JP7192921B2 - Radiation image processing device, scattered radiation correction method and program - Google Patents

Description

The present invention relates to a radiation image processing apparatus, a scattered radiation correction method, and a program.

Conventionally, when taking a radiographic image of a subject using radiation that has passed through the subject, especially if the thickness of the subject is large, the radiation is scattered within the subject and scattered rays are generated. There is a problem that the contrast of the image is lowered. For this reason, when radiographic images are captured, a scattered radiation removal grid (hereinafter simply grid ) may be arranged for shooting. When radiography is performed using the grid, the radiation scattered by the subject is less likely to be irradiated onto the radiation detector, so that the contrast of the radiographic image can be improved. However, using a grid puts a heavy burden on the patient and the work involved in arranging the grid for portable radiography in hospital rooms, etc. Moire patterns corresponding to the pitch of the grid are recorded. there is a problem. Therefore, in order to improve the contrast lowered by the scattered radiation component of the radiation, image processing for correcting the scattered radiation is performed on the radiographic image.

By the way, in the medical field, there is a case where a relatively wide range such as the entire spinal column or the entire lower limb of a human body is photographed. For long-length radiography, for example, a plurality of radiation detectors are placed side by side in a holder of an imaging table for long-length radiography, and radiation is emitted from the radiation generator to the plurality of radiation detectors through the subject. Then, one radiographic image (long image) is acquired by combining the small radiographic images read from each of the plurality of radiation detectors.

In scattered radiation correction, the amount of scattered radiation is estimated for all pixels, and pixel values (pixel signal values) of surrounding pixels are used for estimation of the amount of scattered radiation. Therefore, as shown in FIG. 11, in each small radiographic image that constitutes the long image, scattered radiation can be estimated at pixel A, but when combined as a long image, At the boundary pixel B, the scattered dose cannot be correctly estimated from the pixels within the image area of the small radiation image.

Therefore, for example, in Patent Document 1, it is assumed that the scattered radiation component in the boundary portion of the small radiation images forming the long image is affected by the scattered radiation component included in the adjacent small radiation images, and the scattered radiation amount of the boundary pixel is The use of information from other small radiation images for estimation is described.

JP 2016-32623 A

However, radiation detectors have different radiation detection sensitivities depending on individuals. Therefore, if the amount of scattered radiation is estimated using information from other radiation detectors as described in Patent Document 1, accurate estimation may not be possible, and there is a possibility that a density step will occur after scattered radiation correction.

In addition, even in a radiographic image obtained by imaging using only one radiation detector, for the purpose of increasing the contrast of a certain structure, the removal rate of the scattered dose is increased only in the region of the structure to scatter the radiation. When line correction is performed, a density step occurs at the boundary between that area and another area.

SUMMARY OF THE INVENTION An object of the present invention is to reduce a density step caused by scattered radiation correction.

In order to solve the above problems, the radiation image processing apparatus according to the first aspect of the present invention includes:
Scattered radiation estimation means for estimating the amount of scattered radiation included in the pixel signal value of each pixel of a plurality of radiation images obtained by a plurality of radiation detectors for detecting radiation transmitted through a subject;
determination means for determining a scattered radiation dose to be subtracted from a pixel signal value of each pixel of the radiographic image in scattered radiation correction based on the scattered radiation dose estimated by the scattered radiation estimation means;
Scattered radiation correction means for performing scattered radiation correction on the plurality of radiographic images by subtracting the scattered radiation amount determined by the determining means from the pixel signal value of each pixel;
For the plurality of radiation images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. graininess suppressing means;
density step correction means for correcting a density step between the plurality of radiation images subjected to the scattered radiation correction and the graininess suppression processing based on the sensitivity difference of the plurality of radiation detectors;
Prepare.
Further, the radiographic image processing apparatus according to the second aspect of the present invention includes:
long combining means for generating a long image by combining a plurality of radiation images obtained by a plurality of radiation detectors for detecting radiation transmitted through a subject;
density step correction means for correcting a density step between the plurality of radiographic images forming the long image generated by the long image combining device based on a sensitivity difference between the plurality of radiation detectors;
a dividing unit that divides the long image corrected by the density step correction unit into an arbitrary number of images to generate a plurality of divided images;
Scattered radiation estimation means for estimating a scattered radiation amount included in a pixel signal value of each pixel for each of the plurality of divided images;
determining means for determining a scattered radiation amount to be subtracted from a pixel signal value of each pixel in scattered radiation correction based on the scattered radiation amount estimated by the scattered radiation estimation means for each of the plurality of divided images;
scattered radiation correction means for performing scattered radiation correction by subtracting the determined scattered radiation amount from a pixel signal value of each pixel for each of the plurality of divided images;
For the plurality of divided images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. graininess suppressing means;
recombination means for recombining the plurality of divided images subjected to the scattered radiation correction and the graininess suppression processing;
Prepare.

