JP6061538B2 - Radiation imaging apparatus, radiation imaging apparatus control method, and program - Google Patents

Description

  The present invention relates to a radiation imaging apparatus, a method for controlling the radiation imaging apparatus, and a program, and more particularly to a technique for correcting fixed pattern noise (FPN) generated in radiation imaging using a MOS type imaging device.

  In general, in a MOS type imaging device, fixed pattern noise (FPN) is generated due to a dark current component of a pixel or a variation of an amplification transistor constituting the pixel. Conventionally, various methods have been proposed as a method for suppressing the fixed pattern noise.

  In the non-reference document 1, the signal output from the CMOS image sensor 201 in the light-shielded state is A / D converted by the A / D converter 202 and stored as a reference signal in the frame buffer 203 with the configuration shown in FIG. A technique for removing fixed pattern noise by subtracting a reference signal stored in the frame buffer 203 by a subtracter 204 from an image signal output from the CMOS image sensor 201 that has been accumulated by exposure is disclosed. ing.

  In Patent Document 1, a plurality of dark current image data is acquired in a non-imaging period before radiation imaging of a subject is started, and offset correction data is generated by synthesizing the acquired plurality of dark current image data. A method of removing fixed pattern noise using the generated offset correction data is disclosed. As the number of acquired dark current image data increases, there is an advantage that random component noise is removed by averaging.

  The offset correction data generation is stopped according to a special condition such as receiving a stop command (for example, an imaging start command) during the offset correction data generation period. When the offset correction data generation is stopped, the offset correction is performed using the previous offset correction data.

Japanese Patent No. 4747431

“Basics and Applications of CCD / CMOS Image Sensors” published by CQ Publisher, pages 193 to 194

  However, in the technique described in Patent Document 1, the larger the number of dark current image data used to generate offset correction data, the longer it takes to acquire a dark current image. Therefore, imaging is uniformly performed during the offset correction data generation period. If prohibited, the operability of the radiation imaging apparatus is impaired.

  In addition, when the generation of offset correction data is stopped in response to the reception of the stop command, the offset correction data is received before the radiation command is received or the stop command is received immediately before the generation of the offset correction data is completed. If the cancel command is received when the generation can be completed, the offset correction data being generated is discarded.

  In view of the above problems, an object of the present invention is to efficiently generate offset correction data without impairing the operability of the radiation imaging apparatus.

A radiation imaging apparatus according to the present invention that achieves the above object is as follows.
A radiation imaging apparatus that corrects a radiation image using offset correction data,
Generating means for acquiring a plurality of dark current image data captured without irradiating radiation, performing an averaging process, and generating the offset correction data;
Receiving means for receiving a stop instruction to stop the generation process of the offset correction data by the generating means;
Determination means for determining whether to continue or cancel the generation process based on the progress of the generation process when the stop instruction is received;
The generation means continues or stops the generation process according to the determination result by the determination means, and the determination means acquires and adds a predetermined number of dark current image data when the reception timing of the stop instruction is received. It is determined that the generation process is to be stopped if it is before completion of the process, and it is determined that the generation process is to be continued if the process to be added is completed .

  According to the present invention, it is possible to efficiently generate offset correction data without impairing the operability of the radiation imaging apparatus.

1 is a diagram illustrating an example of a radiation imaging system 10 according to a first embodiment. The flowchart which shows the procedure of the offset correction data generation process which the radiation imaging device 100 which concerns on 1st Embodiment implements. Explanatory drawing of the offset correction | amendment using the several sheets of dark current image data concerning 1st Embodiment. The figure which shows an example of the radiation imaging system 10 which concerns on 2nd Embodiment. 12 is a timing chart of offset correction data generation stop processing using the synchronization control interface 111 according to the second embodiment. The block diagram which shows the principle of fixed pattern noise removal.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
In the first embodiment, in order to correct a radiographic image using offset correction data, a plurality of dark current image data captured without irradiating radiation is acquired, and an addition averaging process is performed to perform offset correction data. Is generated. When a cancel command for canceling the generation processing of offset correction data is received (for example, when a radiographic image capturing start command is received as a stop command), the generation processing is continued or canceled based on the progress of the generation processing. A configuration for determining whether or not to continue or stop the generation process according to the determination result will be described.

