JP2016131805A - X-ray image diagnostic apparatus and method for creating x-ray image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the image quality of a picked-up image when a grid is not used by accurately correcting a scattered radiation component that changes in a subject.SOLUTION: An X-ray diagnostic apparatus includes an X-ray tube for radiating X-rays to a subject, an X-ray plane detector for detecting transmitted C-rays of the subject arranged facing the X-ray tube, and an image processing unit for creating an X-ray image on the basis of image data outputted from the X-ray plane detector. The image processing unit performs positioning correction of scattered radiation original data acquired in advance by using a phantom simulating the subject to the image data, and creates scattered radiation data.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an X-ray image diagnostic apparatus, and more particularly to image correction of scattered radiation components when imaged in a gridless manner.

The X-ray diagnostic imaging apparatus obtains an image of a subject by irradiating the subject with X-rays and detecting the X-ray transmitted through the subject with an X-ray flat panel detector. Here, the X-rays detected by the detector include X-rays scattered by the subject (scattered rays) in addition to the X-rays transmitted through the subject. Such scattered radiation causes a reduction in the image quality of the X-ray image. In the conventional X-ray flat detector, a scattered radiation removal grid (hereinafter referred to as “grid”) is arranged on the X-ray incident surface side of the detector to prevent the scattered radiation from entering the detector.
However, when a grid is used, the labor for mounting the grid increases. In addition, there is a problem that the X-ray dose to be irradiated is increased compared to when the grid is not used and the exposure amount of the subject increases. For this reason, a technique has been proposed in which imaging is performed without using a grid (gridless imaging) and the influence of scattered radiation is removed by image processing.

  For example, Patent Document 1 discloses that a scattered radiation is detected by using a phantom containing water and the thickness of which is changed, and a table showing the distribution of the scattered radiation is created. A technique for correcting the above is disclosed.

International Publication WO2011 / 058612

In the scattered radiation correction described in Patent Document 1, the object to be captured (water phantom) for acquiring scattered radiation data is uniform, and the scattered radiation data created by using the scattered radiation data varies within the actual subject. Does not accurately reflect the line component. For this reason, when such scattered radiation data is used, it may not be possible to correct accurately.
SUMMARY OF THE INVENTION An object of the present invention is to accurately correct a scattered ray component that changes in a subject to improve the image quality of a captured image when a grid is not used in order to solve the above-described problems.

  In order to achieve the above object, the present invention acquires scattered radiation data (hereinafter referred to as “scattered radiation source data”) in advance using a phantom simulating a subject, and processes the scattered radiation source data according to the subject. Then, scattered radiation is removed from the captured image. That is, the X-ray diagnostic imaging apparatus of the present invention includes an X-ray tube that irradiates a subject with X-rays, an X-ray flat panel detector that is disposed opposite to the X-ray tube and detects a transmitted X-ray of the subject, and an X-ray An image processing unit that creates an X-ray image based on image data output from the flat detector. The image processing unit includes a scattered radiation data correction unit that creates a scattered radiation data by aligning and correcting the scattered radiation source data acquired in advance using a phantom simulating a subject with respect to the image data.

  In the method of creating an X-ray image obtained by removing scattered radiation data from captured image data according to the present invention, the scattered radiation source data acquired in advance using a phantom simulating a subject is aligned with the captured image data. And a step of performing thickness correction for correcting the aligned scattered radiation data in accordance with the thickness of the subject. The step of aligning includes a process of enlarging / reducing the position of the scattered radiation source data according to the image data. The step of correcting the thickness includes a process (first thickness correction) for increasing / decreasing the value of the scattered radiation data subjected to the alignment.

  According to the present invention, it is possible to accurately correct the scattered radiation component that changes in the subject and improve the image quality of the captured image when the grid is not used.