The scattered radiation correction method of the present invention is
a scattered radiation estimation step of estimating the amount of scattered radiation contained in the pixel signal value of each pixel of a plurality of radiation images obtained by a plurality of radiation detectors that detect radiation transmitted through a subject;
a determination step of determining a scattered radiation dose to be subtracted from a pixel signal value of each pixel of the radiographic image in scattered radiation correction based on the scattered radiation dose estimated in the scattered radiation estimation step;
a scattered radiation correction step of performing scattered radiation correction on the plurality of radiographic images by subtracting the scattered radiation amount determined in the determination step from the pixel signal value of each pixel;
For the plurality of radiation images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. a graininess reduction step;
a density step correction step of correcting a density step between the plurality of radiation images subjected to the scattered radiation correction and the graininess suppression processing based on the sensitivity difference of the plurality of radiation detectors;
including.

The program of the present invention is
Scattered radiation estimation means for estimating the amount of scattered radiation included in the pixel signal value of each pixel of a plurality of radiation images obtained by a plurality of radiation detectors for detecting radiation transmitted through a subject;
determination means for determining a scattered radiation dose to be subtracted from a pixel signal value of each pixel of the radiographic image in scattered radiation correction based on the scattered radiation dose estimated by the scattered radiation estimation means;
Scattered radiation correction means for performing scattered radiation correction on the plurality of radiographic images by subtracting the scattered radiation amount determined by the determining means from the pixel signal value of each pixel;
A computer used in a radiographic image processing apparatus comprising
For the plurality of radiation images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. graininess suppressing means;
Density level difference correction means for correcting density level differences between the plurality of radiation images subjected to the scattered radiation correction and the graininess suppression processing based on the sensitivity difference of the plurality of radiation detectors;
A program to function as

According to the present invention, it is possible to reduce a density step caused by scattered radiation correction.

It is a figure showing the whole composition of the radiographic imaging system in the embodiment of the present invention. 2 is a block diagram showing the functional configuration of the console of FIG. 1; FIG. 3 is a diagram schematically showing the flow of long image generation processing A executed by the control unit of FIG. 2 in the first embodiment; FIG. 3 is a flow chart showing a long image generation process A executed by the control unit of FIG. 2 in the first embodiment; FIG. 5 is a flow chart showing scattered radiation correction processing executed in step S1 of FIG. 4. FIG. FIG. 10 is a diagram schematically showing density step adjustment; FIG. 10 is a diagram schematically showing the flow of long image generation processing B executed by the control unit of FIG. 2 in the second embodiment; FIG. 10 is a flow chart showing a long image generation process B executed by the control unit of FIG. 2 in the second embodiment; FIG. It is a figure which shows an example of the radiographic image applied to 3rd Embodiment. FIG. 10 is a flow chart showing a scattered radiation correction process for each region executed by the control unit of FIG. 2 in the third embodiment; FIG. It is a figure which shows the pixel which can estimate a scattered ray accurately, and the pixel which cannot estimate.

Embodiments of the present invention will be described below with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

<First Embodiment>
[Configuration of radiographic imaging system 100]
First, the configuration of the first embodiment will be described.
FIG. 1 is a diagram showing an example of the overall configuration of a radiation imaging system 100 according to this embodiment. As shown in FIG. 1, the radiation imaging system 100 is configured by connecting an imaging apparatus 1 and a console 2 so that data can be transmitted and received.

The imaging apparatus 1 includes a plurality of radiation detectors P1 to P3 for performing long-length imaging, an imaging table 11 for long-length imaging to which the radiation detectors P1 to P3 can be loaded, and a radiation generator 12. It is configured. The imaging table 11 is designed so that a plurality of radiation detectors P1 to P3 can be loaded in the holder 11a so that they are partially overlapped in the vertical direction.

In the following description, as shown in FIG. 1, the case where the holder 11a of the radiographic stand 11 can be loaded with three radiation detectors will be described. The number of radiation detectors to be loaded in the device is not limited to three, and may be two or four or more.

The radiation detectors P1 to P3 are composed of semiconductor image sensors such as FPDs (Flat Panel Detectors), and are provided so as to face the radiation generator 12 with the subject H interposed therebetween. The radiation detectors P1 to P3 have, for example, a glass substrate or the like, and detect radiation (X-rays) emitted from the radiation generator 12 at predetermined positions on the substrate and transmitted through at least the subject H according to the intensity thereof. A plurality of detection elements (pixels) are arranged in a matrix to detect the radiation by using the detector, convert the detected radiation into an electric signal, and store the electric signal. Each pixel includes a switching unit such as a TFT (Thin Film Transistor). The radiation detectors P1 to P3 control the switching unit of each pixel based on the image reading conditions input from the console 2, and switch the reading of the electric signal accumulated in each pixel. Image data is obtained by reading the accumulated electrical signals. Then, the radiation detectors P1 to P3 attach position information (referred to as panel position information) of the radiation detector that acquired the image data to the acquired image data, and output the acquired image data to the console 2 . The panel position information includes the coordinate position information of the pixels overlapping the adjacent radiation detectors, and the coordinate position of the boundary pixels adjacent to the image data of the other radiation detectors when combined with the image data of the other radiation detectors. Information and positional information of the radiation generator 12 relative to the tube (for example, front, center, back; in FIG. 1, the radiation detector P1 is the back, the radiation detector P2 is the center, and the radiation detector P3 is the front).

