JP7150558B2 - Radiation image processing system, image processing method, and program - Google Patents

Description

The present invention relates to a system, method, and program for processing an image (transmission image) obtained by irradiating a subject with radiation.

In the medical field, an image obtained by irradiating a subject such as a human body (patient) with radiation such as X-rays and detecting the intensity distribution of the radiation transmitted through the subject with a detector (hereinafter referred to as a transmitted image). are displayed in real time, doctors and technicians perform medical treatments such as treatments and examinations.

ERCP (endoscopic retrograde cholangiopancreatography), which is an example of medical practice and uses an endoscope (gastroscope) to image the bile duct and pancreatic duct, examines the endoscope from the mouth to the duodenum. A catheter (thin tube) is inserted from the tip of the endoscope into an organ such as the pancreatic duct and bile duct, a contrast agent is injected through the catheter, and an X-ray photograph of the organ is taken. At this time, since the diameter of the endoscope is large and it does not enter the internal organs, devices such as catheters and guide wires (thin metal wires) that are easy to pass through are commonly used as an aid. Devices such as catheters and guidewires are referred to herein as procedural devices.

The above-described real-time display of transmission images is used in the medical practice described above to confirm whether or not the surgical device is inserted in the correct position.

When a guide wire is inserted into the pancreatic duct in an ERCP examination, the pancreas is anatomically located across the spine, so the guide wire and the vertebral bodies (individual bones that make up the spine) tend to overlap in a fluoroscopic image. Therefore, since the X-rays are greatly attenuated by the vertebral bodies, the region in which the vertebral bodies are reflected becomes dark in the transmission image. At this time, since the guide wire overlapping the vertebral bodies becomes difficult to see visually, there is a problem that the operation of the guide wire by the doctor is hindered.

Therefore, it is desired to realize an image processing technique that relatively improves the visibility of the surgical device by attenuating the vertebral bodies and the like reflected in the transmission image.

For example, Non-Patent Document 1 describes a technique for recognizing and attenuating ribs and clavicle reflected in a transmission image for the purpose of realizing software for assisting interpretation of pulmonary nodule lesions reflected on plain chest X-ray images. describes an image processing technique that improves visibility within the lung field. In this technology, (1) lung field recognition processing, (2) bone recognition processing, and (3) bone signal attenuation processing are performed, and by attenuating only signal changes caused by bones, abnormal shadows and blood vessels overlapping bones can be detected. Such fine structure signals are left as they are in the original image to improve the visibility of lesions.

Tsuyoshi Kobayashi, et al., "CAD Application for Plain Chest X-ray," Development of Bone Suppression Processing, KONICA MINOLTA TECHNOLOGY REPORT VOL.12 pp.71-76 (2015)

As described above, the technique described in Non-Patent Document 1 describes performing (1) lung field recognition processing, (2) bone recognition processing, and (3) bone signal attenuation processing. According to Non-Patent Document 1, these specific processing contents are as follows.

(1) In lung field recognition processing, the lung fields are classified into four regions (apex of the lung, outer thoracic region, diaphragm, and mediastinum) with different characteristics of the borders, and the edge that is most suitable for each border is classified. The information is used to extract the region.

(2) In the bone recognition process, bone model information constructed from a large amount of data is used to estimate the bone structure based on the prior information shown, and the bone structure unique to the subject measured from the plain chest X-ray image of the subject. By combining these estimation results, we have achieved robust bone recognition that accurately extracts the detailed bone structure.

(3) In bone signal attenuation processing, bone signal components are estimated from the recognized bone candidates and attenuation is performed. The estimation uses the signal changes of structures that do not overlap with the ribs and clavicle.

As described above, the technique described in Non-Patent Document 1 aims at realizing software for supporting the interpretation of pulmonary nodule lesions. By using it, bones and the like reflected in the transmission image are attenuated by non-real time processing (offline processing).

On the other hand, in the above-mentioned ERCP examination, etc., when improving the visibility of the surgical device etc. in real time, it is very difficult to perform advanced image recognition processing etc. by software running on a general-purpose computer such as a personal computer (hereinafter referred to as PC). It takes a long processing time, and there is a problem that the movement of the subject such as the surgical device and internal organs is not smooth and an unnatural transmission image is displayed. Therefore, in order to display a transmissive image in which the movement of the subject is smooth and natural, an expensive device with special computer resources capable of executing high-speed processing is required, which is uneconomical.

The present invention has been made in view of such circumstances, and provides a radiation image processing system capable of reducing the amount of calculation and improving the real-time visibility of a surgical device.

