WO2013150884A1 - X線画像診断装置及びx線発生装置の制御方法 - Google Patents
X線画像診断装置及びx線発生装置の制御方法 Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 75
- 238000003745 diagnosis Methods 0.000 title claims abstract description 5
- 239000002184 metal Substances 0.000 claims description 33
- 238000002059 diagnostic imaging Methods 0.000 claims description 11
- 238000001514 detection method Methods 0.000 claims description 10
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- 238000010586 diagram Methods 0.000 description 12
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- 230000005540 biological transmission Effects 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 3
- 210000000988 bone and bone Anatomy 0.000 description 2
- 238000002594 fluoroscopy Methods 0.000 description 2
- 238000007493 shaping process Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
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- 210000003141 lower extremity Anatomy 0.000 description 1
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- 210000000056 organ Anatomy 0.000 description 1
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Definitions
- the present invention relates to a control method for an X-ray image diagnostic apparatus and an X-ray generation apparatus, and more particularly to brightness control of an X-ray image.
- the X-ray diagnostic imaging system has an automatic brightness control system (hereinafter abbreviated as “ABS”) that automatically controls the tube voltage so that the brightness of the fluoroscopic image is always constant even when the subject thickness changes. ).
- ABS automatic brightness control system
- a region of interest is set for the image region output from the X-ray detector, the average luminance value in the region of interest is used as a feedback signal, and the value of the feedback signal is set in advance as the target luminance.
- the tube voltage is controlled to increase so that the X-ray output increases, and the luminance of the next fluoroscopic image is controlled to be brighter than the image before the increase.
- Patent Document 1 discloses a fluoroscopic imaging apparatus that freely sets a region of interest with a pointing device such as a mouse during X-ray fluoroscopy and feeds back to ABS using image data in the region of interest. It is disclosed.
- Patent Document 1 when the subject position moves such as the movement of the subject or the movement of the X-ray tube during fluoroscopic imaging and the region of interest deviates from the region of interest, the operator may It was necessary to reset and update the position and size of the image, which lowered the inspection efficiency.
- the present invention has been made in view of the above problems, and an object of the present invention is to provide an ABS system that follows the movement of a subject position without performing an operation of setting a region of interest by an operator.
- the present invention generates a plurality of blocks by dividing an X-ray image of a subject into a plurality of regions, and generates a histogram indicating a distribution of luminance values for each of the plurality of blocks.
- image statistical information used for determining the region of interest is calculated, and the region of interest position determination in which the condition for determining the position of the region of interest in the X-ray image is defined using the image statistical information
- a block to be the region of interest is selected from the plurality of blocks, and based on the luminance value of the block selected as the region of interest, the interest
- a feedback value used for controlling the luminance value of the region is calculated, and an X-ray irradiation condition is determined so that the feedback value becomes a predetermined target luminance value.
- the present invention it is possible to perform the ABS control by calculating the feedback value following the movement of the subject position without performing the setting operation of the region of interest by the operator, and the labor of the operator is omitted. be able to.
- the block diagram which shows the structure of the X-ray-image diagnostic apparatus which concerns on this embodiment
- the flowchart which shows the flow of a process of the X-ray image diagnostic apparatus which concerns on 1st embodiment.
- Flow chart showing the flow of ABS control processing
- Explanatory drawing which shows the region of interest position determination condition information which linked
- the X-ray diagnostic imaging apparatus includes an X-ray generator that generates X-rays, an X-ray detector that detects the X-rays that have passed through a subject and outputs a transmitted X-ray signal, and the transmission
- An image generation unit that generates an X-ray image of the subject based on an X-ray signal
- a block generation unit that generates a plurality of blocks by dividing the X-ray image into a plurality of regions, and the plurality of blocks
- a histogram generation unit that generates a histogram indicating the distribution of luminance values, a predetermined region of interest position determination condition, and a histogram of each block are used to select a block as a region of interest from the plurality of blocks
- a region-of-interest position selection unit that calculates a feedback value used for controlling the luminance value of the region of interest based on the luminance value of the block selected as the region of interest, So that a target
- the region of interest position selection unit in the X-ray image diagnostic apparatus selects a block as a region of interest from the plurality of blocks using image statistical information calculated based on the histogram of each block.
- the X-ray image diagnostic apparatus has a block statistical information calculation unit that calculates the image statistical information.
- the image statistical information in the X-ray image diagnostic apparatus is at least one of an average luminance value, the number of histogram beaks, luminance of a histogram peak, and a variance value.
- the X-ray image diagnostic apparatus includes a determination condition storage unit that stores the region of interest position determination condition.
- the X-ray diagnostic imaging apparatus further includes a technique selection unit that selects an examination procedure, and the determination condition storage unit stores the region-of-interest position determination condition corresponding to the examination procedure, and the region of interest
- the position selection unit extracts the region-of-interest position determination condition according to the selected procedure, and selects a block to be the region of interest using the region-of-interest position determination condition.
- the X-ray image diagnostic apparatus further includes a subject region ratio calculation unit that calculates a ratio of a subject region including a region where the subject is captured in the X-ray image, and the block generation unit includes The number of divisions used when the X-ray image is divided into a plurality of regions is determined according to the ratio of the subject region.
- the X-ray diagnostic imaging apparatus further includes a subject block selection unit that selects a block including the subject region, and the block generation unit includes at least two different divisions according to a ratio occupied by the subject region.
- a first block divided by a relatively large number of divisions and a second block divided by a relatively small number of divisions, and the subject block selection unit A block including the subject region is selected from the blocks, and the histogram generation unit generates the histogram for the first block including at least a part of the selected second block.
- the X-ray image diagnosis apparatus includes an overall histogram generation unit that generates a histogram of the entire X-ray image generated by the image generation unit, and a histogram generated by the overall histogram generation unit on the basis of an arbitrary luminance value. Divided into two data groups, the luminance value when the inter-class variance value of the two classes of each data group or the index value that increases or decreases in conjunction with this inter-class variance value is maximized as the subject region threshold.
- a subject region detection unit that detects a data group that is less than the subject region threshold as a subject region, wherein the subject region ratio calculation unit is configured such that the detected subject region is the X-ray image. Calculate the percentage of
- the subject block selection unit in the X-ray image diagnostic apparatus selects a block including a luminance value less than the subject region threshold as a block including the subject region.