  More specifically, if an imaging start command is accepted when the offset correction data generation process is nearing completion, the generation process is continued, and if it takes a certain amount of time to complete, the generation process is stopped. To do.

  First, an example of the radiation imaging system 10 according to the first embodiment will be described with reference to FIG. The radiation imaging system 10 includes a radiation imaging apparatus 100, a system control / image processing apparatus 101, an image display apparatus 102, a radiation generation control apparatus 103, and a radiation tube 104.

  The radiation imaging apparatus 100 converts radiation that has been irradiated from the radiation tube 104 and passed through the subject into visible light by a scintillator, performs photoelectric conversion according to the amount of light, and then performs A / D conversion to obtain frame image data. Generate. Then, the offset corrected image data obtained by subtracting the offset correction data from the generated frame image data is transferred to the system control / image processing apparatus 101. In addition, the radiation imaging apparatus 100 includes an imaging control unit 105 for performing each process of a flowchart described below.

  The system control / image processing apparatus 101 synchronously controls the radiation imaging apparatus 100 and the radiation generation control apparatus 103 when performing radiation imaging. In addition, the system control / image processing apparatus 101 transmits an imaging mode in which various conditions such as a radiation irradiation time, a gain (sensor storage capacity), a storage time (frame rate), and an image size are designated via the command interface 110. To the radiation imaging apparatus 100. Since dark current image data depends on gain (sensor storage capacity), storage time (frame rate), etc., it is necessary to create offset correction data for each shooting mode.

  Further, the system control / image processing apparatus 101 notifies the radiation imaging apparatus 100 of an imaging start command, an offset correction data generation start command, and the like via the command interface 110. Further, the system control / image processing apparatus 101 performs image processing on the offset-corrected image data transferred from the radiation imaging apparatus 100 and outputs the processed image data to the image display apparatus 102.

  The image display device 102 displays the radiation image transferred from the system control / image processing device 101 in real time. The radiation generation control device 103 controls radiation irradiation by the radiation tube 104 under the control of the system control / image processing device 101. The radiation tube 104 irradiates the subject with radiation.

  Next, with reference to the flowchart of FIG. 2A and FIG. 3, the procedure of the offset correction data generation process performed by the radiation imaging apparatus 100 according to the first embodiment will be described. Here, FIG. 3 is an explanatory diagram of the flow of image data according to the first embodiment when offset correction data is generated by combining a plurality of dark current image data to remove fixed pattern noise. .

  First, in S201 of FIG. 2A, the imaging control unit 105 of the radiation imaging apparatus 100 in the non-imaging state, the command for starting offset correction data generation and the imaging mode from the system control / image processing apparatus 101 via the command interface 110. Is acquired, the offset correction data generation stop flag is cleared, and the acquired imaging mode is set.

  In S202, the imaging control unit 105 calculates a processing time necessary for generating offset correction data based on the set imaging mode. Or you may read from the memory memorize | stored previously correspondingly for every imaging mode. In step S <b> 203, the imaging control unit 105 permits an interrupt for stopping the generation of offset correction data according to the imaging start command.

  In step S <b> 204, the imaging control unit 105 determines whether or not to continue generating offset correction data by determining whether or not the offset correction data generation stop flag is set in the radiation imaging apparatus 100. When the offset correction data generation stop flag is set in the radiation imaging apparatus 100, generation of the offset correction data is stopped. Here, since the cancellation flag for offset correction data generation is cleared in S201, the cancellation flag is not set in the radiation imaging apparatus 100, and the offset correction data generation is continued.

  However, if the processing shown in the flowchart of FIG. 2B described later is performed between the interrupt enable in S203 and the interrupt disable in S207 of FIG. 2A and the stop flag is set, the offset correction is performed. Data generation will be stopped.