A brief outline of typical inventions disclosed in the present application is as follows. That is, a radiation image processing system that irradiates a subject with radiation and captures a transmission image, and includes an image generation unit that generates a first transmission image, and a process for improving the visibility of the first transmission image. and an image processing unit, wherein the image processing unit includes a low frequency component extraction unit that extracts low frequency components from the first transmission image, and a division processing unit that divides the first transmission image by the low frequency component. and a halo reduction unit for reducing a halo in the first transmission image.

Advantageous Effects of Invention According to the present invention, it is possible to obtain in real time a transmitted image of a surgical device or the like with improved visibility. Problems, configurations and effects other than those described above will be clarified by the following description of the embodiments.

1 is a block diagram showing an example of the configuration of a radiation image processing system according to Example 1; FIG. 3 is a block diagram showing an example of the configuration of an image processing unit of Example 1; FIG. 5 is a flowchart for explaining an example of processing executed by an image processing unit according to the first embodiment; 4A and 4B are diagrams illustrating a specific example of processing executed by an image processing unit according to the first embodiment; FIG. FIG. 5 is a diagram showing an example of the effect of Example 1; FIG. 11 is a block diagram showing an example of the configuration of an image processing unit of Example 2; FIG. 10 is a diagram illustrating a specific example of processing executed by an image processing unit according to the second embodiment; FIG. 10 is an explanatory diagram of the operation of the halo reduction unit of Example 2; FIG. 11 is a block diagram showing an example of the configuration of a halo reduction unit of Example 2; 10 is a flowchart illustrating an example of processing executed by an image processing unit of Example 2;

The present invention provides a technique for realizing a real-time transmission image with improved visibility of a surgical device or the like.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that although the accompanying drawings show specific embodiments and implementations in accordance with the principles of the present invention, they are for the purpose of understanding the present invention and are by no means intended to limit the interpretation of the present invention. not used.

Although the examples are described in sufficient detail to enable those skilled in the art to practice the invention, other implementations and configurations are possible without departing from the scope and spirit of the invention. It should be understood that changes in configuration and structure and substitution of various elements are possible. Therefore, the following description should not be construed as being limited to this.

In addition, in all the drawings for explaining the embodiments, the same members are basically given the same reference numerals, and the repeated description thereof will be omitted.

<Configuration example of radiation image processing system>
FIG. 1 is a block diagram showing an example of the configuration of a radiation image processing system according to a first embodiment.

As shown in FIG. 1, the radiation image processing system 101 includes an X-ray tube 102, a high voltage generator 103, an X-ray controller 104, an aperture 105, an X-ray compensation filter 106, an aperture/filter controller 107, a table 109, It has a mechanism control unit 110 , an X-ray detector 111 , a detector control unit 112 , a storage unit 113 , a central processing unit 114 , an image processing unit 115 , an input unit 116 and a display unit 117 .

A table 109 is a bed on which a subject 108 such as a person is placed. The mechanism control unit 110 is electrically connected to the table 109 and controls the movement of the table 109 so that the subject 108 is positioned appropriately for photographing. At this time, the X-ray detector 111 may also be configured to move integrally with the table 109 .

The X-ray tube 102 generates X-rays and irradiates the subject 108 placed on the table 109 with the X-rays. The high voltage generator 103 is electrically connected to the X-ray tube 102 and generates a high voltage to be applied to the X-ray tube 102 . The X-ray controller 104 is electrically connected to the high voltage generator 103 and controls the high voltage generator 103 to control the dose and quality of X-rays emitted from the X-ray tube 102 .

The diaphragm 105 is arranged in the X-ray irradiation direction of the X-ray tube 102, and controls the region irradiated with the 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 material with a high X-ray absorptance, and reduces halation by attenuating X-rays that reach parts of the subject 108 with a low X-ray absorptivity.

Aperture/filter control section 107 is electrically connected to aperture 105 and X-ray compensation filter 106 and controls aperture 105 and X-ray compensation filter 106 .

The X-ray detector 111 is arranged to face the X-ray tube 102 with an aperture 105, an X-ray compensation filter 106 and a table 109 interposed therebetween, and functions as an image generator. Specifically, the X-ray detector 111 converts the intensity distribution of the X-ray emitted from the X-ray tube 102 and transmitted through the object 108 into a feature quantity, and converts the transmission image data composed of the feature quantity for each pixel. Output. The feature amount is, for example, a brightness value, a variance value, and the like. In this specification, an image having a luminance value as a feature amount is used for explanation.

