WO2018190243A1

WO2018190243A1 - Radiation imaging device, image processing device, and image processing program

Info

Publication number: WO2018190243A1
Application number: PCT/JP2018/014604
Authority: WO
Inventors: 影山　昌広
Original assignee: 株式会社日立製作所
Priority date: 2017-04-13
Filing date: 2018-04-05
Publication date: 2018-10-18
Also published as: JP6776171B2; JP2018175457A

Abstract

Through the present invention, an image in which image quality fluctuation due to scattered radiation is suppressed is obtained in a short time while repeated processing is not performed or the number of repetitions of processing is significantly reduced. The present invention has a radiation source for radiating radiation to a subject, a radiation detector for detecting an intensity distribution of radiation passing through the subject, an extraction unit for extracting a high-frequency component of a spatial axis direction and/or a time axis direction for the radiation intensity distribution, and a thickness distribution calculation unit for obtaining a thickness distribution of the subject on the basis of the high-frequency component extracted by the extraction unit.

Description

Radiation imaging apparatus, image processing apparatus, and image processing program

The present invention relates to a technique for processing data obtained by detecting radiation that has passed through a subject, and more particularly to a technique for correcting fluctuations caused by radiation scattering.

In a technique for irradiating a subject such as a human body with radiation such as X-rays, detecting the intensity distribution of the radiation transmitted through the subject with a detector and capturing a transmission image, the radiation (primary transmitted through the subject linearly) Line) is added to the primary line image obtained from the radiation (scattered rays) scattered inside the subject etc., so that the contrast of the acquired transmitted image is reduced and the sharpness is reduced. It is generally known that image quality fluctuations occur.

In order to suppress this variation in image quality, a plate called a grid, which consists of thin and alternating layers of a material with high radiation absorption and a material with low absorption, is placed between the subject and the detector, and enters the detector. An imaging method that keeps the scattered dose low is generally used. However, when the grid is installed, the primary dose incident on the detector is also attenuated by the grid, so that it is necessary to irradiate the subject with stronger radiation than when the grid is not used, and the exposure amount of the subject increases.

Therefore, many technologies have been proposed so far that perform signal processing on transparent images acquired without using a grid (gridless images) to obtain image quality equivalent to that of transparent images acquired using a grid (grid image). Has been.

For example, in the technique described in Patent Document 1, by analyzing a transmission image, a body thickness distribution of a subject is estimated to obtain a virtual model of the subject, and an estimated primary line image and an estimated scattered ray estimated from the virtual model An estimated transmission image is generated by combining the images, and the body thickness distribution of the virtual model is corrected so that the difference between the estimated transmission image and the actually acquired transmission image is reduced. As a result, a transmission image in which image quality fluctuation due to scattered radiation is suppressed is obtained. At this time, if the difference between the estimated transmission image and the actually acquired transmission image remains even if the corrected body thickness distribution is used, iteratively repeatedly corrects the body thickness distribution of the virtual model so that this difference is further reduced. Process.

JP 2015-43959 A

In the technique described in Patent Document 1, as described above, the body thickness distribution of the virtual model is corrected using iterative processing so that the difference between the estimated transmission image and the actually acquired transmission image becomes small.

However, when iterative processing as in Patent Document 1 is performed, considerable processing time is required until a final image is obtained, and as a result, the number of images obtained per unit time is reduced. For this reason, when it is desired to display a transmission image as a moving image as in the case of fluoroscopic imaging of an X-ray imaging apparatus, the technique of Patent Document 1 may result in an unnatural moving image in which the movement of the subject is jerky. Further, it is possible to increase the number of images obtained per unit time by using a special calculation resource capable of executing high-speed processing, but in this case, the apparatus becomes expensive.

The present invention has been made in view of such a situation, and it is possible to obtain an image in which image quality variation due to scattered rays is suppressed in a short time while not performing iterative processing or greatly reducing the number of iterations of processing. It is in.

Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows. That is, a typical radiation imaging apparatus includes a radiation source that irradiates a subject with radiation, a radiation detector that detects an intensity distribution of the radiation that has passed through the subject, and a spatial intensity direction and a time axis direction for the radiation intensity distribution. An extraction unit that extracts at least one high-frequency component; and a thickness distribution calculation unit that obtains a thickness distribution of the subject based on the high-frequency component extracted by the extraction unit.

Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. The embodiments of the present invention can be achieved and realized by elements and combinations of various elements and the following detailed description and appended claims.

According to the present invention, it is possible to obtain a radiation image in which image quality fluctuation due to scattered rays is suppressed in a short time.

It is a block diagram which shows the structure of the radiation imaging device of embodiment of this invention. 1 is a block diagram illustrating an example of a configuration of a radiation imaging apparatus in a specific embodiment 1. FIG. (a) And (b) is explanatory drawing explaining the primary ray and scattered ray of the radiation which permeate | transmit a to-be-photographed object. It is a block diagram which shows an example of a structure of the image process part of the radiation imaging device of FIG. (A)-(d) is a block diagram which shows an example of a structure of the high frequency component extraction part of the image processing part of FIG. 4, respectively. FIG. 5 is a block diagram illustrating an example of a configuration of a body thickness distribution calculation unit of the image processing unit in FIG. 4. (A)-(c) is a block diagram which shows an example of a structure of the scattered radiation image estimation part of the image processing part of FIG. 4, respectively. (A) And (b) is a block diagram which shows an example of a structure of the scattered radiation image removal part of the image processing part of FIG. 3 is a flowchart illustrating an example of a processing operation of an image processing unit in FIG. 2. (A) And (b) is a block diagram which shows an example of a structure of the image process part which the radiation imaging device in Embodiment 2 has, respectively. 10 is a block diagram illustrating an example of a configuration of an image processing unit included in a radiation imaging apparatus according to Embodiment 3. FIG. FIG. 10 is a block diagram illustrating an example of a configuration of a radiation imaging apparatus in a fourth embodiment.

The present invention provides a technique for obtaining a radiation image in which image quality fluctuation due to scattered radiation is suppressed in a short time.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The accompanying drawings show specific embodiments in accordance with the principle of the present invention, but these are for the understanding of the present invention, and are never used to limit the interpretation of the present invention. is not.

This embodiment has been described in sufficient detail for those skilled in the art to practice the present invention, but other implementations and configurations are possible without departing from the scope and spirit of the technical idea of the present invention. It is necessary to understand that the configuration and structure can be changed and various elements can be replaced. Therefore, the following description should not be interpreted as being limited to this.

Furthermore, in the embodiment of the present invention, all functions may be implemented by hardware, or a part or all of the functions may be implemented by software running on a general-purpose computer.

In all the drawings for explaining the embodiments, the same members are, in principle, given the same reference numerals, and the repeated explanation thereof is omitted.

Hereinafter, embodiments of the present invention will be described.

FIG. 1 is a block diagram showing a radiation imaging apparatus according to an embodiment of the present invention. As shown in FIG. 1, the radiation imaging apparatus of the present embodiment includes a radiation source 102 that irradiates a subject 108 with radiation, a radiation detector 111 that detects an intensity distribution of radiation that has passed through the subject 108, and a radiation detector 111. 2 extracts an at least one high-frequency component in the spatial axis direction and the time-axis direction, and obtains the thickness distribution of the subject 108 based on the high-frequency component extracted by the extraction unit 301. And a thickness distribution calculation unit 302. Hereinafter, considering the case where the subject 108 is a human body as an example, the thickness distribution is referred to as a body thickness distribution, and the thickness distribution calculation unit 302 is referred to as a body thickness distribution calculation unit 302. Is not limited to a human body imaged.

The radiation detector 111 includes a plurality of detection elements arranged one-dimensionally or two-dimensionally, and detects a spatial intensity distribution of radiation in the arrangement direction of the plurality of detection elements, that is, a radiation image. The high-frequency component of the radiation intensity distribution detected by the radiation detector 111 means at least one high-frequency component in the spatial axis direction and the time axis direction of the radiation intensity distribution (radiation image). The high frequency component is a frequency component in a band in which the intensity of the frequency component constituting the radiation (scattered ray) scattered inside the subject 108 is relatively attenuated among the frequency component bands constituting the radiation intensity distribution. If it is.

The intensity distribution of the radiation detected by the radiation detector 111 is represented by the sum of the intensity distribution of the primary line linearly transmitted through the subject 108 and the intensity distribution of the radiation scattered inside the subject 108 (scattered rays). . The intensity distribution of the primary line corresponds to the thickness distribution of the subject. At this time, a part of the temporal and spatial high-frequency components included in the radiation irradiated from the radiation source 102 to the subject 108 is transmitted linearly through the subject 108 and the other is scattered inside the subject 108. Since the scattered high-frequency component is greatly attenuated in the subject 108, the high-frequency component included in the radiation intensity distribution detected by the radiation detector 111 is almost equal to the high-frequency component of the primary line that has passed through the subject 108 linearly. Is attributed. Therefore, the extraction unit 301 extracts at least one high-frequency component in the spatial axis direction and the time-axis direction included in the intensity distribution of the radiation detected by the radiation detector 111, thereby obtaining the intensity distribution of the primary line (the intensity of the high-frequency component). Distribution). The body thickness distribution calculation unit 302 can calculate the body thickness distribution of the subject 108 from the extracted intensity distribution of the high frequency component.

As described above, since the radiation imaging apparatus of the present embodiment can calculate the body thickness distribution of the subject 108 from the intensity distribution of the high frequency component, the intensity distribution of the scattered radiation is obtained based on the body thickness distribution of the subject 108, The influence of scattered radiation can be removed from the radiation intensity distribution detected by the radiation detector. Therefore, it is possible to obtain an image in which image quality fluctuation due to scattered radiation is suppressed in a short time without performing iterative processing.