- the X-ray diagnostic imaging apparatus further includes an X-ray diaphragm that restricts the X-ray irradiation area, and the entire histogram generation unit is located inside the X-ray image in which the X-ray diaphragm is captured.
- the block generation unit divides the inner area into the plurality of areas.
- the feedback value in the X-ray image diagnostic apparatus is an average luminance value or median of a block selected as the region of interest.
- the X-ray image diagnostic apparatus further includes a metal region threshold value storage unit that defines a metal region threshold value for determining a region in which the metal is photographed in the X-ray image, corresponding to the examination procedure,
- the feedback value calculation unit sets the metal region threshold value according to the selected procedure, and out of the luminance values in the block selected as the region of interest, a luminance value equal to or higher than the set metal region threshold value. To calculate the feedback value.
- the X-ray generation apparatus control method includes a step of dividing an X-ray image of a subject into a plurality of regions to generate a plurality of blocks, and a luminance value for each of the plurality of blocks. Selecting a block to be the region of interest from among the plurality of blocks using a step of generating a histogram showing a distribution of, a predetermined region of interest position determination condition, and a histogram of each block; Based on the luminance value of the block selected as the region of interest, calculating a feedback value used for controlling the luminance value of the region of interest, and the X so that the feedback value becomes a predetermined target luminance value Determining the irradiation condition of the line.
- an X-ray image diagnostic apparatus 10 that generates an X-ray image consisting of a moving image (hereinafter referred to as a ⁇ perspective image '') and an X-ray image consisting of a still image will be described as an example.
- the X-ray image diagnostic apparatus for imaging may be an X-ray image diagnostic apparatus for adjusting the brightness of a plurality of still images or performing only fluoroscopy.
- FIG. 1 is a block diagram showing the configuration of the X-ray image diagnostic apparatus according to the present embodiment.
- FIG. 2 is a functional block diagram of the X-ray image diagnostic apparatus according to the present embodiment.
- the X-ray diagnostic imaging apparatus 10 includes an X-ray tube 1 that generates X-rays, and an irradiation condition signal (for example, tube current / tube voltage) for the X-ray tube 1.
- an irradiation condition signal for example, tube current / tube voltage
- X-ray generator 2 that applies a high voltage in accordance with the signal
- an X-ray control device 3 that transmits a feedback voltage signal for determining irradiation conditions to the X-ray generator 2, and an X-ray tube 1
- an X-ray flat panel detector 4 for detecting X-rays transmitted through the subject
- an X-ray flat panel detector control device 5 for performing control such as reading processing of the detected transmitted X-ray signal, and reading
- a fluoroscopic image is generated based on the transmitted X-ray signal
- a feedback luminance value is calculated based on the fluoroscopic image
- a feedback luminance value signal indicating the value is output to the X-ray control device 3
- a display Image processing device 6 that generates a fluoroscopic image
- image display device 7 that displays a fluoroscopic image
- the X-ray tube 1 is provided with an X-ray diaphragm 11 at a position facing the X-ray flat panel detector 4 to limit the X-ray irradiation area, and the system controller 8 obtains the position information of the X-ray diaphragm 11. And control the amount of aperture.
- the system control device 8 further includes a procedure selection unit 12 that selects a procedure that defines at least one of the imaging region and the type of examination. Selection information from the procedure selection unit 12 is input to the system control unit 8. Sent from the system control device 8 to the image processing device 6. In the present embodiment, a region-of-interest position determination condition is selected corresponding to the selected procedure, details of which will be described later.
- the X-ray tube 1 and the X-ray generator 2 are collectively referred to as an X-ray generator.
- the image processing apparatus 6 roughly calculates an ABS feedback value and an image generation unit 60 that generates a fluoroscopic image based on a transmission X-ray signal output from the X-ray flat panel detector 4.
- An ABS control processing unit 61 and a display image processing unit 62 that performs image display processing based on the fluoroscopic image generated by the image generation unit 60 are included.
- the image generation unit 60 generates an image in units of frames based on the transmitted X-ray signal output from the X-ray flat panel detector 4.
- the ABS control processing unit 61 Based on the image for one frame, the ABS control processing unit 61 generates an entire histogram generation unit 6a that generates a distribution of luminance values of the frame, and the subject included in each frame is based on the histogram.
- a subject region detection unit 6b that detects an imaged region (hereinafter referred to as a “subject region”), a subject region ratio calculation unit 6c that calculates a ratio of the detected subject region to the entire frame, a subject
- a block generation unit 6d that determines the number of divisions according to the specimen ratio and generates a divided image in which one frame is divided into a plurality of regions according to the number of divisions.
- each of the divided images is referred to as a block.
- the block generator 6d refers to a block divided by a relatively large number of divisions as a first block, and a block divided by a relatively small number of divisions as a second block.
- the size of the first block is called the first block size
- the size of the second block is called the second block size.
- the first block size is configured with an image size smaller than the second block size.
- the ABS control processing unit 61 includes a first block histogram generation unit 6e that generates a histogram indicating the distribution of luminance values of the first block, and statistics for use in selecting a region of interest for each histogram of the first block.
- the first block statistical information calculation unit 6f that calculates information, and the region of interest position from the first block in light of the region of interest position determination condition determined according to the technique selected by the technique selection unit 12 Region selection unit 6g for selecting the region, feedback value calculation unit 6h for calculating the ABS feedback luminance value using the luminance value in the region of interest selected by the region of interest position selection unit 6g, and interest corresponding to the procedure
- a determination condition storage unit 6i that stores region-of-interest position determination condition information indicating the region position determination condition.
- the ABS control processing unit 61 prepares a histogram indicating the distribution of luminance values of the second block as a preparation before determining the first block, and for each histogram of the second block.
- a second block statistical information calculation unit 6k that calculates statistical information for determining whether or not the subject region is included, and a second block that includes the subject region based on the statistical information
- the first block histogram generation unit 6e generates a histogram of the first block that overlaps or partially includes the position of the second block selected by the subject block selection unit 6l.
- the second block histogram generation unit 6j, the second block statistical information calculation unit 6k, and the subject block selection unit 6l reduce the number of first blocks that are targets for generating histograms in the first block histogram generation unit 6e.