The detector control unit 112 is electrically connected to the X-ray detector 111 , acquires transmission image data by controlling the X-ray detector 111 , and inputs the transmission image data to the image processing unit 115 . By controlling the X-ray detector 111, the detector control unit 112 may generate a transmission image as a still image, or generate a plurality of transmission images captured at different timings as a moving image. good too. As for the imaging timing for generating the moving image, for example, fixed time intervals such as 30 frames per second and 15 frames per second can be considered. Note that the present invention is not limited to time intervals.

The image processing unit 115 is electrically connected to the detector control unit 112 and executes correction processing of a transmitted image captured by the X-ray detector 111 and input via the detector control unit 112 .

The central processing unit 114 is electrically connected to the X-ray control unit 104, the aperture/filter control unit 107, the mechanism control unit 110, the detector control unit 112, the storage unit 113, the image processing unit 115, the input unit 116, and the display unit 117. It controls each functional unit that is connected and electrically connected. The central processing unit 114 is, for example, a CPU (Central Processing Unit) of a general-purpose computer.

The storage unit 113 includes a recording medium such as a semiconductor memory and a magnetic disk, and stores image acquisition conditions, images, and the like as data. Note that the type of 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. The input unit 116 may have a keyboard, a mouse, control buttons, and the like, or may have a sensor or the like for voice input, gesture input, and the like.

A display unit 117 displays the corrected image. The display unit 117 may include a display, a printer, and the like.

The X-ray control unit 104, aperture/filter control unit 107, mechanism control unit 110, detector control unit 112, and image processing unit 115 are implemented using dedicated hardware, but the present invention is not limited to this. For example, each piece of hardware may be implemented as software. In this case, a program for realizing the function of each piece of hardware is stored in storage unit 113, and central processing unit 114 executes processing according to the program, thereby realizing the function of each piece of hardware.

Details of the image processing unit 115 will be described in detail below.

<Operating Principle of Radiation Image Processing System>
First, a transmission image Im(x, y) output as the intensity distribution of each pixel obtained when radiation (X-rays) passes through an object, and a primary line image Ip(x, y) and the characteristics of the scattered radiation image Is(x, y) output as the intensity distribution of the scattered radiation. Note that (x, y) in the following formula indicates the position of the pixel.

As shown in Equation (1), the transmission image Im(x, y) is expressed as the sum of the primary line image Ip(x, y) and the scattered line image Is(x, y). Here, the primary radiation image Ip(x, y) is given by Equation (2), and the scattered radiation image Is(x, y) is given by Equation (3). Note that the symbols in Equation (3) represent convolution operations.

Equation (2) indicates that the intensity of the primary line image Ip(x,y) decays exponentially according to the subject thickness T(x,y). Io(x, y) in Equation (2) indicates the intensity of the irradiation dose at the position (x, y), and μ indicates the radiation attenuation rate (linear attenuation coefficient) per unit thickness. Equation (3) expresses that the intensity of the scattered radiation image Is (x, y) is expressed by the convolution operation of the intensity of the primary radiation image Ip (x, y) and the point spread function Sσ (T (x, y)) indicates The point spread function Sσ(T(x, y)) is a function that changes according to the thickness T(x, y) of the object.

In general, between the object and the X-ray detector 111, a plate called a grid, in which thin layers of a material with high radiation absorption rate and a material with low radiation absorption rate are laminated alternately, is placed. Operations are carried out to keep the amount of scattered radiation low. Therefore, it can be considered that the intensity of the scattered radiation image Is(x, y) included in the transmitted image Im(x, y) is relatively weak. Therefore, for the sake of simplicity, the scattered radiation image Is(x, y) is treated as being sufficiently small, and the transmission image Im(x, y) is approximately equal to the primary radiation image Ip(x, y) as shown in Equation (4). The principle of operation of this embodiment will be described below by approximation.

In the following description, it is assumed that a surgical device having a thickness Td(x, y) is reflected in the transmitted image Im(x, y). However, Td(x, y)=0 at a position where the surgical device does not exist in the transmission image Im(x, y). At this time, the transmitted image Im(x, y) can be expressed as in Equation (5) from Equations (4) and (2).

Also, a transmission image Id(x, y) in which the surgical device is highlighted can be expressed as in Equation (6).

Here, since the surgical device is made of thin metal, the thickness Td(x, y) changes sharply according to the position (x, y). Therefore, the transmitted image Id(x, y) contains more high frequency components than low frequency components. On the other hand, the thickness T(x, y) of the object (internal organs, bones, results, muscles, etc.) excluding the surgical device changes relatively gently according to the position (x, y). Therefore, it contains more low-frequency components than high-frequency components. Therefore, the transmission image Io(x, y)exp(−μT(x, y)) of the subject excluding the surgical device is the low-frequency component image Iml(x, y) of the transmission image Im(x, y). can be approximated. Specifically, equation (6) can be approximated as equation (7).