It should be noted that the body thickness distribution calculation unit 302 can be configured to obtain the thickness of the subject 108 corresponding to the strength of the high frequency component, for example, from the relationship between the body thickness obtained in advance and the strength of the high frequency component.

In addition, as shown in FIG. 1, the radiation imaging apparatus has a scattered radiation distribution estimation unit that obtains a distribution of scattered radiation caused by radiation passing through the subject 108 from the body thickness distribution of the subject 108 obtained by the body thickness distribution calculation unit 302. 303 may be provided. The radiation imaging apparatus 101 may further include a scattered radiation distribution removing unit 304 that removes the scattered radiation distribution obtained by the scattered radiation distribution estimation unit 303 from the intensity distribution of the radiation detected by the radiation detector 111.

The scattered radiation distribution removing unit 304 generates a scattered radiation distribution equivalent to the scattered radiation distribution generated when a grid is arranged between the subject 108 and the radiation detector 111 based on the body thickness distribution of the subject, You may add with respect to the radiation distribution from which the scattered radiation distribution which the scattered radiation distribution estimation part 303 calculated | required was removed. Thereby, the radiation distribution equivalent to the case where imaging is performed with the grid arranged can be displayed to the user (physician, radiologist, etc.).

Hereinafter, more specific embodiments of the present invention will be described. In the following description, X-rays are used as radiation, and the radiation detector 111 uses a two-dimensional array of X-ray detection elements. Thereby, the radiation detector 111 detects a two-dimensional X-ray distribution and obtains an X-ray image of the subject. However, the radiation imaging apparatus of the present embodiment is not limited to the X-ray imaging apparatus that acquires a two-dimensional X-ray image, and uses an X-ray detector in which X-ray detection elements are arranged at least in one dimension. The present embodiment can also be applied to an X-ray CT apparatus. In the following description, the scattered radiation distribution estimation unit 303 obtains a scattered radiation image of the subject as the scattered radiation distribution.

(Embodiment 1)
A radiation imaging apparatus according to Embodiment 1 of the present invention will be described.

<Configuration example of radiation imaging apparatus>
FIG. 2 is a block diagram showing an example of the configuration of the radiation imaging apparatus according to Embodiment 1 of the present invention.

As shown in FIG. 2, the radiation imaging apparatus (101) is electrically connected to an X-ray tube (radiation source) (102) that generates X-rays and irradiates the subject, and the X-ray tube (102). And a high voltage generator (103) and an X-ray controller (104) electrically connected to the high voltage generator (103). In the X-ray irradiation direction of the X-ray tube (102), an aperture (105), an X-ray compensation filter (106), and a table (109) are sequentially arranged. A mechanism control unit (110) is connected to the table (109). A diaphragm / filter control unit (107) is connected to the diaphragm (105) and the X-ray compensation filter (106). In the X-ray tube (102), an X-ray detector (111) is disposed at a position facing the diaphragm (105), the X-ray compensation filter (106), and the table (109). A detector control unit (112) is connected to the X-ray detector (111), and an image processing unit (115) is connected to the detector control unit (112). A central processing unit (114) is connected to the X-ray control unit (104), the diaphragm / filter control unit (107), the mechanism control unit (110), and the detector control unit (112), and the central processing unit (114). A storage unit (113), an input unit (116), and a display unit (117) are connected to this.

The high voltage generator (103) generates a high voltage applied to the X-ray tube (102). The X-ray tube (102) irradiates the subject (108) disposed on the table (109) with X-rays. The X-ray control unit (104) controls the high voltage generation unit (103), and controls the dose and quality of X-rays emitted from the X-ray tube (102). The diaphragm (105) controls the region irradiated with X-rays generated by the X-ray tube (102) by opening and closing a metal having a high X-ray absorption rate. The X-ray compensation filter (106) is made of a substance having a high X-ray absorption rate, and reduces halation by attenuating X-rays that reach a portion of the subject (108) having a low X-ray absorption rate. The table (109) is a bed on which the subject (108) is placed. The mechanism control unit (110) moves the table (109) and controls the subject (108) to move to a position suitable for photographing. At this time, the X-ray control unit (111) may be configured to move integrally with the table (109).

The X-ray detection unit (111) has a configuration in which X-ray detection elements are two-dimensionally arranged and functions as an image generation unit. That is, the X-ray detection unit (111) detects the X-rays irradiated from the X-ray tube (102) and transmitted through the subject (108) by the X-ray detection elements, respectively, so that an image corresponding to the X-ray intensity distribution is obtained. Data (radiation image, hereinafter referred to as transmission image) is output. The X-rays transmitted through the subject (108) here are the X-rays that linearly pass through the subject (108) and reach the X-ray detection unit (11), and are scattered within the subject (108) and X X-rays reaching the line detection unit (111). Therefore, the transmission image is the sum of an image of a primary line that has been linearly transmitted through the subject (108) and an image of scattered rays scattered inside the subject (108). The detector control unit (112) controls the X-ray detection unit (111) to acquire transmission image data, and inputs the acquired data to the image processing unit (115). When the detector control unit (112) controls the X-ray detector (111), the X-ray detector (111) can also generate a transmission image as a still image. It is also possible to generate a plurality of transmission images taken at different timings and generate them as moving images. At this time, in general, images are often taken at a constant time interval such as 30 frames per second or 15 frames per second, but the time interval is not limited thereto. The image processing unit (115) receives the transmission image (input image) output from the X-ray detector (111) via the detector control unit (112), and performs image processing such as extracting high-frequency components. . The display unit (117) displays the image (output image) after being processed by the image processing unit (115). The storage unit (113) includes a recording medium such as a semiconductor memory or a magnetic disk, and may store images, image acquisition conditions, various characteristics and parameters described later as data, and a software program described below. it can. Note that the type of the recording medium is not limited to this. The input unit (116) is a user interface for the user to set image acquisition conditions and the like. As this input unit (116), a keyboard, a mouse, a control button, or the like may be provided, or a sensor or the like for performing voice input or gesture input may be provided. The central processing unit (114) controls each unit electrically connected.

Note that a general computer configuration represented by a personal computer (PC) usually includes a central processing unit (114) called a CPU, a storage unit (113), an input unit (116), and a display unit (117). In addition, the X-ray control unit (104), the diaphragm / filter control unit (107), the mechanism control unit (110), the detector control unit (112), and the image processing unit (115) can be realized by a software program. . Therefore, central processing unit (114), storage unit (113), input unit (116), display unit (117), X-ray control unit (104), aperture / filter control unit (107), mechanism control unit (110) The detector control unit (112) and the image processing unit (115) may be configured by a computer. The function of the image processing unit (115) may be realized using dedicated hardware, an image processing processor, or the like. The details of the image processing unit (115) will be described later in detail.

<Primary rays and scattered rays of radiation imaging equipment>
FIG. 3 is an explanatory diagram for explaining primary rays and scattered rays of radiation that passes through the subject. FIG. 3 is a diagram used only for explaining primary rays and scattered rays in the radiation imaging apparatus, and is not a diagram for explaining operations in a normal use state.

Here, first, the intensity (intensity distribution) Im (x, y) for each pixel of the transmission image obtained by detecting the X-rays transmitted through the subject, the intensity distribution Ip (x, y) of the primary line image, and the scattered radiation The generally known characteristics of the image intensity distribution Is (x, y) will be described. Note that (x, y) in the following expression indicates the position of a pixel.

Equation (1) indicates that the transmission image Im (x, y) is represented by the sum of the primary line image Ip (x, y) and the scattered line image Is (x, y). Expression (2) indicates that the intensity of the primary line image Ip (x, y) exponentially attenuates according to the thickness T (x, y) of the subject. Here, Io (x, y) represents the incident dose at the position (x, y), and μ represents the X-ray attenuation rate (linear attenuation coefficient) per unit thickness. Equation (3) is expressed by a convolution operation (*) where the intensity of the scattered line image Is (x, y) is the intensity of the primary line image Ip (x, y) and the point diffusion function Sσ (T (x, y)). This point diffusion function Sσ (T (x, y)) changes according to the thickness T (x, y) of the subject. These equations (1), (2), and (3) are equations based on the contents described in Patent Document 1 described above.

In FIG. 3 (a), an experiment is performed in which the irradiation region of X-rays irradiated from the X-ray tube (102) is controlled by a diaphragm (201 (a)) and irradiated to a subject (202) placed on a table (109). It shows how it went. At this time, the diaphragm (201 (a)) may be the same as the diaphragm (105) shown in FIG. 2, but it is different from the diaphragm (105) shown in FIG. It is assumed that the metal has a high X-ray absorption rate. For the purpose of explaining the operation principle, the subject (202) is assumed to be an object having a constant value (T) regardless of the position (x, y), such as an acrylic plate.

When the intensity distribution of X-rays transmitted through the subject (202) and the table (109) is detected by the X-ray detector (111 (a)), as shown in FIG. An intensity distribution Im (x, y) is obtained. This is because the path when the X-ray passes through the subject (202) is slightly longer at the end (left and right ends) than at the center of the X-ray detector (111 (a)). One, but more than that, the influence of the intensity distribution Is (x, y) of the scattered radiation being different between the central portion and the end portion of the X-ray irradiation region is great. That is, at the center of the X-ray irradiation area, scattered rays on both sides (left and right sides) are incident on the X-ray detector (111 (a)), whereas at the end (left end and right end) one side (left end) Then, only the scattered radiation on the right side and the left side on the right end is incident on the X-ray detector (111 (a)), so the intensity of the incident X-ray is stronger at the center than at the end. caused by.

