JP2005253518A - X-ray ct equipment and its three dimensional image reconstruction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide X-ray CT equipment and its three-dimensional image reconstruction method capable of reconstructing a three-dimensional image with little artifact. <P>SOLUTION: This X-ray CT equipment is provided with a means of detecting X-rays generated from an X-ray source and transmitting a subject by a multirow detector which has a plurality of detecting element rows formed by oppositely aligning a plurality of X-ray detecting elements in the both sides of a subject in the X-ray source, on the body axis direction of the subject and outputting a plurality of sliced projection data of the subject; a means of creating a plurality of reference images from the projection data and creating the plurality of reference images in such a manner that continuous two images out of the plurality of created reference images have mutually common parts of the projection data, being the respective creation origins; and a means of reconstructing the three-dimensional image of the subject from the plurality of reference images. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an X-ray CT apparatus and a three-dimensional image reconstruction method thereof, and more particularly to an X-ray CT apparatus having a multi-row detector and a three-dimensional image reconstruction method thereof.

  The multi-row detector type X-ray CT apparatus uses a multi-row detector provided with a plurality of detection element rows in which a plurality of X-ray detection elements are arranged in the body axis direction of the subject, thereby providing a plurality of consecutive subjects. Slice projection data can be collected simultaneously, and a plurality of continuous two-dimensional tomographic images can be reconstructed from the projection data. The slice thickness corresponding to the thickness of one tomographic image is preferably small in order to increase the definition of the tomographic image, and in recent years it can be less than 1 mm.

Patent Document 1 discloses a technique for reconstructing a three-dimensional image from projection data and tomographic images obtained in this way.
JP 2001-104293 A

  When reconstructing a range of 3D images from projection data or tomograms obtained from multiple consecutive slices, the number of slices from which 3D images are created is inversely related to the slice thickness. The portion corresponding to the joint of slices on the constructed three-dimensional image increases as the slice thickness decreases. In many cases, a step-like artifact is generated at a portion corresponding to the joint. That is, a seemingly contradictory phenomenon occurs that the image quality of the three-dimensional image deteriorates as the definition of the tomographic image increases.

  If the slice thickness at the time of projection data acquisition is adjusted to be suitable for reconstruction of a 3D image, artifacts on the 3D image can be reduced, but the definition of tomographic images obtained from the same projection data is reduced. There is a problem. Further, although it is conceivable that the projection data is collected under conditions suitable for three-dimensional image reconstruction and conditions suitable for tomographic image reconstruction, there is a problem in that X-ray exposure of the subject and restraint time increase. .

  The present invention has been made in view of such circumstances, and reconstructs a three-dimensional image with less artifacts without reducing the definition of a tomographic image or increasing the X-ray exposure or restraint time of a subject. An object of the present invention is to provide an X-ray CT apparatus capable of performing the above and a three-dimensional image reconstruction method thereof.

  In order to achieve the above object, an X-ray CT apparatus according to the present invention provides X-rays generated from an X-ray source and transmitted through a subject, and a plurality of X-rays facing each other with the subject sandwiched between the X-ray source. Means for detecting a plurality of detection element arrays in which the detection elements are arranged in a body axis direction of the subject and outputting projection data of a plurality of slices of the subject; A plurality of reference images are created so that two consecutive images out of the plurality of created reference images share a part of the projection data from which they are created. And means for reconstructing a three-dimensional image of the subject from the plurality of reference images.

  Preferably, the means for creating the plurality of reference images from the projection data includes means for reconstructing the tomographic images of the plurality of slices from the projection data of the plurality of slices, and the plurality of the tomographic images of the plurality of slices. Means for generating the reference images of the plurality of slices so that two consecutive images of the plurality of reference images share a part of the tomographic image from which the images are generated. Means for creating a plurality of reference images by repeatedly creating one reference image from tomographic images of at least two slices.

  In order to achieve the above object, the three-dimensional image reconstruction method of the X-ray CT apparatus according to the present invention uses the X-ray generated from the X-ray source and transmitted through the subject to the X-ray source. Is detected by a multi-row detector provided with a plurality of X-ray detection elements arrayed facing each other in the body axis direction of the subject, and projection data of a plurality of slices of the subject are output. And a step of creating a plurality of reference images from the projection data, and two consecutive images among the plurality of created reference images share a part of the projection data from which they are created. A plurality of reference images, and a step of reconstructing a three-dimensional image of the subject from the plurality of reference images.