To summarize the principle of operation of the radiation image processing system 100 described above, the transmission image Id(x, y) is obtained by dividing the transmission image Im(x, y) by its low-frequency component image Iml(x, y). can be approximately calculated by

<Configuration example of image processing unit>
FIG. 2 is a block diagram showing an example of the configuration of the image processing unit 115 according to the first embodiment. FIG. 3 is a flowchart illustrating an example of processing executed by the image processing unit 115 according to the first embodiment.

As shown in FIG. 2, the image processing unit 115 receives a transmitted image Im(x, y) captured by the X-ray detector 111 as an input image from the detector control unit 112 (step S301). The transmission image Im(x, y) is input to the low-frequency component extraction unit 201 and division processing unit 202 .

The low-frequency component extraction unit 201 of the image processing unit 115 extracts the low-frequency component image Iml(x, y) (step S302), and inputs the low-frequency component image Iml(x, y) to the division processing unit 202.

Note that the low-frequency component extraction unit 201 can be realized using a two-dimensional low-pass filter that passes horizontal and vertical low-frequency components. Since the method of extracting low-frequency components using a two-dimensional low-pass filter is well known, detailed description thereof will be omitted. The processing for extracting low-frequency components using a two-dimensional low-pass filter requires a short computation time and a small amount of computation.

The division processing unit 203 of the image processing unit 115 divides the transmission image Im(x, y) by the low-frequency component image Iml(x, y) as shown in Equation (7), thereby obtaining the transmission image Id(x , y) are calculated (step S303).

Division processing is performed for each pixel. Since the division process is a known calculation method, detailed description thereof will be omitted. The division process requires a short calculation time and a small amount of calculation.

The division processing unit 203 of the image processing unit 115 outputs the transmitted image Id(x, y) to the display unit 117 (step S304), and ends the process.

<Operation example of the image processing unit>
FIG. 4 is a diagram illustrating a specific example of processing executed by the image processing unit 115 according to the first embodiment.

FIG. 4A is an example of a transmitted image, and is a part of the transmitted image obtained by photographing a phantom (model) imitating the chest of a human body as the subject 108 . The image shows the shadow of the guidewire 402 and the shadows of a plurality of simulated vertebral bodies 403 aligned along the centerline 401 . Note that the center line 401 is a line added for explanation, and does not appear in the actual transmitted image.

FIG. 4(b) is an image obtained by extracting main contour lines from the image of FIG. 4(a). The positional relationship between the guide wire 402 and the vertebral body 403 in the image of FIG. 4(a) is as shown in FIG. 4(b).

FIG. 4(c) is a graph showing luminance values on the center line 401 of the image shown in FIG. 4(a). The vertical axis of the graph indicates the position in the vertical direction, and the horizontal axis of the graph indicates the luminance value of the image at that position. Note that the left side of the graph has a large value. In FIG. 4C, it can be seen that the signal changes gently at the position where the vertebral body 403 exists, and the signal changes sharply at the position where the guide wire 402 exists. This is because the guide wire is made of thin metal, so the radiation is greatly attenuated at the position where the guide wire exists, and the brightness value sharply decreases compared to the area around the guide wire, that is, the image sharply darkens. show that

FIG. 4(d) shows luminance values of low-frequency components extracted from the signal shown in FIG. 4(c). The signal change at the position where the vertebral body 403 exists is gentler than the signal change shown in FIG. 4(c). On the other hand, it can be seen that the signal at the position where the guide wire 402 exists is almost unchanged. This indicates that since the guide wire 402 is thin, the high-frequency component is the main component in this portion, and the high-frequency component is strongly attenuated by the low-frequency component extractor 201 .

FIG. 4(e) shows the luminance value obtained by dividing the signal shown in FIG. 4(c) by the signal shown in FIG. 4(d). Here, when the luminance value of the signal shown in FIG. 4(c) does not change, the luminance values of the signal shown in FIG. 4(c) and the signal shown in FIG. 4(d) are equal. ) is 1.0. Also, since the change in the luminance value at the position where the vertebral body 403 exists shown in FIG. change is relatively small. On the other hand, since the change in the luminance value at the position where the guide wire 402 exists is relatively steep, the luminance value at the position where the guide wire 402 exists after the division shown in FIG. 4E sharply decreases.