The figure which shows schematic structure of the X-ray-image diagnostic apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows an example of the method of acquiring the scattered radiation original data of embodiment, Comprising: (a) shows the case where data is acquired without using a grid, (a) when acquiring data using a grid. . A flowchart showing a flow of processing according to the embodiment The flowchart which shows the flow of the alignment process of embodiment It is a figure explaining the content of the alignment process of embodiment, (a) And (b) shows the scattered radiation data map of the chest front, (c) shows the picked-up image of the front of the subject's chest, FIG. 5D shows a diagram in which lung field regions are extracted from the image of FIG. 5C, and FIG. 5E shows a diagram for explaining the contents of the enlargement / reduction processing of the lung field processing. Histogram of subject area (A) is a figure explaining the alignment when the pixel value of scattered radiation source data is uniform, (b) is the figure explaining the alignment when the pixel value of scattered radiation source data has an inclination. is there. The flowchart which shows the flow of the process which concerns on thickness correction of embodiment Diagram showing the relationship between the dose rate and the correction factor for scattered radiation data The figure which shows the relationship between the ratio of the lung field maximum value and the diaphragm minimum value and the correction coefficient of the scattered radiation data (A) and (c) show the cases where subtraction processing is not performed using the corrected scattered radiation data acquired from the embodiment in the X-ray image of the thoracic vertebra, and (b) and (d) are (a). The case where the subtraction process of (c) is performed is shown.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, components having the same function are given the same reference numerals, and repeated description thereof is omitted. First, a schematic configuration of the X-ray image diagnostic apparatus according to the present embodiment will be described with reference to FIG.

  An X-ray diagnostic imaging apparatus 11 in FIG. 1 includes an X-ray tube 1 that irradiates a subject 0 with X-rays, and an X-ray flat panel detector 2 that is disposed opposite to the X-ray tube 1 and detects transmitted X-rays of the subject 0. And an image processing unit 10 that creates an X-ray image based on the image data output from the X-ray plane detector 2, and an image display device 3 that displays an image processed by the image processing unit 10. Prepare.

  The image processing unit 10 includes an image storage unit 4 that stores image data of the subject 0 output from the X-ray flat panel detector 2, a scattered radiation data storage unit 5 that stores previously acquired scattered radiation source data, and an image storage. The scattered radiation data correction section 6 that corrects the scattered radiation source data stored in the scattered radiation data storage section 5 using the image data stored in the section 4 and the scattered radiation data correction section 6 are corrected. A scattered radiation removing unit 7 for removing the scattered radiation data from the image data.

Each unit of the image processing unit 10 can be composed of a CPU and a memory. The memory stores in advance a program for executing the function of each unit, and the CPU reads and executes the program in the memory. As a result, the operation of each part can be realized.
For example, a program shown in the flow of FIG. 3 and the like is stored in advance in the memory. When the CPU reads and executes this program, the operations of the scattered radiation data correction unit 6 and the scattered radiation removal unit 7 are realized.

  Note that the processing procedures such as the scattered radiation data correction unit 6 and the scattered radiation removal unit 7 may be implemented by hardware such as ASIC or FPGA instead of being implemented as software.

  An outline of the operation of the X-ray image diagnostic apparatus 11 of FIG. 1 will be described. First, according to a predetermined X-ray condition, the subject 0 is irradiated with X-rays from the X-ray tube 1, and the X-ray plane detector 2 detects transmitted X-rays of the subject 0. The image storage unit 4 stores image data output from the X-ray flat panel detector 2 (hereinafter referred to as “subject image data”). The scattered radiation data storage unit 5 stores scattered radiation source data acquired in advance using a phantom. The scattered radiation data correction unit 6 corrects the scattered radiation source data using the subject image data, and the scattered radiation removal unit 7 uses the corrected scattered radiation data obtained by the scattered radiation data correction unit 6 as subject image data. Remove from. The image display device 3 displays the subject image data after the removal process.

  The main feature of this embodiment is that the scattered radiation data correction unit 6 of the image processing unit 10 corrects the scattered radiation source data. First, acquisition of scattered radiation source data will be described with reference to FIG.

The scattered radiation source data is acquired in advance using the phantom 20 separately from the subject to be imaged. The phantom 20 can be a phantom that simulates a subject (human body).
For such a phantom, a soft tissue equivalent material and a bone equivalent material having an X-ray absorption rate equivalent to that of a living body are used, and a heart, a liver, a kidney, a main lung blood vessel, and the like are arranged. Therefore, unlike the phantom using water etc., scattered radiation information close to the human body can be obtained.