  Preferably, the step of creating the plurality of reference images from the projection data includes the step of reconstructing the tomograms of the plurality of slices from the projection data of the plurality of slices, and the plurality of slice images from the tomograms of the plurality of slices. The reference images of the plurality of slices, so that two consecutive images of the plurality of reference images are common to each other as part of the tomograms from which the images are generated. And creating a plurality of reference images by repeating the creation of one reference image from tomographic images of at least two slices.

  According to the present invention, a plurality of images are created as reference images so that two consecutive images have a common part of information, and a three-dimensional image is reconstructed from the reference images. As described above, with respect to the reference image from which the three-dimensional image is created, by giving a common part of information to two consecutive reference images, the reference image on the three-dimensional image is generated at a portion corresponding to the joint. Stepped artifacts can be reduced. As a result, the definition of the tomographic image is not reduced, and the X-ray exposure of the subject and the restraint time are not increased at all. In addition, when trying to reduce staircase artifacts by filtering or the like, deterioration of the accuracy of the 3D image is inevitable, but according to the present invention, the 3D image is reconstructed based on actual information, Degradation of the accuracy of the original image can be suppressed.

  Hereinafter, preferred embodiments of an X-ray CT apparatus and its three-dimensional image reconstruction method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention. The X-ray CT apparatus 10 mainly includes a scanner 20 for collecting projection data, and a controller 40 that controls the scanner 20 and processes projection data obtained by the scanner 20.

  The scanner 20 mainly includes an X-ray generator 22 for generating X-rays, a subject table 26 on which the subject 24 is placed, and the subject table 26 as a body axis of the subject 24 (hereinafter simply referred to as “body axis”). A subject table moving device 28 that moves in a direction, a multi-row X-ray detector 30 that detects X-rays transmitted through the subject 24, an X-ray generator 22 and a multi-row X-ray detector 30; And a scanner rotating device 34 for continuously rotating the scanner main body 32 including the center around the body axis.

The multi-row X-ray detector 30 includes a plurality of X-ray detection element rows 30A, 30B,... Arranged in the body axis direction. The number of X-ray detection element arrays is several tens to several hundreds, for example. Each of the X-ray detection element arrays 30A, 30B,... Includes a plurality of X-ray detection elements arranged in a line. For example, the X-ray detection element array 30A includes X-ray detection elements 30A ₁ , 30A ₂ ,. The number of X-ray detection elements in one X-ray detection element array is, for example, several tens to several hundreds. The size of the X-ray detection surface of one X-ray detection element is, for example, about 1 × 1 mm, and the width in the body axis direction of one row of X-ray detection element arrays is, for example, about 1 mm.

  The controller 40 has a CPU 42 that controls the entire X-ray CT apparatus 10. When collecting projection data, the X-ray generator controller 44 controls the X-ray generator 22 to generate X-rays, and the multi-row X-ray detector 30 detects X-rays transmitted through the subject 24. To output a measurement signal. At the same time, the scanner rotation control unit 46 controls the scanner rotation device 34 to rotate the scanner body 32, and the subject table movement control unit 48 controls the subject table movement device 28 to place the subject 24. The subject 24 can be helically scanned by moving the subject table 26.

  The measurement signal output from the multi-row X-ray detector 30 is converted into a digital signal by the measurement signal A / D conversion unit 50 and becomes projection data. Then, the reconstruction calculator 52 reconstructs a two-dimensional tomographic image of the subject 24 from the projection data. The reconstructed tomographic image is displayed on the image display display 56 and stored in the data recording device 58 through the data display / storage control unit 54 as necessary. The projection data may be stored in the data recording device 58. The data recording device 58 includes a storage device such as a memory and a magnetic disk built in or external to the controller 40, a device that writes and reads data to and from a removable external medium, and an external storage device via a network. A device that transmits and receives data may be used. Further, the data recording device 58 stores a program for causing the CPU 42 to control the X-ray CT apparatus 10.

  Next, the reference image creation unit 60 creates a reference image to be described later from the projection data or tomogram. The created reference image is stored in the data recording device 58 via the data display / storage control unit 54. Then, the 3D image creation unit 62 creates a 3D image from the reference image or tomographic image. The created three-dimensional image is displayed on the image display display 56 and stored in the data recording device 58 as needed via the data display / storage control unit 54.

  The computing unit control unit 64 controls the measurement signal A / D conversion unit 50, the reconstruction computing unit 52, the data display / storage control unit 54, the reference image creation unit 60, and the 3D image creation unit 62. The console 66 includes input / output means (not shown) such as a keyboard, a pointing device, and a display device (may also be used as the image display display 56), and serves as an interface between the controller 40 and the operator. The bus 68 mediates data transmission / reception of each unit in the controller 40.