This phenomenon can be confirmed experimentally by moving the position of the diaphragm (201 (b)) to a position different from that of the diaphragm (201 (a)) as shown in FIG. 3 (b). In the example shown in Fig. 3 (b), the metal plate on one side (left side toward the left) of the diaphragm (201 (b)) is moved to block the X-rays irradiated to the left side of the X-ray tube (102). ing. Then, although the positional relationship of the X-ray tube (102), the subject (202), and the X-ray detector (111 (b)) and the thickness of the subject (202) are not changed from FIG. 3 (a), As shown in FIG. 3 (b1), the intensity distribution Im (x, y) of the transmission image changes, and the value is smaller overall than the intensity distribution Im (x, y) shown in FIG. 3 (a1). This phenomenon is caused by the absence of X-rays scattered from the left side to the right side of the subject (202) because the X-rays irradiated to the left side of the subject (202) are shielded.

Thus, even if the thickness of the subject (202) is a constant value, the intensity distribution Im (x, y) of the transmission image changes when the position or area of the region irradiated with X-rays changes. In the case of a subject having a locally different thickness, such as a human body, the intensity distribution Im (x, y) of the transmission image changes more complicatedly. For this reason, in the conventional technique, it is difficult to calculate the thickness T (x, y) at the position from only the intensity distribution Im (x, y) of the transmission image at the position (x, y). Ip (x, y) shown in (2) and Is (x, y) shown in equation (3) cannot be calculated easily. Therefore, until now, it has been necessary to calculate the thickness T (x, y) of the subject (202) using an iterative process or the like as described in Patent Document 1.

On the other hand, in the radiation imaging apparatus according to Embodiment 1 of the present invention, attention is paid to the noise shown in FIGS. 3 (a1) and 3 (b1). This noise is included in the transmission image, and in the X-ray tube (102), when an X-ray is generated by colliding an electron beam against a target metal (anode) (not shown) in a vacuum, This occurs because the time interval changes probabilistic each time, and it is essentially difficult to eliminate this noise. That is, such noise is normally generated. In addition, this noise often has an impulse-like waveform, and includes many high-frequency components spatially and temporally.

When X-rays containing such noise are irradiated from the X-ray tube (102) to the subject (202), part of the noise is scattered while passing through the subject (202). According to Equation (3), the intensity of the scattered line image is expressed as a convolution operation of the intensity of the primary line image Ip (x, y) and the point spread function Sσ (T (x, y)), that is, a low-pass filter operation. Therefore, the high frequency component included in the noise is greatly attenuated. In other words, the noise (high-frequency component) remaining in the transmission image shown in FIGS. 3 (a1) and 3 (b1) is not caused by scattered rays but mostly by primary lines. It can be said.

Here, when the transmission image shown in FIG. 3 (a1) is separated into a spatial high-frequency component and a low-frequency component, the high-frequency component is as shown in FIG. 3 (a2), and the low-frequency component is as shown in FIG. 3 (a3). become. Similarly, when the transmission image shown in FIG. 3 (b1) is separated into a high frequency component and a low frequency component, the high frequency component becomes as shown in FIG. 3 (b2) and the low frequency component becomes as shown in FIG. 3 (b3). At this time, as described above, most of the high-frequency components are caused by the primary line. Therefore, from the above equation (2), the high-frequency components shown in FIGS. 3 (a2) and 3 (b2) are Shows substantially the same intensity distribution according to the thickness of the subject. If each intensity distribution in Fig. 3 (a2) and Fig. 3 (b2) is Ip (x, y), then equation (4) can be derived from equation (2), and the incident dose Io (x, y) can be calculated in advance. If measured, the thickness T (x, y) of the subject can be calculated in a short time without using an iterative process. 3 (a2) and 3 (b2) show spatial high-frequency components, the same applies to the high-frequency components in the time axis direction.

In other words, when focusing on the intensity Im (x, y) of the transmission image at a certain position (x, y), the intensity Ip (x, y) of the primary line is expressed by the position (x + dx, y + dy) may be significantly different from the intensity Ip (x + dx, y + dy) of the primary line, but the intensity Is (x, y) of the scattered radiation is the intensity Is ( x + dx, y + dy) is used. That is, as shown in Equation (5), by obtaining the intensity difference (Im (x + dx, y + dy) -Im (x, y), that is, a high frequency component) with neighboring pixels in the transmission image Im, The intensity Is of scattered radiation can be canceled (Is (x + dx, y + dy) -Is (x, y) ≒ 0), and the difference in intensity from neighboring pixels in the primary line image Ip (Ip (x + dx, y + dy) -Ip (x, y)). By utilizing this, the thickness T (x, y) of the subject can be obtained from the expression (2) or the expression (4) without being affected by the scattered radiation Is (x, y) in the expressions (1) and (3). Can be calculated in a short time.

<Configuration Example of Image Processing Unit>
FIG. 4 is a block diagram showing an example of the configuration of the image processing unit (115) included in the radiation imaging apparatus of FIG.

As shown in FIG. 4, the image processing unit (115) includes a high frequency component extraction unit (301), a body thickness distribution calculation unit (302), a scattered radiation image estimation unit (303), and a scattered radiation image removal unit ( 304).

The high-frequency component extraction unit (301) extracts at least one high-frequency component in the spatial axis direction and the time-axis direction from the transmission image (input image) output from the X-ray detector (111), and uses the extracted result as the high-frequency component. Information is input to the body thickness distribution calculation unit (302). This will be described in detail later with reference to FIG.

The body thickness distribution calculation unit (302) calculates body thickness information based on the high frequency component information extracted by the high frequency component extraction unit (301), and calculates a scattered radiation image estimation unit (scattered radiation distribution estimation unit) (303 ). This will be described in detail later with reference to FIG.

The scattered radiation image estimation unit (303) generates a scattered radiation image (estimated scattered radiation image) that is estimated to be included in the input image based on the input image and the body thickness information from the body thickness distribution calculation unit (302). The calculated value is input to the scattered radiation image removal unit (304). This will be described in detail later with reference to FIG.

The scattered radiation image removal unit (304) removes the estimated scattered radiation image obtained by the scattered radiation image estimation unit (303) from the input image, and calculates an output image. This will be described in detail later with reference to FIG.
The image acquisition conditions set in the image processing unit (115) will be described in detail later.

<Configuration example of high-frequency component extraction unit>
FIG. 5 is a block diagram showing an example of the configuration of the high frequency component extraction unit (301) included in the image processing unit (115) of FIG. The high-frequency component extraction unit (301) extracts at least one high-frequency component in the spatial axis direction and the time-axis direction from the transmission image (input image) output from the X-ray detector (111), and uses the extracted result as the high-frequency component. Information is input to the body thickness distribution calculation unit (302).

As shown in FIGS. 5 (a) to 5 (d), various modifications can be considered for the high-frequency component extraction unit (301). Hereinafter, these configurations and operations will be described one by one.

FIG. 5 (a) shows an example (301 (a)) in which the high-frequency component extraction unit (301) is configured with an intra-frame high-pass filter (401). Here, the intra-frame high-pass filter (401) is a filter that uses only one (one frame) input image to extract a high-frequency component of the intensity distribution in the spatial axis direction of each pixel value constituting the input image. A general one-dimensional or two-dimensional high-pass filter can be used as it is. A high-pass filter is a filter having a frequency characteristic in which the amount of attenuation of low-frequency components including direct current is larger than the amount of attenuation of high-frequency components. For example, a general horizontal high-pass filter or vertical high-pass filter (both are one-dimensional high-pass filters) can be used as the intra-frame high-pass filter (401) as it is. In addition, a general horizontal high-pass filter and a vertical high-pass filter may be connected in series or in parallel to form a two-dimensional high-pass filter, which may be used as an intra-frame high-pass filter (401). Note that the intra-frame high-pass filter (401) is not limited to the configuration described here. As described above with reference to FIG. 3, the scattered radiation image (low frequency component including direct current) is greatly increased. It only needs to have a frequency characteristic that attenuates.

FIG. 5 (b) shows another configuration example (301 (b)) of the high-frequency component extraction unit (301). The high frequency component extraction unit (301 (b)) includes an expansion processing unit (402), a contraction processing unit (403), and a subtracter (404). Here, the expansion processing in the expansion processing unit (402) is generally known as dilate processing, and is in the vicinity of the target position (pixel) (x, y) (for example, nine pixels centered on the pixel of the target position). ) Is used as the output signal (pixel value) at the target position. The contraction process in the contraction processing unit (403) is generally known as an erode process, and the minimum value of the input signal (pixel value) in the vicinity of the target position (x, y) is used as the output signal of the target position. (Pixel value).

Therefore, when the difference between the output signals from the expansion processing unit (402) and the contraction processing unit (403) is taken by the subtractor (404), the maximum value and the minimum value of the input signal in the vicinity of the target position (x, y) Therefore, as shown in Equation (5), the difference in intensity from neighboring pixels (Ip (x + dx, y + dy) -Ip (x, y)) in the primary line image Ip is extracted. As a result, a scattered radiation image having a small intensity difference from neighboring pixels can be attenuated.

It should be noted that how many pixels the “neighbor” is set is arbitrary, and when using the X-ray tube (102) with a small half-value width of noise included in the X-ray, the number of pixels (for example, When the X-ray tube (102) having a large half-value width of noise is used, the “neighboring” may be a large number of pixels (for example, horizontal 7 pixels × vertical 7 pixels).

