JP5424542B2 - Imaging control device, control method therefor, and program - Google Patents

Description

  The present invention relates to an imaging control apparatus that controls a sensor that detects incident radiation as an electric charge, a control method therefor, and a program for causing a computer to execute the control method.

  2. Description of the Related Art Conventionally, there has been known an image photographing apparatus using a sensor in which pixels including a photoelectric conversion element and a TFT are two-dimensionally arranged using amorphous silicon or polysilicon formed on a glass substrate as a material. In general, the image capturing apparatus reads out electric charges photoelectrically converted by each photoelectric conversion element from a sensor by performing matrix driving using TFTs.

  Further, for example, in the medical field or the like, an X-ray that is a kind of radiation is irradiated onto a subject (also referred to as “exposure”), X-rays transmitted through the subject are detected, and an X-ray image of the subject is detected. An X-ray imaging apparatus (radiation imaging apparatus) that performs the imaging is used. A method for driving the X-ray imaging apparatus is disclosed in Patent Document 1 below, for example.

  In recent years, an X-ray image capturing apparatus capable of capturing not only a still image but also a moving image has been proposed. For example, Patent Document 2 below discloses.

  In recent years, X-ray imaging apparatuses having a function of performing so-called offset correction have been proposed.

FIG. 7 is a timing chart for explaining general offset correction.
FIG. 7 shows the timing when X-ray irradiation is performed in a pulsed manner. Further, FIG. 7 shows charge accumulation and readout in the sensor as charge accumulation and readout during X-ray irradiation and charge accumulation and readout during X-ray non-irradiation within a frame time of one frame. The timing for performing is shown. In FIG. 7, F1 indicates the first frame, F2 indicates the second frame, F3 indicates the third frame, F4 indicates the fourth frame, and F5 indicates the fifth frame.

Here, it is assumed that the charge readout time is Tr, the charge accumulation time when X-ray irradiation is performed is Tw11, and the charge accumulation time when X-ray irradiation is not performed is Tw12. In addition, the pixel value of the X-ray image taken by irradiating X-rays is Vx, the pixel value of the dark image taken without X-rays is Vd, and the pixel value of the X-ray image after offset correction ( If the offset correction value) is Vo, the offset correction value Vo can be generally calculated by the following equation (1).
Vo = Vx−Vd (1)

Also, assuming that the charge amount per unit time accumulated during non-irradiation with X-rays is Cd and the charge amount per unit time accumulated during X-ray irradiation is Cx, the pixel values Vx and Vd are respectively It can be approximated by equations (2) and (3).
Vx = A · (Cd + Cx) · Tw11 (2)
Vd = A · Cd · Tw12 (3)
Here, A is a proportional constant for converting the amount of accumulated charge into a voltage.

In order to completely remove the offset, it is desirable that the charge accumulation time Tw11 and the charge accumulation time Tw12 are equal. Therefore, if the charge accumulation time Tw11 and the charge accumulation time Tw12 are equal, the offset correction value Vo can be calculated by the following equation (4) from the equations (1), (2), and (3).
Vo = A · Cx · Tw11 (4)
It can be seen from this equation (4) that the offset can be removed.

Further, assuming that the frame time of one frame of the X-ray image at that time is Tf11, the following equation (5) is established.
Tf11 = 2 · (Tr + Tw11) (5)

Therefore, the charge accumulation time Tw11 can be calculated by the following equation (6) from the equation (5).
Tw11 = Tf11 / 2−Tr (6)

Further, assuming that the X-ray irradiation time is Tx, the charge accumulation time Tw11 needs to be longer (longer) than the X-ray irradiation time Tx, and therefore it is necessary to satisfy the following expression (7).
Tw11> Tx (7)

JP 2003-244557 A JP 2003-78124 A

  Since the sensor has a characteristic that the offset voltage fluctuates with time, it is necessary to consider the offset correction described in the background art.

  In the timing chart of FIG. 7 described in the background art, the charge accumulation time Tw11 at the time of X-ray irradiation and the charge accumulation at the time of non-X-ray irradiation are performed in order to completely remove the offset and perform the reliable offset correction. The time Tw12 is set equal. However, in this case, the frame time of one frame is calculated by the above-described equation (5), but there is a problem that it is difficult to improve the frame rate at the time of shooting.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to perform reliable offset correction and to improve the frame rate as compared with the conventional art.

An imaging control apparatus according to the present invention is an imaging control apparatus that controls a sensor that detects incident radiation as an electric charge, irradiates radiation from a radiation generation unit, and captures a radiographic image based on the electric charge detected by the sensor. Radiation image capturing means for performing control processing, dark image capturing means for performing control processing for capturing a dark image based on the charge detected by the sensor in a state in which radiation from the radiation generation unit is not irradiated, and the radiation Frame time determining means for determining a frame time of one frame of an image, accumulation time setting means for setting the charge accumulation time of the sensor in photographing the radiation image and the dark image, and control processing of the dark image photographing means And a dark image taken outside the frame time based on the dark image taken outside the frame time. A first offset value calculating means for calculating an offset value; and a dark image photographed by a control process of the dark image photographing means, wherein the accumulation time is shorter than the accumulation time at the time of photographing the radiation image. Based on the dark image within the frame time taken within the frame time, the second offset value calculating means for calculating the second offset value, the first offset value and the second offset value are used. And offset correction means for performing offset correction of the radiation image.
Another aspect of the imaging control apparatus of the present invention is an imaging control apparatus that controls a sensor that detects incident radiation as an electric charge, and accumulates charges of the sensor based on a period of irradiation of radiation and an irradiation time of radiation. A setting means for setting time, a determination means for determining whether or not an instruction to start irradiation of radiation has been given, and the setting in a state in which the sensor is not irradiated with radiation before the irradiation of radiation is started. Offset data acquisition means for acquiring offset data based on the electric charge accumulated in the sensor during the accumulated accumulation time, and after determining that there has been an instruction to start irradiation of the radiation, the offset data acquisition means between the set accumulation time Radiation image data acquisition means for repeatedly acquiring radiation image data obtained by accumulating radiation as electric charges by the sensor, and the radiation image data A correction means for correcting, based the data to the offset data, and a display controller for displaying a radiographic image based on the corrected radiographic image data on the display unit.
The present invention also includes a control method for the above-described photographing control apparatus and a program for causing a computer to execute the control method.

