JP4400737B2 - Image processing method and radiation tomography apparatus - Google Patents

Description

  The present invention relates to an image processing method for extracting a contour of a tomographic image of a subject constructed by a radiation tomographic imaging apparatus such as an X-ray CT apparatus, and a radiation tomographic imaging apparatus having a contour extraction function using the method. .

  In a radiation tomography apparatus, for example, an X-ray CT apparatus, generally, a holding unit that holds a subject is arranged between an X-ray source and an X-ray detector that are arranged to face each other, and the holding unit is rotated, Alternatively, while rotating a pair of the X-ray source and the X-ray detector around the holding unit, the X-ray transmission data of the subject is captured and stored at every predetermined minute rotation angle, and the stored X-ray transmission data is used. Then, a tomographic image of the subject is reconstructed along a plane orthogonal to the relative rotation center between the holding unit and the pair of the X-ray source and the X-ray detector.

  In various analyzes using such a tomographic image, it may be necessary to obtain the contour of the subject on the tomographic image, that is, the boundary position between the subject and the background (air). Various types of contour extraction methods have been known in the past, but any of them can be obtained by comparing luminance values of pixels on a tomographic image with an appropriately set threshold value. The boundary position between the background (air) and the subject is obtained (see, for example, Patent Document 1).

Further, instead of using a threshold value, a technique has been put into practical use where a place where the positive / negative of the differential value of the density gradient of the pixel on the tomographic image is reversed is used as the boundary between the subject and the background.
JP 2004-226202 A

  By the way, according to the conventional contour extraction method using the pixel information on the tomographic image as described above, there is no particular basis for how to determine the threshold value and how to determine the boundary based on the differential value of the density gradient. As the density (luminance) of the pixel on the tomographic image, for example, a tomographic image of a cylindrical body is illustrated in FIG. 2 described later, and the luminance distribution (line profile) of the pixel along the line C superimposed on the image is illustrated. 6 (A) and FIG. 6 (B) show a graph in which the portion B is enlarged only on the horizontal axis, the gradient is present in the contour portion of the subject on the tomographic image (the boundary portion between the subject image and the air). In addition, since the luminance value of each pixel on the tomographic image is a value obtained by reconstructing the X-ray transmission data, it includes an error (noise) that is inevitably included in the calculation. .

  From the above, in the method of extracting the contour of the subject using the luminance value of the pixel on the tomographic image as in the conventional method, the position of the contour (boundary) in the order smaller than the pixel pitch, that is, in the sub-pixel order. There was a problem that the measurement accuracy was low.

  An object of the present invention is to provide an image processing method capable of performing contour extraction from a tomogram with higher accuracy than conventional methods, and a radiation tomographic imaging apparatus having a contour extraction function using the method. There is.

In order to solve the above problems, an image processing method of the present invention is a method for extracting the contour of a tomographic image of a subject constructed by a radiation tomographic imaging apparatus, and intersects a line passing through the center of the tomographic image of the subject. Radiation of the subject based on the radiation transmission data from the direction orthogonal to the line on the radiation transmission image from the direction orthogonal to the line. It is characterized by calculating | requiring from the luminance distribution of the pixel of the pertinent position vicinity of a transmission image (Claim 1).

In the radiation tomographic imaging apparatus of the present invention, a holding unit that holds an object is disposed between a radiation source and a radiation detector that are arranged to face each other, and the holding unit, the radiation source, and the radiation detection A tomographic image along a plane orthogonal to the rotation axis is obtained by using the radiation transmission data of the subject captured at each minute rotation angle and stored in the memory while relatively rotating the pair of vessels around a predetermined rotation axis. The radiation tomographic imaging apparatus including the reconstruction calculation means for reconstructing includes image processing means for extracting the contour of the reconstructed tomographic image, and the image processing means intersects a line passing through the center of the tomographic image of the subject. a point on the contour, and the position information of the points located on the boundary of the image on the radiation transmission image from the direction perpendicular to the line, of the radiation transmission data stored in the memory Characterized by determining the luminance distribution of the corresponding position near the pixel of a radiation transmission image of the subject based on the radiation transmission data from a direction perpendicular to the line (Claim 2).

