JP2009115643A - Radiological tomographic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiological tomographic device, capable of setting optimally all the time a linear transformation factor for transforming a density data of a pixel of floating point format calculated by reconstitution computation, into luminance data of integral format, without having to depend on the skill of an operator, and is capable of displaying, at all time, clear radiological tomographic images of high contrast. <P>SOLUTION: Characteristic values of the maximum value and the minimum value are extracted from the density data of the pixel comprising the floating point format, calculated by the reconstitution computation, and the optimum linear transformation factor is calculated automatically, using the characteristic values, to be set. The radiological tomographic image of high contrast is displayed all the time by calculating, for example, the linear transformation factor to bring the maximum value of the density data as the maximum luminance value or the vicinity thereof, and to bring the minimum value thereof as the minimum luminance value or the vicinity thereof. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiation tomographic imaging apparatus, and more particularly to an industrial radiation tomographic imaging apparatus.

  A radiation tomography apparatus generally collects radiation projection data obtained by irradiating an object with radiation such as X-rays from the direction of 360 ° around the object at a predetermined minute angle, and the projection data is reproduced again. By performing the configuration calculation, pixel data for constructing a tomographic image of the object is obtained.

  In an industrial radiation tomography apparatus, usually, a rotary table on which an object is mounted and rotated is arranged between a radiation source and a radiation detector arranged opposite to each other, and this rotary table is connected to the radiation source. A structure that rotates around a rotation axis orthogonal to the direction of the radiation optical axis connecting the radiation detectors is often used (see, for example, Patent Document 1). In this configuration, a plane orthogonal to the rotation axis of the rotary table is obtained by collecting radiation projection data of the object at each rotational position while rotating the rotary table by a predetermined minute angle, and reconstructing the collected data. A tomographic image along the line is obtained.

Here, the reconstruction calculation processing is usually performed by calculating the grayscale data of each pixel constituting the tomographic image by calculating the collected X-ray projection data in the floating-point format and displaying it on the display unit in the integer format. Are converted into luminance data of each pixel, and a tomographic image is displayed.
The primary conversion coefficient for converting the grayscale data of the pixels in the floating-point format obtained by the reconstruction operation into the luminance data in the integer format is used by the operator in order to effectively use the limited luminance range in the integer format as much as possible. Is normally set. Conventionally, for this primary conversion coefficient, a method in which an operator selects and sets an optimum value from values prepared in advance (for example, 0.1, 1.0, 10.0, 100.0) has been adopted. Yes.
JP-A-11-344453

  According to the conventional primary conversion coefficient setting method as described above, the optimum value is greatly influenced by the magnification of the tomographic image, the material of the object, and the like. Until it became proficient in this operation, it was necessary to repeatedly perform trial and error to find the optimum value.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radiation tomographic imaging apparatus capable of always setting an optimal primary conversion coefficient without depending on the skill level of an operator.

  In order to solve the above-described problem, the radiation tomography apparatus of the present invention has a table on which an object is mounted between a radiation source and a radiation detector arranged to face each other, the object on the table, Rotation drive means for relatively rotating the radiation source and radiation detector pair around a rotation axis orthogonal to the radiation optical axis direction, and irradiating the object with radiation while driving the rotation drive means. Pixel density data for constructing a tomographic image along a plane orthogonal to the rotation axis is calculated by reconstruction calculation using radiation projection data captured each time the object and the pair are rotated relative to each other at an angle. And a data conversion means for converting the grayscale data of each pixel obtained by the reconstruction calculation into luminance data of each pixel to be displayed on the display using a primary conversion coefficient. In the radiation tomography apparatus, using the feature value extraction means for extracting the feature value from the grayscale data set of each pixel in the floating-point format calculated by the reconstruction calculation, and using the extracted feature value, The present invention is characterized by comprising conversion coefficient calculation means for automatically calculating primary conversion coefficients for converting the grayscale data of each pixel in the floating-point format into luminance data in the integer format (claim 1).