  According to the present invention, reliable offset correction can be performed, and the frame rate can be improved as compared with the prior art.

Next, various embodiments of the imaging control apparatus according to the present invention will be described.
In the following description of the embodiments of the imaging control apparatus according to the present invention, an example of an X-ray imaging apparatus to which X-rays are applied as radiation is shown, but the present invention is not limited to this. The radiation of the present invention is not limited to X-rays, and includes, for example, α-rays, β-rays, γ-rays, light rays, and the like, and an apparatus for processing a radiographic image captured using these radiations is also included in the present invention. Shall be included.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of a schematic configuration of an X-ray imaging apparatus (imaging control apparatus) according to the first embodiment of the present invention.
As shown in FIG. 1, an X-ray imaging apparatus 10 according to the first embodiment includes an X-ray generation unit 1, an operation input unit 2, a control unit 3, a sensor 4, a display unit 5, and a ROM 6. A RAM 7 and a storage unit 8. The control unit 3 includes an X-ray image capturing unit 31, a dark image capturing unit 32, a frame time determining unit 33, an accumulation time setting unit 34, a first offset value calculating unit 35, and a second An offset value calculation unit 36 and an offset correction unit 37 are included as functional configurations.

  The X-ray generation unit (radiation generation unit) 1 is capable of continuously generating X-rays 1a in a pulse shape with respect to the subject (subject) 20, and is composed of, for example, an X-ray tube. ing.

  The operation input unit 2 is operated when the user gives an input instruction to the X-ray imaging apparatus 10. The operation input unit 2 includes an irradiation switch 2a that is operated by the user when generating the X-ray 1a from the X-ray generation unit 1.

  For example, the control unit 3 reads a program or the like stored in the ROM 6 and performs overall control of the X-ray imaging apparatus 10 based on the program. In particular, in the present embodiment, the control unit 3 realizes processing in each functional configuration of 31 to 37 based on a program or the like stored in the ROM 6.

  Here, the X-ray image capturing unit (radiation image capturing unit) 31 emits X-rays from the X-ray generation unit 1 during charge accumulation in the sensor 4, and then reads out charges from the sensor 4. X-ray image capturing processing is performed. The dark image photographing unit 32 accumulates electric charges of the sensor 4 in a state where the X-rays from the X-ray generating unit 1 are not irradiated, and then reads out electric charges from the sensor 4 to perform dark image photographing processing. Do.

  The frame time determination unit 33 determines the imaging time (frame time) of one frame of the X-ray image. The accumulation time setting unit 34 sets the charge accumulation time (in the present embodiment, a first accumulation time and a second accumulation time, which will be described later) in the sensor 4 when taking an X-ray image and a dark image.

  The first offset value calculation unit 35 is a dark image captured by the dark image capturing unit 32, and is based on the dark image outside the capturing time captured outside the capturing time (outside the frame time) of the X-ray image. A first offset value is calculated. The second offset value calculation unit 36 is a dark image photographed by the dark image photographing unit 32, and is based on the dark image within the photographing time photographed within the photographing time (within the frame time) of the X-ray image. A second offset value is calculated. The offset correction unit 37 performs X-ray image offset correction using the first offset value and the second offset value.

  The sensor 4 detects the X-ray 1a irradiated from the X-ray generation unit 1 and transmitted through the subject 20 as an electric signal (charge) based on the control of the control unit 3 (X-ray image capturing unit 31). The sensor 4 detects an electric signal (charge) in a non-irradiated state, that is, a dark state, of the X-ray 1a from the X-ray generation unit 1 based on the control of the control unit 3 (dark image capturing unit 32). To do.

  In the sensor 4, for example, pixels including photoelectric conversion elements and TFTs are two-dimensionally arranged. In this case, for example, a phosphor is provided on each pixel. In this case, the X-rays incident on the sensor 4 are converted into visible light by the phosphor, and the converted visible light enters the photoelectric conversion element of each pixel, and the charge corresponding to the visible light in each photoelectric conversion element. Is generated. In the present embodiment, the above-described phosphor and photoelectric conversion element form a “conversion element” that converts incident X-rays into electric charges. For example, incident X-rays are provided without providing a phosphor. Alternatively, a so-called direct conversion type conversion element that directly converts the light into a charge may be used. Accordingly, in the following description, it is assumed that “conversion elements” are arranged in a two-dimensional manner on the sensor 4.

  Further, as already described in the background art, the sensor 4 can take an X-ray image and a dark image by alternately repeating charge accumulation and charge readout of each conversion element.

  The display unit 5 displays an X-ray image based on the electric charges read from the sensor 4, an operation UI, and the like based on the control of the control unit 3.

  In the ROM 6, for example, the control unit 3 stores processing shown in FIGS. 2 and 6 to be described later, and other programs necessary for controlling the X-ray imaging apparatus.

  The RAM 7 is used, for example, when the control unit 3 performs various controls. For example, the RAM 7 temporarily stores various information calculated by the control unit 3, various information input by the user via the operation input unit 2, and the like. Remember me.

  The accumulation unit 8 accumulates and stores, for example, each X-ray image (each radiation image) based on the charges read from the sensor 4 and image data of each dark image.

  In FIG. 1, when the irradiation switch 2a is operated and turned on, the control unit 3 controls the X-ray generation unit 1 to irradiate the X-ray 1a in pulses. In addition, the control unit 3 reads out charges based on the X-ray 1a transmitted through the subject (subject) 20 from the sensor 4 in synchronization with the pulse of the X-ray 1a, generates an X-ray image, and performs an offset correction process. Then, the X-ray image is displayed on the display unit 5.

