JP4717953B2 - Radiographic image acquisition device, control device and methods thereof - Google Patents

Description

  The present invention relates to a technique for imaging a radiation intensity distribution, and is particularly suitable for acquiring a medical X-ray image.

  The most common technique for non-invasively observing the inside of a human body and used for medical diagnosis is to directly image the X-ray transmittance distribution that has passed through the human body. As such an imaging method, the conventional method of imaging the fluorescence distribution resulting from the X-rays reaching the phosphor with a silver salt film, the photoelectrons due to the fluorescence are amplified with a photomultiplier tube and imaged with a TV camera And a method of exciting and reading the latent image information produced by the X-ray intensity distribution on the photostimulable phosphor with a laser beam to visualize it. More recently, with the advancement of semiconductor technology, using a flat panel detector (FPD) composed of a large-scale solid-state imaging device that can cover the entire breast of the human body, free light generated in heavy metals by fluorescence or X-ray irradiation. A method for imaging the spatial distribution of electrons has been put into practical use.

  The movement of the human body can be separated into parts that depend mainly on autonomic nerves, such as the heart and gastrointestinal tract, and parts that can be moved consciously, such as breathing and limbs. With regard to the part that can be moved consciously, since it is possible to consciously stop the conventional still image shooting, an X-ray image has been shot as a still image. This is because the photographing apparatus is mainly made of a silver salt film or a stimulable phosphor, but medically, it is also important to observe the dynamics at such a site. When shooting with conscious movement instead of consciously stopping, it is possible to control the speed of movement, so there is no need to adjust the shooting speed according to the movement, such as the heart. For example, when observing the respiratory dynamics of the lung, if the subject breathes relatively slowly, the dynamics can be sufficiently observed even at an imaging speed of about 3 frames per second. However, it is also difficult for the subject to move too slowly and consciously, and there is an appropriate exercise speed at each site.

  When observing dynamics that depend on the conventional autonomic nerves, the part can be a very limited part such as the heart, artery, gastrointestinal tract, etc., so the necessary part can be photographed with a TV camera system using a photomultiplier Met. In this case, the important thing was the shooting speed.

J.H.Siewerdsen, L.E.Antonuk; DQE and System Optimization for Indirect-Detection Flat-Panel Imagers in Diagnostic Radiology; SPIE Vol.3336

  On the other hand, for imaging a part that can be moved consciously, especially for imaging respiratory dynamics of the lung, the imaging area is important, although the imaging speed is not so high. In order to observe pulmonary function from dynamics, it is necessary to generally observe the movement of blood vessels inside the lung from the movement of the diaphragm. Therefore, a photomultiplier tube cannot be used, and it is necessary to perform dynamic observation in about 3 images per second by replacing a large film at high speed. However, in order to obtain a plurality of images for dynamic observation, a mechanism for replacing the film at a high speed is required, and a considerable amount of X-ray exposure is necessary for imaging the film. A huge amount of exposure and cost were required and it was not practical. Also, there was no method for optimally observing such multiple images.

  In recent years, with the development of large-format X-ray FPDs, it has become possible to acquire a relatively wide range of human body dynamics such as the chest without performing mechanical operations such as changing the film at high speed. However, even FPDs are practically cost-effective in the same way as conventional films in terms of sensitivity. Therefore, since the sensitivity is not as high as that of a TV system using a photomultiplier tube, a considerable amount of exposure is required to obtain an image with sufficient image quality. For example, according to Non-Patent Document 1, the dose that reaches the normal sensor in chest still image shooting is 3 mR (milli-entrogen), and if a plurality of images for dynamic observation are shot with this dose, a considerable amount The exposure dose is reached.

  The present invention has been made in view of the above-described problems, and an object thereof is to prevent an increase in exposure dose in dynamic imaging.

In order to achieve the above object, a control apparatus according to an aspect of the present invention has the following arrangement. That is,
A control device that controls an acquisition device that converts an intensity distribution of radiation emitted from a radiation generation device into image information to acquire a radiation image,
Determining means for determining imaging conditions for each frame in moving image shooting so that the sum of the exposure doses of a plurality of radiographic images in moving image shooting is equal to or less than the exposure dose required for one still image shooting When,
Control means for controlling the acquisition device so as to acquire a radiographic image of each frame under the imaging condition determined by the determination means.
A control device according to another aspect of the present invention for achieving the above object has the following configuration. That is,
A control device for controlling the generation of radiation of the radiation generator,
Determining means for determining imaging conditions for each frame in moving image shooting so that the sum of the exposure doses of a plurality of radiographic images in moving image shooting is equal to or less than the exposure dose required for one still image shooting When,
Control means for controlling the generation of radiation by the radiation generator so that a radiation image of each frame is acquired under the imaging condition determined by the determination means.
Furthermore, a radiological image acquisition apparatus according to another aspect of the present invention for achieving the above object has the following configuration. That is,
A radiation image acquisition device that controls a radiation generation device and a detection device that converts intensity distribution of radiation emitted from the radiation generation device into image information to acquire a radiation image,
Determining means for determining imaging conditions for each frame in moving image shooting so that the sum of the exposure doses of a plurality of radiographic images in moving image shooting is equal to or less than the exposure dose required for one still image shooting When,
Acquisition means for acquiring a radiographic image of each frame under the imaging conditions determined by the determination means.

