JP4891957B2 - Image processing device - Google Patents

Description

  The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus that classifies fat.

  Fat is roughly classified into subcutaneous fat formed under the skin and visceral fat formed around the viscera. Of these, visceral fat is attracting attention in the diagnosis of lifestyle-related diseases and the like. Therefore, it is desirable not only to measure the amount of body fat that reflects the total amount of fat, but also to determine the type of fat and measure the amount of fat for each type.

  Under such circumstances, the inventor of the present application proposes a technique for classifying fat in a tomographic image obtained from an X-ray CT apparatus or the like in Patent Document 1. Patent Document 1 describes an epoch-making technique capable of discriminating subcutaneous fat and visceral fat in, for example, a tomographic image of an X-ray CT apparatus.

JP 2003-339694 A

  The inventor of the present application has conducted research and development on a revolutionary technology improvement proposed in Patent Document 1. In particular, research and development has been repeated with the goal of more accurate fat types.

  The present invention has been made in the course of research and development, and an object thereof is to classify fat with high accuracy in a tomographic image.

  In order to achieve the above object, an image processing apparatus according to a preferred embodiment of the present invention uses a real tissue threshold value corresponding to a distinction between muscle and fat of real tissue, and a muscle pixel and a fat pixel in a tomographic image of a subject. By identifying a muscle pixel and a fat pixel in the tomographic image using a real tissue image forming unit that forms a real tissue image by identifying a reference threshold value shifted to the fat side of the real tissue threshold value A reference image forming unit that forms a reference image, an image combining unit that forms a composite image by combining fat pixels surrounded by muscle pixels in the reference image and muscle pixels in the real tissue image, and And an expansion processing unit that forms visceral fat pixels corresponding to visceral fat of the real tissue by expanding the fat pixels.

  In a preferred aspect, the reference image forming unit forms a reference image by expanding a muscle pixel after identifying a muscle pixel and a fat pixel using a reference threshold.

  In a preferred aspect, the dilation processing unit dilates the fat pixels up to a muscle pixel surrounding the fat pixels in the synthesized image.

  In a preferred embodiment, the tomographic image includes a muscle pixel corresponding to the testicular levator ani muscle and a fat pixel surrounded by the testicular levator muscle, and the image composition unit includes the testicular levator muscle in the reference image. A synthesis image is formed by synthesizing the fat pixels surrounded by the corresponding muscle pixels and the muscle pixels corresponding to the cremaster muscle in the real tissue image, and the dilation processing unit dilates the fat pixels in the synthesis image. By virtue of this, visceral fat pixels corresponding to the visceral fat surrounded by the levator crevicis are formed.

  In order to achieve the above object, a program according to a preferred aspect of the present invention uses a real tissue threshold corresponding to a distinction between muscle and fat of a real tissue, and a muscle pixel and a fat pixel in a tomographic image of the subject. A reference image is formed by identifying a muscle pixel and a fat pixel in the tomographic image using a function of forming a real tissue image by identifying the reference value and a reference threshold value shifted to the fat side of the real tissue threshold value. A function to form a composite image by combining fat pixels surrounded by muscle pixels in the reference image and muscle pixels in the real tissue image, and by expanding the fat pixels in the composite image. A function of forming a visceral fat pixel corresponding to a visceral fat of a tissue is realized by a computer.

  For example, the program of the above aspect is stored in a storage medium such as a disk or a memory, and is read into the computer via the storage medium. Alternatively, the program may be provided to the computer via a network or the like.

  According to the present invention, fat can be classified with high accuracy in a tomographic image. For example, according to a preferred aspect of the present invention, it is possible to identify visceral fat surrounded by the levator crevicis.

  FIG. 1 is a diagram for explaining a preferred embodiment of the present invention. FIG. 1 shows an image processing system using an image processing apparatus according to the present invention. The system shown in FIG. 1 includes an X-ray CT apparatus 10 and an image processing apparatus 30. In the present embodiment, the X-ray CT apparatus 10 shown in FIG. 1 is used, but another known X-ray CT apparatus may be used instead of the X-ray CT apparatus 10 shown in FIG. Furthermore, instead of the X-ray CT apparatus, another image forming apparatus may be used.