Next, a processing procedure of the X-ray imaging apparatus 10 according to the first embodiment will be described.
FIG. 2 is a flowchart illustrating an example of a processing procedure of the X-ray imaging apparatus (imaging control apparatus) according to the first embodiment of the present invention.

  First, in step S <b> 101, when an imaging condition is input from the user via the operation input unit 2, the control unit 3 detects this, and various information input via the operation input unit 2 is, for example, Store in RAM 7 and set. Here, in this embodiment, the frame rate Fr, the charge readout time Tr of the sensor 4, the X-ray irradiation time Tx, the number of X-ray images (number of X-ray irradiation pulses), and the like are set as imaging conditions by the user. It is assumed that such information is input and stored in the RAM 7.

  Subsequently, in step S102, the control unit 3 determines whether or not the irradiation switch 2a is operated by the user and the irradiation switch 2a is turned on. If the result of this determination is that the irradiation switch 2a is not on, the process waits in step S102 until it is determined in step S102 that the irradiation switch 2a has been turned on.

  On the other hand, as a result of the determination in step S102, if the irradiation switch 2a is turned on, the process proceeds to step S103. In step S103, the frame time determination unit 33 of the control unit 3 determines the imaging time (frame time) of one frame of the X-ray image.

Specifically, in the present embodiment, the frame time determination unit 33 uses the information of the frame rate Fr obtained in step S101 to set the shooting time (frame time) Tf1 of one frame as the following equation (8). Is determined by calculating
Tf1 = 1 / Fr (8)

  Then, the frame time determination unit 33 stores and sets information of the calculated shooting time (frame time) Tf1 of one frame in the RAM 7, for example.

  Subsequently, in step S104, the accumulation time setting unit 34 of the control unit 3 sets the first accumulation time for the charge in the sensor 4 according to the imaging time of one frame determined in step S103. Subsequently, in step S105, the accumulation time setting unit 34 sets a second accumulation time for the charge in the sensor 4 in accordance with the shooting time of one frame determined in step S103. Specific processing in steps S104 and S105 will be described below with reference to FIG.

  FIG. 3 shows an example of the operation of the X-ray imaging apparatus (imaging control apparatus) according to the first embodiment of the present invention, the timing of X-ray irradiation in the moving image imaging mode, and the accumulation of charge in the sensor. It is a timing chart which shows an example of the timing of read-out of electric charge. The timing chart shown in FIG. 3 shows a case where the frame time (shooting time) of one frame is shorter than that in FIG. That is, the case of Tf1 <Tf11 is shown.

  In FIG. 3, charge accumulation and charge readout in each conversion element of the sensor 4 are alternately repeated, and X-ray image photographing processing by the X-ray image photographing unit 31 within one frame photographing time (frame time). A dark image is captured by the dark image capturing unit 32. Further, the timing chart shown in FIG. 3 shows a case where an X-ray image is first captured and then a dark image is captured.

  Further, in the timing chart shown in FIG. 3, before the X-ray image is captured by irradiating X-rays, that is, outside the X-ray image capturing time (outside the frame time), the dark image capturing unit 32 is dark in advance. This shows a case where an image (dark image outside shooting time) is shot twice. Here, regarding the dark image taken before taking the X-ray image, a dark image with a long charge accumulation time is designated as a first dark image (dark image outside the first photography time), and a dark image with a short accumulation time is designated as a dark image. This is referred to as a second dark image (second dark image outside the shooting time). In addition, a dark image that is captured within the imaging time (within the frame time) of each X-ray image is referred to as a third dark image (dark image within the imaging time).

  Also, each frame shown in FIG. 3 indicates the timing at which one X-ray image after offset correction is generated. F1 is the first frame, F2 is the second frame, and F3 is the third frame. , F4 indicate the fourth frame, respectively.

  In FIG. 3, the imaging time (frame time) of one frame is Tf1, the X-ray irradiation time is Tx, and the charge readout time of the sensor 4 is Tr. In the present embodiment, the charge accumulation time when photographing the first dark image and the X-ray image (radiation image) is set to the same first accumulation time Tw1, and the second dark image and the third dark image are photographed. The charge accumulation time at that time is the same second accumulation time Tw2. Then, the accumulation time setting unit 34 sets the second accumulation time Tw2 to be shorter than the first accumulation time Tw1.

The imaging time (frame time) Tf1 determined in step S103, the charge readout time Tr set in step S101, the first accumulation time Tw1 and the second accumulation time Tw2 set by the accumulation time setting unit 34 The following equation (9) holds.
Tf1 = 2Tr + Tw1 + Tw2 (9)

  According to the equation (9), since the charge readout time Tr is a fixed time, when the imaging time (frame time) Tf1 of one frame becomes small (short), the first accumulation time Tw1 and the second accumulation time Tw2 are obtained. The added value becomes smaller (shorter). On the contrary, when the photographing time (frame time) Tf1 of one frame becomes large (long), the value obtained by adding the first accumulation time Tw1 and the second accumulation time Tw2 becomes large (long).

Here, assuming that the minimum value of the first accumulation time Tw1 is Tmin1 and the minimum value of the second accumulation time Tw2 is Tmin2, it is assumed that the following equations (10) and (11) are satisfied.
Tw1 = Tmin1 + α (10)
Tw2 = Tmin2 + α (11)
Here, α is a variable that changes according to the shooting time (frame time) of one frame. That is, here, when the imaging time of one frame is reduced, the first accumulation time Tw1 and the second accumulation time Tw2 are reduced by the same value, and conversely, when the imaging time of one frame is increased, the first accumulation time Tw1. And the second accumulation time Tw2 are assumed to increase by the same value.