  Here, in the present invention, it is possible to adopt a configuration (claim 2) in which the characteristic value is the maximum value and the minimum value of the grayscale data set of each pixel in the floating-point format. The conversion coefficient calculation means is configured to calculate the primary conversion coefficient so that the maximum value and the minimum value of the grayscale data of the pixel are respectively the maximum luminance value and the minimum luminance value that can be displayed on the display device, or the vicinity thereof. (Claim 3) can be preferably employed.

  In the present invention, the reconstruction calculation for extracting the feature value to calculate the primary conversion coefficient is performed prior to the actual reconstruction calculation for constructing the tomographic image to be displayed on the display. In this case, the reconstruction calculation for extracting the characteristic value to calculate the primary conversion coefficient is performed by using the tomographic image to be displayed on the display. It is desirable to employ a configuration (Claim 5) that is a calculation that thins out the number of slices and / or a calculation that thins out pixels that form each tomographic image as compared with the actual reconstruction calculation for constructing. .

  The present invention extracts a feature value from a set of pixel grayscale data obtained by a reconstruction operation, calculates an optimal primary conversion coefficient based on the result, and automatically sets the feature value. Is to solve.

  That is, for example, feature values such as maximum and minimum values are extracted from the grayscale data of each pixel for constructing a tomographic image obtained by reconstruction calculation, and these values are the maximum brightness that can be displayed on the display. A primary conversion coefficient is obtained so as to be converted into a value, a minimum luminance value, or a value in the vicinity thereof. By using the primary conversion coefficient obtained in this way, the tomographic image displayed on the display is always a high gradation image.

  Here, the reconstruction calculation for extracting the feature value to calculate the primary conversion coefficient may be performed from the actual reconstruction calculation result for constructing the tomographic image to be displayed on the display. From the relationship of capacity, etc., as in the invention according to claim 4, the reconstruction calculation for extracting feature values may be performed in advance. In that case, as in the invention according to claim 5, the number of slices to be reconstructed is thinned out, or the operation of thinning out the pixels constituting each tomographic image is performed, and further, the operation combining both of these By doing so, the processing speed can be increased.

  According to the present invention, luminance comprising an integer format when displaying grayscale data of pixels in a floating-point format obtained by reconstruction calculation using radiation projection data obtained by radiography of an object on a display. The primary conversion coefficient to be converted into data is extracted from the set of pixel grayscale data obtained by the reconstruction operation, and is automatically calculated and set using the result. Depending on the skill level of the operator, the setting of the primary conversion coefficient, which has been forced to undergo trial and error, becomes unnecessary, and it becomes possible to always obtain a tomographic image having an optimum contrast regardless of the skill level of the operator.

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 functional configuration.

  The X-ray source 1 is arranged such that its X-ray optical axis is oriented horizontally, and an X-ray detector 2 is arranged facing the X-ray source 1 in the horizontal direction, and a vertical rotation axis is provided therebetween. A turntable 3 that is rotated around R is arranged. The X-ray source 1 generates cone-beam X-rays, and the X-ray detector 2 is a two-dimensional detector. Further, the rotary table 3 can be moved by the moving mechanism 15 in three axis directions orthogonal to each other including the direction of the X-ray optical axis L.

  At the time of CT imaging, the object W is mounted on the rotary table 3 and irradiated with X-rays, while rotating around the rotation axis R, the output of the X-ray detector 2 at each minute rotation angle, that is, the object. The X-ray projection data transmitted through W is taken into the data storage unit 5 through the image taking circuit 4. In FIG. 1, the rotation axis R is orthogonal to the X-ray optical axis L, but CT imaging is possible even if they are not orthogonal to each other. Just do it.