In addition, the control method according to the present invention for achieving the above object is as follows:
A control method for controlling an acquisition apparatus for acquiring a radiation image by converting intensity distribution of radiation emitted from a radiation generation apparatus into image information,
A determining step for determining the imaging condition of each frame in the moving image shooting so that the sum of the exposure doses of the plurality of radiographic shootings in the moving image shooting is equal to or less than the exposure dose required for one still image shooting. When,
A control step of controlling the acquisition device so as to acquire a radiographic image of each frame under the imaging conditions determined in the determination step.
In addition, a control method according to another aspect of the present invention for achieving the above object is as follows:
A control method for controlling the generation of radiation by controlling a radiation generator,
A determining step for determining the imaging condition of each frame in the moving image shooting so that the sum of the exposure doses of the plurality of radiographic shootings in the moving image shooting is equal to or less than the exposure dose required for one still image shooting. When,
And a control step of controlling the generation of radiation by the radiation generator so that a radiographic image of each frame is acquired under the imaging conditions determined in the determination step.
Furthermore, a radiation image acquisition method according to another aspect of the present invention for achieving the above object
A radiation image acquisition method for acquiring a radiation image by controlling a radiation generator and a detection device that converts intensity distribution of radiation emitted from the radiation generator into image information,
A determining step for determining the imaging condition of each frame in the moving image shooting so that the sum of the exposure doses of the plurality of radiographic shootings in the moving image shooting is equal to or less than the exposure dose required for one still image shooting. When,
An acquisition step of acquiring a radiographic image of each frame under the imaging conditions determined in the determination step.

  According to the present invention, for example, even when a low-cost FPD is used, dynamic imaging can be performed while preventing an increase in exposure dose.

It is a block diagram which shows the structure of the radiography apparatus by 1st Embodiment. It is a block diagram which shows the structure of a control unit. 4 is a timing chart of still image shooting and moving image shooting according to the first embodiment. It is a flowchart which shows the process at the time of parameter reception by a processing unit. It is a flowchart which shows the process at the time of still image shooting by a processing unit, and moving image shooting. It is a figure which shows the example of the histogram at the time of video recording in 3rd Embodiment, and the example of the look-up table used for a moving image display. It is a figure explaining the time interval of the flame | frame at the time of image acquisition and display in 4th Embodiment. It is a figure explaining the repetition order of the flame | frame by 5th Embodiment. It is a figure explaining reducing and displaying a frame in a 6th embodiment. It is a block diagram which shows the structural example of the radiography apparatus by 2nd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<First Embodiment>
The present inventor has found that in X-ray dynamic image observation, the total exposure dose during dynamic imaging is important as well as the dose for each frame of image information. This is because there are an afterimage effect of human eyes and recognition and a “recognized image quality improving effect” caused by tracking an unconscious or conscious moving object. For example, image acquisition is attempted by two methods for a stationary subject. One is a case of observing a still image taken with a specific X-ray dose, and the other is a case where a plurality of images are taken and observed as a moving image so that the total X-ray dose is obtained. Theoretically, if all of the latter plurality of images are added and averaged, the X-ray quantum mottle is exactly the same as the former image, so that the same image as the former still image is obtained. When the latter image is repeatedly observed as a moving image, depending on the display speed of the moving image, the human eye and the afterimage effect of recognition produce an effect that is almost equivalent to averaging by computation, and the same recognition as a still image Can be done.

  In addition, when a subject moves, when observing the moving image, a human unconsciously recognizes the structure of the object and inevitably tracks and observes the movement. As a result, with respect to one part, an averaging effect similar to that described above occurs, and recognition can be performed to the same extent as a still image.

  The averaging obtained by these human eyes and the afterimage effect by recognition does not work unless the total dose of multiple images is sufficient, but as mentioned above, it can withstand observation if there is a dose equivalent to that of a still image. It becomes. Therefore, when capturing and observing a dynamic X-ray image with the same image receiving apparatus as the still image, the total dose of the dynamic imaging may be set to be equal to that of the still image in order to obtain the same amount of information as that of the still image. Depending on the image information required for dynamic observation, the total dose during dynamic imaging may be reduced.