- the second block histogram generation unit 6j, the second block statistical information calculation unit 6k, and the subject block selection unit 6l are provided.
- the display image processing unit 62 performs image processing for generating a display perspective image such as display gradation processing on the transmission X-ray signal read from the X-ray flat panel detector 4, and displays the display perspective image. Is output and displayed on the image display device 7.
- the X-ray control device 3 includes a feedback voltage calculation unit 3a that converts the feedback luminance value received from the feedback value calculation unit 6h of the image processing device 6 into a voltage (hereinafter referred to as “feedback voltage”).
- the X-ray generator 2 matches the feedback voltage received from the X-ray control device 3 with a reference voltage obtained by converting a desired luminance value (hereinafter referred to as “target luminance value”) of a region of interest in a fluoroscopic image into a voltage.
- target luminance value a desired luminance value
- an irradiation condition determining unit 2a for determining irradiation conditions is provided.
- the image generation unit 60, each component in the ABS control processing unit 61, and the display image processing unit 62 are configured by combining, for example, a program that realizes the function of each unit and a hardware device that executes the program. May be.
- FIG. 3 is a flowchart showing a process flow of the X-ray image diagnostic apparatus according to the first embodiment.
- FIG. 4 is a flowchart showing the flow of ABS control processing.
- FIG. 5 is an explanatory diagram showing region-of-interest position determination condition information that associates a technique with a region-of-interest determination condition.
- FIG. 6 is an explanatory diagram showing a perspective image and a histogram generated based on the perspective image.
- FIG. 6A shows an example of the perspective image
- FIG. 6B shows a histogram of the perspective image.
- FIG. 7 is an explanatory diagram showing a selected block and a target block and their histograms, and (a) shows a block selected based on the block of the first block size and the histogram of each block, b) shows a histogram of the block of the second block size and the target block.
- FIG. 8 is an explanatory diagram showing a process of selecting a region of interest from the target block.
- FIG. 9 is an explanatory diagram showing a conversion process from feedback luminance values to irradiation conditions.
- the flow of processing of the X-ray image diagnostic apparatus 10 according to the first embodiment will be described with reference to FIGS.
- the flow of the fluoroscopic image display process up to steps S2 and S3 and the flow of the ABS control process from steps S2 and S4 to S9 are executed in parallel.
- description will be made along the order of steps in FIGS.
- Step S1 The operator determines the technique of the examination to be performed from now, selects and inputs the technique in the technique selection unit 12, and starts the examination (fluoroscopic) (S1).
- the procedure determined here includes information such as an imaging region (for example, an arm, a lower limb, and a chest) and an inspection procedure (fluoroscopic imaging).
- the system control device 8 sends information indicating the selected procedure to the region of interest position selection unit 6g.
- the determination condition storage unit 6i in the image processing device 6 stores region-of-interest position determination condition information that associates a technique with a region-of-interest position determination condition in advance.
- Region-of-interest position determination conditions define conditions for determining the position of a region of interest in an X-ray image, and are set using a histogram in an X-ray image or image statistical information calculated based on the histogram.
- the image statistical information is a region of interest position determination parameter that is at least one of an average luminance value, the number of histogram peaks, a luminance value of histogram peaks, a variance value, or a combination thereof, and the region of interest position determination condition is , Using this region of interest location determination parameter.
- region-of-interest determination parameters may be used for each procedure. For example, in the region-of-interest position determination condition information in FIG. 5, in the case of Procedure 1 ⁇ Shaping / Arm '', we want to focus on the bone.
- the region-of-interest position determination conditions are defined.
- Condition 1 A block with one histogram peak
- Condition 2 A block with the smallest average luminance value in the block among the blocks satisfying Condition 1 Region-of-interest position determination conditions differ depending on the procedure, for example, you want to focus on the organ In “Procedure 2”, the following two conditions are defined.
- Condition 1 ' Block with one histogram peak
- Condition 2' Of the blocks satisfying Condition 1 ', the block having the smallest variance value of the luminance value in the block
- the region of interest position determination condition information in FIG. 5 is an example Only.
- the region of interest position determination condition may be determined including three or more conditions.
- the region-of-interest position selection unit 6g searches the determination condition storage unit 6j, and searches for region-of-interest position determination information corresponding to the selected procedure. This information is used in step S624 (see FIG. 4) described later.
- Step S2 A transmission X-ray signal for the nth frame is input from the X-ray flat panel detector 4 to the image generation unit 60, and a perspective image of the nth frame is generated (S2). For example, as shown in FIG. 6, it is assumed that a perspective image 20 for one frame made up of a perspective image of an arm in an orthopedic procedure is input.
- Step S3 The display image processing unit 62 performs an image display process such as a display gradation process on the input fluoroscopic image, generates a fluoroscopic image for display, and displays it on the image display device 7 (S3). Thereafter, the process proceeds to step S9.
- an image display process such as a display gradation process on the input fluoroscopic image
- generates a fluoroscopic image for display and displays it on the image display device 7 (S3). Thereafter, the process proceeds to step S9.
- Step S4 The ratio of the subject area in the entire fluoroscopic image for one frame is calculated (S4).
- Step S41 The entire histogram generation unit 6a generates a histogram indicating the distribution of the entire luminance value (or pixel value) of the perspective image 20 (see (a) of FIG. 6) for one frame input in step S2 (S41). .
- the histogram 23 shown in FIG. 6B is generated.
- a compressed histogram obtained by thinning out an N-bit histogram by several bits may be generated, and the processing in steps S42 and S43 may be performed using the compressed histogram.
- Step S42 The subject region detection unit 6b calculates a luminance value PV threshold that is a threshold value between the subject region and the halation region, using the histogram 23 of the entire one frame generated in step S41 (S42).
- the luminance value PV threshold is referred to as a subject region threshold, and a discriminant analysis method is used as a method for calculating this.
- the subject area detection unit 6b divides the histogram into two with an arbitrary luminance value on the histogram 23 as a boundary, and obtains the luminance value that maximizes the inter-class variance when class 1 and class 2 respectively. Obtained as the specimen region threshold PV threshold . Specifically, the luminance value PV threshold when the value of interclass variance ⁇ calculated from the following equation (1) is maximized is obtained.