  In the present invention, when extracting the contour of a subject on a tomographic image, not only the pixels of the tomographic image are focused, but the raw data used in constructing the tomographic image, that is, the radiation transmission data of the subject is used. , To solve the problem.

That is, a point on the contour (point P in FIG. 2) intersecting with a line passing through the center of the tomographic image of the subject and the image on a radiation transmission image (image in FIG. 3) from a direction orthogonal to the line. a point located in the boundary (contour) (point in Fig. 3 p), by using the radiation transmission data from a direction perpendicular to the line C (see FIG. 2), it is possible to specify the position information I can . Luminance values of the pixels on this radiation transmission image, because it is a raw data not subjected to operation and the like, does not contain errors (noise) by calculation, it is possible to obtain the position information in the sub-pixel order .

According to the present invention, since the position information of the specific part on the contour of the tomographic image of the subject is performed using the radiation transmission data of the subject used to construct the tomographic image, the luminance value of the pixel on the tomographic image As compared with the conventional method of extracting the contour using the, it is possible to eliminate the influence of the error (noise) that enters during the reconstruction calculation, and it becomes possible to extract the sub-pixel order contour. This means that measurement reproducibility and measurement accuracy are dramatically improved in various analyzes using tomographic images. Further, comparison with CAD data and application to a so-called reverse engineering technique for creating CAD data from a tomogram can be expected.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a mechanical configuration and a block diagram showing a system configuration.

  An X-ray detector 2 is disposed opposite to the X-ray source 1, and a rotary stage 3 for mounting the subject W is disposed therebetween. The rotation stage 3 is rotated about a rotation axis R in the z-axis direction perpendicular to the x-axis direction along the X-ray optical axis L from the X-ray source 1. The rotary stage 3 can be moved in the x-, y-, and z-axis directions orthogonal to each other by the stage moving mechanism 4.

  The X-ray source 1 generates X-rays corresponding to the tube voltage and tube current supplied from the high voltage generator 10, and the high voltage generator 10 is controlled by the X-ray controller 11. The rotary stage 3 and the stage drive mechanism 4 are driven and controlled by a drive signal supplied from the stage controller 12. These X-ray controller 11 and stage controller 12 are placed under the control of a CT image reconstruction calculation device 13 mainly composed of a computer and its peripheral devices.

  The CT image reconstruction calculation device 13 rotates the rotary stage 3 on which the subject W is mounted while irradiating the X-ray from the X-ray source 1, and detects the X detected by the X-ray detector 2 at every minute rotation angle. The line transmission data is acquired and stored in the memory 14. After the data for 360 ° is prepared, a tomographic image of the subject W sliced along a plane along the xy plane orthogonal to the rotation axis R is constructed using the X-ray transmission data, and is displayed on the display 15. indicate.

Now, a data processing device 16 is connected to the CT image reconstruction calculation device 13, and this data processing device 16 operates a point on the contour of the tomographic image displayed on the display 15 by the following operation. The position information is calculated by using the X-ray transmission data in the memory 14 as specified by the unit 17.

  That is, for example, when a cylindrical body is used as a subject W and CT imaging is performed on the rotary stage 3 with its axis line oriented in the vertical direction, the tomographic image S has a circular shape as illustrated in FIG. In a state where such a tomographic image S is displayed on the display 15, the operator operates the operation unit 17 to move the linear cursor C to a position passing through the center of the tomographic image. Thereby, the position on the cursor C of the point P where the cursor C and the outline of the tomographic image S of the subject intersect is obtained as follows.

  First, an X-ray transmission image T of the subject W as illustrated in FIG. 3 is called from the memory 14 based on X-ray transmission data from a direction orthogonal to the direction of the cursor C, and a tomogram on the X-ray transmission image T is displayed. A distribution (line profile) of luminance values of pixels on the line Ls along the position is obtained. Examples thereof are shown in FIGS. 4 (A) and 4 (B). FIG. 4B is a graph obtained by enlarging only the horizontal axis of the portion B in FIG. From such a line profile, the boundary position of the X-ray transmission image T of the subject W is obtained. The luminance value of the pixels constituting the X-ray transmission image T is raw X-ray transmission data from the X-ray detector 2 (strictly, a value obtained by normal log conversion of the output of the X-ray detector 2). In the example shown in FIG. 4, there is a boundary between the pixel numbers (channels) 105 and 106 without including any calculation error, and the position of the boundary point p of the transmission image of the subject W can be accurately obtained. From the luminance gradient in the vicinity of the boundary position, it can be inferred that 105.5 channel is the position of the point p.