  As the phantom 20, a full-body phantom of an adult or a child or a phantom created for each part such as a chest can be used, and a commercially available one can be obtained.

  The scattered radiation data acquired using such a phantom 20 is used as scattered radiation source data. At this time, in consideration of the fact that the trunk (eg, chest, abdomen, waist) generates more scattered rays than the extremities (eg, hands, feet), the scattered radiation source data for each part such as the chest is acquired in advance. It is preferable to keep it. Alternatively, whole body scattered radiation source data may be acquired in advance, and may be divided and applied as appropriate for each imaging region.

As a method for acquiring scattered radiation source data, first, as shown in FIG. 2A, a predetermined X-ray condition is used in a state where a grid 21 is mounted on the X-ray incident surface side of the X-ray flat detector 2. The phantom 20 is imaged. In this case, the scattered radiation 23 is removed by the grid 21, the transmitted X-ray 22 is detected by the X-ray flat panel detector 2, and image data A that does not include the scattered radiation 23 is acquired. Next, as shown in FIG. 2B, the phantom 20 is imaged under the same X-ray conditions without using the grid 21. The X-ray flat detector 2 detects the scattered radiation 23 and the transmitted X-ray 22 and acquires image data B including the scattered radiation. By removing image data A from image data B, scattered radiation source data is obtained.
The obtained scattered radiation source data is stored in the scattered radiation data storage unit 5 and used for alignment correction described later.

  Next, the operation of each unit of the image processing unit 10 will be described with reference to FIGS.

  First, the overall flow of the processing of the image processing unit 10 will be described with reference to FIG. 3, and the alignment correction performed by the scattered radiation data correction unit 6 with reference to FIGS. 4 to 7 will be described with reference to FIGS. 8 to 10. The operation of the thickness correction performed by the scattered radiation data correction unit 6 will be described in detail.

  FIG. 3 is a flowchart showing an outline of processing related to the image processing unit 10.

(Step S30)
The scattered radiation data correction unit 6 reads the scattered radiation source data stored in the scattered radiation data storage unit 5 for each part, and generates a scattered radiation data map (two-dimensional data). In the present embodiment, as an example, scattered radiation source data of the front of the chest is read and used as a scattered radiation data map (S30).

(Step S31)
Since the size of the organ etc. in the subject (for example, lung field) varies depending on the subject, the correction is made so that the position of the organ etc. in the scattered radiation source data obtained from the phantom matches the location of the corresponding organ etc. in the subject. I do.
Therefore, the scattered radiation data correction unit 6 reads subject image data (two-dimensional data) from the image storage unit 4. In the present embodiment, the image data read by the scattered radiation data correction unit 6 is chest front data. Next, the scattered radiation data correction unit 6 performs alignment between the lung field region of the subject image data and the lung field region of the scattered radiation source data. Specifically, the scattered radiation data correction unit 6 extracts the subject image data lung field region from the subject region, and aligns the extracted lung field region with the lung field region of the scattered radiation source data read in front of the chest. Perform (S31).

(Step S32)
The scattered radiation data correction unit 6 also performs alignment so that the scattered radiation source data matches the size of the subject image data for the subject region other than the lung field region (S32).

  The processing of step S31 and step S32 is referred to as alignment correction, and the scattered radiation data that has undergone this alignment correction is referred to as first corrected scattered radiation data.

(Step S33)
Since the thickness of the body varies depending on the subject, the thickness of the scattered radiation source data obtained from the phantom is corrected to match the thickness of the subject (first thickness correction). Therefore, the scattered radiation data correction unit 6 contracts and expands the entire first corrected scattered radiation data so as to match the thickness of the subject based on the actual exposure time received from the X-ray image diagnosis apparatus 11 ( S33). The scattered radiation data after the first thickness correction is referred to as second corrected scattered radiation data.

(Step S34)
Since the thickness is different for each region (for example, the abdomen, chest, etc.) inside the subject, a correction that reflects the difference in thickness for each region in the second corrected scattered radiation data is then performed (second thickness correction). Therefore, the scattered radiation data correction unit 6 further performs correction for contracting / expanding data for some of the data for the plurality of regions included in the second corrected scattered radiation data (S34). The scattered radiation data after the second thickness correction is referred to as third corrected scattered radiation data.
In the present embodiment, in order to correct the thickness of the abdomen, the data of the diaphragm region of the second corrected scattered radiation data is contracted and expanded. The diaphragm includes the diaphragm, vertebral body, and lower ribs.