- Equation (1) ⁇ 1 ( ⁇ 1 ⁇ a ) 2 + ⁇ 2 ( ⁇ 2 ⁇ a ) 2 ⁇ / ( ⁇ 1 + ⁇ 2 ) (1) ⁇ : Interclass variance value ⁇ 1: Class 1 pixel ratio ⁇ 2: Class 2 pixel ratio ⁇ 1: Class 1 average brightness value ⁇ 2: Class 2 average brightness value ⁇ a: Average brightness value of entire image Note The denominator ( ⁇ 1 + ⁇ 2 ) on the right side of Equation (1) indicates the total number of pixels of the fluoroscopic image of one frame, and this value is the same value for all the frames constituting the fluoroscopic image.
- Expression (1) ′ is an expression for obtaining an index value ⁇ ′ that is linked to interclass variance.
- ⁇ ′ is also maximized.
- ⁇ ' ⁇ 1 ( ⁇ 1 ⁇ a ) 2 + ⁇ 2 ( ⁇ 2 ⁇ a ) 2 ⁇ ⁇ ⁇ (1)' ⁇ ′: Index value linked to the value of inter-class variance ⁇ 1 : Ratio of the number of pixels in class 1 ⁇ 2 : Ratio of the number of pixels in class 2 ⁇ 1 : Average brightness value of class 1 ⁇ 2 : Average brightness of class 2 Value ⁇ a : Average luminance value of the entire image
- the fluoroscopic image 20 in FIG. 6A is a direct line region 21 where X-rays are directly incident on the X-ray flat detector 4 and X-rays transmitted through the subject are incident. Subject area 22. As shown in FIG.
- the histogram 23 of the perspective image 20 mainly shows the luminance of the pixels constituting the subject region 22 and the region where the high luminance values of the pixels constituting the direct line region 21 are distributed. It has bimodality consisting of an area where values are distributed.
- the luminance value PV threshold (24 in FIG. 6) at which the inter-class variance is maximum is a valley portion between two peaks. Therefore, a data group having a luminance value equal to or higher than the PV threshold (24 in FIG. 6) can be recognized as the direct line region 25, and a data group having a luminance value less than the PV threshold (Target PS) as the subject region 26.
- Step S43 The subject area ratio calculation unit 6c obtains the occupied area ratio P in one frame of the subject area calculated in step S42 (S43).
- the occupied area ratio P is obtained as the ratio of the number of pixels in the subject region 26 to the total number of pixels in the histogram 23 based on the following equation (2).
- the block generation unit 6d determines at least two out of a plurality of types of division numbers prepared in advance based on the occupation area ratio P of the subject region calculated in step S5.
- Three types (a ⁇ a, b ⁇ b, c ⁇ c) (provided that a ⁇ b ⁇ c) are prepared in advance, and two types are determined and created.
- the two types of division numbers the first block is divided by a relatively large division number, and the second block is divided by a relatively small division number. Therefore, when the number of divisions is determined, the block size is also determined.
- the block generation unit 6d is divided into a ⁇ a, b Use xb. Conversely, when P is less than X 1 (%), b ⁇ b and c ⁇ c are used as the number of divisions.
- the first block size is a block size divided by c ⁇ c
- the second block size is a block size divided by b ⁇ b. It becomes.
- Step S6 Image statistical information is calculated based on the histogram of the block, and the region of interest position is selected using this (S6).
- Step S611 The block generation unit 6d generates a block using the second block size among at least two types of division numbers determined in step S5 (S611). In the above example, the block size divided by b ⁇ b is used.
- the second block histogram generation unit 6j generates a histogram indicating the distribution of luminance values for each block of the second block size (S612).
- the second block histogram generation unit 6j divides the perspective image 20 into b ⁇ b as shown in (a) of FIG. 7, and creates a histogram 31 for each block.
- Step S613 The second block statistical information calculation unit 6k calculates image statistical information in each block based on each histogram created in step S612 (S613).
- the luminance value in the block is calculated, but image statistical information used to determine the presence or absence of the subject region may be obtained.
- the magnitudes of the variance values in the above three cases are in the order of (2)> (3)> (1). Therefore, by setting a threshold between (3) and (1) and performing threshold determination, it is possible to determine whether or not the block includes the subject region.
- Step S614 The subject block selection unit 6l selects the second block including the subject region by comparing the subject region threshold PV threshold obtained in step S42 with the luminance value in each block calculated in S613 ( S614).
- the block selected here is referred to as a selection block G1.
- the selection condition includes at least one pixel having a luminance value less than or equal to the subject region threshold PV threshold in each block.
- the block surrounded by a circle is the selected block G1.
- Step S621 The block generation unit 6d generates the first block using the relatively large number of divisions determined in step S5 (S621).
- a block divided by c ⁇ c is generated (see block 32 in FIG. 7B).
- this step is described after step S614.
- this step and step S611 described above may be executed in parallel. .
- the first block histogram generation unit 6e generates a histogram only for blocks that overlap or match the selected block G1 among the first blocks (S622).
- a block that overlaps or coincides with the selected block G1 is referred to as a “target block G2.”
- the block in which the histogram 33 is described is the target block G2.
- the first block statistical information calculation unit 6f uses the histogram 33 of the target block G2 to calculate statistical information used for region of interest position selection (S623).
- the statistical information to be calculated includes, for example, an average luminance value, the number of histogram peaks, a histogram peak luminance value, a variance value of pixels in a block, and the like.
- the region-of-interest position determination condition searched in step S1 is acquired by the first block statistical information calculation unit 6f, and only the statistical information used for the region-of-interest position determination parameter used in this region-of-interest position determination condition is obtained. It may be calculated.
- Step S624 Using the statistical information obtained in step S623 and the region-of-interest position determination condition obtained in step S1, a block to be a region of interest is selected from the target block G2 (S624).
- a broken-line circle block is a target block G2 that satisfies the condition 1
- a double-circle frame block in the image 20 of FIG. 8 is a target block G2 that satisfies the condition 2. Therefore, this double-circle block 34 is selected as the region of interest.
- Step S7 A feedback luminance value PV ABS is obtained based on the luminance value in the region of interest (S7).
- the feedback value calculation unit 6h calculates the average luminance value of the block 34 that is the region of interest selected in step S6, and uses this average luminance value as the feedback luminance value PV ABS .