In this way, when the transmission image Im(x, y) is divided by its low-frequency component image Iml(x, y), the amount of change (amplitude) of the signal at the position where the vertebral body 403 exists is gradually reduced. On the other hand, the amount of change in the signal at the position where the guide wire 402 exists is steeply small. Therefore, the effect of improving the visibility of the guide wire 402 in the image is obtained.

<Example of effect in the image processing unit>
FIG. 5 is a diagram showing an example of the effect of the first embodiment. Hereinafter, the effect of improving the visibility of the guide wire in an actual transmission image will be described using this figure.

FIG. 5(a1) is a transmission image Im(x, y) of a phantom (model) simulating the chest of a human body. there is

FIG. 5(a2) shows an enlarged image of the rectangular portion of FIG. 5(a1). As shown in FIG. 5(a2), in the transmission image Im(x, y) before processing, the image is dark in the portion where the guide wire 501 and the vertebral body 502 overlap, and the guide wire 501 is difficult to see. .

FIG. 5(b1) is a transmission image Id(x, y) output by processing the transmission image Im(x, y) of FIG. 5(a1). In the transmission image Id(x, y), the position where the guide wire 501 exists is clearly displayed, and the position where the vertebral body 502 exists is displayed entirely in gray with a thin outline.

FIG. 5(b2) shows an enlarged image of the rectangular portion of FIG. 5(b1). As shown in FIG. 5(b2), the guide wire 501 can be clearly seen even in the portion where the guide wire 501 and the vertebral body 502 overlap. That is, the transmitted image Id(x, y) has improved visibility of the guide wire 501 compared to the original transmitted image Im(x, y).

<Summary of Example 1>
As described above, the radiographic image processing system 101 according to the first embodiment can output an image in which the luminance sharply decreases at the position where a surgical device made of metal with a steep contour such as a guide wire exists. As a result, there is a contrast difference between the background of the vertebral bodies (bones), internal organs, blood vessels, etc., and the device for manipulation, thereby improving the visibility of the device for manipulation.

Since the processing executed by the image processing unit 115 requires a short calculation time, an image can be displayed in real time. Also, the low-frequency component extraction unit 201 and the division processing unit 202 of the image processing unit 115 can be realized using a general-purpose computer, and there is no need to prepare dedicated computer resources, so costs can be reduced.

Next, Example 2 will be described. The configuration and processing of the image processing unit 115 are partially different in the second embodiment. The second embodiment will be described below, focusing on the differences from the first embodiment.

The configuration of the radiation image processing system 101 of the second embodiment is the same as that of the radiation image processing system 101 of the first embodiment.

<Configuration example of image processing unit>
FIG. 6 is a block diagram showing an example of the configuration of the image processing unit 115 according to the second embodiment.

As shown in FIG. 6, the image processing unit 115 includes a low frequency component extraction unit 201, a division processing unit 202, and a halo reduction unit 601. A low-frequency component extraction unit 201 and a division processing unit 202 have the same configurations as in the first embodiment.

<Operation example of the image processing unit>
FIG. 7 is a diagram illustrating a specific example of processing executed by the image processing unit 115 of the second embodiment.

FIG. 7(a) is a diagram showing a transmission image Id(x, y). A phenomenon in which the luminance value after division increases near the contour of the vertebral body 403, that is, at a position where the luminance value of the signal shown in FIG. 4(c) is greater than the luminance value of the signal shown in FIG. 4(d). , that is, a halo 701 is produced. Such a phenomenon in which the luminance value near the contour is increased (brighter) is called a "halo" because it looks like a "halo" is shining from behind the subject.

Objects that strongly attenuate radiation (X-rays), such as surgical devices and bones, appear dark (black) inside and bright (white) around the object in a transmission image. The low frequency components of this transmission image are slightly darker than the input signal outside the perimeter of the subject's contour. That is, the luminance value of the low-frequency component image becomes smaller than the luminance value of the transmission image. Therefore, when the brightness value of the transmission image is divided by the brightness value of the low-frequency component image, the resulting value is greater than 1.0, and a halo is generated.

In the transmission image Id(x, y) shown in FIG. 7A, in order to improve the visibility of the surgical device, the pass frequency band of the low-frequency component image is narrowed, and the luminance value of the input signal and the low-frequency It is important to increase the difference from the luminance value of the component.

However, when low-frequency component extraction with a narrow passband is performed on a transmitted image of a surgical device that is relatively thick and has a large amount of radiation attenuation, such as an endoscope, the halo becomes thick and bright. Become. If a strong halo is generated around the shadow at the position where the surgical device exists, not only will the image be unnatural, but it may also lead to misdiagnosis and overlooking of the lesion by the doctor. For example, since an endoscope is always used in ERCP, the halo is an eyesore when a doctor views organs around the endoscope.