  Therefore, in the embodiment described below, dynamic imaging is performed so as to “suppress the total imaging dose of dynamic imaging to be equal to or less than that of still image imaging”.

  Therefore, in the first embodiment, still image shooting and dynamic shooting are continuously performed using one FPD, and in dynamic shooting, the total dose is set to be the same as the still image shooting performed immediately before. Is done. That is, by taking a still image before taking a dynamic image, the X-ray dose necessary for taking the still image is monitored, and the result is used for setting the exposure dose for the dynamic image. In this case, the exposure dose is twice that in the case of only taking a still image. However, even in general still image shooting, re-shooting called so-called “shooting loss” due to shooting failure is often performed, and even in this case, the exposure dose may double. Therefore, normally, there is no possibility of adversely affecting the human body at such an exposure dose.

  FIG. 1 is a diagram illustrating a configuration example of an X-ray image acquisition apparatus and a display apparatus according to the first embodiment. In FIG. 1, X-rays generated by the X-ray generator 3 pass through a subject 1 and reach an X-ray flat panel detector (FPD) 2. The FPD 2 images the dose distribution of the reached X-rays. Although not shown, the FPD 2 carries a scattered radiation removal grid for removing scattered X-rays from the subject 1 and the like. This FPD 2 has at least a spatial sampling pitch of 1 mm or less in order to image the details of the human body. Although not shown, the X-ray generator 3 can set tube voltage and tube current values, which are X-ray generation conditions, and can adjust them according to the subject and the purpose of imaging. Is possible.

  A phototimer 4 is provided as an X-ray dose monitor for obtaining an appropriate X-ray exposure during still image shooting. The phototimer 4 outputs the X-ray amount that has passed through the specific part of the subject 1 onto the signal line 25. This signal is accumulated by the control unit 5. Under the control of the control unit 5, when the accumulated value reaches a certain value, X-rays are cut off because a sufficient X-ray dose for capturing a still image is obtained.

  The control unit 5 controls the X-ray generator 3 and the FPD 2. As described above, the control unit 5 accumulates the signal from the phototimer 4 and blocks the X-rays emitted from the X-ray generator 3 based on the accumulated value, or an X-ray pulse having a pulse width as required. Is controlled so as to be continuously output from the X-ray generator 3. The control unit 5 includes an exposure start trigger 19 for starting X-ray exposure and a still image X-ray dose setting level 20 (an X-ray dose level necessary for still image shooting) that is compared with the accumulated value of the phototimer output. ) And the number of frames 21 at the time of acquiring an image for dynamic observation (hereinafter also referred to as a moving image) and a moving image acquisition time 22 are set and input. Further, the control unit 5 outputs a control signal 23 to the X-ray generator 3, a control signal 24 of the FPD 2, and the like.

  The A / D converter 6 converts the output of the FPD 2 into a digital value. The switcher 7 switches the data storage destination between the dark output of the FPD 2 and the image output. The dark output is an output acquired from the FPD 2 in a state where X-rays are not exposed, and is stored in the image memory 9 by connecting the switch 7 to the B side. On the other hand, the image output is an output acquired from the FPD 2 when X-rays are exposed, and is stored in the image memory 8 by connecting the switch 7 to the A side. The dark output may be acquired at any stage such as before and after acquiring the image output. The subtracter 10 subtracts the dark output stored in the image memory 9 from the image output stored in the image memory 8. By this processing, offset correction for image output is performed.

  The look-up table unit 11 has a look-up table (LUT) and converts the image data that has been offset-corrected by the subtractor 10 into a logarithmic value. By converting to a logarithmic value, a division operation is performed by a subsequent subtraction process. The switch 12 is a switch for switching between the gain image and the subject image of the FPD 2. The gain image is an image obtained by obtaining an output from the FPD 2 when X-rays are exposed in the absence of a subject in advance, subtracting the dark output, and then logarithmically converting the look-up table unit 11. The gain image is recorded in the gain image memory 13 by connecting the changeover switch 12 to the B side. Similarly, the subject image is recorded in the memory 14 by setting the switch 12 to the A side. The subtracter 15 subtracts the data stored in the gain image memory 13 from the image data after offset correction stored in the memory 14. By the subtraction processing by the subtracter 15, the gain variation for each pixel in the FPD 2 is corrected. Although not shown in FIG. 1, when there is a defective pixel that is not imaged in the FPD 2, the defective pixel is repaired (interpolated) with the surrounding normal pixel value. The image data thus obtained is stored in the data recording device 16. The image data stored in the data recording device 16 is read by the display control device 17 and displayed on the display monitor 18.