- the feedback value calculation unit 6h sends a signal indicating the feedback luminance value PV ABS (hereinafter referred to as “feedback value signal”) to the X-ray control device 3.
- feedback value signal a signal indicating the feedback luminance value PV ABS
- a median may be used as a representative of the luminance value in the region of interest.
- Step S8 The feedback luminance value PV ABS is converted into a feedback voltage, and the irradiation condition is determined so as to coincide with the luminance value (hereinafter referred to as “target luminance value”) to be kept constant by the ABS control process (S8).
- the feedback voltage calculation unit 3a in the X-ray control device 3 receives the feedback luminance value signal from the feedback value calculation unit 6h. Then, the feedback voltage calculation unit 3a converts the received feedback luminance value into a voltage to be fed back to the X-ray generator 2 (hereinafter referred to as “feedback voltage”).
- the irradiation condition determination unit 2a of the X-ray generator 2 compares the feedback voltage with a predetermined reference voltage (voltage corresponding to the target luminance value), and if the feedback voltage is lower than the reference voltage, the current irradiation condition ( Gradually increase the tube voltage and tube current) and adjust to match the reference voltage (eg 5V). On the other hand, if the feedback voltage is higher than the reference voltage, the current irradiation condition (combination of tube voltage and tube current) is gradually lowered and adjusted to match the reference voltage (for example, 5V).
- the irradiation condition determination unit 2a compares the reference voltage Y ref [V] with the feedback voltage Y 1 [V]. If Y 1 [V] is smaller than the reference voltage Y ref [V], the current irradiation condition is determined. Increase (mA 1 , kV 1 ) to (mA 2 , kV 2 ) (however, mA 1 ⁇ mA 2 , kV 1 ⁇ kV 2 ).
- the irradiation condition is described using a combination of tube current and tube voltage.
- the irradiation condition may be changed by raising or lowering only the tube voltage or only the tube current.
- Step S9 The irradiation condition is changed, and a perspective image of the (n + 1) th frame is captured (S9).
- the X-ray generator 2 outputs a newly determined irradiation condition signal to the X-ray tube 1, and the n + 1th frame of the fluoroscopic image is captured according to the new irradiation condition. Thereafter, the process returns to step S2, and the transmission X-ray signal of the (n + 1) th frame is input to the image processing device 6, and the processing after step S2 is executed again based on this transmission X-ray signal.
- the ABS control by calculating the feedback value following the movement of the subject position without performing the setting operation of the region of interest by the operator, and the labor of the operator is saved. can do.
- the selected block including the subject region is searched using the second block size, which is a relatively large size, and only the block having the first block size that overlaps the selected block is selected as the target block.
- the processing speed can be increased compared to the case where the statistical information for detecting the region of interest position is calculated for all the blocks of the first block size. I can expect.
- FIG. 10 is an explanatory diagram showing the contents of the processing of the second embodiment. Since the processing flow is the same as that in the first embodiment, description will be made using the step numbers in FIGS.
- the perspective image 40 in FIG. 10 shows a state in which the perspective image without the X-ray stop 11 is divided into c ⁇ c (5 ⁇ 5 in FIG. 10) in step S611.
- a perspective image 41 in FIG. 10 is a perspective image in which the X-ray diaphragm 11 is inserted, and shows a state divided into b ⁇ b (4 ⁇ 4 in FIG. 10) in step S611.
- the position information of the X-ray diaphragm 11 is acquired when the system control device 8 controls the operation of the X-ray diaphragm 11. Therefore, by outputting this position information from the system control device 8 to the image processing device 6, it is possible to detect the region 42 in which the X-ray diaphragm 11 is photographed as a fluoroscopic image.
- This detection is performed by the subject region detection unit 6b in step S42, and subject region determination is performed on a fluoroscopic image inside the region 42.
- the occupied area ratio P of the subject area in the image inside the area 42 is calculated.
- the number of divisions (or block size) is determined based on this occupied area ratio
- steps S611 and S621 the image inside the region 42 is determined using the determined number of divisions (block size).
- the fluoroscopic image 41 with the X-ray diaphragm 11 inserted has a larger occupied area ratio of the subject in the image than the fluoroscopic image 40 without the diaphragm.
- the number of divisions determined is determined so that the size of one block is relatively large.
- the X-ray aperture when the X-ray aperture is reflected in the fluoroscopic image, it is possible to exclude the pixel reflecting the luminance value from the calculation target of the ABS control process, and thus the influence of the X-ray aperture is reduced. It is possible to give more appropriate ABS feedback.
- FIG. 11 is an explanatory diagram showing the contents of the processing of the third embodiment. Since the processing flow is the same as that of the first embodiment, description will be made using the step numbers in FIGS.
- metal region threshold value One type of metal region threshold value may be used, but a metal region threshold value having an arbitrary luminance value that differs for each procedure may be used.
- the metal area threshold value data defining the metal area threshold value corresponding to the procedure is stored in advance in the storage unit in the image processing apparatus 6.
- the feedback value calculation unit 6h may search and set a metal area threshold corresponding to the selected technique with reference to the metal area threshold data.
- step S624 if the block selected as the region of interest includes a pixel that is equal to or less than the luminance value of the preset metal region threshold, the feedback luminance value PV ABS is calculated for the pixel in step S7. Exclude from the target pixel.
- Figure 11 shows an example of metal area threshold data.
- the metal region threshold is defined using PV1, PV2, and PV3 and higher luminance values as the procedure 1, procedure 2, procedure 3, and subject thickness increase.
- region threshold value according to a procedure can be used.
- the procedure is shaping and the imaging region is an arm
- the X-ray dose is relatively small because the subject is thin. Therefore, since the metal in the image is also photographed relatively dark, a relatively dark luminance value is set as the metal region threshold value for a procedure including a portion where the subject thickness is thin.
- a metal surgical tool such as a thoracotomy fixture is reflected in the image. Since the chest is relatively thick compared to the extremities, the X-ray dose is also relatively high. As a result, since the metal surgical tool is photographed relatively brightly, a relatively bright luminance value is set as a metal region threshold value for a procedure including a portion where the subject is thick.
- the present embodiment when a metal is photographed in a fluoroscopic image, it is possible to exclude a pixel reflecting the brightness value of the metal from the calculation target of the feedback brightness value PV ABS.
- the influence of the metal region in can be reduced.