The image data obtained from the radiation detectors P1 to P3 are combined to form one long image (radiation image), which is called a small radiation image.

The radiation generator 12 is arranged at a position facing the radiation detectors P1 to P3 with the subject H interposed therebetween, and is loaded into the holder 11a through the patient who is the subject H based on the radiation irradiation conditions input from the console 2. A plurality of radiation detectors P1 to P3 are irradiated with radiation to perform long-length imaging. Radiation irradiation conditions input from the console 2 include, for example, tube current value, tube voltage value, radiation irradiation time, mAs value, SID (shortest distance between the radiation detectors P1 to P3 and the tube of the radiation generator 12 ), etc.

The console 2 outputs radiation irradiation conditions and image reading conditions to the imaging device 1 to control radiation imaging and radiographic image reading operations by the imaging device 1, and performs image processing on small radiation images acquired by the imaging device 1. It functions as a radiographic image processing device that applies radiation.
As shown in FIG. 2, the console 2 includes a control section 21, a storage section 22, an operation section 23, a display section 24, and a communication section 25, which are connected by a bus .

The control unit 21 is configured by a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The CPU of the control unit 21 reads the system program and various processing programs stored in the storage unit 22 according to the operation of the operation unit 23, expands them in the RAM, and operates each unit of the console 2 according to the expanded programs. Also, it centrally controls the radiation irradiation operation and the reading operation of the imaging device 1 . Also, using the small radiographic images transmitted from the radiation detectors P1 to P3 of the imaging apparatus 1, a long image generation process A and the like, which will be described later, is executed.
The control unit 21 functions as scattered radiation estimation means, determination means, scattered radiation correction means, density step estimation means, adjustment means, and acquisition means.

The storage unit 22 is configured by a nonvolatile semiconductor memory, hard disk, or the like. The storage unit 22 stores various programs executed by the control unit 21, parameters necessary for executing processing by the programs, or data such as processing results. Various programs are stored in the form of readable program codes, and the control unit 21 sequentially executes operations according to the program codes.
The storage unit 22 also stores radiation irradiation conditions and image reading conditions corresponding to imaging regions. Further, the storage unit 22 stores radiographing order information transmitted from an unillustrated RIS (Radiology Information System) or the like. The imaging order information includes patient information and examination information (examination ID, imaging site, examination date, etc.). The imaging region may be the imaging region of the entire long image, or may be the imaging region of each image obtained by the radiation detectors P1 to P3.

In addition, the storage unit 22 stores, for each tube voltage, obtained from an experiment in which an acrylic plate of various thicknesses (which has a similar X-ray attenuation factor to the human body) is photographed with a predetermined mAs value and SID by changing the tube voltage. , and the mAs value and SID used in the experiment are stored. The storage unit 22 also stores a table showing the relationship between the body thickness and the scattered radiation content rate for each imaging region, which is obtained in advance by experiment.

The operation unit 23 includes a keyboard having cursor keys, numeric input keys, various function keys, etc., and a pointing device such as a mouse. 21. Further, the operation unit 23 may have a touch panel on the display screen of the display unit 24 , and in this case, outputs an instruction signal input through the touch panel to the control unit 21 . Furthermore, the operation unit 23 is provided with an exposure switch for instructing the radiation generator 12 to perform dynamic imaging.

The display unit 24 is configured by a monitor such as an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube), and displays input instructions, data, etc. from the operation unit 23 according to instructions of display signals input from the control unit 21. do.

The communication unit 25 has an interface for transmitting and receiving data with the radiation generator 12 and the radiation detectors P1 to P3. Communication between the console 2, the radiation generator 12, and the radiation detectors P1 to P3 may be wired or wireless.
The communication unit 25 includes a LAN adapter, a modem, a TA (Terminal Adapter), etc., and controls data transmission/reception with a RIS (not shown) connected to a communication network.

[Operation of radiation imaging system 100]
With the radiation detectors P1 to P3 set in the holder 11a of the imaging apparatus 1, when the imaging order information of the imaging target is selected by the operation unit 23 on the console 2, imaging conditions corresponding to the selected imaging order information are set. (Radiation irradiation conditions and radiation image reading conditions) are transmitted to the imaging device 1 . When the subject H is positioned and the exposure switch is pressed, radiation is emitted from the radiation generator 12 in the imaging device 1, and image data of the radiation image is read by the radiation detectors P1 to P3, respectively. Panel position information is attached to the read image data (that is, the small radiation image) and transmitted to the console 2 .