Then, when the first accumulation time Tw1 and the second accumulation time Tw2 are arranged using the equations (9), (10), and (11), respectively, the following equations (12) and (13) Is obtained.
Tw1 = (Tf1 + Tmin1-Tmin2) / 2-Tr (12)
Tw2 = (Tf1-Tmin1 + Tmin2) / 2-Tr (13)

Here, since the minimum value Tmin1 of the first accumulation time must be longer (longer) than the X-ray irradiation time Tx, it is necessary to satisfy the following expression (14).
Tmin1> Tx (14)

The minimum value Tmin2 of the second accumulation time can be set to an arbitrary value, but in the embodiment, it is set so that the following expression (15) is satisfied.
Tmin1> Tmin2 (15)

  First, the accumulation time setting unit 34 can set the minimum value Tmin1 of the first accumulation time based on the X-ray irradiation time Tx set in step S101 from the equation (14). Thereafter, the accumulation time setting unit 34 can set the minimum value Tmin2 of the second accumulation time based on the set minimum value Tmin1 of the first accumulation time from the equation (15).

Moreover, the following (16) Formula and (17) Formula hold from (10) Formula, (11) Formula, (14) Formula, and (15) Formula.
Tw1> Tx (16)
Tw1> Tw2 (17)

  Usually, since the X-ray irradiation time Tx is a value from several milliseconds to several tens of milliseconds, the minimum value Tmin1 of the first accumulation time is also a value from several milliseconds to several tens of milliseconds. Further, the minimum value Tmin2 of the second accumulation time is about 1 millisecond.

  The accumulation time setting unit 34 is based on the set first accumulation time minimum value Tmin1 and second accumulation time minimum value Tmin2, and the X-ray irradiation time Tx and the charge readout time Tr set in step S101. Thus, the first accumulation time Tw1 is set by the equation (12). Similarly, the accumulation time setting unit 34 sets the second accumulation time Tw2 by the equation (13). At this time, the accumulation time setting unit 34 sets the first accumulation time Tw1 and the second accumulation time Tw2 so as to satisfy the expressions (16) and (17).

  Then, the accumulation time setting unit 34 stores information of the set first accumulation time Tw1 and second accumulation time Tw2 in the RAM 7, for example.

  In the present embodiment, the second accumulation time Tw2 is set shorter (smaller) than the first accumulation time Tw1 from the equation (17), so that the shooting time of one frame can be shortened (smaller), and the frame The rate can be improved.

  However, in this case, since the charge accumulation time differs between the first accumulation time Tw1 and the second accumulation time Tw2, the offset cannot be completely removed by the equation (1) described in the background art. That is, in this embodiment, the charge accumulation time when photographing the first dark image and the third dark image is defined as the first accumulation time Tw1, and the charge accumulation when photographing the second dark image and the X-ray image. The time is the second accumulation time Tw2. For this reason, in the present embodiment, the processing after step S106 shown below is performed.

  In step S106, the dark image capturing unit 32 of the control unit 3 performs X-ray imaging before the X-ray image capturing unit 31 captures an X-ray image, that is, outside the X-ray image capturing time (outside the frame time). A process of photographing a dark image is performed in a state in which the X-ray 1a from the line generator 1 is not irradiated. At this time, the dark image to be shot becomes a dark image outside the shooting time.

  Specifically, in this embodiment, the dark image capturing unit 32 captures a first dark image (first non-shooting time dark image) and a second dark image (second non-shooting time dark image). I do. At this time, as shown in FIG. 3, the first dark image has been imaged with the charge accumulation time as the first accumulation time Tw1, and the second dark image has the charge accumulation time as the second accumulation time. The image is processed as the accumulation time Tw2. Then, the dark image photographing unit 32 stores the image data of the first dark image and the second dark image in the storage unit 8, for example.

  Subsequently, in step S107, the first offset value calculation unit 35 calculates a first offset value based on the dark image photographed in step S106.

  Specifically, in the present embodiment, since the first dark image and the second dark image are captured in step S106, the first offset value calculation unit 35 uses the first offset value based on these images. Is calculated.

Here, when the first offset value is Vo1, the pixel value of the first dark image is Vd1, and the pixel value of the second dark image is Vd2, the first offset value calculation unit 35 sets the first offset value Vo1. It is calculated by the following equation (18).
Vo1 = Vd1−Vd2 (18)
At this time, the first offset value calculation unit 35 calculates the first offset value Vo1 for each pixel of the first dark image and the second dark image.

  Then, the first offset value calculation unit 35 stores the calculated first offset value Vo1 in the RAM 7, for example.

  Thereafter, when the radiographing time of the X-ray image is started, subsequently, in step S108, the X-ray image radiographing unit 31 of the control unit 3 transfers the X-ray image from the X-ray generation unit 1 to the subject 20 while the sensor 4 is accumulating charges. A process of irradiating the X-ray 1a and photographing an X-ray image is performed. At this time, as shown in FIG. 3, the X-ray image capturing process is performed with the charge accumulation time in the sensor 4 as the first accumulation time Tw1. Then, the X-ray image capturing unit 31 stores the image data of the X-ray image in, for example, the storage unit 8.

  Subsequently, in step S109, the dark image photographing unit 32 is dark in a state in which the X-ray 1a from the X-ray generation unit 1 is not irradiated within the photographing time (frame time) of one frame of the X-ray image. Performs processing to capture an image. At this time, the dark image to be shot becomes a dark image within the shooting time.

  Specifically, in the present embodiment, as shown in FIG. 3, the dark image capturing unit 32 captures a third dark image (dark image within the capturing time) in which the charge accumulation time is the second accumulation time Tw2. Process. Then, the dark image photographing unit 32 stores the image data of the third dark image in the storage unit 8, for example.

  Subsequently, in step S110, the second offset value calculator 36 calculates a second offset value based on the third dark image photographed in step S109.

