JP2007020873A - Medical image processing device and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a medical image processing device capable of forming a shaded three-dimensional image preventing artifacts being generated even when a subject is extended off the reconstruction field. <P>SOLUTION: Image reconstruction is made for a portion of a subject and the reconstruction field is designated for generating a tomographic image. Then X-ray transmission data acquired by photographing via X-ray CT device is read (S1). Based on the X-ray transmission data, image is reconstructed for generating the tomographic image(S2). Next, a surrounding region including the boundary line of the reconstruction field in the tomographic image is set as an objective field to be processed (S3). A smoothing process is executed based on the density value of the pixel of the object field to be processed(S4). The third-dimensional image shaded based on the tomographic image smoothing processed is generated and displayed(S5). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a medical image processing apparatus and an image processing program, and more particularly to a technique for reducing artifacts when generating a three-dimensional image based on volume data acquired by an X-ray CT apparatus.

  Conventionally, in order to remove image noise, there are techniques for performing a smoothing process on the entire medical image or performing an adaptive smoothing process for performing a smoothing process for each local region of the medical image.

As an example of adaptive smoothing processing, Patent Document 1 calculates the amount of change in luminance in eight directions at a point of interest on a medical image, obtains the direction in which the amount of change is minimum, and determines the difference in luminance in that direction. An image processing method for performing a corresponding one-dimensional nonlinear smoothing process is disclosed. According to this method, it is possible to perform a smoothing process that recognizes a portion where the pattern of the medical image is fine and a portion where the pattern is not so.
JP-A-9-330399

  When a large subject is imaged, the subject may protrude from the image reconstruction area (hereinafter referred to as “reconstruction area”) of a cone beam X-ray CT apparatus or a fan beam X-ray CT apparatus. Artifacts with striped patterns may occur in the areas that protrude. The cause of this artifact will be described with reference to FIGS.

  FIG. 8 is an explanatory diagram showing a configuration of an X-ray CT apparatus using a flat sensor. The X-ray generator and the flat sensor of the X-ray CT apparatus rotate the trajectory around the subject and rotate it once to obtain several hundred tomographic images 81, 82,... 84,. 87 is reconfigured. Since the planar sensor is a quadrangular shape, a cylindrical reconstruction area 80 is formed as shown in FIG.

  FIG. 9 shows a reconstruction area of a cone beam X-ray CT apparatus. The X-ray generator and the image intensifier rotate the orbit 64 around the subject 63 and make one rotation, whereby hundreds of tomographic images 91, 92,... 97 as shown in FIG. In this case, the reconstruction area of the cone beam X-ray CT apparatus in this case is the internal area of the sphere 90 as shown in FIG.

  When the size of the subject is larger than the reconstruction areas 80 and 90, a shadow obtained by photographing the subject protrudes. FIG. 10 shows a reconstructed image (tomographic image) in which the subject protrudes and a shaded three-dimensional image reconstructed based on the tomographic image. The subject shadow 101 included in the reconstructed image 100 in FIG. 10A has a head protruding from a point 103 to a point 104 on the boundary line in the circular reconstruction region 102. Since a density value having a special value is recorded outside the reconstruction area 102, the boundary line connecting the point 103 to the point 104 includes a part positioned outside and a part positioned inside the boundary line. Concentration value of the color changes greatly. In this way, when the tomograms that the subject protrudes from the reconstruction area 102 are stacked to generate a three-dimensional image, a large change in the density value across the boundary line appears as an artifact consisting of a striped pattern. FIG. 10B schematically shows an artifact 106 generated in the three-dimensional image 105. The three-dimensional image 105 is a three-dimensional image in which the head of the subject is shaded three-dimensionally. FIG. 11 shows artifacts appearing in the actually generated three-dimensional image. The vertical stripe pattern 111 that appears on the side surface in the three-dimensional image 110 of FIG. 11 is the above-described artifact.

  Therefore, the present invention provides a medical image processing apparatus and an image processing program capable of preventing the occurrence of artifacts even when a subject generates a three-dimensional image by accumulating tomographic images protruding from a reconstruction area. With the goal.