  Hereinafter, the configuration of the control unit 5 and the X-ray imaging process will be described in more detail.

  FIG. 2 is a block diagram showing a detailed configuration of the control unit 5. In FIG. 2, the integrator 31 integrates a signal from the phototimer 4, that is, a signal indicating an X-ray dose that has passed through a specific part of the subject 1. The integration output 41 is input to the comparator 32. The comparator 32 compares the set still image X-ray dose setting level 20 with the integration output 41 and outputs a comparison result 40.

  The flip-flop 35 is set by the exposure start trigger 19 and reset by the comparison result 40 output from the comparator 32. A signal from the flip-flop 35 is used as the X-ray generation control signal 23. The processing unit 34 has a built-in microprocessor and accepts the number 21 of moving image frames and the moving image acquisition time 22 set from the outside. Further, the processing unit 34 receives the exposure start trigger 19, detects the timing when the exposure is started, and outputs an X-ray control pulse 38 for moving images. In addition, in order to acquire image data in synchronization with the X-ray control pulse 38, the timing of image acquisition in the FPD 2 is controlled via the signal line 24. Further, the processing unit 34 acquires the pulse width of X-ray exposure during still image shooting from the pulse width measurement unit 33 via the signal line 39. The pulse width measuring unit 33 measures the X-ray pulse width (output of the flip-flop 35) in still image shooting, and transmits the result to the processing unit 34. The OR gate 36 transmits both the X-ray control pulse for still image from the flip-flop 35 or the X-ray control pulse for moving image from the processing unit 34 to the X-ray generator 3. That is, the output of the OR gate 36 is transmitted to the X-ray generator 3 of FIG.

  Next, the X-ray imaging operation by the control unit 5 will be described with reference to the timing chart of FIG. Note that the number of moving image frames set in moving image shooting is N, and the moving image shooting time is Tm. As shown in FIG. 3, the flip-flop 35 is set when the exposure trigger 19 rises, and the X-ray generation control signal 23 is output. While this X-ray generation control signal 23 is ON, X-rays are emitted. When X-rays are emitted, the phototimer 4 outputs a signal indicating the amount of X-rays reached, so that the integration output 41 from the integrator 31 increases as shown in FIG. The integrated output 41 is compared with the stationary X-ray dose setting level 20 by the comparator 32, and reaches the target dose (still image X-ray dose setting level 20) at time A in FIG. At this time A, the comparator 32 outputs the comparison result 40, that is, the comparison result 40 rises, so that the flip-flop 35 is reset, the X-ray generation control signal 23 is turned OFF, and the X-ray exposure is stopped. . As a result, the X-ray generation control signal 23 is output as an X-ray control pulse having a width Tx as shown in the second stage of FIG. 3, and X-rays are output from the X-ray emitting device 3 only during this pulse period.

  The pulse width measurement unit 33 measures the pulse width (time) Tx of the X-ray generation control signal 23. Since the moving image shooting time is set to Tm and the number of frames is set to N as described above, when the processing unit 34 receives Tx from the pulse width measuring unit 33, the moving image shooting pulse width (Tx / N), The time (Tm / N) allocated to one frame of the moving image is calculated. The processing unit 34 outputs a pulse having a width Tx / N as an X-ray generation control signal using Tm / N as a pulse period. As a result, N moving image pulses as shown in the second half of the second stage in FIG. 3 are output. In this way, moving image shooting is continued from still image shooting, and the total X-ray dose for moving image shooting is at the same level as that of the still image.

  It should be noted that the total X-ray dose does not have to be exactly the same as that of the still image when determining the pulse for moving images, and can be set to be smaller depending on the purpose and the burden on the patient. Details of this setting will be described later.

  When the above operation is specifically applied to imaging respiratory dynamics, the patient inhales at the first stage according to the operator's instruction, stops at the maximum inspiration state, and performs still image imaging. When the still image shooting is completed, the patient slowly starts exhalation, and the state of the exhalation is continuously captured as a dynamic state.

  The processing unit 34 in FIG. 2 executes the above-described photographing process by the microprocessor executing a program. The processing will be further described below with reference to the flowcharts shown in FIGS.

  FIG. 4 is a process for accepting the input of the number of moving picture frames and the moving picture shooting time. Although not shown in FIGS. To do. In the process shown in the flowchart of FIG. 4, it is determined whether or not the input value is appropriate, and if it is appropriate, the set value is stored.