  Specifically, in the present embodiment, the second offset value calculation unit 36 of the control unit 3 detects each pixel value of the third dark image, and sets the second offset value for each pixel of the third dark image. calculate. Then, the second offset value calculation unit 36 stores the calculated second offset value in, for example, the RAM 7.

  Subsequently, in step S111, the offset correction unit 37 of the control unit 3 was captured in step S108 using the first offset value calculated in step S107 and the second offset value calculated in step S110. X-ray image offset correction is performed.

The offset correction process in step S111 will be described below.
Here, as shown in FIG. 3, the pixel value of the X-ray image captured in step S108 is Vx, the pixel value of the third dark image, that is, the second offset value is Vd3, and the X-ray image of the X-ray image after offset correction is used. Let the pixel value be Vo2. In this case, the offset correction unit 37 performs offset correction on the X-ray image captured in step S108 by the following equation (19).
Vo2 = Vx−Vd3−Vo1 (19)
At this time, the offset correction unit 37 performs offset correction for each pixel of the X-ray image.

As already described in the background art, assuming that the charge amount per unit time accumulated during non-irradiation of X-rays is Cd and the charge amount per unit time accumulated during X-ray irradiation is Cx, the pixel value Vd1, Vd2, Vx, and Vd3 can be approximated by the following equations (20) to (23), respectively.
Vd1 = A · Cd · Tw1 (20)
Vd2 = A · Cd · Tw2 (21)
Vx = A · (Cd + Cx) · Tw1 (22)
Vd3 = A · Cd · Tw2 (23)

From the equations (18) to (23), the pixel value Vo2 of the X-ray image after the offset correction is shown in the equation (24).
Vo2 = A · Cx · Tw1 (24)
As shown by the equation (24), the pixel value Vo2 of the X-ray image after the offset correction does not include the charge amount Cd that is an offset component, and thus the offset can be removed from the X-ray image. I understand.

  Then, the offset correction unit 37 stores the image data of the X-ray image after the offset correction, for example, in the storage unit 8. Thereafter, the control unit 3 displays the X-ray image on the display unit 5 as necessary.

  Subsequently, in step S112, the control unit 3 determines whether or not imaging is completed for the number of X-ray images to be captured (number of X-ray irradiation pulses) set in step S101. If the result of this determination is that imaging has not been completed for the number of X-ray images (number of X-ray irradiation pulses) set in step S101, the process returns to step S108.

  On the other hand, as a result of the determination in step S112, if the imaging for the number of X-ray images to be captured (number of X-ray irradiation pulses) set in step S101 is completed, the processing of the flowchart shown in FIG.

  In the present embodiment, as shown in FIG. 2, the first offset value calculation process using the equation (18) in step S107 is performed by taking an X-ray image irradiated with the X-ray 1a by the X-ray image taking unit 31. This is performed before the processing (S108). As shown in FIG. 2, the X-ray image offset correction process using the equation (19) in step S <b> 111 is performed every time the X-ray generator 1 emits the X-ray 1 a.

  In the first embodiment, when determining the shooting time (frame time) of one frame, the frame time determination unit 33 is determined by calculation using the equation (8). However, the present invention is limited to this mode. is not. For example, it is a form in which the photographing time (frame time) of one frame directly input from the user via the operation input unit 2 is detected in step S101 and this is determined as the photographing time (frame time) of one frame. Also good.

  In the first embodiment, each of the components 31 to 37 is realized by software by the control unit 3 executing a program stored in the ROM 6. May be realized by hardware.

In the first embodiment, the first offset value calculation unit 35 calculates the first offset value Vo1 by calculating the equation (18). However, the present invention is limited to this form. is not. For example, in the case where the charge amplification factors for capturing the first dark image and the second dark image are different, the first offset value calculation unit 35 sets the first offset value Vo1 as the following equation (25). Calculated by
Vo1 = Vd1−B · Vd2 (25)
Here, B is a constant.

In the first embodiment, the offset correction unit 37 performs the offset correction process on the X-ray image by calculating the equation (19). However, the present invention is not limited to this mode. For example, in the case where the offset value of the charge when photographing the X-ray image and the third dark image is obtained, the offset correction unit 37 performs the offset correction processing of the X-ray image by calculating the following equation (26). Do.
Vo2 = Vx−Vd3−Vo1 + C (26)
Here, C is a constant.

Further, in the first embodiment, it is assumed that the first accumulation time Tw1 and the second accumulation time Tw2 satisfy the expressions (10) and (11), respectively, but the present invention is limited to this form. It is not a thing. For example, it may be assumed that the following equations (27) and (28) hold for the first accumulation time Tw1 and the second accumulation time Tw2, respectively.
Tw1 = Tmin1 + β (27)
Tw2 = Tmin2 (28)
That is, it is assumed that the second accumulation time Tw2 is a small fixed value, while the first accumulation time Tw1 changes in the same manner as the equation (10) when the photographing time (frame time) of one frame changes.

  In the first embodiment, the first offset value calculation unit 35 calculates the first offset value using the first dark image and the second dark image immediately before the X-ray irradiation. However, it is not limited to this form. In the present embodiment, if a dark image before X-ray irradiation is used, it is not always necessary to be immediately before X-ray irradiation. Further, the first offset value used in the present embodiment may be calculated by periodically recalculating it before X-ray irradiation.

  In the first embodiment, the first offset value calculation unit 35 calculates the first offset value using two dark images (dark images outside the shooting time) of the first dark image and the second dark image. However, the present invention is not limited to this form. For example, the first offset value calculation unit 35 may apply a form in which the first offset value is calculated using one dark image instead of two dark images as dark images outside the photographing time. Is possible. In this case, the first offset value calculation unit 35 detects each pixel value of the one dark image, and calculates a first offset value for each pixel of the one dark image. When the one dark image is used, if the charge accumulation time is (Tw1-Tw2) in consideration of the equations (18), (20), and (21), the first dark image and The one dark image can be applied instead of the second dark image. And when this form is taken, about the process after step S108, a process can be performed similarly to what was shown in 1st Embodiment.