  When it is determined that the offset correction data generation is to be continued (S204; YES), the process proceeds to S205. On the other hand, when it is determined that the offset correction data generation is to be stopped (S204; NO), the process is terminated.

  In step S205, the imaging control unit 105 performs an imaging operation in a state where no radiation is irradiated, and reads dark current image data from the CMOS image sensor 201 included in the radiation imaging apparatus 100 as illustrated in FIG. The D converter 202 converts the analog value into a digital value and writes it into the frame buffer 203.

  If the added dark current image data is already stored in the frame buffer 203, the added dark current image data and the dark current image data acquired this time in S205 are added for each pixel by the adder 205. The accumulated dark current image data is generated and written back to the frame buffer 203.

  In step S206, the imaging control unit 105 determines whether the number of dark current image data acquired so far has reached a predetermined number necessary for generating offset correction data. When it is determined that the number of dark current image data has reached the predetermined number (S206; YES), the process proceeds to S207. On the other hand, when it is determined that the number of dark current image data has not reached the predetermined number (S206; NO), the process returns to S204.

  In step S207, the imaging control unit 105 prohibits an interrupt that stops generation of offset correction data. In S <b> 208, the imaging control unit 105 divides the accumulated dark current image data read from the frame buffer 203 by the accumulated number by the divider 206 and writes it back to the offset correction data storage area of the frame buffer 203. Thereby, offset correction data is generated and updated.

  Next, the procedure of offset correction data generation processing performed by the radiation imaging apparatus 100 according to the first embodiment will be described with reference to the flowchart of FIG.

  When performing radiation imaging, the operator operates the system control / image processing apparatus 101 to issue an imaging start command, but the operator is conscious of whether or not the radiation imaging apparatus 100 is generating offset correction data. An imaging start command is issued at an arbitrary timing without any problem.

  The system control / image processing apparatus 101 to the radiation imaging apparatus 100 via the command interface 110 after the offset correction data generation stop interrupt is permitted in S203 of FIG. 2A until the interrupt is prohibited in S207. When a stop command (for example, an imaging start command) is transferred, offset correction data generation stop interrupt processing shown in the flowchart of FIG. 2B is performed.

  In S211, the imaging control unit 105 calculates the remaining time until the offset correction data generation is completed based on the processing time necessary for generating the offset correction data calculated in S202 of FIG. Determine if there is more than an hour. When it is determined that the remaining time is equal to or longer than the predetermined time (S211; YES), the process proceeds to S212. On the other hand, when it is determined that the remaining time is less than the predetermined time (S211; NO), the process ends.

  In step S212, the imaging control unit 105 sets an offset correction data generation stop flag and ends the processing.

  The imaging control unit 105 repeats the processes from S204 to S206 until the addition process is completed after acquiring a predetermined number of dark current image data, and the offset correction data generation is stopped by the offset correction data generation stop interrupt process. When the flag is set, the generation of offset correction data is stopped in S204. When the generation of the offset correction data is stopped, the offset correction data on the frame buffer 203 is not updated.

  As described above, according to the present embodiment, when an imaging start command is issued at an arbitrary timing after the start of offset correction, new offset correction data is obtained if a predetermined time has elapsed after the start of offset correction data generation. The image data on which the offset correction is performed is output. On the other hand, the offset correction data generation is stopped if a predetermined time has elapsed after the offset correction data generation is started, but since the imaging can be started immediately, the operability of the radiation imaging apparatus can be improved. Further, since the offset correction data generation is executed to the end without being stopped depending on the timing when the imaging start command is issued, it is possible to reduce the occurrence of artifacts due to the offset generation of the offset correction data.

  As described above, when an imaging start command is input at an arbitrary timing by the operator during the generation of offset correction data based on the averaging of a plurality of dark current image data, the remaining time until the end of offset correction data generation is calculated. Therefore, it is possible to efficiently generate / update the offset correction data without degrading the operability because the process is determined to be stopped or continued (that is, the process is stopped or continued based on the progress of the offset correction data generation process). It becomes possible to do.