- the X-ray dose varies depending on the thickness of the subject, and the imaging brightness of the metal also changes accordingly.Therefore, by using a metal region threshold value corresponding to the thickness of the subject, the brightness value of the metal can be more accurately fed back.
- the value PV ABS can be excluded from the calculation target.
- the fourth embodiment is an embodiment in which the number of divisions is changed according to the size of a perspective image of one frame.
- two division numbers are determined, but when the subject region is relatively small, only one type of division number for generating the first block is determined, and all the first blocks are determined.
- a histogram may be generated to calculate a statistic for selecting a region of interest position. Since the processing flow of the fourth embodiment overlaps with that of the first embodiment, description will be made using the step numbers of FIGS.
- step S43 the subject region detection unit 6b calculates the total value of the frequencies of the histogram generated in step S41.
- the subject region detection unit 6b passes the comparison result between the total value and the first reference value to the block generation unit 6d, and the block generation unit 6 determines that the total value is equal to or less than the first reference value based on the comparison result.
- steps S611 to S614 are omitted.
- step S622 histograms are generated for all the first blocks, and the process of step S623 is executed based on the entire histograms.
- the image size may be determined by how much the X-ray aperture 11 appears on the screen. For example, when it is detected from the position information of the X-ray diaphragm 11 that the X-ray diaphragm 11 is reflected on a setting value on the screen, for example, X 2 % or more, the block generation unit 6d determines the number of divisions based on the detection result. You may comprise so that only one may be determined.
- the number of divisions of three or more is determined, blocks are generated in order from the smallest number of divisions, and a block including the subject region in the block is selected. This process is repeated until the number of divisions is one more than the maximum number of divisions. Then, the block having the maximum number of divisions and the block selected using the maximum number of divisions overlap or partially include a block.
- the target block when the image size is small, the target block can be directly searched without searching the selected block, and when the image size is large, the selected block can be searched through a plurality of stages.
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Abstract
Description
第一実施形態について、図3乃至図8に基づいて説明する。図3は、第一実施形態に係るX線画像診断装置の処理の流れを示すフローチャートである。図4は、ABS制御の処理の流れを示すフローチャートである。図5は、手技と関心領域決定条件とを関連付けた関心領域位置決定条件情報を示す説明図である。図6は、透視像及びその透視像を基に生成したヒストグラムを示す説明図であって、(a)は、透視像の一例を示し、(b)は、この透視像のヒストグラムを示す。図7は、選出ブロック及び対象ブロックとそれらのヒストグラムとを示す説明図であって、(a)は、第一ブロックサイズのブロック及び各ブロックのヒストグラムを基に選出された選出ブロックを示し、(b)は、第二ブロックサイズのブロック及び対象ブロックのヒストグラムを示す。図8は、対象ブロックの中から関心領域を選出する処理を示す説明図である。図9は、フィードバック輝度値から照射条件への変換処理を示す説明図である。
操作者は、これから行う検査の手技を決定し、手技選択部12において手技を選択入力し、検査(透視)を開始する(S1)。ここで決定される手技には、撮影部位(例えば、腕、下肢、胸部など)や検査手技(透視、撮影)などの情報が含まれる。システム制御装置8は、関心領域位置選出部6gに対して選択された手技を示す情報を送る。
条件2:条件1を満たすブロックのうち、ブロック内の平均輝度値が最小となるブロック 関心領域位置決定条件は手技ごとに異なり、例えば臓器に着眼したい「手技2」では、以下の2条件が規定されている。