When the small radiographic images are received from the radiation detectors P1 to P3, the control unit 21 of the console 2 executes a long image generation process A. FIG. FIG. 3 is a diagram schematically showing the flow of long image generation processing A, and FIG. 4 is a flowchart showing the flow of long image generation processing A. As shown in FIG. The long image generation process A is executed by cooperation between the control unit 21 and a program stored in the storage unit 22 .

First, the control unit 21 performs scattered radiation correction processing on each of the small radiation images received from the radiation detectors P1 to P3 (step S1).

FIG. 5 is a flowchart showing the flow of scattered radiation correction processing.
In the scattered radiation correction process, the control unit 21 first acquires the information on the imaging conditions and the imaging region based on the imaging order information used for imaging, and also acquires the panel position information attached to the small radiation image ( step S101).

Next, the control unit 21 estimates the amount of scattered radiation for each pixel of the small region image based on the acquired imaging conditions, imaging region, and panel position information (step S102).
In step S102, the amount of scattered radiation for each pixel is estimated by the following processes (1) to (4).
Here, in order to estimate the body thickness of (1), an acrylic plate of various thicknesses (which has a similar X-ray attenuation rate to the human body) was prepared by changing the tube voltage and using a predetermined mAs value and SID. ) is photographed, the relational expression between the pixel value obtained in the experiment and the acrylic thickness (the following (Equation 1)) is calculated, and the mAs value, SID, and tube voltage used in the experiment (Equation 1) are stored in the storage unit 22 .
Acrylic thickness = Coefficient A x log (pixel value) + Coefficient B (Formula 1)
Further, the storage unit 22 stores in advance a table showing the relationship between the body thickness and the scattered radiation content rate for each imaging region.

(1) Estimating Body Thickness Based on Imaging Conditions and Panel Position Information First, the SID of the acquired imaging conditions is corrected based on the panel position information. For example, when the position information for the tube of the radiation generator 12 included in the panel position information of the small radiation image is "center", the SID stored in the storage unit 22 is the thickness of the radiation detectors 1P to 3P. Add some α. If the panel position information of the image data is "rear", 2α is added to the SID stored in the storage unit 22 . As a result, an accurate SID can be obtained according to the position of the radiation detector, and a density step due to a scattered radiation correction error due to a difference in imaging distance for each radiation detector can be reduced.
Next, the pixel value p_1 of the small radiographic image acquired by imaging is converted into the pixel value p_0 when imaged under the imaging conditions of the above experiment by the following (Equation 2).
p_0 = p_1 x (mAs_1/mAs_0) x {(SID_0) ² /(SID_1) ² } (Formula 2)
Here, mAs_0 is the mAs value used in the experiment, mAs_1 is the mAs value used in the actual imaging, SID_0 is the SID used in the experiment, and SID_1 is the SID (corrected SID) used in the actual imaging. (Formula 2) is based on the knowledge that the pixel value of the image data obtained by the radiation detector is proportional to the mAs value and inversely proportional to the SID.
Next, the converted pixel value p_0 is substituted into (Equation 1), and the obtained acrylic thickness is estimated as the body thickness.

(2) Estimating the scattered radiation content rate from the body thickness Based on the table showing the relationship between the body thickness and the scattered radiation content rate according to the imaging site stored in the storage unit 22, the calculated in (1) The scattered radiation content is estimated from the body thickness.

(3) Extract the low-frequency component of the small radiographic image to generate a low-frequency component image Extract the ingredients. For example, if each pixel of the small radiographic image is affected by scattered rays generated from an area of n pixels×n pixels (where n is a positive integer) around the pixel (target pixel), A low-frequency component image is generated by performing filter processing for each pixel using a filter of n pixels×n pixels centered on that pixel.
Note that, when a long image is formed, there are cases where the surrounding n pixels×n pixels do not all exist within the small radiation area with respect to the boundary pixels adjacent to other small radiation images and the pixels in the vicinity thereof. In this case, the pixel value of the corresponding pixel is estimated as the pixel value of the closest pixel in the small radiation image.

(4) Estimate the amount of scattered radiation for each pixel from the pixel value of the low-frequency component image.
The amount of scattered radiation is estimated by multiplying the pixel value of the low-frequency component image by the content of scattered radiation.

Next, based on the estimated scattered radiation dose, the control unit 21 determines the scattered radiation dose to be removed from each pixel of the small radiation image (subtracted from the pixel value of each pixel) by scattered radiation correction (step S103).
For example, the scattered radiation dose to be removed is determined by multiplying the scattered radiation dose estimated for each pixel by a predetermined scattered radiation removal rate.