  In the first embodiment, the offset correction data generation start command is received by the system control / image processing apparatus 101 and the offset correction data generation is started. However, the period between the imaging start command and the imaging end command is described. Is the imaging period, and the other period is the non-imaging period, the radiation imaging apparatus 100 may automatically start the offset correction generation process in the non-imaging period. Also in this case, when the imaging start command is received, it is possible to select continuation or cancellation of processing from the remaining time for generating offset correction data.

  In the first embodiment, the offset correction data generation stop interrupt process is described as being started upon reception of the imaging start command. However, the offset correction data generation stop command is used separately from the imaging start command, Generation stop interrupt processing may be started.

  It should be noted that when there are a plurality of imaging modes, for example, 10 modes, offset correction data for 7 modes is generated, and offset correction data is updated for which mode corresponding to the case where imaging is started / restarted there. You may memorize whether it is finished. Further, the update timing of the offset correction data may be stored for each shooting mode.

  In the first embodiment, the configuration in which the remaining time until the end of offset correction data generation is calculated to determine whether to stop or continue the processing has been described. However, the number of dark current image data necessary for generating offset correction data is described. It is possible to decide whether to stop or continue the processing based on whether or not a certain number of images have been completed. Thus, the progress may be determined based on information such as how many dark current image data have been captured up to now and how many dark current image data need to be captured.

  Further, when the reception timing of the offset correction data generation stop command (for example, the imaging start command) is before the completion of the process of acquiring and adding a predetermined number of dark current image data, the offset correction data generation process is stopped. If the averaging process is performed after the addition process is completed, the offset correction data generation process may be continued. That is, the progress may be determined depending on whether the addition process or the averaging process is being performed.

  In such cases, the imaging control unit 105 of the radiation imaging apparatus 100 counts, for example, a count unit (not shown) that counts the number of times each time dark current image data is captured, and counts the count unit. Accordingly, it has a determination unit (not shown) that determines whether to interrupt or continue the generation of the offset correction data and sets a flag. The threshold of the number of sheets used for the determination is stored in the memory of the radiation imaging apparatus 100, or externally in a serviceman mode or the like so that the responsiveness of the system can be changed according to the request or usage scene of each hospital. The setting may be possible.

  In addition, the imaging control unit 105 of the radiation imaging apparatus 100 may include a time measuring unit (not shown) that measures time from the start of offset correction data generation. In this case, the progress may be defined as the time from the start of offset correction data generation. In this case, the time required to generate each offset correction data corresponding to each imaging mode is known in advance, and this time is stored in the memory.

  Further, when dark current image data imaging is started for offset correction data corresponding to a certain imaging mode, the time measurement unit starts time measurement, and when a stop command is received, the determination unit displays the time and memory at that time. It is possible to compare the time required for the generation stored in, and stop if the difference is larger than a predetermined threshold, or continue if the difference is smaller.

  Since the image capturing time for one image differs greatly depending on the image capturing mode (33 ms-500 ms), in this case, as compared with the case of counting by the number of captured images, the stop or continue in a fixed time regardless of the image capturing mode. Can be carved. Of course, it may be configured such that a threshold relating to time can be set for each photographing mode.

(Second Embodiment)
FIG. 4 is a diagram illustrating an example of the radiation imaging system 10 according to the second embodiment. Except for the addition of the synchronization control interface 111, the configuration is the same as that of FIG.

  FIGS. 5A to 5C are timing charts of the offset correction data generation stop process using the synchronization control interface 111. FIG. A synchronization signal SYNC between the radiation imaging apparatus 100 and the radiation generation control apparatus 103 and a synchronization valid signal SYNC_EN indicating that the synchronization signal SYNC is valid are transmitted via the synchronization control interface 111. A period in which the synchronization valid signal SYNC_EN is at a high level is an imaging period, and a period in which the synchronization valid signal SYNC_EN is at a low level is a non-imaging period.

