JP2006110324A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To photograph two kinds of tomographic images different in an X-ray energy through the use of one kind of X-ray detector without changing-over an X-ray tube voltage. <P>SOLUTION: The energies of the X-ray to be respectively made incident to the front half channel and the rear half channel of a multi-channel X-ray detector (106) are made to be mutually different (150, 160). Respective kinds of mirror point data are generated based on X-ray detection data of the front half channel and X-ray detection data of the rear half channel which are obtained by rotation of 360°. The first kind of tomographic image and the second kind of tomographic image are respectively re-constituted, based on the combination of the X-ray detection data of the front half channel with the mirror point data and the combination of the X-ray detection data of the rear half channel with the mirror point data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus, and more particularly to an X-ray CT apparatus that captures two types of tomographic images having different X-ray energies.

  In the X-ray CT apparatus, two types of tomographic images having different X-ray energies are taken. One of the two types of tomographic images is a tomographic image of a soft tissue (such as fat) taken using low-energy X-rays of about 80 kV, for example, and the other is using high-energy X-rays of about 140 kV, for example. This is a tomographic image of a hard tissue (bone etc.) taken in

Differentiation of X-ray energy is performed by switching the tube voltage of the X-ray tube in two stages (see, for example, Patent Document 1). Alternatively, it is performed by using two types of X-ray detectors arranged in series in the X-ray transmission direction and having different energy absorption characteristics (see, for example, Patent Document 2).
Japanese Patent Laying-Open No. 2004-65975 (page 7-9, FIG. 2-3) JP 2004-181017 A (page 4-6, FIG. 1-5)

  When X-ray energy is differentiated by switching the tube voltage, the tube voltage must be switched alternately during one scan, so that a high-speed and highly accurate control device is required. When the tube voltage is switched every scan, the amount of exposure increases because two scans are required. When two types of X-ray detectors having different energy absorption characteristics are used, two X-ray detectors are required.

  Accordingly, an object of the present invention is to realize an X-ray CT apparatus that captures two types of tomographic images having different X-ray energies using one type of X-ray detector without switching tube voltage.

  In order to solve the above problems, the present invention collects X-ray detection data by rotating an X-ray source and a multi-channel X-ray detector around an isocenter in a state where they face each other with a subject interposed therebetween, An X-ray CT apparatus for reconstructing a tomographic image of an object based on X-rays incident on the first half channel and the second half channel of the multi-channel X-ray detector with an X-ray irradiation point passing through an isocenter as a boundary. Differentiating means for making energy different from each other, data generating means for generating respective mirror point data from the X-ray detection data of the first half channel and the X-ray detection data of the second half channel obtained by rotation of 360 °, and X of the first half channel X-ray detection data of the latter half channel and its mirror poi Based on a combination of Todeta, respectively, an X-ray CT apparatus characterized by comprising a reconstructing means for reconstructing a tomographic image of the tomographic image and the second type of the first kind, the.

  The multi-channel X-ray detector has a plurality of channel rows, and the differentiating means alternately inverts the energy differentiation pattern in the first half channel and the second half channel for each adjacent channel row. This is preferable in that two different types of scout images are taken simultaneously.

  The reconstruction means converts the first-type tomogram and the second-type tomogram into a half-scan and a latter-channel X-ray detection of a combination of the first-half channel X-ray detection data and its mirror point data, respectively. Reconstruction based on a half scan of a combination of data and its mirror point data is preferable from the viewpoint of obtaining a tomographic image from minimum data.

It is preferable that the differentiating means has an X-ray filter from the viewpoint of appropriately differentiating X-ray energy.
The X-ray filter is preferably provided on the X-ray emission side of the X-ray source from the viewpoint of emitting differentiated X-rays.

It is preferable that the X-ray filter is provided on the X-ray incident side of the multi-channel X-ray detector in terms of making differentiated X-rays incident.
The X-ray filters are preferably provided on the X-ray emission side of the X-ray source and the X-ray incident side of the multi-channel X-ray detector, respectively, from the viewpoint of thorough differentiation of X-ray energy.

  It is preferable that the X-ray filter differentiates the X-ray energy into 80 kV and 140 kV from the viewpoint of obtaining a soft tissue tomogram and a hard tissue tomogram, respectively.