  When the photographing time Tm is accepted in step S1, it is determined whether or not the time is 5 seconds or more in step S2. If a time shorter than 5 seconds is designated, the process proceeds to step S3, where a warning is given to the operator and a change of the photographing time is urged. If 5 seconds or more are set, the process proceeds to step S4, and the designated number N of moving image frames is accepted. The reason for setting the moving image shooting time Tm to 5 seconds or more will be described later. Next, using the designated number of frames N and moving image shooting time Tm, a moving image frame time Tm / N corresponding to a moving image frame period is calculated, and it is determined whether or not this value is 1/3 second. If it is not less than 1/3 second, the process proceeds to step S6, a warning is given to the operator, and a change in the number of frames is urged. If it is determined in step S5 that it is 1/3 second or less, the process proceeds to step S7, and the setting values Tm and N are held in a memory (not shown) in the processing unit 34. The reason for setting the moving image frame time to 1/3 second or less will be described later.

  Note that there are three parameters that must be determined in this setting: “moving image shooting time (Tm)”, “moving image frame number (N)”, and “moving image frame time (Tm / N)”. Each of these three parameters is related, and if the two are determined, the other one can be calculated. Therefore, although “moving image capturing time Tm” and “number N of moving image frames” are input in FIG. 4, it is obvious that a combination of two other parameters may be input. Even in this case, the condition that the moving image shooting time Tm is 5 seconds or more and the moving image frame time Tm / N is 1/3 second or less is determined so as to satisfy the conditions for appropriate dynamic observation.

  In this embodiment, the moving image shooting time is 5 seconds or more, and the moving image shooting speed is 3 frames or more per second. The reason is as follows. As described above in the problem section, there is a limit to slowing down the moving speed when the human body is consciously moved by breathing or the like. For example, for breathing, the speed is about 5 seconds of exhalation, even if it is consciously slow, and the speed of about 5 seconds of inspiration (any movement is performed in 5 seconds at any part). If it is slower than that, the movement becomes very awkward and stable movement cannot be expected. The present inventor has found that when such a motion is imaged and observed, stable tracking recognition cannot be performed unless it is acquired at least 3 frames per second. The dynamic imaging time requires one imaging time of 5 seconds or more because one movement is performed in the above 5 seconds. In addition, when observing the respiratory dynamics of the chest, it is also important to use an FPD of a size that encompasses at least the entire human chest. It should be noted that it is desirable to set an upper limit on the dynamic image capturing time. In the case of the present embodiment, an upper limit of, for example, 10 seconds or less may be provided from the viewpoint that the expiration and inhalation speeds for 5 seconds are the limits for guaranteeing stable operation as described above.

  FIG. 5 is a flowchart for explaining the control by the processing unit 34 in the case of actually shooting after the moving image parameters are determined. When the processing unit 34 executes the process shown in FIG. 5, the operation described in the time chart of FIG. 3 is realized.

  From step S11 and step S12, it is determined from the start of X-ray exposure in still image shooting to the end. In this embodiment, the exposure trigger input 19 is monitored to determine the start of X-ray exposure, and the output of the pulse width measurement unit 33 is monitored to determine the end of X-ray exposure. Note that the start and end of the X money exposure may be determined by monitoring the output signal of the flip-flop 35. In step S13, the exposure time Tx required for the still image shooting is read, and the shooting conditions for each frame are set using the set number N of frames and moving image shooting time Tm. For example, the exposure time per frame is set to Tx / N, and the frame period (exposure period) is set to Tm / N. Further, the image data photographed at this time is stored in the storage device 16 through the units shown in FIG. In step S14, it is a waiting time until the start of moving image shooting. The waiting time is appropriately set according to the operation of the patient and may be omitted. Or you may make it progress to after step S15 according to the operation input which instruct | indicates the start of video recording.

  When moving image shooting is started, the processes of steps S15 to S19 are executed. First, in step S15, it is determined whether or not a moving image pulse has been output N times. For example, every time one frame of X-ray irradiation is performed, the counter memory is accumulated to determine N exposures (completion of N frame imaging). If N exposures have not been completed, a moving image X-ray control pulse 38 is output so that X-rays are emitted according to the timing shown in FIG. That is, in step S16, the moving image X-ray control pulse 38 is turned ON, and in step S17, waiting is performed for a waiting time of Tx / N. When the waiting time of Tx / N has passed, the X-ray control pulse 38 is passed in step S18. Is turned off. Thus, one frame of exposure is completed. Then, in step S19, the waiting is executed for the waiting time (Tm−Tx) / N corresponding to the pulse interval, and the process returns to step S15. By repeating the above process N times (step S15), N X-ray images (frame images) are obtained. Even in this case, every time an X-ray pulse is generated, the frame images are sequentially recorded in the storage device 16 through the processing units shown in FIG.