  FIG. 5A is an example of a case where imaging is resumed after generation of offset correction data is completed. When the radiation imaging apparatus 100 receives an imaging start command from the system control / image processing apparatus 101 via the command interface 110 at time t1, the imaging mode included in the imaging start command or the imaging mode received together with the imaging start command Accordingly, imaging preparation is started, and imaging preparation is completed at time t2.

  At time t <b> 3, the system control / image processing apparatus 101 transmits a high-level synchronization valid signal SYNC_EN to the radiation imaging apparatus 100 via the synchronization control interface 111. At time t4 after the elapse of the synchronization signal Setup time Ts from time t3, the system control / image processing apparatus 101 starts outputting the synchronization signal SYNC, and the radiation generation control of the radiation tube 104 by the radiation generation control apparatus 103 and the radiation imaging apparatus 100. The imaging control by is performed in synchronization with the synchronization signal SYNC, and moving image imaging is performed.

  When the operator stops imaging at time t5, the system control / image processing apparatus 101 transmits a low-level synchronization valid signal SYNC_EN and stops outputting the synchronization signal SYNC. In order to reduce offset fluctuation due to the temperature of the flat panel sensor 106 that has risen due to moving image capturing, the system control / image processing apparatus 101 issues an offset correction data generation start command at time t6. The radiation imaging apparatus 100 starts generating offset correction data at time t7, and the update of the offset correction data is completed at time t8. At time t9, the operator instructs the resumption of imaging, and the synchronization signal SYNC is output from time t10 after the synchronization signal Setup time Ts, and the moving image imaging is resumed.

  FIG. 5B is a timing chart in a case where the imaging resumption instruction by the operator is given at a timing after the remaining time Tr for generating the offset correction data becomes less than a predetermined time. From time t1 to time t7 is the same as in FIG.

  When the operator instructs to resume imaging at time t8, the synchronization valid signal SYNC_EN becomes High level. The radiation imaging apparatus 100 that has detected this calculates the remaining time Tr for generating the offset correction data. Since the calculated remaining time Tr of the offset correction data generation is shorter than the synchronization signal setup time Ts from the transition of the synchronization valid signal SYNC_EN to the high level to the output of the synchronization signal SYNC, the offset correction data generation is continued. Then, at time t9, the update of the offset correction data is completed, and at time t10 after the synchronization signal Setup time Ts, the synchronization signal SYNC is output and moving image capturing is resumed.

  FIG. 5C is a timing chart showing an example when the generation of offset correction data is stopped. From time t1 to time t7 is the same as in FIG.

  When the operator instructs to resume imaging at time t8, the synchronization valid signal SYNC_EN becomes High level. The radiation imaging apparatus 100 that has detected this calculates the remaining time Tr for generating the offset correction data. Since the calculated remaining time Tr of offset correction data is longer than the synchronization signal Setup time Ts, the generation of offset correction data is stopped.

  As described above, according to the present embodiment, offset correction data can be updated without reducing the operability of the radiation imaging apparatus.

  In the second embodiment, when the offset correction data generation stop request is detected, the offset correction data generation remaining time Tr is calculated, and compared with the synchronization signal Setup time Ts, the offset correction data generation is continued or stopped. However, the offset correction data obtained by reading out the accumulated dark current image data stored in the frame buffer 203 and dividing it by the accumulated number is written back to the frame buffer 203. If it is set to be longer than the time, it is not necessary to calculate the remaining time Tr, so that the control can be simplified.

  If a certain dark current image data is being acquired / added out of a predetermined number of dark current image data necessary for generating offset correction data, the dark current image data acquisition / addition process is completed. May continue processing, perform division by the number of added images, obtain the addition average data, and update the addition average data as offset correction data. As a result, the effect of reducing random component noise is somewhat inferior because the predetermined number of sheets is insufficient, but it is possible to suppress fixed pattern noise due to dark current components caused by temperature changes without deteriorating operability.