条件2’:条件1’を満たすブロックの内、ブロック内の輝度値の分散値が最小となるブロック
図5の関心領域位置決定条件情報は一例に過ぎない。例えば、関心領域位置決定条件は、3つ以上の条件を含んで決定してもよい。
X線平面検出器4からn番目フレーム分の透過X線信号が画像生成部60に入力され、n番目フレームの透視像が生成される(S2)。例えば、図6に示すように、整形手技における腕の透視像からなる1フレーム分の透視像20が入力されたとする。
表示用画像処理部62は、入力された透視像に対し画像表示処理、例えば表示階調処理等を施し、表示用の透視像を生成し、画像表示装置7に表示する(S3)。その後、ステップS9へ進む。
1フレーム分の透視像全体に占める被検体領域割合を算出する(S4)。
全体ヒストグラム生成部6aは、ステップS2で入力された1フレーム分の透視像20(図6の(a)参照)の全体の輝度値(又は画素値)の分布を示すヒストグラムを生成する(S41)。本実施形態では、図6の(b)に示すヒストグラム23が生成されたとする。なお、下記ステップS42の処理をより高速に行うため、Nビットのヒストグラムを数ビットずつ間引いた圧縮ヒストグラムを生成し、これを用いてステップS42、S43の処理を行ってもよい。
被検体領域検出部6bは、ステップS41で生成された1フレーム全体のヒストグラム23を用いて、被検体領域とハレーション領域との閾値となる輝度値PVthresholdを算出する(S42)。本実施形態では、輝度値PVthresholdを被検体領域閾値といい、これを算出する手法として判別分析法を用いる。
Δ:クラス間分散の値
ω1:クラス1の画素数の割合
ω2:クラス2の画素数の割合
μ1:クラス1の平均輝度値
μ2:クラス2の平均輝度値
μa:画像全体の平均輝度値
なお、式(1)の右辺の分母(ω1+ω2)は、1フレームの透視像の全画素数を示しており、この値は、透視像を構成する全てのフレームにおいて同じ値となる。よって、クラス間分散Δが最大となるときの輝度値PVthresholdを求める際に、式(1)の右辺において(ω1+ω2)で除する演算を省き、下記式(1)’を用いてもよい。式(1)’は、クラス間分散に連動する指標値Δ’を求める式であるが、Δ’が最大となるとき、クラス間分散Δも最大となる。式(1)に代えて式(1)’を用いることにより、(ω1+ω2)で除する演算が省略でき、より高速な演算処理が可能となる。
Δ’:クラス間分散の値に連動する指標値
ω1:クラス1の画素数の割合
ω2:クラス2の画素数の割合
μ1:クラス1の平均輝度値
μ2:クラス2の平均輝度値
μa:画像全体の平均輝度値
図6の(a)の透視像20は、X線平面検出器4にX線が直接入射した直接線領域21と、被検体を透過したX線が入射した被検体領域22と、から成る。この透視像20のヒストグラム23は、図6の(b)に示すように、主に直接線領域21を構成する画素の高輝度値が分布する領域と、被検体領域22を構成する画素の輝度値が分布する領域と、からなる双峰性を持つ。この場合、クラス間分散が最大となる輝度値PVthreshold(図6における24)は、2山の間の谷の部分となる。したがってPVthreshold(図6における24)以上の輝度値のデータ群を直接線領域25、PVthreshold未満の輝度値のデータ群(Target PS)を被検体領域26と認識することが出来る。
被検体領域割合算出部6cは、ステップS42で算出した被検体領域の、1フレーム内における占有面積割合Pを求める(S43)。占有面積割合Pは、下式(2)に基づいて、ヒストグラム23の全画素数に対する被検体領域26の画素数の割合として求める。
P:ヒストグラム23の全体に対する算出された被検体領域26の割合
Csp:ヒストグラム23内の被検体領域26の画素数
Call:ヒストグラム23全体の画素数
(ステップS5)
被検体領域の占有面積割合Pを基に、1フレーム分の透視像を複数の領域に分割するための分割数を決定する(S5)。
予め、3種類(a×a、b×b 、c×c)(但し、a<b<cとする。)の分割数を用意しておき、その中から2種類を決定、作成する。2種類の分割数のうち、相対的に多い分割数で分割されたものが第一ブロック、相対的に少ない分割数で分割されたものが第二ブロックとなる。よって、分割数が定まるとブロックサイズも定まる。
ブロックのヒストグラムを基に画像統計情報を算出し、これを用いて関心領域位置を選出する(S6)。
ブロック生成部6dは、ステップS5で決定した少なくとも2種類の分割数のうち、第二ブロックサイズを用いてブロックを生成する(S611)。上記の例では、b×bで分割したブロックサイズを用いる。
第二ブロックヒストグラム生成部6jは、第二ブロックサイズの各ブロックについて、輝度値の分布を示すヒストグラムを生成する(S612)。上記の例では、第二ブロックヒストグラム生成部6jは、図7の(a)に示すように、透視像20をb×bに分割し、各ブロックのヒストグラム31を作成する。
第二ブロック統計情報算出部6kは、ステップS612で作成した各ヒストグラムを基に、各ブロック内の画像統計情報を算出する(S613)。本実施形態では、ブロック内にある輝度値を算出するが、被検体領域の有無の判別に用いる画像統計情報を求めてもよい。
被検体ブロック選出部6lは、ステップS42で求めた被検体領域閾値PVthresholdと、S613で算出した各ブロックにある輝度値と、を比較して、被検体領域を含む第二ブロックを選出する(S614)。以下、ここで選出されるブロックを選出ブロックG1という。
ブロック生成部6dは、ステップS5で決定した相対的に多い分割数を用いて第一ブロックを生成する(S621)。本実施形態は、c×cで分割したブロックを生成する(図7の(b)のブロック32参照)。なお、説明の便宜上、本ステップをステップS614の次に説明しているが、ステップS5で二種類の分割数を決定した後、本ステップと既述ステップS611とを並行して実行してもよい。
第一ブロックヒストグラム生成部6eは、第一ブロックのうち、選出ブロックG1と重なる又は一致するブロックについてのみ、ヒストグラムを生成する(S622)。以下、第一ブロックのうち、選出ブロックG1と重なる又は一致するブロックを「対象ブロックG2」という。
第一ブロック統計情報算出部6fは、対象ブロックG2のヒストグラム33を用いて、関心領域位置選出に用いる統計情報を算出する(S623)。算出する統計情報は、例えば、平均輝度値、ヒストグラムピークの数、ヒストグラムピーク輝度値、ブロック内画素の分散値などがある。
ステップS623により得た統計情報と、ステップS1で求めた関心領域位置決定条件と、を用いて、対象ブロックG2の中から関心領域となるブロックを選出する(S624)。
関心領域内の輝度値を基にフィードバック輝度値PVABSを求める(S7)。本実施形態では、フィードバック値算出部6hは、ステップS6で選出した関心領域となるブロック34の平均輝度値を算出し、この平均輝度値をフィードバック輝度値PVABSとして用いる。フィードバック値算出部6hは、フィードバック輝度値PVABSを示す信号(以下「フィードバック値信号」という)をX線制御装置3に送る。平均輝度値に代わり、関心領域内の輝度値を代表するものとして、メジアンを用いてもよい。
フィードバック輝度値PVABSをフィードバック電圧に換算し、これが、ABS制御処理により一定に保ちたい輝度値(以下「目標輝度値」という)に一致するように照射条件を決定する(S8)。