FIG. 5 (c) shows still another configuration example (301 (c)) of the high-frequency component extraction unit (301). The high-frequency component extraction unit (301 (c)) includes a frame memory (405) and a subtracter (406) .The difference between the current input image and the input image one frame before (that is, in the time direction) (High frequency component) is output. With this configuration, a noise component can be extracted when the subject is stationary. Note that the configuration for extracting high-frequency components in the time direction is not limited to the configuration described here, and the number of frame memories (405) may be increased to obtain a difference between a plurality of frames. When the subject is stationary, the intensity of the primary line may vary greatly from frame to frame due to noise, whereas the intensity of the scattered line is averaged between the neighborhoods in one frame, so it is ergodic. Therefore, the high frequency component extraction unit (301 (c)) only needs to have a frequency characteristic that greatly attenuates the low frequency component including the direct current at the time frequency. The ergodic property is a property in which the time average and the set average statistically match, and here, the average value of scattered radiation between frames (time average) and the average value within one frame (set average) Represents a statistically consistent property.

FIG. 5 (d) shows still another configuration example (301 (d)) of the high-frequency component extraction unit (301). The high-frequency component extraction unit (301 (d)) includes a high-frequency component extraction unit (301 (a)) that extracts a high-frequency component in the spatial axis direction shown in FIG. 5 (a) and a high-frequency component extraction unit (301 (d)) shown in FIG. A high-frequency component extraction unit (301 (c)) that extracts high-frequency components in the time axis direction, a motion detector (407), and a mixer (408).

The configuration and operation of the high-frequency component extraction unit (301 (a)) are as described above, and the high-frequency component in the spatial axis direction in the frame is extracted from the input image and output. The configuration and operation of the high-frequency component extraction unit (301 (c)) are as described above, and high-frequency components between frames (in the time axis direction) are extracted from the input image and output. Here, the high frequency component extraction unit (301 (a)) that extracts the high frequency component in the spatial axis direction extracts not only the noise component (high frequency component) but also the contour component of the subject included in the input image. In the contour portion, an error is included in the thickness T (x, y) of the subject calculated using the formula (2) or the formula (4). On the other hand, the high-frequency component extraction unit (301 (c)) that extracts high-frequency components in the time axis direction extracts only noise components (high-frequency components) regardless of the outline of the subject in the area where the subject is stationary. On the other hand, in the area where the subject is moving, not only the noise component but also the component that changes according to the difference in the subject's thickness T (x, y) at each position (x, y) is extracted. End up. Therefore, in the region where the subject moves, an error is included in the subject thickness T (x, y) calculated using Equation (2) or Equation (4).

Therefore, the motion information k (x, y) of the subject is detected using the motion detector (407), and the high-frequency component extraction unit (301 (a)) is used in a region where the motion of the subject is large as shown in Equation (6). ) Result (A (x, y)) as high-frequency component information Y (x, y), and in a region where the movement of the subject is small, the result (B (x, y)) of the high-frequency component extraction unit (301 (c)) Is controlled to be high-frequency component information Y (x, y). As a result, it is possible to extract a high frequency component that reduces an error in the thickness T (x, y).

Here, the motion information k (x, y) is information indicating the magnitude of the frame difference for each position (x, y), and 0 (still) <= k (x, y) <= 1 (motion) Normalize so that

The motion detector (407) is a known technique using, for example, an operation for obtaining an absolute value of the frame difference for each position (x, y) and a divider for normalization (division by a constant). Since it is realizable by, it abbreviate | omits illustration.

<Configuration example of body thickness distribution calculation unit>
FIG. 6 is a block diagram illustrating an example of a configuration in the body thickness distribution calculation unit (302) included in the image processing unit (115) in FIG. The body thickness distribution calculation unit (302) calculates body thickness information based on the high frequency component information extracted by the high frequency component extraction unit (301), and inputs the body thickness information to the scattered radiation image estimation unit (303).

As shown in FIG. 6, the body thickness distribution calculation unit (302) includes an absolute value calculation unit (501), a smoothing processing unit (502), and a lookup table (503). In the look-up table (503), the relationship between the average value of the noise component (high frequency component) intensity and the body thickness (conversion characteristics (504)) obtained in advance is determined based on the image acquisition conditions (tube voltage value, tube current). And combinations of aperture values and the like).

The high-frequency component information input from the high-frequency component extraction unit (301) to the body thickness distribution calculation unit (302) has both positive and negative polarities and has an impulse waveform as shown in FIG. Many. Therefore, the absolute value calculation unit (501) takes the absolute value of the high frequency component information received from the high frequency component extraction unit (301), and the smoothing processing unit (502) performs a low pass filter process, thereby The average value of the noise component in the vicinity of (pixel) (x, y) is calculated. Thereafter, the body thickness distribution calculation unit (302) performs the image acquisition conditions (tube voltage value, tube current value, tube current value, set in the X-ray control unit (104) and the diaphragm / filter control unit (107) shown in FIG. The smoothing processing unit (502) calculates the aperture value by referring to the relationship between the average value of the noise component intensity and the body thickness under the image acquisition conditions stored in the lookup table (503). The average value of the noise component intensity near the target position (x, y) is converted into body thickness information at the position (x, y) and output.

The method for obtaining the relationship (conversion characteristics (504)) between the average value of the noise component intensity stored in the lookup table (503) and the body thickness will be described. For example, using the configuration shown in FIG. 3A, the transmission image shown in FIG. 3A1 is acquired while variously changing the image acquisition conditions and the thickness of the subject 202 having a constant thickness. Thereafter, the high frequency component information is extracted by the function of the high frequency component extraction unit (301) shown in FIG. 4, and the position of interest (by the functions of the absolute value calculation unit (501) and the smoothing processing unit (502) shown in FIG. The average value of noise component intensities near x, y) is calculated. Specifically, while changing the thickness of the subject (202) to T = 0cm, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, etc., the tube voltage value at each thickness is 60kV, 70KV, 80KV, 90KV, 100KV, etc. In addition, by changing the tube current value to 1 mA, 2 mA, 4 mA, 8 mA, etc. for each tube voltage value, X-ray detectors (111 (111 ( By obtaining the average value of the noise component intensity at the position corresponding to the central part of a)), the conversion characteristic (504) from the average value of the noise component intensity to the thickness can be obtained. A lookup table (503) storing the conversion characteristics (504) is created.

At this time, if an acrylic plate having a linear attenuation coefficient and scattering characteristics similar to those of the human body is used as the subject (202), the above-described thickness can be read as the body thickness as it is. In addition, each value shown here is an example for description, It is not limited to this. Further, a value not set in advance (for example, tube voltage value = 63 KV) may be interpolated using an average value of noise component intensities in the vicinity thereof. For example, the average value of the noise component intensity at the tube voltage value = 63KV is divided into 7: 3 by dividing the average value of the noise component intensity at the tube voltage value = 60KV and the average value of the noise component intensity at the tube voltage value = 70KV. Find it. Also, using a generally known technique such as curve fitting, a conversion function approximately representing the conversion characteristic (504) is obtained, and parameters (coefficients, etc.) of the conversion function are stored in the lookup table (503). It may be stored.

<Configuration example of scattered radiation image estimation unit>
FIG. 7 is a block diagram illustrating an example of the configuration of the scattered radiation image estimation unit (303) included in the image processing unit (115) of FIG. The scattered radiation image estimation unit (303) generates a scattered radiation image (estimated scattered radiation image) that is estimated to be included in the input image based on the input image and the body thickness information from the body thickness distribution calculation unit (302). calculate.

First, the principle of calculating the estimated scattered radiation image from the body thickness in the scattered radiation image estimating section (303) of the image processing section (115) in FIG. 4 will be described below.

When the point spread function Sσ (T (x, y)) is convoluted with both sides of the above-described equation (1), equation (7) is obtained.

By replacing the first term on the right side of Expression (7) with Is (x, y) using Expression (3) and rearranging, Expression (7) can be converted into Expression (8).

Here, paying attention to the second term of equation (8), the point spread function Sσ (T (x, y)) is further convolved with the scattered radiation image (Is (x, y)). Compared with the primary line image Ip (x, y), it can be considered that the high-frequency component is significantly attenuated, and the second term of the equation (8) is set to a constant value (independent of the position (x, y)). (DC image) may be approximated. Further, the intensity of the constant value (DC image) is considered to be extremely small, and the second term of Expression (8) may be set to 0 by simplifying. By this simplification, an approximate expression of Expression (9) can be obtained from Expression (8).

Therefore, the scattered radiation image estimation unit (303) is configured to calculate the right side of Equation (9) and output it as an estimated scattered radiation image.

As shown in FIGS. 7 (a) to (c), the scattered radiation image estimation unit (303) can be variously modified. Hereinafter, these configurations and operations will be described one by one.

FIG. 7 (a) shows an example (303 (a)) in which the scattered radiation image estimation unit (303) is configured as a two-dimensional low-pass filter (601). Here, the two-dimensional low-pass filter (601) convolves the scattered image point spread function Sσ (T (x, y)) (602) shown in Equation (3) with the input image, and generates an estimated scattered radiation image. To get.

The characteristics of the two-dimensional low-pass filter (601) are the same as the characteristics of the look-up table (503) described above, using the configuration shown in FIG. The transmission image shown in FIG. 3 (a1) was acquired and obtained while changing the image acquisition conditions in various ways. At this time, on the outside of the end (left end or right end) of the X-ray detector (111 (a)) (the portion where the X-ray is shielded by the diaphragm (201 (a))), the scattered radiation not including the primary line Therefore, the point diffusion function Sσ (T (x, y)) (602) of the scattered radiation can be obtained using this intensity distribution. Specifically, when the X-ray irradiated to the subject (202) is a step input in which the dose outside the end is 0 and the dose inside the end is 1, the response due to scattering in the subject ( Since the step response is obtained as the intensity distribution of the transmission image, the impulse response (that is, the point spread function Sσ (T (x, y)) (602) can be obtained by differentiating the step response.

In the configuration shown in FIG. 7A, in the case of a subject whose body thickness changes in accordance with the position (x, y), the point spread function Sσ (T (x, y)) (602) is also in the position (x , y), the process becomes complicated. Therefore, the configuration shown in FIG.

