaluating the noise amount, a method of dividing the dark current image into a plurality of regions of interest and obtaining the standard deviation of the output in each region of interest can be considered.
In this way, the evaluation step 143 can perform an evaluation for determining during the dark current imaging cycle whether or not the next dark current imaging is necessary.

When the standard deviation is used for the noise amount evaluation, the calculation used in the evaluation step 143 is such that the number of times of photographing is n, the prescribed noise amount to be satisfied is A, and the noise amount in each dark current image is Bi, It is expressed by the following equation.

[0070]

[Equation 7]

Next, the evaluation of the artifacts included in the dark current image will be described. Since the dark current image is a weak signal as described above, an artifact may occur due to the influence of ambient disturbance. Therefore, the dark current image is evaluated for each dark current image, and it is confirmed that the artifact is lower than the specified value. As a method of evaluating artifacts, in order to evaluate so-called line noise connected in a line, the dark current image is divided into a plurality of regions of interest, and vertical and horizontal projections are created in each region of interest. A method of obtaining the standard deviation of the projection can be considered. In this way, the evaluation step 143 evaluates whether or not the dark current imaging of this time is valid, and if the dark current image is invalid, the dark current image of this time is discarded, and at the same time, the dark current imaging is performed again in the judgment branch step 144. Can be instructed to.

The cross-correlation evaluation of the dark current image will be further described. The dark current image is required to be the same at each imaging time except for the random component. Let D ₁ (x, y) be the first dark current image that is considered to be the closest to the dark current image that is superimposed on the radiation image, and D _n (x, y) be the _nth dark current image. By evaluating the cross-correlation between the two, the identity of both can be evaluated. The cross-correlation evaluation is effective not only for the amount of noise, but also for artifact evaluation, particularly low-frequency artifacts. When the cross-correlation between the two is C _1n and the correlation value and the correlation length that C _1n should satisfy are C and L, respectively, the calculation used in the evaluation step 143 is expressed by the following equation.

[0073]

[Equation 8]

Similarly, for the nth dark current image D _n (x, y), the average image D _{1 (n-1)} (x,
A modified example of obtaining the cross-correlation with y) is also conceivable.

The judgment branch step 144 judges whether or not the next dark current imaging is necessary based on the evaluation result of the evaluation step 143, performs dark current imaging if necessary, and executes the calculation step if not necessary. move on. In the calculation step 145, a dark current image captured a plurality of times is averaged to create a corrected image for dark current correction. The correction step 146 uses the radiation image output by the radiation imaging step 141 and the correction image output by the calculation step 145 to obtain (3)
The dark current correction shown in the formula is performed.

As described above, according to the radiation imaging method of the present embodiment, the evaluation step 143 and the judgment branching step 144 are provided, so that the number of times characteristic data is acquired for one radiation imaging can be determined during the characteristic data acquisition period. Can be optimized. Particularly, by using the dark current image as the characteristic data and performing the noise amount evaluation of the dark current image, the artifact evaluation, and the cross-correlation evaluation of the dark current image, the characteristic data evaluation can be accurately performed.

In the present embodiment, for simplicity of explanation,
No limit was placed on the number of times characteristic data was acquired. However, in practice, unless the number of times characteristic data is acquired is limited, the work efficiency of the operator may be significantly reduced. Therefore, a modification in which the number of times characteristic data is acquired is limited and the characteristic data is not acquired a predetermined number of times or more can be considered. In this case, a method of issuing a warning that the performance of the characteristic data does not satisfy the predetermined performance can be considered. Further, a method of giving a warning that the characteristic data does not satisfy the predetermined performance each time the characteristic data is acquired can be considered.

(Third Embodiment) In the second embodiment, a specified value is set for the noise amount upper limit or the artifact upper limit included in the average dark current image, and the dark current imaging frequency is determined so as to reach this specified value. went. In the present embodiment, an example will be described in which a captured radiation image is analyzed and the allowable threshold is changed based on this analysis.