Next, the control unit 21 estimates the density step after the scattered radiation correction of the boundary pixels between other small radiographic images that will be adjacent when combined as a long image (step S104).
For example, the value obtained by subtracting the amount of scattered radiation to be removed from the pixel value of the boundary pixel of the small radiographic image is compared with the value obtained by subtracting the amount of scattered radiation to be removed from the pixel value of the boundary pixel of another adjacent small radiographic image to determine the density. Estimate steps.
For example, as shown in FIG. 6, the pixel value of pixel B1, which is the boundary pixel of the small radiographic image obtained by radiation detector P1, is 500, the amount of scattered radiation to be removed is 200, and the amount of scattered radiation to be removed is 200. When the pixel value of the pixel B2 adjacent to the pixel B1 of the small radiation image is 600 and the amount of scattered radiation to be removed is 250, the pixel value (density value) after the scattered radiation correction of the pixel B1 is 300, and the scattered radiation correction of the pixel B2 is 300. The subsequent pixel value (density value) is 350, and the density difference between the pixel B1 and the pixel B2 is estimated to be 50 after the scattered radiation correction.

Next, the control unit 21 adjusts the pixel value of the boundary pixel in the scattered radiation correction so that the density difference between the boundary pixel of the small radiation image after the scattered radiation correction and the adjacent boundary pixels of the other small radiation images becomes 0. to adjust the amount of scattered radiation to be subtracted from (step S105).
For example, in the case of the pixel B1 and the pixel B2 shown in FIG. 6, the amount of scattered radiation to be removed (subtracted) from the pixel B1 is set to 200 so that the pixel values after the scattered radiation correction of the pixel B1 and the pixel B2 are both 325. −25=175, and the scattered dose to be removed from pixel B2 is 250+25=275
adjust to

In step S105, the amount of scattered radiation to be subtracted may also be changed for a plurality of pixels within a predetermined range from the boundary pixel so that the density near the boundary changes stepwise smoothly.
In addition, the irradiation field recognition and the direct X-ray region recognition are performed on the small radiation image in advance, and the processing time is shortened by removing these regions outside the subject from the processing target region of the density step adjustment in steps S104 and S105. good too.

Then, the control unit 21 performs scattered radiation correction by subtracting the determined scattered radiation dose (the adjusted scattered radiation dose for the boundary pixels) from the pixel value of each pixel of the small radiation image (step S106). The radiographic image is subjected to graininess reduction processing (step S107), and the process proceeds to step S2 in FIG.

Here, in the present embodiment, the circuit board portion of the radiation detector P2 overlaps the coupling portion of the radiation detector P1 with the radiation detector P2. Therefore, the circuit board of the radiation detector P2 is reflected in a predetermined area of the small radiation image transmitted from the radiation detector P1. The area where the circuit board is reflected has poor graininess. Therefore, in the graininess reduction process, it is preferable to change the graininess reduction level between the circuit board portion and the other regions in the small radiographic image based on the panel position information. Alternatively, the magnitude of noise may be estimated based on the variance or standard deviation of pixel values, and the graininess suppression level may be changed based on the estimated magnitude of noise.

At step S2 in FIG. 4, the control unit 21 executes long-length combining processing for combining a plurality of small radiation images (step S2).
In step S2, first, based on the panel position information, a plurality of small radiation images corrected for scattered radiation are combined to generate a long image. Density steps between the combined radiographic images are then corrected. For example, since the radiation detectors P1 to P3 have different sensitivities, a difference in density between small radiation images caused by the difference in sensitivity is corrected. In addition, it corrects the density difference caused by the positional relationship of the radiation detectors P1 to P3. For example, since a radiation detector closer to the tube reduces the amount of radiation reaching the radiation detector behind the tube, the density value corresponding to the reduced amount of radiation reaching the radiation detector behind the tube is the pixel value. add to In addition, if there is reflection of the board portion of the radiation detector that overlaps in front, it is corrected.
When the long image combining process ends, the control unit 21 ends the long image generation process A. FIG.

Thus, in the first embodiment, the control unit 21 estimates the scattered dose included in the pixel value of each pixel of a plurality of small radiation images, and calculates the scattered dose to be subtracted from the pixel value based on the estimated scattered dose. is determined, and the density step that occurs when subtracting the determined scattered dose from the pixel value by scattered radiation correction at the boundary pixels of a plurality of small radiation images that are adjacent to each other when combined as a long image is estimated. The amount of scattered radiation to be subtracted from the pixel value of the boundary pixel in the scattered radiation correction is adjusted so that the resulting density step becomes zero. Then, after performing scattered radiation correction on the plurality of small radiographic images using the determined or adjusted scattered dose, the plurality of small radiographic images are combined to generate a long image. Therefore, it is possible to reduce density steps at the boundaries of a plurality of small radiographic images caused by scattered radiation correction in a long image.

<Second embodiment>
Next, a second embodiment of the invention will be described.
In the first embodiment, as shown in FIG. 3, a plurality of small radiation images obtained by the radiation detectors P1 to P3 are subjected to scattered radiation correction processing, and then long-length combining processing is performed and combined. However, in the second embodiment, as shown in FIG. 7, first, a plurality of small radiographic images obtained by the radiation detectors P1 to P3 are subjected to long-length combining processing and then combined. A case will be described in which the combined long image is divided into an arbitrary number of locations, the scattered radiation correction process is executed, and then the divided images are recombined. The second embodiment divides a long image into a number that can be parallel-computed and performs parallel processing of scattered radiation correction processing when it is desired to divide an image at an inconspicuous density step or when parallel calculation of scattered radiation correction processing is possible. This embodiment assumes a case where it is desired to increase the processing speed by performing

Since the configuration and shooting operation of the second embodiment are the same as those described in the first embodiment, the description is incorporated, and the operation of the console 2 in the second embodiment will be described below.