FIG. 7B shows an example (303 (b)) in which the scattered radiation image estimation unit (303) is configured by a multiplier (603), a lookup table (604), and a two-dimensional low-pass filter (605). Show. Here, the point diffusion function Sσ (606) of the two-dimensional low-pass filter (605) has a characteristic that is invariable with respect to the thickness T (x, y). 601).

As a general feature of scattered radiation, the intensity of scattered radiation is weak where the body thickness is thin, and the intensity of scattered radiation increases as the body thickness increases. On the other hand, when the body thickness is thicker than a certain level, the primary line transmitted through the subject becomes weak, so that the scattered radiation generated from the primary line also becomes weak. This characteristic is obtained in advance in the same manner as when obtaining the characteristic of the two-dimensional low-pass filter (601) described above.

That is, using the configuration shown in FIG. 3A, the transmission image shown in FIG. 3A1 is acquired while the thickness of the subject 202 and the image acquisition conditions are changed variously, and FIG. ) Is obtained. At this time, the thickness when the point spread function Sσ (T (x, y)) (602) is most expanded is obtained by the configuration of FIG. 7A, and the point spread function Sσ (T (x, y, y)) (602) is fixed as the point spread function Sσ (606) of the two-dimensional low-pass filter (605). Subsequently, the output of the two-dimensional low-pass filter (601) shown in FIG. 7A and the result of the two-dimensional low-pass filter (605) shown in FIG. Determine the strength factor to be used. While appropriately changing the body thickness (thickness), obtain the relationship between the body thickness (thickness) and the strength coefficient, and store it in the lookup table (604) as the conversion characteristic (607) that converts the body thickness (thickness) to the strength coefficient To do.

Also, using a generally known technique such as curve fitting, a conversion function that approximately represents the conversion characteristic (607) is obtained, and parameters (coefficients, etc.) of the conversion function are stored in the lookup table (604). It may be stored. Each value shown in the conversion characteristic (607) is an example for explanation, and the present invention is not limited to this.

As described above, even if the characteristic of the two-dimensional low-pass filter (605) in the scattered radiation image estimation unit (303 (b)) shown in FIG. 7 (b) is not changed with respect to the thickness T (x, y), FIG. An estimated scattered radiation image similar to the output of the scattered radiation image estimation unit (303 (a)) shown in (a) can be approximately obtained.

7 (c) shows a scattered radiation image estimation unit (303), multipliers (608) and (609), a mask information generation unit (612), and a scattered radiation image estimation unit (303 (b) -1) -1 ( An example (303 (c)) composed of 303 (b) -2) and an adder (613) is shown.

When actually using the radiation imaging apparatus of FIG. 2, a transmission image of the subject (108) smaller than the X-ray detector (111) may be acquired. In this case, outside the subject, the X-rays irradiated from the X-ray tube (102) enter the X-ray detector directly through only the air layer. Even in the air layer, X-rays are scattered, but the degree of scattering is smaller than in the interior of the subject (108).

Therefore, as shown in FIG. 7 (c), the scattered radiation image estimation unit (303 (b) -1) for estimating the scattering inside the subject and the scattered radiation for estimating the scattering outside the subject (air layer). The image estimation unit (303 (b) -2) is provided separately, and is generated by the mask information generation unit (612) and the mask information (610) indicating the inner area of the subject generated by the mask information generation unit (612). Using the mask information (611) indicating the outer area of the subject and the multipliers (608) and (609), the input image is divided into each area, and then the scattered radiation image estimation unit (303 (b) -1) (303 (b) -2) Obtain each estimated scattered radiation image, and finally adder (613) adds both estimated scattered radiation images and outputs the final estimated scattered radiation image. .

Here, the mask information (610) indicating the inner region of the subject has a value of 1 at the position (x, y) of the inner region of the subject and 0 at the position (x, y) of the outer region of the subject. Information. In the mask information generation unit (612), an area where the luminance value of the input image is smaller than a predetermined threshold is set as an inner area of the subject, and an area where the luminance value of the input image is larger than the predetermined threshold is set as an outer area of the subject. Information (610) is generated.

Note that the mask information (610) generated by binarization in this way is low-pass filtered so that the value is an intermediate value between 0 and 1 at the position (x, y) of the inner and outer boundary regions. Also good.

The mask information (611) indicating the outer area of the subject may be a value complementary to the mask information (610) indicating the inner area of the subject, and each value of the mask information (610) and the mask information (611) May be set to 1 by adding for each position (x, y).

The configuration of the scattered radiation image estimation unit (303 (b) -1) (303 (b) -2) is the same as that of the scattered radiation image estimation unit (303 (b)) shown in FIG. However, the two-dimensional low-pass filters (605-1) and (605-2) have different characteristics. That is, the two-dimensional low-pass filter (605-1) performs a convolution operation of the point diffusion function Sσ (606-1) that simulates scattering in the inner area of the subject, and the two-dimensional low-pass filter (605-2) Convolution of a point diffusion function Sσ (606-2) that simulates scattering in a region is performed.

The point spread function Sσ (606-1) and the lookup table (604-1) are the same as the point spread function Sσ (606) and the lookup table (604) shown in FIG. Characteristic is sufficient. On the other hand, for the point spread function Sσ (606-2) and the look-up table (604-2), the procedure similar to the above is performed after the subject (202) is not installed in the configuration of FIG. Thus, each characteristic of the point spread function Sσ (606-2) and the look-up table (604-2) may be obtained.

Although not shown, the scattered radiation image estimation unit (303 (b) -1) in the configuration of FIG. 7C may be subdivided. At this time, for example, a scattered radiation image estimation unit for a region with a small body thickness such as the lung (for a region with a large amount of X-ray transmission), a scattered radiation image estimation for a region with a small amount of X-ray transmission such as bone Or a scattered radiation image estimation unit for other regions (built-in or for muscles). In that case, for example, in the configuration of FIG. 3A, the subject (202) is replaced with a subject simulating the characteristics of each region, and the point spread function Sσ (606) and the look-up table (604) are obtained in the same procedure as described above. ) For each characteristic. The mask information generation unit (612) may be configured to generate mask information for each area according to the luminance value of the input image.

The contents of the lookup tables (503) and (604) and the characteristics of the point spread function (602) and (606) are obtained in advance and recorded in the storage unit (113) shown in FIG. 2 may be controlled by the central processing unit (114) shown in FIG. 2 so that each content is read out from the storage unit (113) and set in each unit when used.

<Configuration example of scattered radiation image removing unit>
FIG. 8 is a block diagram showing an example of the configuration of the scattered radiation image removal unit (304) included in the image processing unit (115) of FIG. The scattered radiation image removal unit (304) removes the estimated scattered radiation image obtained by the scattered radiation image estimation unit (303) from the input image, and calculates an output image.

As shown in FIGS. 8A and 8B, the scattered radiation image removing unit 304 can have various modifications. Hereinafter, these configurations and operations will be described one by one.

As shown in FIG. 8 (a), an example (scattered ray image removing unit (304 (a)) in which the scattered radiation image removing unit (304) is configured by only a subtractor (701) is shown.

Here, when Equation (1) described above is solved for Ip (x, y), Equation (10) is obtained.

By approximating the second term (Is (x, y)) of equation (10) with the output (ie, estimated scattered radiation image) of the scattered radiation image estimating unit (303) shown in FIG. An image (Ip (x, y)) can be obtained.

In accordance with this equation (10), in the configuration of the scattered radiation image removal unit (304 (a)) shown in FIG. 8 (a), the estimated scattered radiation image is subtracted from the input image by the subtractor (701), and the estimated primary radiation image is obtained. Is output as an output image. As a result, an output image (estimated primary line image) in which image quality fluctuations due to scattered rays are suppressed can be obtained.

Since the estimated primary line image obtained in this way does not include a scattered radiation image, the user may have an impression that the image quality is significantly different from the grid image described as the background art. The reason is that even if the grid is used, the scattered radiation cannot be completely suppressed, so the user is accustomed to the grid image in which a part of the scattered radiation remains and may not be accustomed to the estimated primary line image. is there.

Therefore, in the configuration of FIG. 8B, an equivalent scattered ray image generated when the grid is arranged is generated and added to the estimated primary line image. Thereby, an output image equivalent to the case of using the grid is obtained. That is, in the configuration of FIG. 8 (b), the configuration (304 (a)) of FIG. 8 (a) and the second scattered radiation image estimation unit (304 (b)) and the second scattered radiation image estimation unit (304 (b)) 303), a multiplier (702), and an adder (703). Then, the estimated primary line image output from the scattered radiation image removal unit (304 (a)) is input to the second scattered radiation image estimation unit (303), and the output (estimated scattered radiation image) is multiplied. Using the device (702), the grid loss coefficient is multiplied to generate a scattered radiation image equivalent to the case where the grid is arranged.

This scattered radiation image is added to the output (estimated primary line image) of the scattered radiation image removal unit (304 (a)) using an adder (703) to obtain an output image (an image simulating a grid image). . Here, the grid loss coefficient is a coefficient indicating the rate at which scattered radiation is attenuated by the grid, and may be a constant value regardless of the position (x, y) of the image. This grid loss coefficient is the end (left edge) when the grid is inserted between the table (109) and the X-ray detector (111 (a)) and when it is not inserted in the configuration shown in FIG. Alternatively, it may be obtained by measuring the ratio of scattered radiation intensity outside the right end).

<Operation example of image processing unit>
FIG. 9 is a flowchart showing an example of processing operations in the units (301) to (304) of the image processing unit (115).

The image processing unit (115) described above is constituted by a computer including a calculation unit such as a CPU and a storage unit in which a program is stored in advance, and the calculation unit reads and executes the program in the storage unit, The configuration may be such that the functions of the units (301) to (304) are realized by software processing, or some or all of the functions of the units (301) to (304) of the image processing unit (115) may be implemented by an ASIC ( The configuration may be realized by hardware such as Application (Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array).