  It should be noted that by taking the waiting time in step S17 as (Tx−α) / N and the waiting time in step S19 as (Tm−Tx + α) / N, an appropriate numerical value α (α ≧ 0) is used. Can be reduced according to the purpose and patient burden. If α is set to less than 0, the total exposure dose in moving image shooting is set to be larger than the exposure dose in still image shooting. In this embodiment, α ≧ 0 is set so that the total exposure dose in moving image shooting is equal to or less than the exposure dose in still image shooting. However, the exposure dose in moving image shooting is within a predetermined allowable range. The exposure dose at the time of imaging may be exceeded. For example, if the number of frames N is large, the X-ray dose per time is reduced. Therefore, when N is larger than a predetermined value, it is conceivable to set α to be negative according to N.

  In some cases, the FPD 2 can change the output voltage gain by changing the gain of the internal amplifier or the capacity for carrying the image information by setting the external input. Of course, it is also possible to change the output voltage gain during still image shooting and during moving image shooting.

  As described above, according to the first embodiment, since the total exposure dose at the time of moving image shooting is controlled to be equal to the exposure dose when a still image is acquired with the same device, safe exposure is possible. The amount of moving image data that can withstand dynamic observation can be acquired.

<Second Embodiment>
In the first embodiment described above, the X-ray dose during still image shooting is monitored. However, the exposure dose required for still images is known from past experience without measurement. For example, Non-Patent Document 1 (JHSiewerdsen, LEAntonuk; DQE and System Optimization for Indirect-Detection Flat -Panel Imagers in Diagnostic Radiology; SPIE Vol.3336), the dose that reaches the sensor in chest radiographing is usually 3 mR. Therefore, in the second embodiment, when performing dynamic imaging, the total maximum dose reaching the sensor is set to 3 mR or less. That is, the total X-ray dose is set to 3 mR or less, which is a normal still image shooting dose on the sensor, and dynamic imaging of the chest is performed without performing still image shooting.

Specifically, the X dose Ax at a predetermined time T0 is measured in advance with an X dosimeter at a specific radiation quality (tube voltage), and the pulse width and the number of pulses per frame are determined based on the values. . For example, assuming that the factor that attenuates the X-ray dose in front of the sensor is the transmittance P of the X-rays, the irradiation time Tx required to make the dose 3 mR on the sensor is:
Tx = 3 mR / (Ax / (T0 × P))
It is represented by In addition, as an element which produces the transmittance | permeability P, a scattered radiation removal grid is mention | raise | lifted and it is normally considered that the transmittance | permeability of 50 to 60%.

  Shooting conditions for moving image shooting can be set by the procedure described in the first embodiment using Tx obtained as described above.

  In order to adjust the exposure amount more reliably, as shown in FIG. 10, an X-ray monitor 51 is provided in a portion unrelated to the subject 1 (the back portion of the subject 1 or the direct line area behind the FPD 2). The radiation dose during movie shooting may be measured. That is, when the output of the X-ray monitor 51 reaches the same amount as that of the still image (a dose corresponding to 3 mR on the front surface of the sensor), the dynamic observation is terminated to prevent excessive exposure. For example, when the X-ray monitor 51 is arranged on the back surface of the subject 1, the moving image shooting is ended when the integrated value of the X-ray dose becomes 3 mR / P.

<Third Embodiment>
In the third embodiment, a configuration for suitably displaying a moving image shot as described above will be described. That is, the control for displaying the moving image data stored in the data recording device 16 shown in FIG. 1 on the monitor 18 by the display control device 17 will be described in detail.

  Even if the total dose in dynamic imaging is the same as that in still image imaging, if the dose per frame is too small, quantization (A / D conversion) error becomes dominant, and even if it is not imaged or imaged A meaningless part arises. For example, the mediastinum or the abdomen when the chest is photographed. Therefore, in the third embodiment, gradation conversion is performed by ignoring the portion that cannot be imaged, and only the portion that can be observed is imaged. This is because it is sufficient in many cases for displaying moving images.

  A gradation conversion process for displaying an image on the monitor 18 is executed by the display control device 17. Normally, a look-up table in which input gradation values (X-ray dose) and output gradation values are associated one-to-one is used for gradation conversion processing, but in the third embodiment, a region with a small dose is not imaged. Such a lookup table is generated according to the moving image to be displayed, and gradation conversion is performed. That is, in the third embodiment, the display control device 17 creates an X-ray dose histogram as shown in FIG. 6A for one of the frames to be displayed, and based on this, the look as shown in FIG. Generate uptable. Then, the generated lookup table is stored in a memory (not shown).