  When the offset correction data is updated by dividing the number of added dark current image data in this way, the accumulated dark current image data in the process of generating the offset correction data is stored in the frame buffer 203 even after the start of imaging. The remaining processing may be resumed after the imaging is completed.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

A radiation imaging apparatus that corrects a radiation image using offset correction data,
Generating means for acquiring a plurality of dark current image data captured without irradiating radiation, performing an averaging process, and generating the offset correction data;
Receiving means for receiving a stop instruction to stop the generation process of the offset correction data by the generating means;
Determination means for determining whether to continue or cancel the generation process based on the progress of the generation process when the stop instruction is received;
The generation means continues or stops the generation process according to the determination result by the determination means, and the determination means acquires and adds a predetermined number of dark current image data when the reception timing of the stop instruction is received. The radiation imaging apparatus according to claim 1, wherein it is determined that the generation process is to be stopped if it is before completion, and the generation process is determined to be continued if the process to be added is completed . The determination means calculates a remaining processing time until the generation process is completed based on the reception timing of the stop instruction,
It is determined that the generation process is continued when the remaining processing time is less than a predetermined time, and it is determined that the generation process is stopped when the remaining processing time is equal to or longer than the predetermined time. The radiation imaging apparatus according to claim 1. 3. The radiation imaging apparatus according to claim 1, wherein the receiving unit receives an imaging start instruction for the radiation image as the stop instruction. 4. The generation unit restarts the generation process after the radiographic image has been captured when the determination unit determines that the generation process is to be stopped and the generation process is stopped. Item 4. The radiation imaging apparatus according to Item 3 . A radiation imaging apparatus that corrects a radiation image using a plurality of offset correction data for a plurality of imaging modes ,
Receiving means for receiving a stop command for stopping the generation processing of the plurality of offset correction data by the generating means;
A generation means for acquiring a plurality of dark current image data captured without irradiating radiation and performing an averaging process to generate the plurality of offset correction data, and when the stop instruction is received, Generating means for generating the plurality of offset correction data by executing an averaging process based on the dark current image data that has been added at the reception timing of the cancellation instruction and the number of the added pieces ;
Corresponding to the case where the stop command is received, storage means for storing which of the plurality of offset correction data for which shooting mode offset correction data has been generated;
Radiation imaging apparatus characterized by obtaining Bei a. A control method for a radiation imaging apparatus, comprising a generating means, a receiving means, and a determining means, and correcting a radiation image using offset correction data,
The generation unit generates a plurality of dark current image data captured without irradiating radiation, performs an averaging process, and generates the offset correction data; and
The receiving means for receiving a stop command for stopping the generation process of the offset correction data by the generating step; and
A determination step of determining whether to continue or cancel the generation process based on the progress of the generation process when the determination instruction is received;
In the generation step, the generation process is continued or stopped according to the determination result of the determination step ,
In the determination step, when the reception timing of the stop command is before completion of the process of acquiring and adding a predetermined number of dark current image data, it is determined to stop the generation process, and the process of adding is completed A control method for a radiation imaging apparatus, characterized in that, in the latter case, the generation process is determined to continue . A control method for a radiation imaging apparatus, comprising a generating means, a receiving means, and a storage means, and correcting a radiation image using a plurality of offset correction data for a plurality of imaging modes ,
And
A receiving step in which the receiving means receives a stop instruction to stop the generation process of the offset correction data by the generating step;
The generation means is a generation step of acquiring a plurality of dark current image data imaged without irradiating radiation, performing an averaging process, and generating the offset correction data, wherein the stop command is received The generation process of generating the plurality of offset correction data by performing an averaging process based on the dark current image data added at the reception timing of the cancellation instruction and the added number of sheets,
A storing step in which the storage means stores the offset correction data for which shooting mode of the plurality of offset correction data is generated in response to the reception of the stop command;
The method of the radiation imaging apparatus according to claim that you have a. The program for making a computer perform each process of the control method of the radiation imaging device of Claim 6 . The program for making a computer perform each process of the control method of the radiation imaging device of Claim 7 .

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