Hereinafter, the processing operation of the image processing unit (115) will be described with reference to the flowchart of FIG. Here, a case where the functions of the units (301) to (304) of the image processing unit (115) are realized by software processing will be described as an example.

First, the central processing unit 114 has an X-ray control unit (104), an aperture / filter control unit (107), a mechanism control unit (110), according to the image acquisition conditions received from the user via the input unit (116), By controlling the detector control unit (112), the X-ray tube (102) irradiates the subject (108) with X-rays, and the X-rays that have passed through the subject (108) become X-ray detector (111). By detecting this, a transmission image is generated.

The image processing unit (115) starts the following processing by operating the functions of the units (301) to (304) when the calculation unit reads and executes the program in the storage unit in step (1001) of FIG. In step (1002), the image processing unit (115) acquires a transmission image (hereinafter also referred to as an input image) generated by the X-ray detector (111) via the detector control unit (112).

In step (1003), the high frequency component extraction unit (301) of the image processing unit (115) extracts at least one high frequency component in the spatial axis direction and the time axis direction from the input image. In step (1004), the body thickness distribution calculation unit (302) calculates the body thickness distribution from the high frequency component. In step (1005), the scattered radiation image estimation unit (303) estimates a scattered radiation image from the body thickness distribution calculated in step (1004). In step (1006), the scattered radiation image removal unit (304) generates an output image by subtracting the scattered radiation image estimated in step (1005) from the input image. In step (1007), the image processing unit (115) outputs the output image generated in step (1006), and the process ends in step (1008).

Note that the content of the processing in each of these steps is the same as the processing operation of each unit (301) to (304) described with reference to FIG. 2 to FIG. Also for the processing not specifically shown in FIG. 9, the operations of the units (301) to (304) in the configuration shown in FIGS. 2 to 8 can be realized by software.

As described above, a software program that operates on a general computer configuration represented by a personal computer (PC) can obtain an image in which image quality fluctuation due to scattered radiation is suppressed in a short time.

<Summary of Embodiment 1>
As described above, in the radiation imaging apparatus of the first embodiment, by using the configuration and operation of each unit shown in FIGS. 2 to 9, the body thickness distribution of the subject can be obtained in a short time without performing any iterative process. In addition to this, it is possible to obtain an image in which image quality fluctuations due to scattered rays are suppressed by using this body thickness distribution.

(Embodiment 2)
A radiation imaging apparatus according to Embodiment 2 of the present invention will be described.

<Another configuration example of the image processing unit>
The radiation imaging apparatus according to the second embodiment has a configuration in which the image processing unit (115) in the radiation imaging apparatus according to the first embodiment shown in FIG. 2 is replaced with an image processing unit (801) shown in FIG. Description of blocks common to FIG. 2 is omitted, and the image processing unit (801) after replacement will be described below.

FIG. 10 is a block diagram showing an example of the configuration of the image processing unit (801) included in the radiation imaging apparatus according to the second embodiment. The image processing unit (801) of the second embodiment suppresses the influence even when halation (out-of-white) due to saturation of the X-ray detector (111) occurs in the transmission image, thereby reducing the body thickness. Find the distribution. That is, when the X-ray detector that detects the transmission image is saturated with X-rays and the X-ray detector (111) is saturated, the body thickness distribution at the saturated position The replacement unit replaces the body thickness calculated by the calculation unit (302) with a different value.

As described with reference to FIG. 3, the radiation imaging apparatus according to the first embodiment of the present invention pays attention to the X-ray noise (high frequency component) as shown in FIGS. 3 (a1) and 3 (b1). The transmission image was separated into a high frequency component and a low frequency component, and a body thickness distribution was obtained from the intensity of the high frequency component. However, if the intensity of X-rays emitted from the X-ray tube (102) is too strong, the X-ray detector (111) will be saturated, causing halation (whiteout) in the brightness of the transmitted image, and high-frequency components May seem to disappear. In this case, the average value of the noise component intensity is 0, and the body thickness distribution calculation unit (302) shown in FIG. 6 refers to the conversion characteristic (504) of the lookup table (503) and is different from the actual body. The thickness is calculated. That is, since the average value of the noise component intensity is 0 in spite of the region where the X-ray intensity is strong (i.e., the region where the body thickness is thin), the body thickness distribution calculation unit (302) An extremely thick body thickness that does not penetrate is calculated. Therefore, the image processing unit (115) shown in FIG. 4 may result in an incorrect output image.

Therefore, in the image processing unit (801) shown in FIG. 10 (a), the high-frequency component extracting unit (301), the body thickness distribution calculating unit (302), and the scattered radiation constituting the image processing unit (115) shown in FIG. Based on the image estimation unit (303) and the scattered radiation image removal unit (304), a new body thickness distribution calculation unit (802), a comparator (detection unit) (803), and a switch (replacement unit) ( 804) is added. Hereinafter, the operation of each unit will be described.

First, the body thickness distribution calculation unit (802) calculates the body thickness distribution for each position (x, y) using the luminance value of the input image instead of the high frequency component. More specifically, the relationship (conversion characteristics) between the subject thickness and the average value of the luminance values of the input images obtained in advance in each image acquisition condition is stored in a lookup table (not shown), and the body thickness The distribution calculation unit (802) refers to the conversion characteristics of the lookup table, obtains the body thickness from the luminance value of the input image for each position (x, y), and outputs the obtained body thickness distribution as body thickness information. To do. The relationship between the thickness of the subject and the average value of the luminance values of the input image is as shown in FIG. 3 for each image acquisition condition while appropriately changing the thickness of the subject (202) using the configuration shown in FIG. After acquiring the transmission image shown in a1), the relationship between the thickness under each image acquisition condition and the average value of the luminance values of the input image may be obtained.

Subsequently, the comparator (803) compares the body thickness information calculated by the body thickness distribution calculation unit (802) with a predetermined threshold for each position (xy), and the body thickness at each position is less than the threshold. When it is small (thin), it is determined that there is a possibility that the transmitted image at the position (x, y) is whiteout. Using this determination result, the switch (804) uses the body thickness information output from the body thickness estimation unit (302) for the position (x, y) where the transmission image may be whiteout. Instead, the body thickness information output from the body thickness estimation unit (802) is input to the scattered radiation image estimation unit (303).

As a result, the scattered radiation image estimation unit (303) allows the X-ray detector (111) to saturate, and even if halation occurs in the brightness of the transmitted image, Since the body thickness information obtained from the luminance value of the transmission image can be used, the scattered radiation image can be estimated based on the body thickness without being affected by the whiteout.

On the other hand, the image processing unit (805) illustrated in FIG. 10B is a configuration example in which the configuration of the image processing unit (804) illustrated in FIG. The image processing unit (805) includes a high frequency component extraction unit (301), a body thickness distribution calculation unit (302), a scattered radiation image estimation unit (303), and the image processing unit (115) shown in FIG. Based on the scattered radiation image removal unit (304), a comparator (806) and a switch (807) are newly added. The operation of each added part will be described below.

The comparator (806) compares the luminance value of the input image with a predetermined threshold value for each position (x, y), and when the luminance value at each position is larger than the threshold value, the position (x, y) It is determined that there is a possibility that the transparent image is whiteout. Using this determination result, at the position (x, y) where the transmission image may be overexposed, the switch (807) replaces the body thickness information output from the body thickness estimation unit (302). Then, the body thickness setting value is input to the scattered radiation image estimation unit (303). At this time, as the body thickness setting value, a predetermined constant may be used, for example, a setting value representing body thickness = 0 cm.

Thereby, the scattered radiation image estimation unit (303) can use a predetermined body thickness setting value for the position at which whiteout occurs even when halation (whiteout) occurs in the brightness of the transmitted image. Therefore, it is possible to estimate a scattered radiation image in which the influence of whiteout is reduced.

<Summary of Embodiment 2>
If the image processing unit (801) or the image processing unit (805) is configured as described above and used instead of the image processing unit (115), the image processing unit (801 ) (805) can be prevented from outputting an incorrect image.

(Embodiment 3)
A radiation imaging apparatus according to Embodiment 3 will be described.
<Another configuration example of the image processing unit>
The radiation imaging apparatus according to the third embodiment has a configuration in which the image processing unit (115) in the radiation imaging apparatus according to the first embodiment shown in FIG. 2 is replaced with an image processing unit (901) shown in FIG. Description of blocks common to FIG. 2 will be omitted, and the image processing unit (901) after replacement will be described below.

FIG. 11 is a block diagram illustrating an example of a configuration in the image processing unit (901) of the third embodiment.

In the configurations and operations of the first and second embodiments described above, the body thickness distribution is calculated by putting some approximations, so errors due to the approximation may be mixed in the output image. In applications where the user observes a moving image (X-ray fluoroscopy), it is sufficient to allow this error and give priority to high-speed processing. On the other hand, when the user observes a still image (X-ray imaging) or the like, it may be better to reduce the error at the expense of processing speed.

Therefore, in the image processing unit (901) shown in FIG. 11, the body thickness distribution correction unit (902) for correcting the body thickness value calculated by the body thickness distribution calculation unit (302) and the correction unit (902) output An estimated transmission line image (estimated input image) generation unit (904) that generates an estimated transmission line image based on the corrected body thickness and a transmission image (input image, that is, radiation) output from the X-ray detector (111) A comparison unit (905) for comparing the intensity distribution) and the estimated transmission line image. The correction unit (902) adjusts the correction amount based on the output of the comparison unit (905).