  According to the present invention, the X-ray CT apparatus makes the X-ray energy incident on the first half channel and the second half channel of the multi-channel X-ray detector different from each other with the X-ray irradiation point passing through the isocenter as a boundary. And data generation means for generating respective mirror point data from the X-ray detection data of the first half channel and the X-ray detection data of the second half channel obtained by rotation of 360 °, the X-ray detection data of the first half channel and its mirror point data And a reconstruction means for reconstructing the first type of tomogram and the second type of tomogram based on the combination of the X-ray detection data of the latter half channel and the mirror point data thereof, respectively. Using a single X-ray detector without switching the tube voltage, Two tomograms that can be captured.

  The best mode for carrying out the invention will be described below with reference to the drawings. Note that the present invention is not limited to the best mode for carrying out the invention. FIG. 1 shows the configuration of the X-ray CT apparatus. This apparatus is an example of the best mode for carrying out the present invention. An example of the best mode for carrying out the present invention relating to an X-ray CT apparatus is shown by the configuration of the apparatus.

  As shown in the figure, the apparatus includes a gantry 100, a table 200, and an operator console 300. The gantry 100 scans the subject 10 carried by the table 200 with the X-ray irradiation / detection device 102 and collects X-ray detection data (data).

  The gantry 100 scans under a predetermined scanning condition, and the table 200 positions the subject 10 in the imaging space so that a predetermined part is scanned. Positioning is performed by adjusting the height of the top plate 202 and the horizontal movement distance of the cradle 204 thereon by a built-in position adjustment mechanism.

  The height of the top plate 202 is adjusted by swinging the support column 206 around the attachment portion with the base 208. The top plate 202 is displaced vertically and horizontally by the swing of the support column 206. The cradle 204 is displaced horizontally on the top plate 202. Depending on the scanning conditions, scanning is performed with the gantry 100 tilted. The gantry 100 is tilted by a built-in tilt mechanism.

  The operator console 300 gives a scan plan to the gantry 100 and the table 200 to perform scanning based on the scan plan, inputs X-ray detection data from the gantry 100, and performs image reconstruction based on the X-ray detection data. That is, the operator console 300 has a function as a host that supplies a scan plan to the gantry 100 and the table 200 and a function as an image reconstruction device that reconstructs an image from X-ray detection data.

  Corresponding to these two functions, the operator console 300 has two displays 302 and 304. One display 302 is a display for the host, and the other display 304 is a display for the image reconstruction device.

  FIG. 2 schematically shows the configuration of the X-ray irradiation / detection apparatus 102. As shown in the figure, the X-ray irradiation / detection device 102 detects an X-ray 140 emitted from the focal point of the X-ray tube 104 by an X-ray detector 106. The X-ray 140 is formed by a collimator (not shown) to become a fan beam X-ray. The X-ray detector 106 is curved so as to form an arc corresponding to the fan beam X-ray 140.

  The X-ray detector 106 is a multi-channel detector. The angle of each channel viewed from the X-ray focal point is represented by γ. The reference line of the channel angle γ is a straight line connecting the center beam of the fan beam X-ray 140, that is, the X-ray focal point and the isocenter ISO.

  The X-ray irradiation / detection device 102 rotates around an isocenter ISO. The rotation angle is represented by β. The reference line of the rotation angle β is a straight line connecting the X-ray focal point and the isocenter ISO when the X-ray irradiation / detection device 102 is in a vertical state as shown in the figure.

  An irradiation filter 150 is provided on the front surface of the X-ray tube 104. X-rays emitted from the X-ray tube 104 are irradiated to the imaging space through the irradiation filter 150. This filter is also called a bowtie filter because of its shape similarity.

  The irradiation filter 150 is configured so that the right-half portion 152 and the left-half portion 154 have different energy transmission characteristics with the central beam as a boundary. An example of the energy passing characteristics of the right half 152 and the left half 154 is shown in FIG. As shown in the figure, the right half 152 has a relatively high energy pass characteristic, and the left half 154 has a relatively low energy pass characteristic. Hereinafter, the right half 152 is also referred to as a high energy part, and the left half 154 is also referred to as a low energy part. Each filter having such energy transmission characteristics is made of a material having appropriate X-ray energy absorption characteristics. The irradiation filter 150 is an example of a differentiating unit in the present invention.