With reference to FIG. 2, a 3D image reconstruction method according to an embodiment of the present invention will be described. The acquisition of projection data as described above, the slice 1 position _{P 1} of consecutive subject 24, slice 2 position _{P 2,} ... from (FIG. 2 (A)), the projection data 1, the projection data 2, ... ( FIG. 2 (B)) is obtained. In order for the reconstruction calculator 52 to reconstruct a high-definition tomographic image, the slice thickness T of each slice is preferably as small as possible.

  According to the helical scan using the multi-row X-ray detector 30, isotropic projection data having substantially the same resolution in any direction of the subject 24 can be collected. The direction in which the slices 2,... Are arranged (P-axis direction in FIG. 2) can be arbitrarily selected. Further, a non-helical scan is performed in which only the scanner body 32 is rotated and the subject 24 is not moved, and projection data obtained by the X-ray detection element array 30A is obtained by the projection data A and X-ray detection element array 30B. The data may be projection data B,..., In which case the body axis direction is the P-axis direction in FIG.

  Next, the reconstruction calculator 52 reconstructs the tomographic image 1, the tomographic image 2,... (FIG. 2C) from the projection data 1, the projection data 2,. It is stored in the recording device 58. As a result, a tomographic image having a small slice thickness and a high definition can be secured.

  The three-dimensional image creation unit 62 can read out the tomographic image 1, the tomographic image 2,... Stored in the data recording device 58 and directly reconstruct the three-dimensional image therefrom, but the slice thickness is small. When a three-dimensional image is reconstructed from a tomographic image, a stepped artifact often occurs in a portion corresponding to the joint of the tomographic image on the three-dimensional image. Therefore, in the present embodiment, the reference image creation unit 60 first creates a plurality of reference images (FIG. 2D) from the tomogram, and the 3D image creation unit 62 creates a 3D image (FIG. 2 (D) from the reference image. Reconfigure E)).

  In the example of FIG. 2D, the reference image creation unit 60 uses the image obtained by adding the tomographic image 1 and the tomographic image 2 as the reference image 1, and the image obtained by adding the tomographic image 2 and the tomographic image 3 as the reference image 2. ... and so on. As a result, for example, the reference image 1 and the reference image 2 share the tomographic image 2 out of the tomographic images that are the respective creation sources, and the reference image 2 and the reference image 3 are the tomographic images that are the respective creation sources. Among them, the tomographic image 3 is common. That is, two consecutive images among a plurality of reference images share a part of a tomographic image as a creation source, and thus share a part of projection data as a creation source.

  In the above-described example, the reconstruction calculator 52 reconstructs a tomographic image from the projection data, and the reference image creation unit 60 creates a reference image from the tomographic image. However, the reference image creation unit 60 directly uses the projection data. Alternatively, the reference image may be reconstructed. In that case, the reference image creation unit 60 converts the image reconstructed from the data obtained by adding the projection data 1 and the projection data 2 to the image reconstructed from the data obtained by adding the reference data 1, the projection data 2, and the projection data 3. Reference image 2, and so on. Also in this way, in two consecutive images among the plurality of reference images, a part of the projection data as the respective creation sources is common to each other.

  As described above, the reference image on which the three-dimensional image creation unit 62 creates the three-dimensional image has a common part of information in two consecutive reference images, thereby connecting the reference images on the three-dimensional image. It is possible to reduce stepped artifacts that occur in the portion corresponding to the eyes.

  FIG. 3 shows another example of creating a reference image. 3A to 3C are the same as FIGS. 2A to 2C and 2E. In the example of FIG. 3D, the reference image creating unit 60 adds an image obtained by adding 1/2 of the tomographic image 1 and 1/2 of the tomographic image 3 to the tomographic image 2 to the tomographic image 3. An image obtained by adding 1/2 of the image 2 and 1/2 of the tomographic image 4 is referred to as a reference image 3. As a result, for example, the reference image 1 and the reference image 2 have a common half of the tomographic image 1 and 1/2 of the tomographic image 2 out of the tomographic images that are the creation sources, and the reference image 2 and the reference image 3 is common to 1/2 of the tomographic image 2 and 1/2 of the tomographic image 3 among the tomographic images from which the images are created. When the reference image creation unit 60 reconstructs a reference image directly from projection data, reconstruction is performed from data obtained by adding 1/2 of projection data 1 and 1/2 of projection data 3 to projection data 2. The reconstructed image is a reference image 2, and an image reconstructed from data obtained by adding 1/2 of projection data 2 and 1/2 of projection data 4 to projection data 3 is referred to as reference image 3,. As described above, by distributing the projection data or tomographic image obtained from one slice to each of the two consecutive reference images, the two consecutive reference images may have a common part of information. .