  FIG. 6A shows a typical histogram of one frame image in the obtained moving image, where the horizontal axis represents the pixel value (luminance value) and the vertical axis represents the frequency. The portion indicated by reference numeral 53 in FIG. 16A is very small in data, and is buried in the A / D conversion quantum noise. Therefore, a reference table (LUT) as shown in FIG. 6B is created, and settings are made so as not to display the portion indicated by 53 that cannot be imaged. The display control device 17 sequentially displays images that have been subjected to gradation conversion using such a lookup table. In addition, as a setting method of this area | region 53, it is good also as an area | region of the pixel value below a preset value. Alternatively, the region 53 may be determined by creating and analyzing a histogram. In this case, for example, a method is conceivable in which a region below the lowest pixel value among the minimum values of the histogram is set as the region 53. It is sufficient to analyze the histogram with respect to image data of the first frame in the moving image, for example. Of course, if processing capability permits, histogram analysis may be performed on image data of each frame.

  As described above, according to the display control of the third embodiment, it is determined that it is sufficient for imaging in the display of a moving image in which the total imaging dose of dynamic imaging is equal to or less than that of still image imaging. Since the moving image is reproduced based on the information on the dose, the unnecessary image portion is not reproduced, and an image with high recognition positive can be obtained.

<Fourth embodiment>
In the fourth embodiment, when observing the dynamic image obtained in the first embodiment or the second embodiment, the display speed is made faster than the shooting speed. According to such display, averaging by the afterimage effect is further promoted, and the recognition rate is improved. Furthermore, the averaging and recognition rate are further promoted by repeatedly displaying dynamic images.

  In order to stably observe a moving image obtained at a low dose, the afterimage effect of human eyes and recognition can be used. Therefore, it is desirable to define the speed at the time of display.

  7A shows an example in which a moving image of 30 frames is acquired at every time interval T1, and FIG. 7B shows a state in which the display interval when displaying a moving image as shown in FIG. 7A is T2. ing. In general, the afterimage effect can be further enhanced by setting T2 <T1. Also, as shown in FIG. 7B, all the frames of the moving image (30 frames in the example of FIG. 7) are repeatedly displayed and observed, thereby enhancing the afterimage effect and tracking a specific part. It becomes possible.

  The present inventor has found that T2 <1/6 second in order to obtain a stable afterimage effect. Therefore, whatever time interval is taken as T1, T2 may be set to a constant value of 1/6 second or less. If T2 is a constant value regardless of the frame interval at the time of acquisition, the observer can also observe stably regardless of the frame interval at the time of acquisition.

<Fifth Embodiment>
In the fifth embodiment, when the dynamic image display is repeated as described in the fourth embodiment, when all the dynamic image displays are completed, the dynamic image display is performed in the reverse direction, and the repeated moving image display is performed. To improve the image recognition rate by afterimage and object tracking.

  FIG. 8 is a view for explaining moving image display according to the fifth embodiment. In the repeated display method in FIG. 7B, when all frames are displayed, the display is started from the first frame. In the fifth embodiment, however, after sequentially displaying 1 to 30 frames, 29 and 28 frames are descending in descending order. When the first frame is reached, it is displayed again in ascending order. With such a display method, more continuity can be provided. That is, according to the display method of the fifth embodiment, there are no repeated breaks, and the observer can more stably track the site / structure in the image, so that stable image observation by the afterimage effect can be performed.

<Sixth Embodiment>
Further, in the sixth embodiment, when observing the dynamic image obtained in the first embodiment or the second embodiment, the image is reduced and displayed from the substance, and the reduction display effect (the effect of reducing the noise level of one pixel) ) To improve the recognition rate of dynamics.

  Since an image obtained with a low X-ray dose has a small number of X-ray particles per pixel, the image has a larger variation than the average value, and is an image having a poor S / N. In the case of observing this, an image can be reduced and displayed in order to improve the S / N within a range that can be observed by the human eye. Assuming that the minimum range that is noticed by the human eye is a [mm], when the pixel information varies and is displayed in the unit, the observer feels variation in the image information, which hinders normal observation. At a normal observation distance, a is about 0.5 mm.

  Therefore, in the sixth embodiment, when a moving image is displayed, reduced display is performed in which peripheral pixels are collectively (averaged) as a new pixel. By performing such reduced display, the variation for each pixel is reduced and the entire image can be easily observed.