Similarly, when the contrast medium is used undiluted, a thick and bright halo is produced around the contrast medium, and the bile duct wall appears unnatural in the transmission image, which may lead to misdiagnosis. In addition, EUS-BD (EUS-guided biliary drainage) uses a needle (metal), so a halo is likely to occur, making it difficult to recognize the tissue around the needle. There is a risk of interfering with the doctor's technique.

Thus, the occurrence of a strong halo can cause serious problems. Therefore, in the second embodiment, the halo reduction unit 601 executes processing for reducing the halo 702 as shown in FIG. 7B.

<Operation example of the halo reduction section>
FIG. 8 is an explanatory diagram of the operation of the halo reduction unit 601 of the second embodiment.

The halo reduction unit 601 can be realized as a luminance value converter having input/output characteristics as shown in FIG. 8(a) or 8(b).

FIG. 8(a) shows a luminance value converter having a line-shaped input/output characteristic such that the slope becomes smaller than 1.0 when the luminance value to be input is larger than 1.0. The brightness value converter has the characteristic that when the input value (u) is 1.0 or less, the output value (v) becomes a straight line 801 of v=u, and when the input value (u) is 1.0 or more , the output value (v) is a straight line 802 of v=k(u−1)+1. However, k is larger than 0.0 and smaller than 1.0. Halos with luminance values greater than 1.0 can be obscured by using the activation transducer.

FIG. 8(b) shows luminance value conversion with input/output characteristics of curve 803. FIG. The luminance value converter avoids an unnatural output image by continuously changing the slope of the curve around (u, v)=(1.0, 1.0), and By reducing the output value (v) corresponding to the halo for which the input value (u) is greater than 1.0, the halo can be made inconspicuous. Further, when the input value (u) is smaller than 1.0, the transmission image Id(x, In y), a thin shadow such as a diluted contrast medium is emphasized, so visibility can be improved.

The specific input/output characteristics of the curve 803 may be determined based on the balance between the effect of weakening dark shadows such as the vertebral bodies 403 and the effect of emphasizing thin shadows such as diluted contrast medium. For example, the characteristics may be determined by prior experiments or the like while confirming the visibility of each object in the transmission image.

The conversion of the luminance value is performed by a linear expression, a higher-order polynomial, a fractional expression, an exponential expression, a logarithmic expression, and a function combining these, which have input/output characteristics as shown in FIGS. 8(a) and 8(b). It may be realized by an expression or by a lookup table. The input/output characteristics of the lookup table may be determined experimentally. For example, if the input value (u) is greater than 1.0, set the output value (v) to be smaller than the input value (u) while checking how the halo looks, and set the input value (u) to If it is smaller than 1.0, the output value (v) is set based on the balance between the effect of weakening dark shadows such as the vertebral body 403 and the effect of emphasizing thin shadows such as diluted contrast medium.

<Configuration example of halo reduction unit>
FIG. 9 is a block diagram showing an example of the configuration of the halo reduction unit 601 according to the second embodiment. FIG. 10 is a flowchart illustrating an example of processing executed by the image processing unit 115 according to the second embodiment.

The processing from step S1001 to step S1003 is the same as the processing from step S301 to step S303. The transmission image Id(x, y) calculated by the division processing unit 202 is input to the halo reduction unit 601 .

The halo reduction unit 601 subtracts a predetermined luminance value from the transmitted image Id(x, y) (step S1004). This is because the halo has the property that the luminance value in the transmission image Id(x, y) is greater than 1.0.

Specifically, the subtractor 901 subtracts the brightness value of each pixel of the transmission image Id(x, y) by a predetermined brightness value. The luminance value to be subtracted can be set arbitrarily. For example, 1.0.

The halo reduction unit 601 determines whether the luminance value of each pixel is a positive component (step S1005).

When it is determined that the luminance value is a positive component, the positive component extractor 902 extracts the signal component according to the magnitude of the luminance value, and the low frequency component extractor 903 extracts the signal component extracted by the positive component extractor 902. A low-frequency component (low-frequency component image) is extracted from the obtained signal (step S1006).

The positive component extraction unit 902 calculates the output value (v) from the input value (u), for example, according to Equation (8). Equation (8) represents a function that outputs the larger of the input value (u) and 0.

A strong halo that interferes with a doctor's procedure is mainly composed of low-frequency components. Therefore, the halo reduction unit 601 extracts the positive low-frequency component as a halo.