(Second Embodiment)
Below, the 2nd Embodiment of this invention is described using an accompanying drawing.

  Here, the schematic configuration of the X-ray imaging apparatus (imaging control apparatus) according to the second embodiment is the same as the schematic configuration of the X-ray imaging apparatus 10 according to the first embodiment shown in FIG. Further, the processing procedure of the X-ray imaging apparatus 10 according to the second embodiment is obtained by reversing the order of the processing in step S108 and the processing in step S109 shown in FIG.

  FIG. 4 shows an example of the operation of the X-ray imaging apparatus (imaging control apparatus) according to the second embodiment of the present invention, the timing of X-ray irradiation in the moving image imaging mode, and the accumulation of charge in the sensor. It is a timing chart which shows an example of the timing of read-out of an electric charge. In the timing chart shown in FIG. 4, the same components as those in the timing chart shown in FIG.

  FIG. 4 shows a case where the third dark image (dark image within the shooting time) is first shot and then the X-ray image is shot within the shooting time of one frame (within the frame time). In addition, as for the dark image to be photographed outside the photographing time (outside the frame time) of the X-ray image before the X-ray 1a is irradiated, the second dark image is photographed first, and then the first dark image is photographed. Taken at. This is because the first dark image and the X-ray image correspond to each other, and the second dark image and the third dark image correspond to each other. Along with this, the order of photographing the first dark image and the second dark image is reversed.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 5 is a block diagram showing an example of a schematic configuration of an X-ray imaging apparatus (imaging control apparatus) according to the third embodiment of the present invention. In FIG. 5, the same components as those shown in FIG.

  The X-ray imaging apparatus 30 according to the third embodiment further includes a comparison unit 38 in the control unit 330 in addition to the configuration of the X-ray imaging apparatus 10 according to the first embodiment. . Further, in the third embodiment, the accumulation time setting unit 34 further sets a third accumulation time to be described later in addition to the first accumulation time and the second accumulation time in the first embodiment.

Next, a processing procedure of the X-ray imaging apparatus 30 according to the third embodiment will be described.
FIG. 6 is a flowchart illustrating an example of a processing procedure of the X-ray imaging apparatus (imaging control apparatus) according to the third embodiment of the present invention. In FIG. 6, the same processing steps as the processing steps shown in FIG.

  First, in the third embodiment, the processes of steps S101 to S103 shown in FIG. 2 are performed.

  Subsequently, in step S301, the accumulation time setting unit 34 determines the charge accumulation time related to the X-ray image and the charge accumulation time related to the dark image within the imaging time according to the imaging time of one frame determined in step S103. And the third accumulation time is calculated. Specific processing in step S301 will be described below.

  Specifically, the accumulation time setting unit 34 calculates the charge accumulation time Tw11 as the third accumulation time using the equation (6) described in the background art. The third accumulation time Tw11 corresponds to the charge accumulation time related to the X-ray image (pixel value Vx) shown in FIG. Further, the third accumulation time Tw11 calculated by the equation (6) is assumed to be the same time as the charge accumulation time Tw12 related to the dark image (pixel value Vd) within the photographing time shown in FIG. Yes. Note that the shooting time (frame time) of one frame at this time is Tf11.

  Subsequently, in step S302, the comparison unit 38 of the control unit 330 compares the third accumulation time calculated in step S301 with the reference time as a reference, and the third accumulation time is longer than the reference time ( Large).

  Here, in this embodiment, the X-ray irradiation time Tx is applied as the reference time. That is, in step S302, it is determined whether the third accumulation time Tw11 is longer (larger) than the X-ray irradiation time Tx, that is, whether the equation (7) is satisfied.

  As a result of the determination in step S302, if the third accumulation time is not longer than the reference time, that is, if the third accumulation time is equal to or less than the reference time, the process proceeds to step S104, and FIG. 2 in the first embodiment. Steps S104 to S112 shown in FIG. In this case, the timing chart shown in FIG. 3 is executed. Note that the processing after step S104 shown in FIG. 7 is the processing procedure of the first embodiment, but the processing procedure of the second embodiment is applied and the timing chart shown in FIG. 4 is executed. May be.

  On the other hand, as a result of the determination in step S302, if the third accumulation time is longer than the reference time, the process proceeds to step S303. In step S303, the accumulation time setting unit 34 sets the charge accumulation time related to the X-ray image and the charge accumulation time related to the dark image within the imaging time as the same third accumulation time.

  Specifically, the accumulation time setting unit 34 sets the same charge accumulation time for the X-ray image (pixel value Vx) shown in FIG. 7 and the charge accumulation time for the dark image (pixel value Vd) within the imaging time. 3 is set as an accumulation time Tw11. The accumulation time setting unit 34 stores information on the set third accumulation time Tw11 in the RAM 7, for example.

  Thereafter, when the radiographing time of the X-ray image is started, subsequently, in step S304, the X-ray image radiographing unit 31 of the control unit 330 transfers the X-ray image from the X-ray generation unit 1 to the subject 20 during charge accumulation in the sensor 4. A process of irradiating the X-ray 1a and photographing an X-ray image is performed. At this time, as shown in FIG. 7, the X-ray image capturing process is performed with the charge accumulation time in the sensor 4 as the third accumulation time Tw11. Then, the X-ray image capturing unit 31 stores the image data of the X-ray image in, for example, the storage unit 8.

  Subsequently, in step S305, the dark image capturing unit 32 of the control unit 330 does not irradiate the X-ray 1a from the X-ray generation unit 1 within the capturing time (frame time) of one frame of the X-ray image. In this state, a process of shooting a dark image within the shooting time is performed. At this time, the photographing process of the dark image within the photographing time is performed by using the charge accumulation time in the sensor 4 as the third accumulation time Tw11. The X-ray image photographing unit 31 stores the image data of the dark image within the photographing time in, for example, the storage unit 8.