  For example, when an image acquired by FPD at 0.2 mm is displayed as it is, the variation for each pixel is visible to the human eye. However, if the image is displayed, for example, with an average value of 4 pixels for every 2 pixels in the vertical and horizontal directions as 1 pixel, the display image size becomes 1/4, but the variation (standard deviation value) for each pixel becomes 1/2. Therefore, an image with little noise can be observed.

  FIG. 9A shows an example in which a 30-frame moving image is acquired at each time interval T1, and FIG. 9B shows a display interval when T2 is displayed. As described in the fourth and fifth embodiments, the afterimage effect is further enhanced by repeating the display with T2 <T1. Then, as shown in FIG. 9B, by reducing the image size to be displayed and displaying it smaller, the ease of observing the entire image is improved. In FIG. 9B, the display is repeated in order from the first frame as shown in FIG. 7B. However, the display may be repeated and displayed repeatedly as shown in FIG. In addition, the said 3rd-6th embodiment may each be implemented independently, and may be implemented in combination suitably.

  As described above, according to each of the above-described embodiments, the total exposure dose at the time of dynamic imaging is equal to or less than that of the still image even when the dynamics are imaged and observed using the relatively low sensitivity FPD. By doing so, stable dynamic imaging can be performed. In addition, it has gradation characteristics that ignore parts that cannot be imaged at the time of display, and more stable observation can be achieved by combining display, repeat display, wrap-around repeat display, reduced display, etc. at higher speeds than shooting. become.

Claims (9)

A control device that controls an acquisition device that converts an intensity distribution of radiation emitted from a radiation generation device into image information to acquire a radiation image,
So that the total irradiation dose of the plurality of radiation imaging is one of exposure dose equivalent to or less than required for still image capturing performed in the video, determining means for determining a photographing condition of each frame in the moving image shooting When,
Control apparatus characterized by and a control means for controlling the acquisition device to acquire radiation image of each frame in imaging condition determined by the determining means.   The control device according to claim 1, wherein the determining unit determines a radiation irradiation time and an irradiation time interval of each frame.   The determining means determines a radiation irradiation time and an irradiation time interval of each frame in the moving image shooting based on the total shooting time of the moving image shooting, at least two of the number of frames and the frame time, and the total of the exposure dose. The control device according to claim 1.   The control device according to any one of claims 1 to 3, wherein the acquisition device includes an X-ray flat panel detector and an A / D converter that converts an output thereof to a digital value. A control device for controlling the generation of radiation of the radiation generator ,
So that the total irradiation dose of the plurality of radiation imaging is one of exposure dose equivalent to or less than required for still image capturing performed in the video, determining means for determining a photographing condition of each frame in the moving image shooting When,
Control device characterized by comprising a control means for controlling the generation of radiation by said radiation generator as the radiation image of each frame at the determined imaging condition is obtained by the determining means. A radiation image acquisition device that controls a radiation generation device and a detection device that converts intensity distribution of radiation emitted from the radiation generation device into image information to acquire a radiation image,
So that the total irradiation dose of the plurality of radiation imaging is one of exposure dose equivalent to or less than required for still image capturing performed in the video, determining means for determining a photographing condition of each frame in the moving image shooting When,
A radiation image acquiring apparatus , comprising: an acquisition unit configured to acquire a radiographic image of each frame under an imaging condition determined by the determination unit.   A control method for controlling an acquisition device that converts an intensity distribution of radiation emitted from a radiation generation device into image information to acquire a radiation image,
  A determining step for determining the imaging condition of each frame in the moving image shooting so that the sum of the exposure doses of the plurality of radiographic shootings in the moving image shooting is equal to or less than the exposure dose required for one still image shooting. When,
  And a control step of controlling the acquisition device so as to acquire a radiographic image of each frame under the imaging conditions determined in the determination step.   A control method for controlling the generation of radiation by controlling a radiation generator,
  A determining step for determining the imaging condition of each frame in the moving image shooting so that the sum of the exposure doses of the plurality of radiographic shootings in the moving image shooting is equal to or less than the exposure dose required for one still image shooting. When,
  And a control step of controlling the generation of radiation by the radiation generator so that a radiation image of each frame is acquired under the imaging conditions determined in the determination step.   A radiation image acquisition method for acquiring a radiation image by controlling a radiation generator and a detection device that converts intensity distribution of radiation emitted from the radiation generator into image information,
  A determining step for determining the imaging condition of each frame in the moving image shooting so that the sum of the exposure doses of the plurality of radiographic shootings in the moving image shooting is equal to or less than the exposure dose required for one still image shooting. When,
  A radiological image acquisition method comprising: an acquisition step of acquiring a radiographic image of each frame under the imaging conditions determined in the determination step.

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