  In order to achieve the above object, the present invention provides X-ray transmission data obtained by imaging an X-ray CT apparatus including a region of a subject in a reconstruction area, and includes tomographic images 3 Means for reading X-ray transmission data capable of generating a three-dimensional image, reconstruction means for performing image reconstruction processing based on the X-ray transmission data and generating at least one tomogram, A setting unit that sets a peripheral region including a boundary line of a configuration region as a processing target region; a smoothing unit that performs a smoothing process based on a density value of a pixel that configures the processing target region for each tomographic image; The image processing apparatus includes a generating unit that generates a three-dimensional image based on the tomographic image that has been smoothed, and a display unit that displays the three-dimensional image.

  Further, the setting means detects a partial boundary line corresponding to a portion where the part of the subject protrudes from the boundary line of the reconstruction area, and sets a peripheral area including the partial boundary line as a processing target area. May be.

  The smoothing means may change the density value inside the boundary line so as to approach the density value outside the boundary line as it approaches the boundary line of the reconstruction area from the center of the reconstruction area. Good.

  Further, the generation unit may configure a shaded three-dimensional image based on the tomographic image that has been subjected to the smoothing process.

  In addition, the image processing program according to the present invention is X-ray transmission data obtained by an X-ray CT apparatus that includes a region of a subject in a reconstruction area, and is a three-dimensional image obtained by accumulating tomographic images. A step of reading X-ray transmission data capable of generating an image, a step of generating at least one tomographic image by performing image reconstruction processing based on the X-ray transmission data, and a step of generating the reconstruction area for each of the tomographic images. A step of setting a peripheral region including a boundary line as a processing target region, a step of performing a smoothing process based on a density value of a pixel constituting the processing target region for each tomographic image, and the smoothing processing A step of generating a three-dimensional image based on the tomographic image and a step of displaying the three-dimensional image are executed by a computer.

  According to the present invention, since the boundary line of the reconstruction area of each tomographic image is smoothed and a three-dimensional image is generated, even when the subject protrudes from the reconstruction area, the generation of the artifact is prevented while preventing the occurrence of the artifact. An image can be generated.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, the best embodiment of the invention will be described with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.

〔System configuration〕
FIG. 1 is a hardware configuration diagram showing a configuration of a medical image processing system 1 according to the present embodiment.

  A medical image processing system 1 in FIG. 1 includes a cone beam X-ray CT apparatus 2 and a fan beam X-ray CT apparatus 3 as medical image capturing apparatuses for capturing a tomographic image of a subject, and three-dimensional shading based on the tomographic image. A medical image processing apparatus 10 that generates an image is provided, and the medical image photographing apparatus and the medical image processing apparatus 10 are connected to a network such as a LAN 5.

  The medical image processing apparatus 10 includes a central processing unit (CPU) 11 that mainly controls the operation of each component, a main memory 12 that stores a control program for the apparatus and that serves as a work area when the program is executed, and an operating system. (OS), a device drive of a peripheral device, a magnetic disk 13 storing various application software including a program for generating a three-dimensional image described later, a display memory 14 for temporarily storing display data, A monitor 15 such as a CRT monitor or a liquid crystal monitor that displays an image based on data from the display memory 14, a mouse 16 as a position input device, and the state of the mouse 16 are detected to detect the position of the mouse pointer on the monitor 15 and the mouse. A controller 16a for outputting signals such as 16 states to the CPU 11, and the keyboard 1; When a communication interface (hereinafter referred to as "communication I / F") 18, and a bus 19 which connects the above components.

  Next, an image processing program executed by the medical image processing apparatus 10 will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the image processing program.

  An image processing program reads an X-ray transmission data obtained by imaging with an X-ray CT apparatus by designating a reconstruction area which is an area for generating a tomographic image by reconstructing an image from a portion of a subject 11a, a reconstruction unit 11b that generates a tomographic image by performing image reconstruction processing based on the X-ray transmission data, and a setting unit 11c that sets a peripheral region including the boundary of the reconstruction region in the tomographic image as a processing target region A smoothing processing unit 11d that performs a smoothing process based on the density values of the pixels that constitute the processing target region, and a three-dimensional image generation unit 11e that generates a three-dimensional image based on the tomographic image that has been subjected to the smoothing process. And a display control unit 11f that controls display of a three-dimensional image.

  The CPU 11 of the medical image processing apparatus 10 reads the image processing program from the magnetic disk 13, loads it into the main memory 12, and executes it.

[Process flow]
A processing flow of the medical image processing system 1 will be described with reference to FIG. FIG. 3 is a flowchart showing a processing flow of the medical image processing system 1.