  Subsequently, in step S306, the offset correction unit 37 of the control unit 330 performs offset correction of the X-ray image photographed in step S304 using the dark image within the photographing time photographed in step S305.

  Specifically, the offset correction unit 37 calculates the equation (1), where Vx is the pixel value of the X-ray image captured in step S304 and Vd is the pixel value of the dark image within the imaging time captured in step S304. To correct the offset of the X-ray image. The pixel value Vo of the X-ray image after offset correction is obtained by the calculation according to the equation (1), and the offset correction unit 37 performs offset correction for each pixel of the X-ray image. Then, the offset correction unit 37 stores the image data of the X-ray image after the offset correction, for example, in the storage unit 8. Thereafter, the control unit 3 displays the X-ray image on the display unit 5 as necessary.

  Subsequently, in step S307, the control unit 3 determines whether or not imaging is completed for the number of X-ray images to be captured (number of X-ray irradiation pulses) set in step S101. If the result of this determination is that imaging has not been completed for the number of X-ray images captured (number of X-ray irradiation pulses) set in step S101, the process returns to step S304.

  On the other hand, as a result of the determination in step S307, if the imaging for the number of X-ray images (number of X-ray irradiation pulses) set in step S101 is completed, the processing of the flowchart shown in FIG.

  According to the X-ray imaging apparatus 10 according to each embodiment of the present invention, it is possible to perform reliable offset correction and to improve the frame rate as compared with the related art.

  1 and FIG. 5 constituting the X-ray imaging apparatus according to each of the embodiments described above, and the steps of FIG. 2 and FIG. 6 showing the control method of the X-ray imaging apparatus are stored in the ROM 6. It can be realized by operating the programmed program. This program and a computer-readable storage medium storing the program are included in the present invention.

  Specifically, the program is recorded in a storage medium such as a CD-ROM, or provided to a computer via various transmission media. As a storage medium for recording the program, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, a nonvolatile memory card, and the like can be used in addition to the CD-ROM. On the other hand, as the transmission medium of the program, a communication medium 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 can be used. In addition, examples of the communication medium at this time include a wired line such as an optical fiber, a wireless line, and the like.

  Further, the function of the X-ray imaging apparatus according to each embodiment is not only realized by executing a program supplied by a computer. The program is also included in the present invention even when the function of the X-ray imaging apparatus according to each embodiment is realized in cooperation with an OS (operating system) or other application software running on the computer. It is. In addition, when all or part of the processing of the supplied program is performed by a function expansion board or function expansion unit of a computer and the functions of the X-ray imaging apparatus according to each embodiment are realized, the program is It is included in the present invention.

  In addition, all of the above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. . That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  The imaging control apparatus according to the present invention can perform reliable offset correction and can improve the frame rate as compared with the conventional art. Therefore, it is expected to be effectively used in the medical field where a radiographic imaging apparatus that captures a radiographic image at a higher speed is required.

1 is a block diagram illustrating an example of a schematic configuration of an X-ray imaging apparatus (imaging control apparatus) according to a first embodiment of the present invention. It is a flowchart which shows an example of the process sequence of the X-ray-image imaging device (imaging control apparatus) which concerns on the 1st Embodiment of this invention. 2 shows an example of the operation of the X-ray imaging apparatus (imaging control apparatus) according to the first embodiment of the present invention, the timing of X-ray irradiation in the moving image imaging mode, and the accumulation and readout of charges of the sensor. It is a timing chart which shows an example of timing. 6 shows an example of the operation of an X-ray imaging apparatus (imaging control apparatus) according to a second embodiment of the present invention, showing the timing of X-ray irradiation in the moving image imaging mode, and the accumulation and readout of charges from the sensor. It is a timing chart which shows an example of timing. It is a block diagram which shows an example of schematic structure of the X-ray-image imaging device (imaging control apparatus) which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows an example of the process sequence of the X-ray imaging apparatus (imaging control apparatus) which concerns on the 3rd Embodiment of this invention. It is a timing chart for demonstrating general offset correction.

Explanation of symbols

1: X-ray generator (radiation generator)
2: Operation input unit 2a: Irradiation switch 3: Control unit 31: X-ray image capturing unit 32: Dark image capturing unit 33: Frame time determining unit 34: Accumulating time setting unit 35: First offset value calculating unit 36: First 2 offset value calculation unit 37: offset correction unit 4: sensor 5: display unit 6: ROM
7: RAM
8: Accumulator 10: X-ray imaging apparatus (imaging control apparatus)
20: Subject (subject)

Claims (16)