(Step S35)
The scattered radiation removal unit 7 removes the third corrected scattered radiation data from the subject image data (S35). Thereby, subject image data from which the influence of scattered radiation is removed is obtained. The subject image data after the removal process is displayed on the image display device 3.

  Next, the alignment correction (step S31 and step S32) will be described in detail with reference to FIG. 4 and FIG. FIG. 4 is a flowchart for explaining the alignment correction process. FIG. 5A shows a scattered radiation data map of the front of the chest, FIG. 5B shows a scattered radiation data map displaying the center position of the lung field area of FIG. 5A, and FIG. FIG. 6D shows a captured image of the front of the chest, and FIG. 5D is a diagram in which the lung region is extracted by removing the direct line region and the X-ray aperture region of FIG. (E) is a figure explaining the content of the expansion / contraction process of the lung field process which concerns on alignment correction.

  The alignment correction will be described along the flowchart of FIG.

(Step S41)
The scattered radiation data correction unit 6 reads the subject image data from the image storage unit 4 (FIG. 5C). A subject region 57 is extracted from the subject image by excluding the direct line region 52 and the X-ray aperture region 51 (not shown) (S41).

(Step S42)
The scattered radiation data correction unit 6 creates a histogram indicating the relationship between the pixel value of the X-ray image and the frequency as shown in FIG. 6 from the subject region 57 extracted in step S41 (S42). In the created histogram, the diaphragm region is distributed in a lower pixel value (dark), and the lung field region is distributed in a higher pixel value (bright).

(Step S43)
As shown in FIG. 6, the scattered radiation data correction unit 6 performs threshold processing for selecting pixel values greater than or equal to the threshold A in which the lung field region is distributed, and extracts the lung field region 53 from the subject region 57 (S43). . An extracted image of the lung field region 53 is shown in FIG.

(Step S44)
The scattered radiation data correction unit 6 calculates the extracted lung field region 53 from the left and right lengths L1 and the upper and lower lengths L2a and L2b of the lung field region (hereinafter, “extracted lung field region”) 53 extracted in step S43. The center position 54 is determined (FIG. 5 (d)).
Since the center position 55 (FIG. 5B) of the lung field region (hereinafter referred to as “scattered radiation lung field region”) 56 in the scattered radiation data map (FIG. 5A) is set in advance, the scattered radiation data correction is performed. The unit 6 superimposes the center position 55 of the scattered radiation lung region 56 on the determined center position 54 of the extracted lung field region 53 (S44).

(Step S45)
Next, the scattered radiation data correction unit 6 enlarges / reduces the scattered radiation lung field region 56 so as to match the scattered radiation lung field region 56 with the area of the extracted lung field region 53 (S45). This alignment correction will be described using the extracted lung field region 53 and the scattered radiation lung field region 56 shown in FIG. In FIG. 5E, as described in step S <b> 44, the center position 55 of the scattered radiation lung field region 56 is superimposed on the center position 54 of the extracted lung field region 53.

  For example, assuming that the direction parallel to the body axis direction is the y axis and the direction perpendicular to the body axis direction is the x axis, the overlapped center positions 54 and 55 are (0, 0). Three points of the extracted lung field region 53, for example, the highest point 53a (x1, y1) on the y axis in the left lung field, the lowest point 53b (x3, y3) on the y axis, the center of the lower end of the lung field A point 53c (x5, y5) close to the position 54 is selected. Three points 56a (x2, y2), 56b (x4, y4), and 56c (x6, y6) of the scattered radiation lung field region 56 corresponding to these are selected. The selected point, 56a point, 56b point, and 56c point of the scattered radiation lung region 56 are extracted to match the selected point, point 53a, point 53b, and 53c, respectively, and then the scattered radiation lung field region The scattered radiation lung field region 56 is enlarged / reduced so that the area of 56 matches the area of the extracted lung field region 53 (arrows 59a, 59b, and 59c). Thereby, the outline of the scattered radiation lung region 56 can be matched with the contour of the extracted lung field region 53. Repeat in the right lung field.