  An incident filter 160 is provided in front of the X-ray detector 106. X-rays that have passed through the imaging space enter the light receiving surface of the X-ray detector 106 through the filter 160. The incident filter 160 is configured such that the right-half portion 162 and the left-half portion 164 have different energy transmission characteristics with the central beam irradiation point as a boundary. An example of the energy transmission characteristics of the right half 162 and the left half 164 is shown in FIG. As shown in the figure, the right half 162 has a relatively high energy pass characteristic, and the left half 164 has a relatively low energy pass characteristic. Hereinafter, the right half 162 is also referred to as a high energy part, and the left half 164 is also referred to as a low energy part. Each filter having such energy transmission characteristics is made of a material having appropriate X-ray energy absorption characteristics. The incident filter 160 is an example of a differentiating unit in the present invention.

  By the irradiation filter 150 and the incident filter 160, X-rays having different energies are respectively incident on the right half and the left half of the X-ray detector 106 with the incident point of the central beam as a boundary. That is, relatively high energy X-rays enter the right half, and relatively low energy X-rays enter the left half. The energy of the high energy X-ray is, for example, 140 kV, and the energy of the low energy X-ray is, for example, 80 kV. Note that only one of the irradiation filter 150 and the incident filter 160 may be used.

  Assuming that each channel of the X-ray detector 106 is numbered sequentially from the right end to the left end, the right half is the first half channel and the left half is the second half channel. Hereinafter, the right half is also called the first half channel, and the left half is also called the second half channel.

  Since the X-ray irradiation / detection device 102 has such a configuration, view-channel data obtained by scanning at a rotation angle of 360 ° is shown in FIG. The X-ray energy differs between the right half (first half channel) and the left half (second half channel) with the line of γ = 0. The right half is high energy and the left half is low energy.

  On the other hand, in the view channel space, the two coordinates (β, γ) and (β + π + 2γ, −γ) are in a mirror point relationship. A mirror point is a coordinate where the X-ray beam path for obtaining the data of the position is the same and the direction is opposite. Data at such coordinates is called mirror point data. The mirror point data pairs have the same value.

  The distribution of mirror points in the view channel space is shown in FIG. In the figure, mirror points are indicated by the same graphic pattern. As shown in the figure, the mirror point data of the data on the first half channel side exists on the second half channel side, and the mirror point data of the data on the second half channel side exists on the first half channel side.

  By using this relationship, it is possible to fill the latter channel side with the mirror point data of the data on the first half channel side, and to make all the data in the view channel space into high energy X-ray data. The first half channel side is filled with the mirror point data of the side data, and all the data in the view channel space can be converted into low energy X-ray data.

  As a result, complete view channel data can be obtained for each set of high energy and low energy, and by performing image reconstruction using each data set, a tomogram and low energy X-rays by high energy X-rays can be obtained. A tomographic image can be obtained. Therefore, it is possible to take two types of tomographic images having different X-ray energies using one system of X-ray detector without switching the tube voltage.

  Note that image reconstruction is possible with half-scan worth of view channel data, so instead of filling the entire view channel space with both high energy and low energy, the range indicated by the quadrilateral ABCD and X-ray detection data and You may make it fill with mirror point data. As a result, image reconstruction can be performed with a minimum number of data. Further, generation of mirror point data can be minimized.

  FIG. 7 shows a functional block diagram of the operator console 300 that performs mirror point data generation and image reconstruction as described above. As shown in the figure, the operator console 300 uses the mirror point data generation unit 310 to generate the mirror point data from the data of the first half channel and to generate the mirror point data from the data of the second half channel.

  Then, the image reconstruction unit 312 reconstructs a high-energy tomogram based on the combination of the first half channel data and the mirror point data. This tomographic image is a tomographic image of a hard tissue such as a bone.

  Further, the image reconstruction unit 314 reconstructs a low energy tomographic image based on the combination of the latter half channel data and its mirror point. This tomographic image is a tomographic image of a soft tissue such as fat.

  For the high energy tomographic image and the low energy tomographic image, a sum or difference image is obtained as necessary. The mirror point data generation unit 310 is an example of data generation means in the present invention. The image reconstruction units 312 and 314 are an example of reconstruction means in the present invention.