Specifically, the high-frequency component extraction unit (301), the body thickness distribution calculation unit (302), the scattered radiation image estimation unit (303), and the scattered radiation image removal that constitute the image processing unit (115) shown in FIG. Based on the unit (304), the image processing unit (901) newly includes a body thickness distribution correction unit (902), a switch (903), an estimated input image generation unit (904), and a comparator (905). to add. Hereinafter, a parameter acquisition method prepared in advance will be described before the operation of each unit is described.

First, using the configuration shown in FIG. 3 (a), the brightness value of the transmitted image detected by the X-ray detector (111 (a)) while appropriately changing the image acquisition conditions and the thickness of the subject (202). And the line attenuation coefficient μ is obtained in advance based on the equation (2). Subsequently, using the method described above, the point spread function Sσ (T (x, y)) (602) or the point spread function Sσ (606) when the X-ray is scattered in the subject (202) is obtained. deep.

Subsequently, the operation of each part when the radiation imaging apparatus is actually used will be described.

In the image processing unit (901), body thickness information (T (x, y)) is obtained from the input image via the high frequency component extraction unit (301) and the body thickness distribution calculation unit (302). The operation so far (initial operation) is the same as the operation of each unit in the image processing unit (115) shown in FIG.

Next, in the initial operation, body thickness information (x, y) is input to the estimated input image generation unit (904) via the switch (903) switched to the upper path in FIG. Based on this body thickness information (T (x, y)), the estimated input image generation unit (904) generates an estimated input image using the above-described equations (1), (2), and (3).

Specifically, using the previously obtained linear attenuation coefficient μ, body thickness information (T (x, y)) and dose Io (x, y), the estimated primary line image Ip (x , y). Also, using this estimated primary line image Ip (x, y) and the point diffusion function Sσ (T (x, y)) or the point diffusion function Sσ obtained in advance, the estimated scattered radiation image from Equation (3) Find Is (x, y). Subsequently, an estimated input image Im (x, y) is obtained from Expression (1) using the obtained estimated primary line image Ip (x, y) and estimated scattered radiation image Is (x, y).

The luminance value of the estimated input image Im (x, y) thus obtained and the luminance value of the actual input image are compared for each position (x, y) by the comparator (905), and the difference between both images is compared. δ (x, y) is obtained, and this difference δ (x, y) is input to the body thickness distribution correction unit (902).

The body thickness distribution correction unit (902) corrects the body thickness information T (x, y) based on the sign (positive / negative) of the value of the difference δ (x, y). If the difference δ (x, y) is positive (i.e., if the luminance value of the estimated input image is larger than the luminance value of the actual input image (x, y)), the position (x, y ) Body thickness information T (x, y) is corrected to a slightly larger value (T (x, y) + Δ, where Δ is a positive value). Conversely, when the difference δ (x, y) is negative (i.e., when the luminance value of the estimated input image is smaller than the luminance value of the actual input image (x, y)), the position ( The body thickness information T (x, y) of x, y) is corrected to a slightly smaller value (T (x, y) −Δ, where Δ is a positive value). The corrected body thickness information (T (x, y) ± Δ) is output as new body thickness information T (x, y) from the body thickness distribution correction unit (902).

Here, the switch (903) is switched to the lower path in FIG. 11, and the estimated input image (904), the comparator (905), the body thickness distribution correction unit ( When the operations in 902) are repeated, the absolute value of the difference δ (x, y) between the luminance value of the estimated input image and the luminance value of the actual input image gradually decreases. When the absolute value of the difference δ (x, y) is smaller than a predetermined threshold value at all positions (x, y) or when a predetermined number of repetitions is reached, a corrected body The thickness information T (x, y) is regarded as final body thickness information T (x, y), and the iterative process is terminated.

Using this final body thickness information T (x, y) and the input image, the scattered radiation image estimation unit (303) obtains an estimated scattered radiation image, and the scattered radiation image removal unit (304) estimates the scattered light from the input image. The line image is subtracted to obtain an output image of the image processing unit (901).

Before processing a new input image, the switch (903) is switched to the upper path in FIG. 11 to return to the initial operation.

As described above, the image processing unit (901) of the third embodiment can reduce errors included in the body thickness calculated by the body thickness distribution calculating unit (302) by performing iterative processing.

In the configuration example of the image processing unit (901) shown in FIG. 11, the body thickness distribution correction unit (902), the estimated input image generation unit (904), and the comparator (905) are controlled so as not to function. If the switch (903) is left switched to the upper path in FIG. 11, the output of the body thickness distribution calculation unit (302) is input to the scattered radiation image estimation unit (303). The image processing unit (901) shown in FIG. 11 has the same function as the image processing unit (115) shown in FIG. In this way, by configuring the path of body thickness information to be switched, the function can be switched between the application where the user observes the movie (X-ray fluoroscopy) and the application where the user observes the still image (X-ray imaging). Can be used.

In the apparatus using the iterative processing as described above, the initial value of the body thickness information T (x, y) (that is, the body thickness information T (x, y) output from the body thickness distribution calculation unit (302)) Depending on the accuracy, the number of iterations varies greatly. In the radiation imaging apparatus according to the third embodiment, as described above, the body thickness information is estimated from the noise (high frequency component) included in the transmission image. Therefore, the body thickness is determined from the intensity distribution Im (x, y) of the transmission image. Since the influence of scattered radiation can be suppressed rather than estimating information, and the accuracy of body thickness information can be kept high, the number of iterations can be greatly reduced, and an image in which fluctuations in image quality due to scattered radiation are suppressed can be obtained in a short time. It becomes possible.

<Summary of Embodiment 3>
As described above, the radiation imaging apparatus according to Embodiment 3 can reduce errors mixed in the output image due to errors included in the calculated body thickness. In addition, compared with the prior art, the number of processing iterations can be greatly reduced, and an image in which fluctuations in image quality due to scattered rays are suppressed can be obtained in a short time.

(Embodiment 4)
A radiation imaging apparatus according to Embodiment 4 will be described.
<Another configuration example of radiation imaging apparatus>
FIG. 12 is a block diagram illustrating an example of a configuration of the radiation imaging apparatus according to the fourth embodiment.

In the configuration example of the radiation imaging apparatus according to Embodiment 1 shown in FIG. 2, it is assumed that each unit configuring this apparatus is incorporated into the same apparatus or a plurality of apparatuses arranged close to each other. Therefore, it is necessary to incorporate an image processing unit for each apparatus.

Therefore, in the fourth embodiment, as shown in FIG. 12, the radiation imaging apparatus (1101) is separated into a client unit (1102) that acquires and displays a transmission image and a server unit (1105) that performs image processing. The two are connected by a communication network (1104).

The client unit (1102) removes the image processing unit (115) from the configuration example of the radiation imaging apparatus according to the first embodiment shown in FIG. 2, and is provided with a network interface (I / F) unit (1103) instead. It is a configuration. The components other than the network I / F unit (1103) are the same as the configuration and operation of each unit shown in FIG.

The network I / F unit (1103) included in the client unit (1102) includes a network transmission I / F unit (not shown) for transmitting image data to the communication network (1104), and includes HTTP (HyperText Transfer Protocol) and FTP ( Using a general network protocol such as File (Transfer Protocol), the transmission image (input image) detected by the X-ray detection unit (111) is transmitted to the server unit (1105) via the communication network (1104). . The network I / F unit (1103) includes a network reception I / F unit (not shown) for receiving image data from the communication network (1104), and an image (output image) processed by the server unit (1105). Is transmitted via the communication network (1104) and sent to the display unit (117).

The network I / F unit (1103) may be configured to be connected to and controlled by the central processing unit (114). Since the network I / F unit (1103) can be realized by a general technique, detailed description thereof is omitted.

The communication network (1104) may be a general Internet or an intranet, a private network closed in a facility, a public network such as a fixed telephone line or a wireless telephone line, or a wireless LAN or BlueTooth (registration). (Trademark) or the like.

The server unit (1105) includes a network I / F unit (1106), an image processing unit (1107), a central processing unit (1108), and a storage unit (1109).

The network I / F unit (1106) included in the server unit (1105) includes a network reception I / F unit (not shown) for receiving image data from the communication network (1104), and includes HTTP (HyperText Transfer Protocol) and FTP ( The input image transmitted from the client unit is received via the communication network (1104) using a general network protocol typified by File (Transfer Protocol). In addition, a network transmission I / F unit (not shown) for transmitting image data to the communication network (1104) is provided, and an image processed by the image processing unit (1107) is transferred to the client unit (1102) via the communication network (1104). ). The network I / F unit (1106) may be configured to be connected to and controlled by the central processing unit (1108). Since the network I / F unit (1106) can be realized by a general technique, detailed description thereof is omitted.

The image processing unit (1107) receives the input image received from the client (1102) via the network I / F unit (1106) (that is, the radiation intensity distribution obtained by detecting the radiation that has passed through the subject (108)). The extraction unit (301) for extracting at least one high-frequency component in the spatial axis direction and the time-axis direction, and the thickness distribution calculation for obtaining the thickness distribution of the subject based on the high-frequency component extracted by the extraction unit (301) Part (body thickness distribution calculation unit) (302) and a scattered ray distribution for obtaining a distribution of scattered rays generated by radiation passing through the subject based on the thickness distribution of the subject calculated by the thickness distribution calculation unit (302) An estimation unit (303) and a scattered radiation distribution removal unit (304) that removes the scattered radiation distribution obtained by the scattered radiation distribution estimation unit (303) from the input image. The image processing unit (1107) includes the image processing unit (115) shown in FIGS. 2 and 4, the image processing units (801) and (805) shown in FIG. 10, and the image processing unit (901) shown in FIG. Of these, the same configuration can be realized. Further, by using the program shown in the flowchart shown in FIG. 9, the computer functions as an extraction unit (extraction unit) (301), a body thickness distribution calculation unit (body thickness distribution calculation unit) (302), and the like. Also good. The image processing unit (1107) may be configured to be connected to and controlled by the central processing unit (1108).