FIG. 7A schematically shows the alignment in the X-axis direction. In FIG. 7, “xa, xb” is the position on the X-axis of the scattered radiation source data (see FIG. 5E), and “xa, xb ′” is the scattered radiation source data after alignment (first corrected scattering). (Line data) corresponding to the extracted lung field region 53 (see FIG. 5E).
Note that the number of points to be selected described above is not limited to three, and the number of selection points may be increased. In particular, the number of selection points may be increased at a location adjacent to the diaphragm (abdomen).

(Step S46)
The scattered radiation data correction unit 6 also applies to regions other than the scattered radiation lung field region 56 in the subject region (hereinafter referred to as “scattered radiation subject region”) 58 of the scattered radiation data map other than the extracted lung field region 53 in the subject region 57. The image is enlarged or reduced so as to match the area of the region (S46). For example, the specific points 58a, 58b, 58c, and 58d at the end of the scattered radiation subject area 58 are matched with the points 57a, 57b, 57c, and 57d corresponding to these points in the subject area 57. The scattered radiation subject area 58 is enlarged / reduced so that the scattered radiation subject area 58 overlaps the subject area 57.

  In this way, the alignment correction (step S31 and step S32) for the subject image data of the entire scattered radiation source data is completed. Thereby, the first corrected scattered radiation data obtained by aligning the subject image data with respect to the scattered radiation source data is obtained.

  In the enlargement / reduction processing in step S45 and step S46, it has been described on the assumption that the pixel values of the scattered radiation source data are uniform as shown in FIG. 7A, but as shown in FIG. 7B. If the pixel value has changed (indicated by a linear change in the figure), it is desirable to perform alignment processing (FIG. 7 (b-2)) by converting the pixel value in consideration of the change.

  Next, the first thickness correction (step S33) and the second thickness correction (step S34) will be described in detail using FIG. 8, FIG. 9, and FIG. First, the thickness correction will be described along the flow of FIG.

(Step S71)
The thickness of the part of the subject is estimated from the X-ray conditions when irradiating X-rays. In general, X-ray imaging employs a technique (automatic exposure control) that automatically controls the lung field to have the same pixel value regardless of the thickness in order to ensure the image quality of the lung field region. In the automatic exposure control, the irradiation time (sec) is stopped when the average pixel value of the lung field region (ROI average value of the lung field region) becomes a constant pixel value. For example, an X-ray condition is 1 mAs for a subject with a thin chest, and 2 mAs for a subject with a thick chest, and sec is controlled (shortened or lengthened) to obtain a pixel value of 1000 counts in the lung field region. ing. Therefore, the thickness can be estimated from the difference in the X-ray conditions.
For example, when the X-ray conditions for actual exposure are high, it can be estimated that the thickness of the chest is thick, and the ratio of the X-ray conditions (X-ray dose) when imaging subjects with different thicknesses is assumed to be the thickness ratio. it can. Therefore, the scattered radiation data correction unit 6 compares the X-ray conditions when acquiring the scattered radiation source data with the X-ray conditions of actual exposure at the time of photographing the subject (S71). X-ray conditions include, for example, tube current (mA), irradiation time (sec), tube voltage (kV), SID (Source Image Distance), etc., but the SID is fixed to simplify the explanation. Compare X-ray conditions related to other X-ray doses.

  In the present embodiment, for example, X-ray dose (mAs) (product of tube current (mA) and irradiation time (sec)) is used as the X-ray condition, and X-ray dose and subject imaging when acquiring scattered radiation source data are used. The thickness is corrected (step S72) by using the ratio of the actual exposure to the X-ray dose. Specifically, the X-ray dose rate of actual exposure at the time of subject imaging with respect to the X-ray dose used when acquiring the source of scattered radiation (acquired X-ray dose of scattered radiation / original data at the time of subject imaging) X dose) (hereinafter referred to as “X dose ratio”).