When the image data is received from the radiation detectors P1 to P3, in the console 2, the long image generation process B is executed by the controller 21. FIG. FIG. 8 is a flow chart showing the flow of long image generation processing B. As shown in FIG. The long image generation process B is executed by cooperation between the control unit 21 and a program stored in the storage unit 22 .

First, the control unit 21 executes long image combining processing to generate a long image (step S11).
In step S11, first, based on the panel position information, a long image is generated by combining a plurality of small radiation images. Density steps between the combined radiographic images are then corrected. For example, since the radiation detectors P1 to P3 have different sensitivities, a difference in density between small radiation images caused by the difference in sensitivity is corrected. In addition, it corrects the density difference caused by the positional relationship of the radiation detectors P1 to P3. For example, since a radiation detector closer to the tube reduces the amount of radiation reaching the radiation detector behind the tube, the density value corresponding to the reduced amount of radiation reaching the radiation detector behind the tube is the pixel value. add to In addition, if there is reflection of the board portion of the radiation detector that overlaps in front, it is corrected.

Next, the long image generated in step S11 is divided to generate a plurality of divided images (step S12).
The user can arbitrarily designate the division position and division number of the long image using the operation unit 23 .

Next, the control unit 21 performs scattered radiation correction processing on each of the plurality of divided images (step S13).
In step S13, the process described with reference to FIG. 5 in the first embodiment is executed for each of the plurality of divided images. However, in step S104, if the divided image includes image regions of a plurality of small radiation images, the density difference after scattered radiation correction between the boundary pixels of the image regions of the plurality of small radiation images included in the divided image. to estimate In step S105, the amount of scattered radiation to be subtracted from the pixel value of the boundary pixel in the scattered radiation correction is adjusted so that the density difference between the boundary pixels of the plurality of small radiation images in the divided image after the scattered radiation correction becomes 0. .

When the scattered radiation correction process ends, the control unit 21 recombines the divided images after the scattered radiation correction (step S14), and ends the long image generation process B. FIG.

As described above, in the second embodiment, the control unit 21 generates a plurality of divided images by image-dividing a long image obtained by combining and combining a plurality of small radiographic images at arbitrary positions, and generates a plurality of divided images. For each of the images, the scattered dose included in the pixel value of each pixel is estimated, the scattered dose to be subtracted from the pixel value is determined based on the estimated scattered dose, and a plurality of small radiation images included in the divided image. Estimate the density difference that occurs when the determined scattered radiation amount at the boundary pixel is subtracted from the pixel value, and adjust the scattered radiation amount to be subtracted from the pixel value of the boundary pixel in the scattered radiation correction so that the estimated density difference becomes 0. do. Then, after performing scattered radiation correction on the divided images using the determined or adjusted scattered radiation dose, the plurality of divided images are recombined. Therefore, it is possible to reduce the density step at the boundary portion of a plurality of small radiographic images caused by the scattered radiation correction in the long image. In addition, it is possible to divide a long image into any number of locations and perform scattered radiation correction processing. It is possible to increase the processing speed by dividing the long image into a computable number.

<Third Embodiment>
Next, a third embodiment of the invention will be described.
When it is desired to increase the contrast of a certain portion (for example, a specific structure) in a single radiographic image, the contrast can be increased by setting the scattered radiation removal rate higher for that portion than for other regions (Fig. 9 inside the rectangle). However, in this case, a difference in density occurs after scattered radiation correction between the portion where the scattered radiation removal rate is increased and the other region.
Therefore, in the third embodiment, an example of reducing the density difference caused by the difference in the scattered radiation removal rate in one radiographic image will be described.

In the first embodiment, three radiation detectors P1 to P3 are used to acquire three small radiographic images. A radiation detector P can be attached. Since other configurations are the same as those described in the first embodiment, the description is incorporated, and the operation in the third embodiment will be described below.

With the radiation detector P set on the holder 11a of the imaging apparatus 1, when the imaging order information of the imaging target is selected by the operation unit 23 on the console 2, imaging conditions (radiation irradiation conditions and radiation image reading conditions) are transmitted to the imaging device 1 . When the subject H is positioned and the exposure switch is pressed, radiation is emitted from the radiation generator 12 in the imaging apparatus 1, a radiation image is read by the radiation detector P, and the read radiation image is displayed on the console. 2.

When a radiographic image is received from the radiation detector P, in the console 2 , the control unit 21 executes region-based scattered radiation correction processing. FIG. 10 is a flow chart showing the flow of the scattered radiation correction process for each area. The scattered radiation correction process for each area is executed by cooperation between the control unit 21 and the program stored in the storage unit 22 .