  The X-ray CT apparatus 10 has a dynamic variable function of magnification. For example, an animal such as a mouse is a measurement target. Of course, other specimens may be measured. The X-ray CT apparatus 10 is provided with an X-ray generator 52 on one side and an X-ray detector 60 on the other side with the rotation center axis O therebetween. A collimator 54 is provided on the irradiation side of the X-ray generator 52. The X-ray generator 52 generates a divergent or fan-shaped (here, fan-beam shaped) X-ray beam 56 as shown. On the other hand, the X-ray detector 60 is configured as a plurality of (for example, 100) X-ray sensors arranged in a line, and an X-ray receiving opening is set according to the opening angle of the X-ray beam 56. Incidentally, the arrangement of the plurality of X-ray sensors may be linear or arcuate.

  In FIG. 1, a high voltage source used with the X-ray generator 52, a data processing circuit used with the X-ray detector 60, and the like are not shown.

  In FIG. 1, reference numeral 58 denotes an effective field of view. This is a circular region in which a CT image can be formed when the X-ray beam 56 is rotationally scanned. Incidentally, the effective visual field 58 is determined according to the positional relationship between the subject or the rotation center axis O and the X-ray generator 52 and the X-ray detector 60. In the present embodiment, since a displacement mechanism 62 described below is provided, it is possible to change the positional relationship between them and mechanically vary the magnification of the CT image.

  In other words, the X-ray generator 52 and the X-ray detector 60 are connected to the displacement mechanism 62. In this embodiment, the displacement mechanism 62 is a distance between the X-ray generator 52 and the X-ray detector 60. The function of displacing them (that is, the measurement unit) in the beam axis direction of the X-ray beam 56 is maintained. In this case, the rotation center axis O is not changed, that is, the magnification can be changed by moving the measurement unit without moving the subject. The displacement mechanism 62 includes a motor 62A for generating a displacement force. In the present embodiment, the displacement amount can be individually set for each CT imaging, that is, the measurement magnification can be individually set. When such control is performed, the shape of the housing member (especially the outer diameter at the CT imaging position) is used as a reference, and the housing member is prevented from contacting or colliding with the gantry or the measurement unit when the magnification is variable. Has been.

  The gantry rotation mechanism 66 is a mechanism that rotates the entire base including the displacement mechanism mounted thereon by rotating the rotation base. Since the measurement unit is mounted on the displacement mechanism 62, the measurement unit positioned at a desired position by the displacement mechanism 62 is rotationally driven while maintaining the position. The gantry rotating mechanism 66 has a motor 66A for generating the driving force. Note that the measurement magnification does not change during one rotation. The slide mechanism 68 is a moving mechanism that slides an arm (not shown), and the driving force is generated by a motor 68A. The arm slides the mounting table on which the subject is placed in the direction of the rotation center axis. Then, CT imaging of the subject is performed at each slide position.

  Incidentally, although various mechanisms 62, 66, 68 and the like are shown in FIG. 1, it is desirable to provide a sensor in order to detect a position or a change due to these mechanisms. Then, it is desirable that an arithmetic control unit (not shown) performs so-called feedback control based on the output signals of those sensors. In the example shown in FIG. 1, the slide mechanism 68 has the motor 68A as a drive source. However, the slide force may be artificially generated. The overall operation of the X-ray CT apparatus 10 is controlled by an operation control unit (not shown). The operation control unit is preferably provided inside the X-ray CT apparatus 10.

  The image processing apparatus 30 is configured by hardware such as a CPU, a memory, and a hard disk, and software such as an operation control program. FIG. 1 shows typical functions realized by the cooperation of the hardware and software. That is, the image processing apparatus 30 includes a real tissue image forming unit 310, a reference image forming unit 320, an image composition unit 330, an expansion processing unit 340, and the like. The computer may be operated as the image processing apparatus 30 using a program corresponding to these functions.

  Note that a display device 32, a storage device 34, a keyboard 36, a mouse 38, a printer 40, and the like are connected to the image processing device 30. The storage device 34 stores X-ray CT tomographic image data 34A as necessary.