(Step S72)
When the X-ray dose ratio obtained in step S71 is greater than 1, that is, the scattered radiation data correction unit 6 is larger than the X-ray dose used when acquiring the scattered radiation source data. Since it can be estimated that the subject is thick, the first corrected scattered radiation data is expanded (increased).

  On the other hand, when the X-ray dose ratio is smaller than 1, that is, when the X-ray dose of the actual exposure at the time of photographing the subject is smaller than the X-ray dose used when acquiring the scattered radiation source data, the scattered radiation data correction unit 6 Therefore, the first corrected scattered radiation data is contracted (decreased). (First thickness correction) (S72).

  As the above-described expansion and contraction ratios, those obtained in advance by using the correction coefficient K as the ratio of change in scattered radiation data when the dose rate is changed are used. FIG. 9 shows the relationship between the dose rate and the correction coefficient K. The horizontal axis shows the dose rate of X doses with different thicknesses relative to the X dose of reference thickness, and the vertical axis shows the rate of change with respect to scattered radiation obtained with the X doses of reference thickness, that is, correction factors. K is shown.

  The graph of FIG. 9 can be obtained based on the detection value of the obtained X-ray flat panel detector by changing a plurality of phantom thicknesses, irradiating the X-ray dose corresponding to each thickness. For example, when the X-ray doses corresponding to phantom thicknesses acm, bcm, and ccm are determined as AmAs, BmAs, and CmAs, respectively, A, B, and ccm phantoms are X-ray doses of CmAs are respectively irradiated, and detection values D, E, and F of the X-ray flat panel detector are obtained, respectively. When a phantom having a thickness of bcm is used as a reference, the dose rate is A / B, B / B (that is, dose rate 1) and C / B, and the change rate of scattered radiation is D / E, E / E, ( That is, the correction coefficient is 1) F / E. The graph in FIG. 9 associates such a dose rate with the scattered radiation data change rate.

  The data of the graph shown in FIG. 9 is stored in a correction coefficient storage unit (not shown) provided in the scattered radiation data storage unit 5 in the form of a table, for example. The scattered radiation data correction unit 6 performs the first thickness correction using this table. That is, the scattered radiation data correction unit 6 calculates the correction coefficient K corresponding to the X-ray dose ratio from the graph of FIG. 9 and multiplies the first corrected scattered radiation data.

Thereby, when the X-ray dose ratio is larger than 1, the correction coefficient K becomes larger than 1 (FIG. 9), and the first corrected scattered radiation data is expanded (increased). On the other hand, when the X-ray dose ratio is smaller than 1, the correction coefficient K is smaller than 1 (FIG. 9), and the first corrected scattered radiation data is contracted (decreased).
When the X-ray dose of the actual exposure at the time of photographing the subject is the same as the X-ray dose at the time of acquiring the scattered radiation source data (X dose ratio is 1 and the correction coefficient is 1), the first corrected scattered radiation data Is used as is.

  With the first thickness correction, scattered radiation data (second corrected scattered radiation data) in which the thickness of the subject is reflected in the first corrected scattered radiation data can be acquired.

(Step S73)
Here, correction (second thickness correction) is performed in order to reflect the difference in thickness of the other part (difference depending on the subject) on the basis of the lung field portion in the scattered radiation data. Hereinafter, the case where the scattered radiation data (second corrected scattered radiation data) of the diaphragm region is corrected as another part will be described.
The scattered radiation data correction unit 6 calculates a ratio between the pixel values of the lung field and the diaphragm (hereinafter referred to as “lung field / diaphragm ratio”) from the subject image data (S73). This lung field / diaphragm ratio substantially corresponds to the ratio of the lung field of the subject to the thickness of the diaphragm.
As the pixel value, any one of an average value, a maximum value, and a minimum value may be used. Here, the maximum pixel value of the lung field region through which X-rays are most transmitted and the diaphragm portion at which X-rays are absorbed most. The minimum pixel value of the area is used.
For example, when the “ratio between the pixel value of the lung field and the pixel value of the phrenic region” (reference value) of the phantom simulating the subject used when acquiring the scattered radiation source data is used as a reference, the lungs of the subject If the field / diaphragm ratio is larger than the reference value, the subject is thick and the scattered rays increase, but if it is smaller than the reference value, the subject is thin and the scattered rays are small.