The third embodiment of the present invention will be described with reference to FIG. FIG. 11 is a flow chart of this embodiment.
1 is a radiography step, 152 is a threshold value determining step for determining a threshold value that should be satisfied by the characteristic data, 153 is a characteristic data acquiring step for acquiring the characteristic data, 154 is an evaluating step for evaluating the characteristic data, and 155 is an evaluating step 154. Judgment branching step of judging whether the output satisfies the condition of the threshold value determining step 152 and branching the flow according to the judgment result, 156 is a calculation step of calculating characteristic data, 157 is a correction for correcting the radiation image by the characteristic data It is a process. In this embodiment, the radiation detector is an FPD, and the characteristic data is a dark current image of the FPD.

The radiation imaging apparatus carries out the radiation imaging step 151 in response to the radiation exposure request issued by the operator. Subsequently, the radiation imaging apparatus performs a threshold value determination step 152, evaluates the captured radiation image, and determines a threshold value that the noise amount included in the dark current correction image should satisfy. For example, when the dose is relatively small and the signal level of the radiation image is low, it is necessary to prevent the signal noise ratio from being lowered due to dark current correction as much as possible. Therefore, the threshold value determination step 152 determines a threshold value lower than usual. On the contrary, when the signal level of the radiographic image is high, the signal noise ratio reduction due to the dark current correction does not pose a problem, so the threshold value is set higher than usual with emphasis on throughput.

Next, the radiation imaging apparatus performs dark current imaging,
Subsequently, the evaluation step 154 evaluates the amount of noise included in the dark current image. The judgment branching step 155 compares the noise amount output by the evaluation step 154 with the threshold value output by the threshold value determining step,
If the former is smaller than the latter, dark current imaging is ended, and a calculation step 156 for averaging dark current images is performed. On the other hand, when the former is the latter or more, the process returns to the characteristic data acquisition step 153 to perform dark current imaging. The evaluation step 154 newly evaluates the noise amount using the noise amount of the dark current image captured before that and the noise amount of the current dark current image. Similarly, the judgment branching step 155 compares the noise amount output by the evaluation step 154 with the threshold value output by the threshold value determining step, terminates dark current imaging when the former is smaller than the latter, and when the former is equal to or greater than the latter. The loop process of returning to the characteristic data acquisition step 153 is performed again.

When the standard deviation is used for the noise amount evaluation, the calculation used in the decision branching step 155 is S for radiation image level, n for number of times of photographing, threshold A (S), noise amount in each dark current image. When Bi is given, it is expressed by the following equation.

[0083]

[Equation 9]

As described above, the threshold value determining step 152 is used to variably set the threshold value that should be satisfied by the dark current image according to the signal level of the radiation image, thereby changing the signal level of the radiation image. Also makes it possible to automatically set the optimal number of dark current shots.

(Fourth Embodiment) In the present embodiment, the characteristic data is acquired a predetermined number of times, the characteristic data is evaluated after the characteristic data is acquired, and usable characteristic data is selected. explain.

A fourth embodiment of the present invention will be described with reference to FIG. FIG. 12 is a flowchart of this embodiment.
In Numeral 12, 161 is a step of determining the number of times the characteristic data of the radiation detector is acquired, 162 is a radiation imaging step of exposing the radiation to drive the radiation detector to perform radiation imaging, and 163 is a characteristic of the radiation detector. A characteristic data acquisition step of acquiring data, 164 is a judgment branch step of changing the processing flow by judging whether the characteristic data acquisition number has reached N times based on the output (N times) of the number of times determination step, and 165 is acquired 166 is a step of evaluating characteristic data, 166 is a characteristic data selection step of selecting only valid characteristic data from N characteristic data based on the output of the characteristic evaluation step 165, 167 is an operation for the acquired characteristic data A calculation step 168 is a correction step of creating a correction image using the radiation image and the calculated characteristic data. In this embodiment, the radiation detector is FP
The characteristic data will be described as an FPD dark current image.

Since steps 161 to 164 are the same as steps 101 to 104 in the first embodiment, the description thereof will be omitted. The evaluation step 165 is a step of evaluating the noise amount and the artifact amount of the dark current image. The characteristic data selection step 166 selects a dark current image satisfying the criteria of the noise amount and the artifact amount from the N dark current images based on the output of the evaluation step 165. When the standard deviation is used as the noise amount evaluation value, the standard to be selected is represented by the following formula, where the dark current image to be selected is the nth image.