The storage unit (1109) is connected to the central processing unit (1109), and the contents of the aforementioned look-up tables (503) and (604) and the characteristics of the point spread function (602) necessary for the operation of the image processing unit (1107). ) (606) is stored.

As described above, the radiation imaging apparatus (1101) is separated into a client unit (1102) that acquires and displays a transmission image and a server unit (1105) that performs image processing, and both are connected by a communication network (1104). By adopting a connection configuration, the following effects can be obtained.

First, since it is only necessary to install one server unit (1105) for a plurality of client units (1102), a large-scale radiation imaging apparatus can be constructed economically.

Also, by using the Internet or the like as the communication network (1104), the client unit (1102) and the server unit (1105) can be installed at remote locations.

Furthermore, if a login control unit (not shown) is provided in the client unit (1102) and a user authentication / management unit and a billing processing unit (not shown) are provided in the server unit (1105), the client unit (1102) is operated. A billing business using the server unit (1105) can be implemented for the user.

The login control unit is software program processing executed by the central processing unit (114) of the client unit (1102), and the user authentication / management unit and billing processing unit are executed by the central processing unit (1108) of the server unit (1105). If the software program processing is performed, each part can be easily realized by using a generally known technique, and a detailed description of each part will be omitted.

<Summary of Embodiment 4>
As described above, if the radiation imaging apparatus according to the fourth embodiment is used, it is possible to obtain an image in which image quality fluctuations due to scattered rays are suppressed through a network, and a large-scale radiation imaging apparatus is economical. Can be constructed in a remote location, can be installed in a remote location, or can be charged.

<Overall summary>
(I) According to the embodiment of the present invention described above, the radiation source that irradiates the subject with radiation, the radiation detector that detects the intensity distribution of the radiation that has passed through the subject, and the radiation intensity distribution in the spatial axis direction And an extraction unit that extracts at least one high-frequency component in the time axis direction, and a body thickness distribution calculation unit that obtains the thickness distribution of the subject based on the high-frequency component extracted by the extraction unit A radiation transmission image with suppressed fluctuations can be obtained in a short time.
(Ii) The present invention can be realized by hardware and software program codes that implement the functions of the embodiments.

For functions implemented by software program codes, a storage medium in which the program codes are recorded is provided to an apparatus or device, and the apparatus or a computer (or CPU or MPU) of the apparatus stores the program code stored in the storage medium. read out. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention. As a storage medium for supplying such program code, for example, a flexible disk, CD-ROM, DVD-ROM, hard disk, optical disk, magneto-optical disk, CD-R, magnetic tape, nonvolatile memory card, ROM Etc. are used.

Further, based on the instruction of the program code, an OS (operating device) or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. May be. Further, after the program code read from the storage medium is written in the memory on the computer, the computer CPU or the like performs part or all of the actual processing based on the instruction of the program code. Thus, the functions of the above-described embodiments may be realized.

Furthermore, by distributing the program code of the software that realizes the functions of the embodiments via a network, the program code is stored in a device or a storage means such as a hard disk or a memory, or a storage medium such as a CD-RW or CD-R. The device or the computer (or CPU or MPU) of the device may read and execute the program code stored in the storage means or the storage medium when used.

Finally, it should be understood that the processing content and techniques described here are not inherently related to any particular device, and can be implemented with any suitable combination of components. In addition, various types of devices for general purpose can be used in accordance with the teachings described herein. It may prove useful to build a dedicated device to perform the method steps described herein. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined. Although the present invention has been described with reference to specific examples, these are in all respects illustrative rather than restrictive.

Those skilled in the field will appreciate that there are numerous combinations of hardware, software, and firmware that are suitable for implementing the present invention. For example, the described hardware may be implemented by ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), etc., and the described software is assembler, C / C ++, perl, Shell, PHP, Python. , Java (registered trademark) or a wide range of programs or script languages may be used.

Furthermore, in the above-described embodiment, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. All the components may be connected to each other.

In addition, other implementations of the invention will become apparent to those skilled in the art from consideration of the specification and embodiments of the invention disclosed herein. Various aspects and / or components of the described embodiments can be used alone or in any combination in a computerized storage device having the capability of managing data.

101, 1101 ...

Radiation imaging devices

108, 202 ...

Subjects

115, 801, 805, 901, 1106 ... Image processing unit 301 ... High frequency component extraction unit 302 ... Body thickness distribution calculation unit 303 .. Scattered ray image estimation unit 304... Scattered ray

image removal units

503 and 604... Lookup tables 602 and 606... Scattered ray point diffusion functions 610 and 611. Unit 1104 ... Communication network 1105 ... Server unit

Claims

A radiation source that irradiates the subject with radiation, a radiation detector that detects an intensity distribution of the radiation that has passed through the subject, and at least one high-frequency component in the spatial axis direction and the time axis direction are extracted from the radiation intensity distribution. A radiation imaging apparatus comprising: an extraction unit; and a thickness distribution calculation unit that obtains the thickness distribution of the subject based on the high-frequency component extracted by the extraction unit.
The radiation imaging apparatus according to claim 1, wherein the thickness distribution calculation unit is configured to calculate the thickness of the subject corresponding to the strength of the high-frequency component based on the relationship between the thickness of the subject obtained in advance and the strength of the high-frequency component. A radiation imaging apparatus characterized by obtaining a thickness.
2. The radiation imaging apparatus according to claim 1, wherein a scattered radiation for obtaining a distribution of scattered radiation generated by the radiation passing through the subject from the thickness distribution of the subject obtained by the thickness distribution calculating unit. A radiation imaging apparatus further comprising a distribution estimation unit.
The radiation imaging apparatus according to claim 3, further comprising a scattered radiation distribution removing unit that removes the scattered radiation distribution obtained by the scattered radiation distribution estimation unit from the intensity distribution of the radiation detected by the radiation detector. A radiation imaging apparatus.
4. The radiation imaging apparatus according to claim 3, wherein the scattered radiation distribution estimation unit includes a filter that obtains a degree of spread of the radiation according to a thickness of the subject at each position of the subject. A radiation imaging apparatus.
The radiation imaging apparatus according to claim 4, wherein the scattered radiation distribution removing unit has a scattered radiation distribution equivalent to a scattered radiation distribution generated when a grid is disposed between the subject and the radiation detector. A radiation imaging apparatus, wherein the radiation imaging apparatus generates the radiation intensity distribution based on the distribution of the thickness of the subject and adds the radiation intensity distribution obtained by removing the scattered radiation distribution obtained by the scattered radiation distribution estimation unit.
5. The radiation imaging apparatus according to claim 4, wherein the radiation intensity distribution is a radiation image of the subject, the scattered radiation distribution is an image of scattered radiation generated by the subject, and the scattered radiation distribution is removed. The unit removes the image of the scattered radiation from the radiation image.
The radiation imaging apparatus according to claim 1, wherein the detection unit determines whether the radiation detector that has detected the intensity distribution of the radiation is saturated with the radiation,
When the radiation detector is saturated, the radiation imaging apparatus further includes a replacement unit that replaces the thickness calculated by the thickness distribution calculation unit with a different value at a saturated position.
The radiation imaging apparatus according to claim 8, wherein the replacement unit replaces the thickness at the saturated position with a thickness obtained from the radiation intensity detected by the radiation detector. A radiation imaging apparatus.
9. The radiation imaging apparatus according to claim 8, wherein the replacement unit replaces the thickness at the saturated position with a predetermined value.
The radiation imaging apparatus according to claim 1,
A correction unit for correcting the thickness value calculated by the thickness distribution calculation unit;
An estimated transmission line image generation unit that generates an estimated transmission line image based on the corrected thickness output by the correction unit;
A comparison unit that compares the intensity distribution of the radiation and the estimated transmission line image;
The correction unit repeats an operation of adjusting a correction amount for the thickness value of the correction unit based on an output of the comparison unit one or more times.
The radiation imaging apparatus according to claim 1,
The extraction unit includes at least one of a high-pass filter that extracts high-frequency components in the radiation intensity distribution and a high-pass filter that extracts high-frequency components between the plurality of radiation intensity distributions detected at different times. Radiation imaging device.
An extraction unit that receives a radiation intensity distribution obtained by detecting radiation that has passed through a subject from the outside, and extracts at least one high-frequency component in a spatial axis direction and a time axis direction for the radiation intensity distribution; and An image processing apparatus comprising: a thickness distribution calculation unit that obtains the thickness distribution of the subject based on the extracted high-frequency component.
The image processing apparatus according to claim 13,
A network reception interface unit that receives and acquires the radiation intensity distribution via a communication network;
An image processing unit;
A network transmission interface unit that transmits and outputs the image generated by the image processing unit via the communication network;
The image processing unit is configured to detect scattered radiation generated by the radiation passing through the subject based on the thickness distribution of the subject calculated by the extracting unit, the thickness distribution calculating unit, and the thickness distribution calculating unit. A scattered radiation distribution estimation unit for obtaining a distribution; and a scattered radiation distribution removal unit for removing the scattered radiation distribution obtained by the scattered radiation distribution estimation unit from the radiation intensity distribution, wherein the scattered radiation distribution removal unit is the scattered radiation An image processing apparatus that generates an image from the radiation intensity distribution from which the distribution is removed.
An extraction means for receiving from the outside a radiation intensity distribution obtained by detecting radiation that has passed through the computer, and extracting at least one high-frequency component in the spatial axis direction and the time axis direction of the radiation intensity distribution;
An image processing program for functioning as a thickness distribution calculating means for obtaining a thickness distribution of the subject based on a high frequency component extracted by the extracting means.