(Step S74)
The scattered radiation data correction unit 6 contracts / expands a partial area of the second corrected scattered radiation data, that is, the data of the diaphragm area in the above-described example (second thickness correction) (S74).
In the present embodiment, the relationship between the above-described lung field / diaphragm ratio and scattered radiation is obtained in advance, and the thickness of the scattered radiation data is corrected based on the relationship. FIG. 10 shows the relationship between the lung field / diaphragm ratio determined in advance and the change rate of scattered radiation. In the graph shown in FIG. 10, the horizontal axis represents the lung field / diaphragm ratio, and the vertical axis represents the change rate of scattered radiation based on the phantom lung field / diaphragm ratio (about 3), that is, the correction coefficient L. ing. Such data can be measured, for example, by measuring scattered radiation data when the thickness of the lung field in the reference phantom is constant and the thickness of the abdomen is varied.

  10 is stored in a correction coefficient storage unit (not shown) provided in the scattered radiation data storage unit 5 in the form of a table, for example. The scattered radiation data correction unit 6 performs the second thickness correction using a table. That is, the scattered radiation data correction unit 6 calculates the correction coefficient L from the graph of FIG. 10 based on the lung field / diaphragm ratio of the subject data, and divides it into the data of the diaphragm region of the second corrected scattered radiation data. .

  Specifically, when the lung field / diaphragm ratio of the captured image is smaller than the reference phantom lung field / diaphragm ratio, the abdomen is thin. Using the large correction coefficient L, the data of the diaphragm area of the second corrected scattered radiation data is reduced. On the other hand, when the ratio is large, the abdomen is thick, so that the scattered radiation data correction unit 6 expands the scattered radiation data in the diaphragm region of the second corrected scattered radiation data using a correction coefficient L smaller than 1. Let When the ratio is the same (that is, about 3), the scattered radiation data of the diaphragm region of the second corrected scattered radiation data is used as it is.

  As described above, the case of correcting the diaphragm region of the scattered radiation data has been described. For example, for the region other than the diaphragm region, for example, the mediastinum portion, the same is obtained by obtaining the ratio of the pixel value to the lung field region of the subject image. Can be corrected using the correction coefficient L.

  In addition, since the minimum value of a diaphragm part is affected when a metal etc. are contained, it is desirable to remove a metal by a general metal removal process in step S42.

  In this way, the second thickness correction that reflects the thickness of the partial area of the subject (eg, the thickness of the abdomen) can be performed in a partial area of the second corrected scattered radiation data. The scattered radiation data obtained by the second thickness correction is referred to as third corrected scattered radiation data. A scattered radiation removal step (step S35) is performed using the third corrected scattered radiation data. That is, the third corrected scattered radiation data is removed from the subject image data.

  With the first thickness correction and the second thickness correction, the scattered radiation data corresponding not only to the thickness of the subject's body but also to the difference in the thickness of a part of the subject area (for example, the abdomen) depending on the subject. You can get it.

  As described above, in this embodiment, accurate scattered radiation can be estimated and accurate scattered radiation correction can be performed. Thereby, the image quality of the X-ray image when the grid is not used can be improved.

  In the present embodiment, the chest is used as the imaging region. However, the present embodiment can also be used for imaging other regions such as the head, neck, abdomen, and pelvis. Depending on the imaging region, it is not necessary to perform the second thickness correction, and the second corrected scattered radiation data that has been processed up to the first thickness correction may be used.

  In the present embodiment, the threshold processing method (step S43) and the alignment method (step S45, step S46) have been described. However, the present invention is not limited to these methods, and template matching (normalized correlation) and boundary tracking are performed. A method may be used.

Scattered ray removal processing was performed on the X-ray image of the thoracic vertebra of the subject using the third corrected scattered ray data obtained by the present embodiment. The result is shown in FIG.
11A and 11B are X-ray images of the thoracic vertebra, and FIG. 11A is an image before subtracting the third corrected scattered radiation data from the subject image data (before the scattered radiation removal process), and FIG. Is the image after subtracting the third corrected scattered ray data from the subject image data (after the scattered ray removal process), and (c) is the pixel value on the line segment connecting point A and point A ′ in (a). Profile (d) shows a profile of pixel values on a line segment connecting point B and point B ′ in (b).
As can be seen by comparing (a) and (b) or (c) and (d) in the figure, the subtraction of the third corrected scattered radiation data obtained by the present embodiment enables the subtraction after subtraction. The contrast of the image is clearer.