[0088]

[Equation 10]

That is, the standard deviation calculated including the nth image to be selected is compared with the standard deviation calculated excluding the nth image, and the standard deviation calculated excluding the nth image is smaller. Decides to exclude the n-th image. By using this evaluation method, it is possible to selectively exclude invalid dark current images.

As described above, the characteristic data is acquired a predetermined number of times, and the step of selecting only the effective characteristic data before the correction step is performed, so that a part of the characteristic data can be saved. It is possible to provide a radiation imaging method capable of performing image correction without being affected by a problem even if one problem occurs.

The above first to fourth embodiments can be summarized as follows. A first radiation imaging method is a radiation imaging step of capturing radiation that has passed through an object using a radiation detector to acquire a radiation image of the object, and characteristic data for acquiring characteristic data representing characteristics of the radiation detector. An acquisition step, a number-of-times determination step of determining the number of times of acquiring the characteristic data, and a correction step of acquiring a corrected image obtained by correcting the radiation image using the characteristic data are provided.

Further, the first radiation imaging method is provided with a calculation step such as an average calculation using a plurality of the characteristic data. In addition, the first radiation imaging method is
The characteristic data is a dark current image of the radiation detector. In addition, the first radiographic imaging method determines the number of times of dark current imaging based on subject information such as the patient's physique and imaging site.

Further, the first radiation imaging method comprises a storage step of storing the subject information and the characteristic data acquisition frequency in association with each other. In particular, as a method of storing them in association with each other, both are stored in the shooting menu. The first radiographic imaging method prepares a unique dark current imaging frequency setting algorithm according to the imaging purpose, and sets the optimum dark current imaging frequency based on the algorithm. In particular, a dark current imaging number setting algorithm specialized for calibration, which is one of the imaging purposes, is prepared.

Further, the first radiation imaging method comprises a characteristic data evaluation step of evaluating the characteristic data. In addition, the first radiation imaging method operates the evaluation step every time the characteristic data acquisition step is operated.

Further, the first radiation imaging method is provided with a judgment branching step for changing the processing flow based on the output of the evaluation step each time the evaluation step is operated. In particular, if the output of the evaluation step is NG, the decision branch step changes the processing flow so as to repeat the previous period characteristic data acquisition step, and conversely if the output of the evaluation step is OK, the next step is executed. It changes the flow.

In the first radiation imaging method, the evaluation step is to calculate at least one of the standard deviation of pixel values of the dark current image, the artifact analysis value, and the cross-correlation between the dark current images. In the first radiation imaging method, the number of times characteristic data is acquired is limited, and the characteristic data is not acquired a predetermined number of times or more. In addition, the first radiographic imaging method includes a step of issuing a warning that the performance of the characteristic data does not satisfy the predetermined performance.

In the first radiation imaging method, the evaluation step variably sets the evaluation contents according to the signal level of the radiation image. In addition, the first radiographic imaging method includes a threshold value determining step of changing a threshold value for the pass / fail judgment according to the signal level of the radiographic image.

In the second radiation imaging method, the radiation imaging step of capturing the radiation transmitted through the subject by using the radiation detector to obtain the radiation image of the subject, and the characteristic data representing the characteristics of the radiation detector. And a selecting step of selecting the characteristic data, and a correcting step of acquiring a corrected image obtained by correcting the radiation image using the characteristic data.

The second radiation imaging method comprises an evaluation step of evaluating the characteristic data acquired by the characteristic data acquisition step. Further, in the second radiographic imaging method, the selection step selects the characteristic data based on the output of the evaluation step.

The above radiation imaging method can obtain the following effects. It is possible to realize the setting of the number of times of dark current photography suitable for the purpose of photography and the requirement for photography without instructing the operator every time. As a result, good image quality is obtained and the throughput of the radiation imaging apparatus is optimized.

Further, it is possible to minimize the deterioration of the signal noise ratio due to the dark current correction and to improve the throughput of the calibration photographing. In addition, the number of times characteristic data is acquired for one radiography can be optimized during the characteristic data acquisition period.

Further, it becomes possible to accurately carry out the characteristic data evaluation. You can also find a compromise between image quality and work efficiency. In addition, it is possible to inform the operator that there is concern about the image quality at an early stage, and it is possible to find a compromise in work efficiency.