Note that the low-frequency component extraction unit 903 can be realized using a two-dimensional low-pass filter, like the low-frequency component extraction unit 201. FIG. The number of taps (filter length) and pass frequency characteristics of the low-frequency component extraction unit 903 may be determined so as to match the frequency characteristics of the halo to be suppressed, or may be determined experimentally while checking how the halo looks. may decide.

Next, the subtractor 905 of the halo reduction unit 601 subtracts the low frequency component from the signal extracted by the positive component extraction unit 902 (step S1007). This makes it possible to suppress halos. If processing has not been completed for all pixels, the halo reduction unit 601 returns to step S1005 and performs similar processing. If all pixels have been processed, the halo reduction unit 601 proceeds to step S1009.

If it is determined in step S1005 that the luminance value is a negative component, the negative component extraction unit 904 extracts a signal component according to the magnitude of the luminance value (step S1008). If processing has not been completed for all pixels, the halo reduction unit 601 returns to step S1005 and performs similar processing. If all pixels have been processed, the halo reduction unit 601 proceeds to step S1009.

The negative component extraction unit 904 calculates the output value (v) from the input value (u), for example, according to Equation (9). Equation (9) represents a function that outputs the smaller of the input value (u) and 0.

In step S1009, adder 906 adds the output values of subtractor 905 and negative component extractor 904 (step S1009). Further, adder 907 adds a predetermined luminance value to the output value of adder 906 (step S1010).

Next, the halo reduction unit 601 uses the lookup table 908 to perform luminance value conversion for emphasizing a thin shadow such as a diluted contrast medium (step S1011).

The halo reduction unit 601 outputs the processed transmission image Id(x, y) to the display unit 117 (step S1012), and ends the process.

Note that the low frequency component extractor 903 and the subtractor 905 may be replaced with a high frequency component extractor. Also, the process of step S1011 may be omitted.

<Summary of Example 2>
As described above, the radiographic image processing system 101 of the second embodiment can suppress halos that occur around surgical devices, undiluted contrast medium, and thick bones such as vertebral bodies. As a result, the visibility of the surgical device is further improved, so that the doctor can smoothly proceed with the surgical procedure.

Further, as in the first embodiment, the processing executed by the image processing unit 115 has a short computation time, so that an image can be displayed in real time. In addition, the low-frequency component extraction unit 201, the division processing unit 202, and the halo reduction unit 601 included in the image processing unit 115 can be realized using a general-purpose computer, and there is no need to prepare dedicated computer resources, thereby reducing costs. be able to.

<Overall summary>
(i) According to one aspect of the present invention described above, a transmission image with improved visibility of a surgical device or the like can be obtained in real time. In a procedure in which a surgical device overlaps an object such as a bone that greatly attenuates radiation, the visibility of the surgical device can be improved without making an unnecessary halo stand out.

(ii) Applications of the radiation image processing system 100 realized using the present invention are not limited to ERCP and EUS-BD. In addition to these, for example, PFC (pancreatic and peripancreatic fluid collections: drainage for pancreatic and peripancreatic fluid retention associated with pancreatitis), PTCD (percutaneous transhepatic cholangiodrainage: percutaneous transhepatobiliary drainage), shunt imaging (angiography) A wide range of applications such as

(iii) The present invention is not limited to the above-described embodiments, and includes various modifications. Further, for example, the above-described embodiments are detailed descriptions of the configurations for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations. Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

Further, each of the above configurations, functions, processing units, processing means, and the like may be realized by hardware, for example, by designing them in an integrated circuit. The present invention can also be implemented by software program code that implements the functions of the embodiments. In this case, a computer is provided with a storage medium recording the program code, and a processor included in the computer reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiments, and the program code itself and the storage medium storing it constitute the present invention. Examples of storage media for supplying such program code include flexible disks, CD-ROMs, DVD-ROMs, hard disks, SSDs (Solid State Drives), optical disks, magneto-optical disks, CD-Rs, magnetic tapes, A nonvolatile memory card, ROM, or the like is used.

Also, the program code that implements the functions described in this embodiment can be implemented in a wide range of programs or scripting languages, such as assembler, C/C++, perl, Shell, PHP, Python, and Java (registered trademark).

Furthermore, by distributing the program code of the software that realizes the functions of the embodiment via a network, it can be stored in storage means such as a hard disk or memory of a computer or in a storage medium such as a CD-RW or CD-R. Alternatively, a processor provided in the computer may read and execute the program code stored in the storage means or the storage medium.

In the above-described embodiments, the control lines and information lines indicate those considered necessary for explanation, and not all control lines and information lines are necessarily indicated on the product. All configurations may be interconnected.