First, the control unit 21 performs area recognition processing on the received radiation image (step S21). Here, an area of a predetermined specific structure is recognized. For example, the area recognition may be automatically performed by image analysis, or the user may designate the area from the image displayed on the display unit 24 using the operation unit 23 .

Next, the control unit 21 divides the received radiographic image into a plurality of image regions based on the result of the region recognition (step S22).
For example, the received radiographic image is divided into a region of a recognized specific structure and other regions.

Next, the control unit 21 acquires information on the imaging conditions and imaging regions based on the imaging order information used for imaging, and estimates the scattered dose for each pixel of the radiographic image based on the acquired imaging conditions and imaging regions. (step S23). The processing of step S23 is the same as the processing performed on the small radiation area in step S102 of FIG. 5 in the first embodiment, so the description is cited.

Next, the control unit 21 sets the scattered radiation removal rate for each divided image region, and removes the scattered radiation from each pixel of the radiographic image based on the estimated scattered radiation dose and the set scattered radiation removal rate for each pixel ( The amount of scattered radiation to be subtracted from the pixel value of each pixel is determined (step S24).
For example, for example, an input of the scattered radiation removal rate (0% to 100%) of the region of the specific structure recognized by the operation of the operation unit 23 by the user is received, and the input scattered radiation removal for the region of the specific structure For other regions, a predetermined scattered radiation removal rate is set. Then, the scattered radiation dose to be removed is determined by multiplying the scattered radiation dose estimated for each pixel by the set scattered radiation removal rate.

Next, the control unit 21 estimates density steps after the scattered radiation correction at boundary pixels of a plurality of image regions adjacent to each other (step S25).
In step S25, a value obtained by subtracting the amount of scattered radiation to be removed from the pixel value of the boundary pixel in the image area of the specific structure, and a value obtained by subtracting the amount of scattered radiation to be removed from the pixel value of the boundary pixel of another adjacent image area. are compared to estimate the density difference (see FIG. 6).

Next, the control unit 21 adjusts the amount of scattered radiation to be subtracted by the scattered radiation correction so that the density difference between the boundary pixels after the scattered radiation correction becomes 0 (step S26).

In the processing of step S26, the amount of scattered radiation to be subtracted may be changed so that the density near the boundary portion smoothly changes step by step for a plurality of pixels within a predetermined range from the boundary pixel.
Alternatively, irradiation field recognition and direct X-ray area recognition may be performed in advance, and these areas outside the subject may be excluded from the process target areas for density step adjustment in steps S25 and S26, thereby shortening the processing time.

Then, the determined scattered radiation amount (the adjusted scattered radiation amount for the boundary pixels) is subtracted from the pixel value of each pixel of the radiographic image to correct the scattered radiation (step S27), and graininess suppression processing is performed on the radiographic image after the scattered radiation correction. (step S28), and the scattered radiation correction process for each area ends.

Thus, in the third embodiment, the control unit 21 divides the radiographic image into a plurality of image regions, sets the scattered radiation removal rate for each divided region, and adjusts the estimated scattered radiation dose for each pixel. Density generated when the amount of scattered radiation to be subtracted from the pixel value is determined by multiplying the set scattered radiation removal rate, and the determined scattered radiation amount is subtracted from the pixel value by scattered radiation correction at the boundary pixels of multiple image areas. A level difference is estimated, and the amount of scattered radiation to be subtracted from the pixel value of the boundary pixel in the scattered radiation correction is adjusted so that the estimated density level difference becomes zero. Then, the radiographic image is subjected to scattered radiation correction using the determined or adjusted scattered radiation dose. Therefore, when the scattered radiation removal rate is changed depending on the image area in the radiographic image, it is possible to reduce the density difference caused by the difference in the scattered radiation removal rate in the radiographic image.

As described above, the control unit 21 of the console 2 estimates the scattered radiation dose included in the pixel value of each pixel of the radiographic image obtained by radiography of the subject, and scatters radiation based on the estimated scattered radiation dose. Determine the amount of scattered radiation to be subtracted from the pixel values of the boundary pixels of multiple image areas in the radiographic image in the line correction, and estimate the density step that occurs when the determined scattered radiation amount is subtracted from the pixel values of the boundary pixels of the multiple image areas. Then, the amount of scattered radiation to be subtracted from the pixel value of the boundary pixel is adjusted so that the estimated density step becomes zero. Then, the radiographic image is subjected to scattered radiation correction using the adjusted scattered radiation dose. Therefore, it is possible to reduce the density difference caused by the scattered radiation correction in the radiographic image.

It should be noted that the description in the above embodiment is a preferred example of the present invention, and the present invention is not limited to this.

For example, in the above embodiment, the case where the present invention is applied to a radiographic image of the chest has been described as an example, but the present invention may be applied to a radiographic image of another region.

Further, in the above embodiment, the console 2 that controls the imaging device 1 has a function as a radiation image processing device, but the radiation image processing device may be separate from the console.

Further, in the above embodiment, as a preferable example, the density difference is reduced to 0, but the present invention is not limited to this.