  In the present embodiment, the tomographic image obtained by the X-ray CT apparatus 10 is processed by the image processing apparatus 30 to identify visceral fat surrounded by the levator crevices in the tomographic image. Therefore, each function in the image processing apparatus 30 will be described in detail below. In addition, about the part (structure) shown in FIG. 1, the code | symbol of FIG. 1 is utilized also in the following description.

  FIG. 2 is a diagram illustrating an example of an image processed in the image processing apparatus 30. A tomographic image 100 shown in FIG. 2 is a schematic view of an X-ray CT image obtained by imaging the lower abdomen of a subject (eg, an animal such as a mouse) with the X-ray CT apparatus 10.

  The tomographic image 100 shows a cross section of the lower abdomen of the subject, and includes the testicular muscle 112, the visceral fat 122 surrounded by the testicular muscle 112, the thigh fat 124, and the like. Note that tissue such as bone is also shown in the image obtained by the X-ray CT apparatus 10, but is not shown in FIG.

  When the tomographic image 100 is formed by the X-ray CT apparatus 10, image data corresponding to the tomographic image 100 is supplied to the image processing apparatus 30. First, the image processing apparatus 30 sets a cursor 200 indicating a target area for image processing in the tomographic image 100. For example, the cursor 200 is set so as to surround the levator ani muscle 112 in accordance with a user operation of viewing the tomographic image 100 displayed on the display 32. Thereby, the thigh fat 124 and the like are excluded from the processing target.

  The cursor 200 is not limited to a rectangular shape as shown in FIG. For example, the cursor 200 may be formed in an elliptical shape. Further, when the cursor 200 is set for a plurality of tomographic images 100 that are obtained from the same subject and are close to each other, for example, the cursor 200 is set for the tomographic images 100 at both ends in accordance with a user operation, Using the set cursor 200 as a reference, the cursor 200 may be automatically set for the remaining tomographic images 100 by interpolation processing or the like.

  FIG. 3 is a diagram showing a real tissue image. The real tissue image forming unit 310 forms a real tissue image by identifying the muscle pixel 110 and the fat pixel 120 in the image of the subject surrounded by the cursor 200 of the tomographic image obtained from the X-ray CT apparatus 10. . The real tissue image forming unit 310 identifies the muscle pixel 110 and the fat pixel 120 based on the pixel value (CT value) of each pixel in the cursor 200.

  When attention is paid to each pixel in the tomographic image obtained by the X-ray CT apparatus 10, a CT value corresponding to the degree of X-ray absorption in the pixel portion corresponds. The CT value of water is defined as 0, and the CT value of air is defined as -1000. For example, the CT value of fleshy tissue such as muscle is about -120 to +350, and the CT value of fat is about -500 to -120. .

  Therefore, the real tissue image forming unit 310 uses a real tissue threshold value corresponding to the CT value, which is a guideline for distinguishing muscles and fats that are actual tissues. For the real tissue threshold, for example, the lower limit value of muscle is set to −120, and the upper limit value of muscle is set to +350. Further, the lower limit value of fat is -500, and the upper limit value of fat is -120. Thereby, a pixel having a CT value of −120 to +350 is determined as the muscle pixel 110, and a pixel having a CT value of −500 to −120 is determined as the fat pixel 120.

  In the real tissue image formed by the real tissue image forming unit 310, the muscle pixel 110 corresponding to the testicular muscle may not form a closed curve. Since the testicular muscle is a thin muscle layer (for example, a thickness of about 1 to 3 pixels), the discrimination based on the real tissue threshold does not accurately identify the thin muscle layer due to the influence of surrounding fat, and Some muscles may be recognized as fat. In this case, as shown in FIG. 3, the muscle pixel 110 corresponding to the testicular muscle is interrupted on the upper side, for example.

  In order to identify visceral fat surrounded by the testicular muscle, it is desirable that the muscle pixel 110 corresponding to the testicular muscle forms a closed curve. Therefore, in the present embodiment, the reference image is formed by the reference image forming unit 320 so that the muscle pixels 110 corresponding to the cremaster muscle form a closed curve.