DESCRIPTION OF SYMBOLS 0 ... Subject, 1 ... X-ray tube, 2 ... X-ray plane detector, 10 ... Image processing part, 6 ... Scattered ray data correction part, 11 ... X-ray image Diagnostic equipment

Claims (12)

An X-ray tube that irradiates the subject with X-rays;
An X-ray plane detector disposed opposite to the X-ray tube and detecting transmitted X-rays of the subject; an image processing unit for generating an X-ray image based on image data output from the X-ray plane detector; An X-ray diagnostic imaging apparatus comprising:
The image processing unit includes a scattered radiation data correction unit that generates scattered radiation data by aligning and correcting the scattered radiation source data acquired in advance using a phantom simulating the subject with respect to the image data. X-ray image diagnostic apparatus. The X-ray diagnostic imaging apparatus according to claim 1,
The X-ray diagnostic imaging apparatus characterized in that the alignment correction performed by the scattered radiation data correction unit includes a process of enlarging / reducing the position of the scattered radiation source data according to the image data. The X-ray diagnostic imaging apparatus according to claim 1 or 2,
The X-ray diagnostic imaging apparatus, wherein the scattered radiation data correction unit further performs thickness correction for correcting the aligned scattered radiation data according to the thickness of the subject. The X-ray diagnostic imaging apparatus according to claim 3,
The X-ray diagnostic imaging apparatus according to claim 1, wherein the thickness correction includes a first thickness correction for increasing / decreasing the value of the scattered radiation data. The X-ray diagnostic imaging apparatus according to claim 4,
The X-ray diagnostic imaging apparatus according to claim 1, wherein the thickness correction further includes a second thickness correction for increasing / decreasing data of a part of the plurality of areas of data included in the scattered radiation data. The X-ray diagnostic imaging apparatus according to claim 4,
The first thickness correction includes performing based on a comparison result between an X-ray condition when acquiring the scattered radiation source data and an X-ray condition when acquiring the image data. Line image diagnostic device. The X-ray diagnostic imaging apparatus according to claim 6,
The comparison result is a ratio between an X-ray dose when acquiring the scattered radiation source data and an X-ray dose when acquiring the image data,
The thickness correction includes a process of increasing the value of the scattered radiation data when the X-ray dose ratio is greater than 1 and decreasing the scattered radiation data when the X-ray dose ratio is less than 1. The X-ray diagnostic imaging apparatus according to claim 7,
The image processing unit includes a scattered radiation data storage unit,
The scattered radiation data storage unit includes a correction coefficient storage unit that stores a relationship between the X-ray dose ratio and a correction coefficient. The X-ray diagnostic imaging apparatus according to claim 5,
The thickness correction unit performs the second thickness correction based on a ratio between a data value for the partial region and a data value for the other portion of the data regarding the plurality of regions. An X-ray diagnostic imaging apparatus characterized by the above. The X-ray diagnostic imaging apparatus according to claim 9,
The scattered radiation data storage unit includes a correction coefficient storage unit that stores a relationship between a ratio of the data and a correction coefficient. A method of creating an X-ray image obtained by removing scattered radiation data from captured image data,
A step of aligning the scattered radiation source data acquired in advance using a phantom simulating a subject with respect to the captured image data;
A thickness correction step for correcting the aligned scattered radiation data according to the thickness of the subject, and
The step of aligning includes a process of enlarging / reducing the position of the scattered radiation source data according to the image data,
The method of creating an X-ray image, wherein the step of performing the thickness correction includes performing a first thickness correction for increasing or decreasing the value of the scattered radiation data subjected to the alignment. A method for creating an X-ray image according to claim 11, comprising:
The step of performing the thickness correction further includes a second thickness correction for increasing / decreasing data of a part of the data of a plurality of regions included in the scattered radiation data subjected to the first thickness correction. Of creating an X-ray image characterized by

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