  After CT imaging, that is, after the X-ray projection data for 360 ° has been prepared in the data storage unit 5, these data are subjected to reconstruction calculation by the reconstruction calculation unit 6. In this reconstruction calculation unit 6, pixels that respectively form a plurality of tomographic images along a plane orthogonal to the rotation axis R using a 360 ° X-ray transmission data based on a preset slice width. Is calculated. The grayscale data (CT value) of each pixel constituting each tomographic image is converted into luminance data of the pixel to be displayed on the display device 8 in the pixel data conversion unit 7, and then for each tomographic image. Are stored in the tomographic image data storage unit 9 and displayed on the display device 8.

  In the pixel data conversion unit 7, the primary conversion coefficient used when the pixel grayscale data calculated by the reconstruction calculation unit 6 is converted into luminance data is automatically calculated by the primary conversion coefficient calculation unit 10. The details will be described later.

  The image capturing circuit 4, the data storage unit 5, the reconstruction calculation unit 6, the pixel data conversion unit 7, the display device 8, the tomographic image data storage unit 9, and the primary conversion coefficient calculation unit 10 are under the control of the control unit 11. These are actually configured by a computer and its peripheral devices, and operate according to a program installed in the computer. In FIG. 1, for convenience of explanation, these are shown in a block diagram for each function. ing.

  An operation unit 12 including a joystick, a keyboard, a mouse, and the like is connected to the control unit 11. By operating this operation unit 12, the X-ray source 1 is turned on / off, a condition is changed, and the like through the X-ray controller 13. Further, a drive command for the rotary table 3 or a drive command for moving the rotary table 3 by the moving mechanism 15 can be given through the stage controller 14.

  The feature of this example is that the pixel data conversion unit 7 converts a primary conversion coefficient to be converted into luminance data of pixels of a tomographic image for displaying on the display device 10 the pixel grayscale data obtained by the reconstruction calculation. The operation procedure will be described below with reference to FIG.

  FIG. 2A is a flowchart showing an operation procedure for obtaining a primary conversion coefficient, and FIG. 2B shows a tomographic image by converting pixel data into luminance data using the obtained primary conversion coefficient. It is a flowchart which shows the operation | movement procedure to perform.

  After completion of CT imaging, first, as shown in FIG. 2A, preliminary reconstruction calculation is performed using the collected X-ray projection data. This preliminary reconstruction calculation does not obtain all the tomographic images for each slice width set through the operation unit 12, but for the setting, for example, the grayscale data of the pixels that construct a tomographic image with 10 jumps. Is calculated. This operation is performed in a floating-point format, and the obtained grayscale data of each pixel is therefore all floating-point values.

  When the reconstruction calculation for the required number is completed, feature points are extracted from the grayscale data of all the pixels. As the feature value, a maximum value and a minimum value can be effectively employed. When extraction of such feature values is completed, an optimal primary conversion coefficient is calculated based on the feature values. In the calculation method, for example, the maximum value of the light and shade data is applied to the maximum luminance value in the display device 10 or a specified value near it, and the minimum value of the light and shade data is similarly applied to the minimum luminance value or a specified value in the vicinity thereof The slope of a line connecting these coordinates with a straight line on the graph is defined as a primary conversion coefficient.

  When the calculation of the primary conversion coefficient is completed by the above procedure, the X-ray projection data already collected and stored is read out as shown in FIG. 2B, and the tomographic image for each set slice width is read. Perform reconstruction operations to build The grayscale data of the pixels in the floating point format thus obtained is converted into luminance data in the integer format using the previously calculated primary conversion coefficient, and the tomographic image data storage unit is used as the luminance data of the pixels constituting the tomographic image. 8 is stored.

  In the tomographic image composed of the luminance data of the pixels obtained in this way, the maximum value of the grayscale data of all the pixels obtained by the reconstruction calculation becomes the maximum luminance value that can be displayed or its neighboring value, and the minimum of the grayscale data. As a result of the value being displayed on the display device 10 as the minimum luminance value or its neighboring value, as shown in FIG. 3, a tomographic image with sufficient contrast is obtained. Incidentally, when a coefficient smaller than the optimum value is set as the primary conversion coefficient, as shown in FIG. 4, the gradation of the tomographic image obtained becomes low and the image becomes difficult to see.