照射条件を変更して、n+1番目フレームの透視像を撮像する(S9)。X線発生器2は、新たに決定した照射条件信号をX線管球1に出力し、その新たな照射条件に従ってn+1番目フレームの透視像の撮像が行われる。その後、ステップS2へ戻り、n+1番目フレームの透過X線信号が画像処理装置6へ入力され、この透過X線信号に基づいて、再度ステップS2以後の処理が実行される。
第二実施形態は、第一実施形態に加え、X線絞りの輝度値が反映された画素をABS制御処理の対象から除外する実施形態である。透視像取得中にX線絞り11の挿入や透視像拡大があった場合、X線絞り11が挿入されている位置を自動的に検出し、X線絞り11の内側の画素のみを用いて被検体領域判定、ブロック生成を行う。以下、図10に基づいて第二実施形態について説明する。図10は、第二実施形態の処理の内容を示す説明図である。なお、処理の流れは第一実施形態と同様なので、図3及び図4のステップ番号を流用して説明する。
第三実施形態では、第一実施形態に加え、金属が撮影された領域の輝度値が反映された画素をABS制御処理の対象から除外する実施形態である。以下、図11に基づいて第三実施形態について説明する。図11は、第三実施形態の処理の内容を示す説明図である。
処理の流れは第一実施形態と同様なので、図3及び図4のステップ番号を流用して説明する。
第四実施形態は、1フレームの透視像の大きさに応じて分割数の種類数を変える実施形態である。第一実施形態では、二つの分割数を決定したが、被検体領域が相対的に小さい場合、第一ブロックを生成するための一種類の分割数のみを決定し、全ての第一ブロックに対してヒストグラムを生成し、関心領域位置を選出するための統計量を算出しても良い。第四実施形態の処理の流れは第一実施形態と重複するところもあるので、図3及び図4のステップ番号を流用して説明する。
この場合、三以上の分割数を決定し、最も少ない分割数から順にブロックを生成し、そのブロックの内の被検体領域を含むブロックを選出ブロックとする。この処理を、最大数の分割数よりも一つ多い分割数のブロックまで繰り返す。そして、最大数の分割数のブロックと、最大数の分割数を用いて選出した選出ブロックとが重なる又は一部に含むブロックを対象ブロックとする。
Claims (14)
- X線を発生するX線発生装置と、
被検体を透過した前記X線を検出して透過X線信号を出力するX線検出器と、
前記透過X線信号に基づいて、前記被検体のX線画像を生成する画像生成部と、
前記X線画像を複数の領域に分割して、複数のブロックを生成するブロック生成部と、
前記複数のブロックのそれぞれについて、輝度値の分布を示すヒストグラムを生成するヒストグラム生成部と、
所定の関心領域位置決定条件と前記各ブロックのヒストグラムを用いて、
前記複数のブロックの中から関心領域とするブロックを選出する関心領域位置選出部と、
前記関心領域として選出されたブロックの輝度値に基づいて、前記関心領域の輝度値の制御に用いるフィードバック値を算出するフィードバック値算出部と、
前記フィードバック値が予め定めた目標輝度値となるように、前記X線の照射条件を決定する照射条件決定部と、
前記X線画像を表示する画像表示装置と、
を備えることを特徴とするX線画像診断装置。 - 前記関心領域位置選出部は、
前記各ブロックのヒストグラムに基づいて算出した画像統計情報を用いて、
前記複数のブロックの中から関心領域とするブロックを選出することを特長とする請求項1に記載のX線画像診断装置。 - 前記画像統計情報を算出するブロック統計情報算出部を有することを特徴とする請求項2に記載のX線画像診断装置。
- 前記画像統計情報とは、平均輝度値、ヒストグラムビークの数、ヒストグラムピークの輝度、又は分散値の少なくとも何れか一つであることを特徴とする請求項3に記載のX線画像診断装置。
- 前記関心領域位置決定条件を記憶する決定条件記憶部を有することを特徴とする請求項1に記載のX線画像診断装置。
- 検査の手技を選択する手技選択部を更に備え、
前記決定条件記憶部は、前記検査の手技に対応した前記関心領域位置決定条件を記憶し、前記関心領域位置選出部は、前記選択された手技に応じた前記関心領域位置決定条件を出し、その関心領域位置決定条件を用いて前記関心領域とするブロックを選出することを特徴とする請求項5に記載のX線画像診断装置。 - 前記X線画像において、
前記被検体が撮影された領域からなる被検体領域が占める割合を算出する被検体領域割合算出部を更に備え、
前記ブロック生成部は、前記被検体領域が占める割合に応じて、
前記X線画像を複数の領域に分割する際に用いる分割数を決定することを特徴とする請求項1に記載のX線画像診断装置。 - 前記被検体領域を含むブロックを選出する被検体ブロック選出部を更に備え、
前記ブロック生成部は、前記被検体領域が占める割合に応じて少なくとも二つの異なる分割数を決定し、相対的に多い分割数で分割された第一ブロックと、相対的に少ない分割数で分割された第二ブロックと、を生成し、前記被検体ブロック選出部は、前記第二ブロックの中から前記被検体領域を含むブロックを選出し、
前記ヒストグラム生成部は、前記選出された第二ブロックの少なくとも一部を含む前記第一ブロックについて、前記ヒストグラムを生成することを特徴とする請求項7に記載のX線画像診断装置。 - 前記画像生成部が生成したX線画像全体のヒストグラムを生成する全体ヒストグラム生成部と、
前記全体ヒストグラム生成部が生成したヒストグラムを任意の輝度値を境に二つのデータ群に分割し、各データ群からなる二つのクラスのクラス間分散値、又はこのクラス間分散値に連動して増減する指標値、が最大となるときの輝度値を被検体領域閾値とし、この被検体領域閾値未満のデータ群を被検体領域として検出する被検体領域検出部と、を更に備え、
前記被検体領域割合算出部は、前記検出された被検体領域が、前記X線画像に占める割合を算出することを特徴とする請求項8に記載のX線画像診断装置。 - 前記被検体ブロック選出部は、前記被検体領域閾値未満の輝度値を含むブロックを、前記被検体領域を含むブロックとして選出することを特徴とする請求項9に記載のX線画像診断装置。
- 前記X線の照射領域を制限するX線絞りを更に備え、
前記全体ヒストグラム生成部は、前記X線画像において前記X線絞りが撮像された領域よりも内側の領域のヒストグラムを生成し、
前記ブロック生成部は、前記内側の領域を前記複数の領域に分割することを特徴とする請求項9に記載のX線画像診断装置。 - 前記フィードバック値は、前記関心領域として選出されたブロックの平均輝度値又はメジアンであることを特徴とする請求項1に記載のX線画像診断装置。
- 前記検査の手技に対応して、前記X線画像において金属が撮影された領域を判別するための金属領域閾値を規定した金属領域閾値記憶部を更に備え、
前記フィードバック値算出部は、前記選択された手技に応じた前記金属領域閾値を設定し、前記関心領域として選出されたブロック内の輝度値のうち、前記設定された金属領域閾値以上の輝度値を用いて前記フィードバック値を算出することを特徴とする請求項6に記載のX線画像診断装置。 - 被検体のX線画像を複数の領域に分割して、複数のブロックを生成するステップと、
前記複数のブロックのそれぞれについて、輝度値の分布を示すヒストグラムを生成するステップと、
所定の関心領域位置決定条件と、前記各ブロックのヒストグラムと、を用いて、前記複数のブロックの中から前記関心領域とするブロックを選出するステップと、
前記関心領域として選出されたブロックの輝度値に基づいて、前記関心領域の輝度値の制御に用いるフィードバック値を算出するステップと、
前記フィードバック値が予め定めた目標輝度値となるように、前記X線の照射条件を決定するステップと、
を含むことを特徴とするX線発生装置の制御方法。
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