Further, even if the signal level of the radiation image changes, it becomes possible to automatically set the optimum number of times of dark current imaging. Further, it is possible to provide a radiation imaging method capable of performing image correction without being affected by a problem even if a part of the characteristic data fails.

The above-described embodiments are merely examples of specific embodiments for carrying out the present invention.
The technical scope of the present invention should not be limitedly interpreted by these. That is, the present invention can be implemented in various forms without departing from its technical idea or its main features.

[0105]

As described above, according to the present invention,
By determining the number of times of acquisition of the characteristic data, good image quality can be obtained, and the throughput of radiography can be optimized.

[Brief description of drawings]

FIG. 1 is a flowchart illustrating a radiation imaging method according to a first exemplary embodiment.

FIG. 2 is a sensor driving flowchart.

FIG. 3 is a timing chart explaining the timing of radiation exposure and sensor driving.

FIG. 4 is a diagram of a radiation imaging system that implements the radiation imaging method of the present embodiment.

FIG. 5 is a flowchart illustrating a work menu which is a number-of-times determining step and is used by an operator to select an operation to be performed.

FIG. 6 is a flowchart when the operator selects calibration shooting 123 in the shooting menu 121.

FIG. 7 is a diagram illustrating a sensor reading operation principle.

FIG. 8 is a configuration diagram of an MIS type sensor.

FIG. 9 is an energy band diagram of a photoelectric conversion element.

FIG. 10 is a flowchart illustrating a radiation imaging method according to a second exemplary embodiment.

FIG. 11 is a flowchart illustrating a radiation imaging method according to a third exemplary embodiment.

FIG. 12 is a flowchart illustrating a radiation imaging method according to a fourth exemplary embodiment.

[Explanation of symbols]

21 Idling drive process 22 Initialization drive process 23 Imaging drive process 24 Initialization drive process 25 Imaging drive process 26 Radiation exposure 31 Radiation exposure request signal 32 Radiation exposure permission signal 33 Radiation exposure timing 34 Driving method 1 drive timing 35 Driving timing of driving method 2 40 Radiography 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 driver 82 Upper electrode (D electrode) 83 n + doped layer 84 a-Si intrinsic semiconductor i layer 85 Insulating layer 86 Lower part Electrode (G electrode) 101 Number of times determination step 102 Radiography step 103 Characteristic data acquisition step 104 Judgment branching step 105 Calculation step 106 Correction step 120 Number of times determination step and work menu 121 Imaging menu -122 Patient imaging 123 Calibration imaging 124 Imaging part menu 125 Imaging part button 130 Calibration imaging menu 131 Calibration imaging number input 132 Branch processing 133 Calibration dark current imaging setting when the number of imaging is 4 or more 134 Calibration Dark current shooting count setting when the shooting count is less than 4

Claims (34)