101 Radiation image processing system 102 X-ray tube 103 High voltage generator 104 X-ray controller 105 Diaphragm 106 X-ray compensation filter 107 Diaphragm/filter controller 108 Object 109 Table 110 Mechanism controller 111 X-ray detector 112 Detector controller 113 storage unit 114 central processing unit 115 image processing unit 116 input unit 117 display unit 201, 903 low frequency component extraction unit 202 division processing unit 203 division processing unit 601 halo reduction units 901, 905 subtractor 902 positive component extraction unit 904 negative component Extractor 906, 907 Adder 908 Lookup table

Claims (6)

A radiation image processing system for irradiating a subject with radiation and capturing a transmission image,
an image generator that generates a first transmission image;
an image processing unit that performs processing for improving the visibility of the first transmission image,
The image processing unit
a low-frequency component extraction unit that extracts low-frequency components from the first transmission image;
a division processing unit that divides the first transmission image by the low frequency component;
a halo reduction unit that reduces the halo of the first transmission image,
Equipped with a display unit for displaying an image,
The first transmission image is an image composed of luminance values of a plurality of pixels,
The division processing unit calculates a second transmission image by dividing the first transmission image by the low frequency component, and outputs the second transmission image to the halo reduction unit;
The halo reduction unit is
calculating a third transmission image by subtracting the luminance value of each pixel of the second transmission image by the first luminance value;
calculating a fourth transmission image by extracting pixels having positive luminance values in the third transmission image;
calculating a fifth transmission image by extracting low-frequency components of the fourth transmission image;
calculating a sixth transmission image with the halo reduced using the fifth transmission image and the fourth transmission image;
A radiation image processing system, wherein the sixth transmission image is output to the display unit. The radiographic image processing system according to claim 1 ,
The halo reduction unit is
calculating a seventh transmission image by performing luminance value conversion processing for adjusting the luminance value of an area having an arbitrary characteristic on the sixth transmission image;
A radiation image processing system, wherein the seventh transmission image is output to the display section. An image processing method executed by a radiation image processing system that generates a transmission image by irradiating a subject with radiation,
The radiation image processing system includes an image generation unit that generates the transmission image, and an image processing unit that performs processing for improving visibility of the transmission image,
The image processing method is
a first step in which the image generator generates a first transmission image;
a second step in which the image processing unit extracts low frequency components from the first transmission image and calculates a second transmission image by dividing the first transmission image by the low frequency components;
a third step in which the image processing unit performs processing to reduce halos in the second transmission image;
The radiation image processing system has a display unit for displaying an image,
The first transmission image is an image composed of luminance values of a plurality of pixels,
The third step is
the image processing unit subtracting the luminance value of each pixel of the second transmission image by the first luminance value to calculate a third transmission image;
a step in which the image processing unit calculates a fourth transmission image by extracting pixels having a positive luminance value in the third transmission image;
the image processing unit calculating a fifth transmission image by extracting low-frequency components of the fourth transmission image;
the image processing unit calculating a sixth transmission image with the halo reduced using the fifth transmission image and the fourth transmission image;
and a step of outputting the sixth transmission image to the display unit by the image processing unit. The image processing method according to claim 3 ,
The third step is
a step of calculating a seventh transmission image by the image processing unit performing luminance value conversion processing for adjusting a luminance value of a region having an arbitrary characteristic on the sixth transmission image;
and a step of outputting the seventh transmission image to the display unit by the image processing unit. A program to be executed by a computer that processes a transmission image generated by irradiating a subject with radiation,
a first procedure of receiving a first transmission image;
a second step of extracting low frequency components from the first transmission image and calculating a second transmission image by dividing the first transmission image by the low frequency components;
causing the computer to execute a third procedure of performing processing for reducing the halo of the second transmission image;
The computer is connected to a display device that displays an image,
The first transmission image is an image composed of luminance values of a plurality of pixels,
The third step is
a step of subtracting the luminance value of each pixel of the second transmission image by the first luminance value to calculate a third transmission image;
a step of calculating a fourth transmission image by extracting pixels having positive luminance values in the third transmission image;
calculating a fifth transmission image by extracting low frequency components of the fourth transmission image;
calculating a sixth transmission image with reduced halo using the fifth transmission image and the fourth transmission image;
and a step of outputting the sixth transmission image to the display device. The program according to claim 5 ,
The third step is
a step of calculating a seventh transmission image by executing a luminance value conversion process for adjusting a luminance value of an area having an arbitrary characteristic on the sixth transmission image;
and a step of outputting the seventh transmission image to the display device.

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