An imaging control device that controls a sensor that detects incident radiation as an electric charge,
Radiation image capturing means for performing a control process of irradiating radiation from a radiation generation unit and capturing a radiation image based on the charge detected by the sensor;
Dark image capturing means for performing control processing for capturing a dark image based on the charge detected by the sensor in a state in which the radiation from the radiation generating unit is not irradiated;
Frame time determining means for determining a frame time of one frame of the radiation image;
An accumulation time setting means for setting an accumulation time of charge of the sensor in photographing the radiation image and the dark image;
First offset value calculation means for calculating a first offset value based on a dark image taken by the control process of the dark image photographing means and being taken outside the frame time. When,
A dark image taken by the control processing of the dark image capturing means, the radiation image on the photographed in short the storage time than the accumulation time in the frame time frame within the time dark image when capturing the Based on a second offset value calculating means for calculating a second offset value,
An imaging control apparatus comprising: an offset correction unit that performs offset correction of the radiation image using the first offset value and the second offset value. Wherein the dark imaging means, as the frame overtime dark image, and it performs a first frame overtime dark image, a control process for photographing a second frame overtime dark image,
The first offset value calculating means calculates the first offset value based on the first non-frame time dark image and the second non-frame time dark image. The imaging control apparatus according to 1. The accumulation time setting means, and wherein the storage time of the charge of the second frame overtime dark image, the set shorter than the charge accumulation time according to the first frame overtime dark image The photographing control apparatus according to claim 2. When the first offset value is Vo1, the pixel value of the first non-frame dark image is Vd1, and the pixel value of the second non-frame dark image is Vd2,
The first offset value calculating means calculates the first offset value as follows:
Vo1 = Vd1-Vd2
The imaging control apparatus according to claim 2, wherein the imaging control apparatus calculates the image by: If the pixel value of the radiation image is Vx, the first offset value is Vo1, the second offset value is Vd3, and the pixel value of the radiation image after the offset correction is Vo2,
The offset correction means, the radiographic image,
Vo2 = Vx−Vd3−Vo1
The imaging control apparatus according to claim 1, wherein the offset correction is performed by the method.   The said 1st offset value calculation means performs calculation of the said 1st offset value before imaging | photography of the said radiographic image by the said radiographic image imaging means. The imaging | photography control apparatus as described in. The imaging control apparatus according to claim 1, wherein the offset correction unit performs the offset correction every time radiation is emitted from the radiation generation unit . The accumulation time setting means sets the charge accumulation time related to the dark image outside the first frame time and the charge accumulation time related to the radiation image as the same first accumulation time, and the second accumulation time 5. The charge accumulation time for the dark image outside the frame time and the charge accumulation time for the dark image within the frame time are set as the same second accumulation time. The imaging control apparatus according to item 1. 9. The accumulation time setting unit according to claim 8, wherein the first accumulation time and the second accumulation time are set according to the frame time determined by the frame time determination unit . Shooting control device. The accumulation time setting means further includes an accumulation time of the charge related to the radiation image and an accumulation time of the charge related to the dark image within the frame time according to the frame time determined by the frame time determination means. The third accumulation time is calculated for the same time,
A comparison means for comparing the third accumulation time with a reference time as a reference;
As a result of comparison by the comparison means, when the third accumulation time is equal to or less than the reference time, the accumulation time setting means is configured to determine the charge accumulation time related to the dark image outside the first frame time and the charge accumulation time. The charge accumulation time related to the radiographic image is set as the same first accumulation time, and the charge accumulation time related to the second non-frame time dark image and the charge accumulation related to the dark image within the frame time are set. 5. The photographing control apparatus according to claim 2, wherein the time is set as the same second accumulation time. The first accumulation time is Tw1, the frame time determined by the frame time determination means is Tf1, the charge readout time of the sensor is Tr, the minimum value of the first accumulation time is Tmin1, and the second If the minimum value of the accumulation time is Tmin2,
The accumulation time setting means sets the first accumulation time as
Tw1 = (Tf1 + Tmin1-Tmin2) / 2-Tr
The imaging control device according to claim 8, wherein the imaging control device is set according to claim 8. The second accumulation time is Tw2, the frame time determined by the frame time determination means is Tf1, the charge readout time of the sensor is Tr, the minimum value of the first accumulation time is Tmin1, and the second If the minimum value of the accumulation time is Tmin2,
The accumulation time setting means sets the second accumulation time as
Tw2 = (Tf1-Tmin1 + Tmin2) / 2-Tr
The imaging control device according to claim 8, wherein the imaging control device is set according to claim 8. An imaging control device that controls a sensor that detects incident radiation as an electric charge,
Setting means for setting a charge accumulation time of the sensor based on a period of radiation irradiation and a radiation irradiation time;
Determining means for determining whether or not there has been an instruction to start irradiation with the radiation;
Offset data acquisition means for acquiring offset data based on the charge accumulated in the sensor during the set accumulation time in a state in which the sensor is not irradiated with radiation before the radiation irradiation is started;
Radiological image data acquisition means for repeatedly acquiring radiological image data obtained by accumulating radiation as electric charges during the set accumulation time after it is determined that there is an instruction to start the radiation irradiation; ,
Correction means for correcting the radiation image data based on the offset data;
Display control means for displaying a radiographic image based on the corrected radiographic image data on a display unit. A sensor for detecting incident radiation as a charge, radiation is irradiated from the radiation generating unit, and a radiation image capturing means for controlling processing of capturing a radiographic image based on the detected charge in the sensor, from the radiation generating unit A control method of an imaging control apparatus including a dark image capturing unit that performs a control process of capturing a dark image based on the charge detected by the sensor in a non-irradiated state,
A frame time determining step for determining a frame time of one frame of the radiation image;
And accumulation time setting step of setting the radiographic image and the dark image collector load accumulation time of the sensor in the shooting,
A first offset value calculating step of calculating a first offset value based on a dark image taken by control processing of the dark image photographing means and taken outside the frame time. When,
A dark image taken by the control processing of the dark image capturing means, the radiation image on the photographed in short the storage time than the accumulation time in the frame time frame within the time dark image when capturing the Based on a second offset value calculating step for calculating a second offset value,
An imaging control apparatus control method comprising: an offset correction step for performing offset correction of the radiation image using the first offset value and the second offset value. A method for controlling an imaging control device that controls a sensor that detects incident radiation as an electric charge,
A setting step for setting a charge accumulation time of the sensor based on a period of radiation irradiation and a radiation irradiation time;
A determination step of determining whether or not there is an instruction to start irradiation with the radiation;
An offset data acquisition step for acquiring offset data based on the charge accumulated in the sensor during the set accumulation time in a state in which the sensor is not irradiated with radiation before the radiation irradiation is started;
A radiation image data acquisition step for repeatedly acquiring radiation image data obtained by the sensor storing radiation as electric charges during the set accumulation time after it is determined that there is an instruction to start the radiation irradiation; ,
A correction step of correcting the radiation image data based on the offset data;
And a display control step of displaying a radiographic image based on the corrected radiographic image data on a display unit. The program for making a computer perform each step of the control method of the imaging | photography control apparatus of Claim 14 or 15 .

Images