  According to the above embodiment of the present invention, the tomographic image displayed on the display device 10 is always an easy-to-see image with high contrast without the operator setting a primary conversion coefficient, and thus regardless of the skill level of the operator. It becomes.

  In the above embodiments, X-rays are used as radiation. However, the present invention may use other radiation, such as gamma rays, or a pair of an X-ray source and an X-ray detector. As a method of giving relative rotation between the object and the object, a method of rotating a pair of the X-ray source and the X-ray detector around the object may be used.

It is a block diagram of embodiment of this invention, and is the figure which writes together and shows the schematic diagram showing a mechanical structure, and the block diagram showing a function. FIG. 2 is an operation explanatory diagram of an embodiment of the present invention, where (A) is a flowchart showing the contents of a calculation program for a primary conversion coefficient, and (B) is a pixel data obtained by reconstruction calculation, which is converted into luminance data. It is a flowchart showing the content of a program. It is a figure which shows the example of the tomogram obtained by embodiment of this invention. It is a figure which shows the example of the tomogram obtained when a primary transformation coefficient is set smaller than an optimal value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray source 2 X-ray detector 3 Rotation table 4 Image data capture circuit 5 Data storage part 6 Reconstruction calculating part 7 Pixel data conversion part 8 Tomographic image data storage part 9 Primary conversion coefficient calculation part 10 Display apparatus 11 Control part 12 Operation unit 13 X-ray controller 14 Stage controller 15 Moving mechanism L X-ray optical axis R Rotating axis W Object

Claims (5)

A table on which an object is mounted is disposed between the radiation source and the radiation detector that are arranged opposite to each other, and the object on the table and the pair of the radiation source and the radiation detector are arranged in the radiation optical axis direction. Rotation drive means for relatively rotating around orthogonal rotation axes, and radiation captured every time the object and the pair are rotated relative to each other by a predetermined angle by driving the rotation drive means while irradiating the object with radiation. Reconstruction calculation means for calculating grayscale data of pixels for constructing a tomographic image along a plane orthogonal to the rotation axis by reconstruction calculation using projection data, and each pixel obtained by the reconstruction calculation In the radiation tomography apparatus provided with data conversion means for converting the grayscale data into luminance data of each pixel to be displayed on the display using a primary conversion coefficient,
Feature value extraction means for extracting the feature value from the grayscale data set of each pixel in the floating point format calculated by the reconstruction operation, and each pixel in the floating point format using the extracted feature value A radiation tomography apparatus comprising conversion coefficient calculation means for automatically calculating a primary conversion coefficient for converting each grayscale data into luminance data in an integer format.   The radiation tomographic imaging apparatus according to claim 1, wherein the characteristic values are a maximum value and a minimum value of a set of grayscale data of each pixel in the floating point format.   The conversion coefficient calculation means calculates the primary conversion coefficient so that the maximum value and the minimum value of the grayscale data of the pixel are respectively the maximum luminance value and the minimum luminance value that can be displayed on the display unit, or the vicinity thereof. The radiation tomographic imaging apparatus according to claim 2.   The reconstruction calculation for extracting a feature value to calculate the primary conversion coefficient is performed prior to the actual reconstruction calculation for constructing a tomographic image to be displayed on the display. Item 4. The radiation tomographic imaging apparatus according to any one of Items 1, 2, or 3.   The reconstruction calculation for extracting the feature value to calculate the primary conversion coefficient is thinned out compared to the actual reconstruction calculation for constructing the tomographic image to be displayed on the display. The radiation tomography apparatus according to claim 4, wherein the calculation is performed and / or the calculation is performed by thinning out pixels forming each tomographic image.

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