  FIG. 4 is a diagram illustrating a reference image. The reference image forming unit 320 identifies the muscle pixel 110 and the fat pixel 120 by using a reference threshold in the image of the subject surrounded by the cursor 200 of the tomographic image obtained from the X-ray CT apparatus 10. A reference image is formed.

  The reference threshold value is a threshold value shifted to the fat side with respect to the real tissue threshold value when the real tissue image (FIG. 3) is formed. In the previous example, the lower limit value of the muscle was −120, the upper limit value of the muscle was +350, the lower limit value of the fat was −500, and the upper limit value of the fat was −120. Thus, for example, the lower limit value of the muscle is shifted to −180 to set the upper limit value of the muscle to +350, the lower limit value of fat is set to −500, and the upper limit value of fat is shifted to −180. That is, the threshold corresponding to the boundary between muscle and fat is shifted from −120 to −180 toward the fat side.

  Therefore, in the reference image of FIG. 4 obtained using the reference threshold, the muscle pixel 110 corresponding to the testicular levator becomes thicker and clearer than the real tissue image (FIG. 3), and the testicular muscle A part of which is recognized as fat and cut off becomes smaller. In comparison with the real tissue image (FIG. 3), in the reference image of FIG. 4, muscle pixels 110 appear in a region corresponding to visceral fat surrounded by the levator crevicis. This is because a reference threshold value shifted to the fat side of the real tissue threshold value is used, and therefore, a part of pixels originally corresponding to fat is recognized as the muscle pixel 110.

  Next, the reference image forming unit 320 performs an expansion process on the muscle pixel 110 in the reference image.

  FIG. 5 is a diagram illustrating a reference image that has been subjected to expansion processing. The reference image forming unit 320 performs an expansion process on the muscle pixels 110 included in the reference image. Thereby, only the muscle pixel 110 is swollen as a whole in the reference image after expansion in FIG. 5 as compared with the reference image before expansion (FIG. 4). In particular, the muscle pixel 110 corresponding to the testicular muscle is thicker and clearer, and a part of the testicular muscle that has been interrupted disappears. In this way, the reference image is formed by the reference image forming unit 320 so that the muscle pixels 110 corresponding to the cremaster muscle form a closed curve.

  If the muscle pixel 110 corresponding to the testicular muscle forms a closed curve at the stage of the reference image (FIG. 4) formed using the reference threshold value, the expansion process for the muscle pixel 110 is omitted. It is also possible.

  When the reference image is formed so that the muscle pixel 110 corresponding to the testicular muscle has a closed curve, a composite image is formed by the image composition unit 330.

  FIG. 6 shows a composite image. The image synthesis unit 330 synthesizes the fat pixel 120 surrounded by the muscle pixel 110 forming a closed curve in the reference image of FIG. 5 and the muscle pixel 110 in the real tissue image of FIG. Form an image.

  In the composite image, the fat pixel 120 is contracted slightly inward from the muscle pixel 110 surrounding it. This is because the fat pixel 120 of FIG. 6 is obtained from the reference image (FIG. 5), and the muscle pixel 110 is identified by the reference threshold in the reference image and further expanded and expanded. This is because the fat pixel 120 is contracted as an adverse effect. Also, several portions missing in the fat pixel 120 in FIG. 6 are misidentified as muscle pixels 110 in the reference image (FIG. 5).

  When the composite image is formed by the image composition unit 330, the expansion processing unit 340 performs expansion processing on the fat pixels 120 in the composite image.

  FIG. 7 is a diagram illustrating a composite image that has been subjected to expansion processing. The expansion processing unit 340 performs expansion processing on the fat pixels 120 included in the composite image of FIG. For example, the fat pixels 120 are expanded by the number of pixels set empirically (for example, two pixels). At that time, the fat pixel 120 is expanded with the muscle pixel 110 surrounding the fat pixel 120 as a limit. That is, in the portion where the fat pixel 120 expands and contacts the muscle pixel 110, further expansion is prohibited.