Incidentally, although it can be inferred from the line profile of the pixels on the tomographic image S shown in FIG. 6 that the boundary point P of the subject W is between 104 and 107, it is difficult to determine uniquely.
Here, in the above embodiment, for the sake of convenience of explanation, an example in which a simple cylindrical body is used as an object has been shown. However, even in a polygonal object, the position information of a specific point on the contour of the tomographic image is accurately obtained. Can be sought.

  That is, in the tomographic image as shown in FIG. 5, for each point on the contour indicated by P1, P2,... In the figure, each line C1, connecting each point P1, P2,. . Located at the boundary point of the image on the X-ray fluoroscopic image from the direction orthogonal to C2,..., And thus the positional information on the lines C1, C2,. Similar to the above example, it can be accurately obtained from the X-ray fluoroscopic image. If the position information obtained from the tomogram is corrected using the position information of each point P obtained in this way, the contour of the subject in the tomogram can be extracted more accurately.

  In the embodiment described above, an example in which the present invention is applied to an X-ray CT apparatus provided with a rotating stage mounted with a subject between an X-ray source and an X-ray detector and rotated is shown. Of course, the present invention can be equally applied to an X-ray CT apparatus of a type that rotates a pair of an X-ray source and an X-ray detector around a subject.

  In the above embodiment, an example in which a function for obtaining a point on the contour of a tomographic image by image processing using X-ray transmission data is attached to the tomographic imaging apparatus has been described. It goes without saying that an equivalent function can be realized using a personal computer.

In the configuration diagram of the embodiment of the present invention, a schematic diagram showing a mechanical configuration and a block diagram showing a system configuration are shown together. It is explanatory drawing of the example of the tomogram displayed on the indicator in the embodiment of this invention. It is explanatory drawing of the example of the X-ray transmission image of the to-be-photographed object called in embodiment of this invention. FIG. 4 is a graph (A) showing an example of a line profile of a pixel along a slice plane on the X-ray transmission image of FIG. It is explanatory drawing in the case of calculating | requiring the positional information on the point on the outline of a polygonal object by embodiment of this invention. It is a figure for demonstrating the outline extraction method of the conventional tomogram, The graph (A) which shows the example of the line profile of the pixel along the line C on the tomogram of FIG. It is the enlarged graph (B).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray source 2 X-ray detector 3 Rotation stage 4 Stage moving mechanism 10 High voltage power supply 11 X-ray controller 12 Stage controller 13 CT image reconstruction calculation apparatus 14 Memory 15 Display 16 Data processing apparatus 17 Operation part C Cursor S Tomography Image T X-ray transmission image R Rotation axis W Subject

Claims (2)

A method for extracting a contour of a tomographic image of a subject constructed by a radiation tomographic imaging apparatus, the method being a point on the contour intersecting a line passing through the center of the tomographic image of the subject and from a direction orthogonal to the line The position information of the point located at the boundary of the image on the radiation transmission image is obtained from the luminance distribution of the pixels near the corresponding position of the radiation transmission image of the subject based on the radiation transmission data from the direction orthogonal to the line. An image processing method. Between the radiation source and the radiation detector arranged to face each other, a holding unit for holding the subject is arranged, and the holding unit and the pair of the radiation source and the radiation detector are centered on a predetermined rotation axis. Radiation equipped with reconstruction calculation means for reconstructing a tomographic image along a plane orthogonal to the rotation axis using the radiation transmission data of the subject captured at every minute rotation angle and stored in the memory while relatively rotating as In tomographic imaging equipment,
An image processing unit for extracting a contour of the reconstructed tomographic image, the image processing unit being a point on the contour intersecting with a line passing through the center of the tomographic image of the subject and from a direction orthogonal to the line; The position information of the point located at the boundary of the image on the radiation transmission image is the radiation transmission data of the subject based on the radiation transmission data from the direction orthogonal to the line among the radiation transmission data stored in the memory. A radiation tomography apparatus characterized in that it is obtained from a luminance distribution of pixels in the vicinity of a corresponding position.

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