[Claims] 1. A radiation imaging unit that acquires a radiation image of a subject using a radiation detector, a characteristic data acquisition unit that acquires characteristic data representing characteristics of the radiation detector, and a number of times the characteristic data is acquired. A radiation imaging apparatus comprising: a determination means for determining the number of times of determination and a correction means for acquiring a corrected image obtained by correcting the radiation image using the characteristic data. 2. The radiation imaging apparatus according to claim 1, further comprising an arithmetic unit that performs an arithmetic operation using the characteristic data. 3. The radiation imaging apparatus according to claim 1, wherein the characteristic data is a dark current image of the radiation detector. 4. The radiation imaging apparatus according to claim 1, wherein the number-of-times determination unit determines the number of times of acquisition of characteristic data based on subject information. 5. The radiation imaging apparatus according to claim 4, further comprising a storage unit that stores the subject information and the number of times of acquiring the characteristic data in association with each other. 6. The radiation imaging apparatus according to claim 1, wherein the number-of-times determining unit determines the number of times of characteristic data acquisition based on an imaging purpose. 7. The radiation imaging apparatus according to claim 1, further comprising an evaluation unit that evaluates the characteristic data acquired by the characteristic data acquisition unit. 8. The radiation imaging apparatus according to claim 7, wherein each time the characteristic data acquisition unit is operated, an evaluation unit that evaluates the characteristic data acquired by the characteristic data acquisition unit is operated. 9. The radiation imaging apparatus according to claim 8, further comprising a judgment branching unit that changes a processing flow based on an output of the evaluation unit each time the evaluation unit is operated. 10. The evaluation unit calculates at least one of a standard deviation of pixel values of a dark current image, an artifact analysis value, and a cross-correlation between dark current images. Radiography equipment. 11. The radiation imaging apparatus according to claim 9, further comprising a number limiter that limits the number of times the characteristic data is acquired. 12. The radiation imaging apparatus according to claim 7, further comprising warning means for issuing a warning based on the output of the evaluation means. 13. The radiation imaging apparatus according to claim 7, wherein the evaluation unit changes the evaluation content according to the signal level of the radiation image. 14. The radiographic apparatus according to claim 7, further comprising a threshold value determining unit that changes a threshold value for the pass / fail judgment in the evaluation unit according to a signal level of the radiographic image. 15. A radiation imaging unit that acquires a radiation image of a subject using a radiation detector, a characteristic data acquisition unit that acquires characteristic data representing characteristics of the radiation detector, and a selection unit that selects the characteristic data. And a correction unit that acquires a corrected image obtained by correcting the radiation image using the characteristic data. 16. The radiation imaging apparatus according to claim 15, further comprising an evaluation unit that evaluates the characteristic data acquired by the characteristic data acquisition unit. 17. The radiation imaging apparatus according to claim 16, wherein the selection unit selects the characteristic data based on an output of the evaluation unit. 18. A radiation imaging step of acquiring a radiation image of an object using a radiation detector, a characteristic data acquisition step of acquiring characteristic data representing characteristics of the radiation detector, and a number of times of acquiring the characteristic data. A radiation imaging method comprising: a determination step of determining the number of determinations; and a correction step of acquiring a corrected image obtained by correcting the radiation image using the characteristic data. 19. The method according to claim 18, further comprising an operation step of performing an operation using the characteristic data.
The radiographic method described. 20. The radiation imaging method according to claim 18, wherein the characteristic data is a dark current image of the radiation detector. 21. The radiation imaging method according to claim 18, wherein the number of times determination step determines the number of times characteristic data is acquired based on subject information. 22. The radiation imaging method according to claim 21, further comprising a storage step of storing the subject information and the number of times of acquisition of the characteristic data in association with each other. 23. The radiation imaging method according to claim 18, wherein the number of times determining step determines the number of times of acquiring characteristic data based on an imaging purpose. 24. The radiation imaging method according to claim 18, further comprising an evaluation step of evaluating the characteristic data acquired by the characteristic data acquisition step. 25. The evaluation step of evaluating the characteristic data acquired by the characteristic data acquisition step is operated every time the characteristic data acquisition step is operated.
4. The radiographic method described in 4. 26. The radiation imaging method according to claim 25, further comprising a judgment branch step of changing a processing flow based on an output of the evaluation step each time the evaluation step is operated. 27. The method according to claim 25, wherein the evaluation step calculates at least one of a standard deviation of pixel values of the dark current image, an artifact analysis value, and a cross-correlation between the dark current images. Radiography method. 28. The radiographic method according to claim 26, further comprising a step of limiting the number of times of acquiring the characteristic data. 29. The radiation imaging method according to claim 24, further comprising a warning step of issuing a warning based on the output of the evaluation step. 30. The radiation imaging method according to claim 24, wherein in the evaluation step, evaluation contents are changed according to a signal level of the radiation image. 31. The radiographic imaging method according to claim 24, further comprising a threshold value determining step of changing a threshold value for the pass / fail judgment in the evaluation step according to a signal level of the radiographic image. 32. A radiation imaging step of acquiring a radiation image of a subject using a radiation detector, a characteristic data acquisition step of acquiring characteristic data representing characteristics of the radiation detector, and a selection step of selecting the characteristic data. And a correction step of obtaining a corrected image obtained by correcting the radiation image using the characteristic data. 33. The radiation imaging method according to claim 32, further comprising an evaluation step of evaluating the characteristic data acquired by the characteristic data acquisition step. 34. The radiation imaging method according to claim 33, wherein the selection step selects the characteristic data based on an output of the evaluation step.