Further, for example, in the above description, an example using a hard disk, a semiconductor non-volatile memory, or the like is disclosed as a computer-readable medium for the program according to the present invention, but the present invention is not limited to this example. As another computer-readable medium, a portable recording medium such as a CD-ROM can be applied. A carrier wave is also applied as a medium for providing program data according to the present invention via a communication line.

In addition, the detailed configuration and detailed operation of each device that constitutes the radiographic imaging system can be changed as appropriate without departing from the gist of the present invention.

100 Radiation imaging system 1 Imaging device 11 Imaging table 11a Holder 12 Radiation generators P1 to P3 Radiation detector 2 Console 21 Control unit 22 Storage unit 23 Operation unit 24 Display unit 25 Communication unit 26 Bus

Claims (6)

Scattered radiation estimation means for estimating the amount of scattered radiation included in the pixel signal value of each pixel of a plurality of radiation images obtained by a plurality of radiation detectors for detecting radiation transmitted through a subject;
determination means for determining a scattered radiation dose to be subtracted from a pixel signal value of each pixel of the radiographic image in scattered radiation correction based on the scattered radiation dose estimated by the scattered radiation estimation means;
Scattered radiation correction means for performing scattered radiation correction on the plurality of radiographic images by subtracting the scattered radiation amount determined by the determining means from the pixel signal value of each pixel;
For the plurality of radiation images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. graininess suppressing means;
density step correction means for correcting a density step between the plurality of radiation images subjected to the scattered radiation correction and the graininess suppression processing based on the sensitivity difference of the plurality of radiation detectors;
A radiation image processing device comprising: long combining means for combining the plurality of radiation images corrected by the scattered radiation correction means to generate a long image;
2. The radiographic image processing apparatus according to claim 1 , wherein said density step correction means corrects density steps of said plurality of radiographic images forming the long image generated by said long image combining means. long combining means for generating a long image by combining a plurality of radiation images obtained by a plurality of radiation detectors for detecting radiation transmitted through a subject;
density step correction means for correcting a density step between the plurality of radiographic images forming the long image generated by the long image combining device based on a sensitivity difference between the plurality of radiation detectors;
a dividing unit that divides the long image corrected by the density step correction unit into an arbitrary number of images to generate a plurality of divided images;
Scattered radiation estimation means for estimating a scattered radiation amount included in a pixel signal value of each pixel for each of the plurality of divided images;
determining means for determining a scattered radiation amount to be subtracted from a pixel signal value of each pixel in scattered radiation correction based on the scattered radiation amount estimated by the scattered radiation estimation means for each of the plurality of divided images;
scattered radiation correction means for performing scattered radiation correction by subtracting the determined scattered radiation amount from a pixel signal value of each pixel for each of the plurality of divided images;
For the plurality of divided images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. graininess suppressing means;
recombination means for recombining the plurality of divided images subjected to the scattered radiation correction and the graininess suppression processing;
A radiation image processing device comprising: 4. The radiation image processing apparatus according to claim 1 , wherein said density step correction means further corrects a density step between said radiation images based on the positional relationship of said plurality of radiation detectors. a scattered radiation estimation step of estimating the amount of scattered radiation contained in the pixel signal value of each pixel of a plurality of radiation images obtained by a plurality of radiation detectors that detect radiation transmitted through a subject;
a determination step of determining a scattered radiation dose to be subtracted from a pixel signal value of each pixel of the radiographic image in scattered radiation correction based on the scattered radiation dose estimated in the scattered radiation estimation step;
a scattered radiation correction step of performing scattered radiation correction on the plurality of radiographic images by subtracting the scattered radiation amount determined in the determination step from the pixel signal value of each pixel;
For the plurality of radiation images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. a graininess reduction step;
a density step correction step of correcting a density step between the plurality of radiation images subjected to the scattered radiation correction and the graininess suppression processing based on the sensitivity difference of the plurality of radiation detectors;
Scatter correction method including. Scattered radiation estimation means for estimating the amount of scattered radiation included in the pixel signal value of each pixel of a plurality of radiation images obtained by a plurality of radiation detectors for detecting radiation transmitted through a subject;
determination means for determining a scattered radiation dose to be subtracted from a pixel signal value of each pixel of the radiographic image in scattered radiation correction based on the scattered radiation dose estimated by the scattered radiation estimation means;
Scattered radiation correction means for performing scattered radiation correction on the plurality of radiographic images by subtracting the scattered radiation amount determined by the determining means from the pixel signal value of each pixel;
A computer used in a radiographic image processing apparatus comprising
For the plurality of radiation images subjected to the scattered radiation correction, graininess suppression processing is performed by varying graininess suppression levels between the area where the circuit board of the radiation detector overlaps and the other area. graininess suppressing means;
Density level difference correction means for correcting density level differences between the plurality of radiation images subjected to the scattered radiation correction and the graininess suppression processing based on the sensitivity difference of the plurality of radiation detectors;
A program to function as

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