  The result of performing the expansion process on the fat pixel 120 in FIG. 6 is the visceral fat (pixel) 122 in FIG. In the combined image after expansion in FIG. 7, the visceral fat (pixel) 122 is expanded until it contacts the muscle pixel 110. In addition, in the fat pixel 120 in FIG. 6, several portions missing due to misidentification become the fat pixel 120 due to the effect of the expansion process, and are included in the visceral fat (pixel) 122 in FIG. 7.

  In this way, the visceral fat (pixel) 122 in the composite image of FIG. 7 is formed by the image processing device 30 so as to contact the muscle pixel 110 corresponding to the actual testicular muscle obtained from the real tissue image of FIG. Pixels corresponding to visceral fat surrounded by the tissue cremaster muscle are identified.

  As mentioned above, although preferred embodiment of this invention was described, according to embodiment mentioned above, it becomes possible to identify the visceral fat surrounded by the cremaster muscle comparatively correctly. In addition, for example, the processing time for recognition can be shortened as compared with the case where visceral fat is recognized by adding manual correction by an operator. Further, according to the above-described embodiment, since visceral fat is automatically recognized according to a certain rule, objective and highly reproducible measurement is possible.

  The above-described embodiments are merely examples in all respects, and do not limit the scope of the present invention. For example, when the abdominal muscles are thinly identified in the upper abdomen, the present invention can be used when identifying visceral fat surrounded by the abdominal muscles. As described above, the present invention includes various modifications without departing from the essence thereof.

It is a figure which shows the image processing system using the image processing apparatus which concerns on this invention. 4 is a diagram illustrating an example of an image processed in the image processing apparatus 30. FIG. It is a figure which shows a real tissue image. It is a figure which shows a reference image. It is a figure which shows the reference image by which the expansion process was carried out. It is a figure which shows a synthesized image. It is a figure which shows the synthesized image by which the expansion process was carried out.

Explanation of symbols

  30 image processing device, 310 real tissue image forming unit, 320 reference image forming unit, 330 image compositing unit, 340 expansion processing unit.

Claims (5)

A real tissue image forming unit that forms a real tissue image by identifying a muscle pixel and a fat pixel in a tomographic image of a subject using a real tissue threshold corresponding to the differentiation between muscle and fat of the real tissue;
A reference image forming unit that forms a reference image by identifying a muscle pixel and a fat pixel in the tomographic image using a reference threshold value shifted to a fat side from a real tissue threshold value;
An image compositing unit that forms a composite image by combining fat pixels surrounded by muscle pixels in a reference image and muscle pixels in a real tissue image;
An expansion processing unit that forms visceral fat pixels corresponding to visceral fat of the real tissue by expanding the fat pixels in the composite image;
Having
An image processing apparatus. The image processing apparatus according to claim 1.
The reference image forming unit forms a reference image by expanding muscle pixels after identifying muscle pixels and fat pixels using a reference threshold,
An image processing apparatus. The image processing apparatus according to claim 1 or 2,
The expansion processing unit expands fat pixels with a limit to muscle pixels surrounding the fat pixels in the composite image,
An image processing apparatus. In the image processing device according to any one of claims 1 to 3,
The tomographic image includes muscle pixels corresponding to the testicular cremaster muscle and fat pixels surrounded by the testicular muscle,
The image synthesis unit forms a synthesized image by synthesizing fat pixels surrounded by muscle pixels corresponding to the levator ani muscle in the reference image and muscle pixels corresponding to the cremaster muscle in the real tissue image,
The expansion processing unit forms visceral fat pixels corresponding to the visceral fat surrounded by the cremaster muscle by expanding the fat pixels in the composite image.
An image processing apparatus. A function of forming a real tissue image by identifying a muscle pixel and a fat pixel in a tomographic image of a subject using a real tissue threshold corresponding to the differentiation between muscle and fat of the real tissue;
A function of forming a reference image by identifying a muscle pixel and a fat pixel in the tomographic image using a reference threshold value shifted to a fat side from a real tissue threshold value;
A function of forming a composite image by combining fat pixels surrounded by muscle pixels in a reference image and muscle pixels in a real tissue image;
A function of forming visceral fat pixels corresponding to the visceral fat of the real tissue by expanding the fat pixels in the composite image;
A program characterized by causing a computer to realize.

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