  When the X-ray detector 106 has two rows of channels, the configuration of the incident filter 160 is as shown in FIG. That is, the arrangement of the high energy part 162 and the low energy part 164 is such that the first half is the high energy part 162 and the second half is the low energy part 164 in one column, and the second half is the high energy part 162 in the other column. The first half is the low energy part 164. As for the irradiation filter 150, as shown in FIG. 9, the arrangement of the high energy part 152 and the low energy part 154 is matched with the arrangement of the incident filter 160. The same procedure is used when the X-ray detector 106 has three or more rows.

  By doing so, it is also easy to capture a scout image with two types of high and low X-ray energies. That is, the scout image is imaged by fixing the X-ray irradiation direction in, for example, the vertical direction and sending the subject 10 in the body axis direction, but the high energy portion and the low energy portion in the irradiation filter 150 and the incident filter 160 are captured. With the above arrangement, the same portion of the subject 10 is alternately photographed with high energy X-rays and low energy X-rays, so that two types of scout images with different X-ray energies can be obtained simultaneously. As for these scout images, sum or difference images are obtained as necessary.

It is a figure which shows the structure of the X-ray CT apparatus of an example of the best form for implementing this invention. It is a figure which shows the structure of a X-ray irradiation / detection apparatus. It is a figure which shows the X-ray energy passage characteristic of an irradiation filter. It is a figure which shows the X-ray energy passage characteristic of an incident filter. It is a figure which shows view channel space. It is a figure which shows the mirror point pair in view channel space. It is a block diagram which shows the function of an operator console. It is a figure which shows arrangement | positioning of the high energy part and low energy part in an incident filter. It is a figure which shows arrangement | positioning of the high energy part and low energy part in an irradiation filter.

Explanation of symbols

100 Gantry 200 Table 300 Operator console 102 X-ray irradiation / detection device 104 X-ray tube 106 X-ray detector 140 X-ray 150 Irradiation filter 152 High energy part 154 Low energy part 160 Incident filter 162 High energy part 164 Low energy part 310 Mirror Point data generation units 312, 314 Image reconstruction unit

Claims (8)

X-ray detection data is collected by rotating the X-ray source and the multi-channel X-ray detector around the isocenter in a state where they are opposed to each other with the subject interposed therebetween, and a tomographic image of the subject is reconstructed based on the X-ray detection data A line CT apparatus,
Differentiating means for making the energy of X-rays incident on the first half channel and the second half channel of the multi-channel X-ray detector different from each other at the X-ray irradiation point passing through the isocenter,
Data generation means for generating respective mirror point data from the X-ray detection data of the first half channel and the X-ray detection data of the second half channel obtained by rotation of 360 °;
Based on the combination of the X-ray detection data of the first half channel and its mirror point data and the combination of the X-ray detection data of the second half channel and its mirror point data, respectively, the first type tomogram and the second type of tomogram, respectively. Reconfiguration means for reconfiguring,
An X-ray CT apparatus comprising: The multi-channel X-ray detector has a plurality of channel rows;
The differentiating means alternately inverts the energy differentiation pattern in the first half channel and the second half channel for each adjacent channel row,
The X-ray CT apparatus according to claim 1. The reconstruction means converts the first-type tomogram and the second-type tomogram into a half-scan and a latter-channel X-ray detection of a combination of the first-half channel X-ray detection data and its mirror point data, respectively. Reconstruct based on half scan of data and its mirror point data combination,
The X-ray CT apparatus according to claim 1 or 2, characterized by the above. The differentiating means comprises an X-ray filter;
The X-ray CT apparatus according to any one of claims 1 to 3, wherein the X-ray CT apparatus is characterized by the above. The X-ray filter is provided on the X-ray emission side of the X-ray source;
The X-ray CT apparatus according to claim 4. The X-ray filter is provided on the X-ray incident side of the multi-channel X-ray detector;
The X-ray CT apparatus according to claim 4. The X-ray filters are respectively provided on the X-ray emission side of the X-ray source and on the X-ray incident side of the multi-channel X-ray detector;
The X-ray CT apparatus according to claim 4. The X-ray filter differentiates X-ray energy into 80 kV and 140 kV,
The X-ray CT apparatus according to any one of claims 4 to 7, wherein the X-ray CT apparatus is characterized by the above.

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