(Step S1)
In S <b> 1, the reading unit 11 a outputs X-rays in a state where a part of the body part of the subject from which the tomographic image is to be generated is located within the effective visual field range from the cone beam X-ray CT apparatus 2 or the fan beam X-ray CT apparatus 3. X-ray transmission data obtained by detecting X-rays irradiated and transmitted through the effective visual field range is read (S1). The effective visual field range set at the time of volume scanning by the X-ray CT apparatus corresponds to the reconstruction area. The X-ray transmission data may be read from data stored in advance on the magnetic disk 13 or may be acquired from the cone beam X-ray CT apparatus 2 or the fan beam X-ray CT apparatus 3 via the LAN 5. This X-ray transmission data is volume data that can generate tomographic images of a plurality of slices taken along the body axis direction of the subject.

(Step S2)
In S2, the reconstruction unit 11b performs preprocessing, backprojection processing, and postprocessing based on the X-ray transmission data read in S1, and reconstructs a plurality of tomographic images (S2).

(Step S3)
In S3, the setting unit 11c sets a peripheral region including the boundary line of the reconstruction region of each tomographic image reconstructed in S2 as a processing target region (S3). The “peripheral area” is an area having a predetermined number of pixels around the boundary line of the reconstruction area. The setting of the peripheral area will be described with reference to FIGS.

  As illustrated in FIG. 4, the setting unit 11 c detects a boundary line 41 (represented by a solid line) of the reconstruction area included in the tomographic image 40. Next, an outer line 41a (displayed by a dotted line) located, for example, 5 pixels outside the boundary line 41 and an inner line 41b (displayed by a dotted line) located, for example, 5 pixels inside from the boundary line 41 are set, and the outer side A hatched area surrounded by the line 41a and the inner line 41b is set as a process target area. As a result, all the protruding areas of the subject can be set as processing target areas.

  FIG. 5 shows another mode of processing target area setting. The setting unit 11 c detects both end portions 42 and 43 of the region where the subject protrudes from the boundary line 41 of the reconstruction region included in the tomographic image 40. The center of the reconstruction area is defined as an origin O, the right direction passing through the origin O is defined as a reference line 1 having an angle of 0 degrees, the angle Θ1 between the reference line 1 and the radius passing through the origin O and the end 42, and the reference line l. And an angle Θ2 between the origin O and the radius passing through the end 43 are detected. Then, the partial boundary line 41 ′ included in the angle (Θ 2 −Θ 1) may be detected, and the peripheral region including the partial boundary line 41 ′ may be set as the processing target region. Thereby, compared with the case where a process target area | region is set based on the perimeter of the boundary line 41, a calculation amount can be reduced and a high-speed calculation is attained. Note that FIG. 5 shows a state in which the region that protrudes from the head of the subject is detected, but the processing target region is set by detecting both ends of the protruding region of the subject's neck as described above. To do.

  FIG. 6 is a diagram showing another aspect of setting the processing target area. 4 and 5, the setting unit 11 c sets the outer line 41 a and the inner line 41 b of the boundary line 41 to obtain a peripheral area and sets this as a processing target area, but the outer line 41 a and the inner line are set. Instead of setting 41b, an N × M matrix region 44 centered on the pixel on the boundary line 41 may be set, and this matrix region 44 may be set as a processing target region.

  FIG. 7 is a diagram showing another mode of setting the processing target area. The setting unit 11c sets a moving radius 45 with the center of the boundary line 41 of the reconstruction area as the origin. Then, an area 45a of several pixels including the boundary line 41 of the reconstruction area in the moving radius 45 may be set as the processing target area.

(Step S4)
The smoothing processing unit 11d performs a smoothing process on the processing target area (S4). The smoothing processing unit 11d obtains the average value of the density values of the processing target area set in S3, and performs the smoothing process by replacing the density value on the boundary line with the average value. In the case of FIG. 4, a special density value between the boundary line 41 and the outer line 41a of the reconstruction area and a density value based on the X-ray transmission data between the boundary line and the outer line 41a. Find the average value. Then, the average value is replaced with the density value on the boundary line. In the case of FIG. 5, the smoothing process is performed only on the boundary line where the subject protrudes from the reconstruction area. In the case of FIG. 6, the average value of the density values of the pixels constituting the matrix region 44 is calculated, and this average value is replaced with the density value on the boundary line. In the case of FIG. 7, the average value of the density values in the region 45a (density value in the radial direction) is calculated and replaced with the density value on the boundary line. Alternatively, in the case of FIG. 7, the density value in the radial direction may be weighted so as to approach the density value outside the boundary line as it approaches the boundary line from the inside of the reconstruction area, and the smoothing process may be performed. .

(Step S5)
The three-dimensional image generation unit 11e generates a shaded three-dimensional image based on the plurality of tomographic images that have been smoothed in S4 (S5).

(Step S6)
The display control unit 11f displays the shaded three-dimensional image on the monitor 15 (S6).

  According to the present embodiment, in order to generate a shaded three-dimensional image based on the tomographic image obtained by smoothing the density value of the boundary 41 of the reconstruction area on the inside and outside of the reconstruction area, It is possible to prevent the occurrence of artifacts appearing in the shaded three-dimensional image due to the difference in density value across the boundary of the reconstruction area.

The hardware block diagram of a medical image processing system. The block diagram which shows the structure of an image processing program. The flowchart which shows the flow of a process of a medical image processing system. The schematic diagram which shows the one aspect | mode of a process target area | region. The schematic diagram which shows the one aspect | mode of a process target area | region. The schematic diagram which shows the one aspect | mode of a process target area | region. The schematic diagram which shows the one aspect | mode of a process target area | region. The schematic diagram which shows the reconstruction area | region in a fan beam X-ray CT apparatus. The schematic diagram which shows the reconstruction area | region in a cone beam X-ray CT apparatus. (A) is a schematic diagram which shows the tomogram which the subject protruded from the reconstruction area | region, (b) is a schematic diagram which shows the shaded three-dimensional image produced | generated based on this tomogram. Detailed view showing a shaded three-dimensional image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Medical image processing system, 2 ... Cone beam X-ray CT apparatus, 3 ... Fan beam X-ray CT apparatus, 5 ... LAN, 10 ... Medical image processing apparatus, 11 ... CPU, 12 ... Main memory, 13 ... Magnetic disk, 14 ... Display memory, 15 ... Monitor, 16 ... Mouse, 16a ... Controller, 17 ... Keyboard, 18 ... Communication I / F, 19 ... Bus

Claims (5)

X-ray transmission data obtained by an X-ray CT apparatus including a region of the subject in the reconstruction area and reading the X-ray transmission data that can generate a three-dimensional image obtained by stacking tomographic images is read. Means to
Reconstruction means for performing image reconstruction processing based on the X-ray transmission data and generating at least one tomographic image;
Setting means for setting a peripheral region including a boundary line of the reconstruction region for each tomographic image as a processing target region;
Smoothing means for performing a smoothing process based on a density value of pixels constituting the processing target area for each tomographic image;
Generating means for generating a three-dimensional image based on the tomographic image subjected to the smoothing process;
Display means for displaying the three-dimensional image;
A medical image processing apparatus comprising: The setting unit detects a partial boundary line corresponding to a portion where the part of the subject protrudes from the boundary line of the reconstruction area, and sets a peripheral area including the partial boundary line as a processing target area;
The medical image processing apparatus according to claim 1. The smoothing means changes the density value inside the boundary line so as to approach the density value outside the boundary line as it approaches the boundary line of the reconstruction area from the center of the reconstruction area.
The medical image processing apparatus according to claim 1, wherein the medical image processing apparatus is a medical image processing apparatus. The generating means configures a shaded three-dimensional image based on the tomographic image subjected to the smoothing process.
The medical image processing apparatus according to claim 1, wherein the medical image processing apparatus is a medical image processing apparatus. X-ray transmission data obtained by an X-ray CT apparatus including a region of the subject in the reconstruction area and reading the X-ray transmission data that can generate a three-dimensional image obtained by stacking tomographic images is read. Step
Performing image reconstruction processing based on the X-ray transmission data to generate at least one tomographic image;
Setting a peripheral region including a boundary line of the reconstruction region for each tomographic image as a processing target region;
Performing a smoothing process based on a density value of a pixel constituting the processing target area for each tomographic image;
Generating a 3D image based on the smoothed tomographic image;
Displaying the three-dimensional image;
An image processing program for causing a computer to execute.

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