  FIG. 4 shows another example of creating a reference image. 4A to 4C are the same as FIGS. 2A to 2C. In the example of FIG. 4D, the reference image creation unit 60 uses the image obtained by adding the tomographic image 1, the tomographic image 2, and the tomographic image 3 as the reference image 1, the tomographic image 2, the tomographic image 3, and the tomographic image 4. Let the added image be a reference image 2. As a result, for example, the reference image 1 and the reference image 2 have the same tomographic image 2 and tomographic image 3 among the tomographic images that are the respective creation sources, and the reference image 2 and the reference image 3 are the respective creation sources. Among the tomographic images, the tomographic image 3 and the tomographic image 4 are common. When the reference image creation unit 60 reconstructs a reference image directly from projection data, an image reconstructed from data obtained by adding projection data 1, projection data 2, and projection data 3 is referred to as reference image 1, An image reconstructed from data obtained by adding the data 2, the projection data 3, and the projection data 4 is referred to as a reference image 2,.

  In the example of FIG. 4, the ratio of the common part of two consecutive reference images is 2/3, but this ratio may be further increased. As described above, the reference image that is the creation source of the three-dimensional image (FIG. 4E) by the three-dimensional image creation unit 62 gives more information common parts to two consecutive reference images. It is possible to further reduce staircase artifacts that occur at portions corresponding to the joints of the reference images on the three-dimensional image.

  FIG. 5 shows another example of creating a reference image. 5A to 5C are the same as FIGS. 2A to 2C. In the example of FIG. 5D, the reference image creation unit 60 uses the image obtained by adding the tomographic image 1, the tomographic image 2, and the tomographic image 3 as the reference image 1, the tomographic image 3, the tomographic image 4, and the tomographic image 5. The added image is referred to as a reference image 2, and an image obtained by adding the tomographic image 5, the tomographic image 6, and the tomographic image 7 is referred to as a reference image 3. As a result, for example, the reference image 1 and the reference image 2 share the tomographic image 3 among the tomographic images that are the respective creation sources, and the reference image 2 and the reference image 3 are the tomographic images that are the respective creation sources. Among them, the tomographic image 5 is common. When the reference image creation unit 60 reconstructs a reference image directly from projection data, an image reconstructed from data obtained by adding projection data 1, projection data 2, and projection data 3 is referred to as reference image 1, An image reconstructed from data obtained by adding the data 3, the projection data 4, and the projection data 5 is referred to as a reference image 2,.

  In the example of FIG. 5, the ratio of the common part of two consecutive reference images is 1/3. However, this ratio may be further reduced, and there is still an effect of reducing stepped artifacts on the three-dimensional image. . In this way, by increasing the number of slices from which a single reference image is created, the proportion of the common part of two consecutive reference images is reduced, so that the 3D image creation unit 62 can obtain a 3D image (see FIG. 5 (E)) can be reduced in the number of reference images, the calculation amount of the three-dimensional image creation unit 62 can be reduced, and the calculation time can be shortened.

The relationship between the position P _{1 of} the slice ₁ , the position P _{2 of} the slice ₂ , and the slice thickness T is P ₂ −P ₁ = T in the examples of FIGS. 2 to 5, but may be other than that. In the following, the reference image creation unit 60 weights and adds the tomographic image ₁ of the slice 1 at the position P 1 and the tomographic image 2 of the slice 2 at the position P ₂ (P ₁ <P ₂ ) to refer to the position X. An example of creating an image will be described. When the reference image creation unit 60 reconstructs the reference image at the position X directly from the projection data of the slice 1 and the slice 2, an image reconstructed from data obtained by weighting and adding the projection data in the same manner is used as the reference image. good.

  There are various requirements for the reconstruction of a three-dimensional image, such as reduction of artifacts, reduction of calculation time, and improvement of resolution. However, since the priority order thereof varies depending on circumstances, the operator executes the reference image creation unit 60. The optimum reference image creation method to be performed may be selected from the various methods as described above via the console 66, and further, the 3D image creation unit 62 can use the projection data or tomographic image without using the reference image. It may be possible to select to directly reconstruct a three-dimensional image. In addition, the operator can select a desired mode from a low artifact mode, a short calculation time mode, a high resolution mode, and the like, and the CPU 42 automatically selects an optimal three-dimensional image reconstruction method based on the selection. May be executed.

FIG. 1 is a schematic configuration diagram showing an embodiment of an X-ray CT apparatus according to the present invention. FIG. 2 is a diagram used for explaining the first embodiment of the three-dimensional image reconstruction method according to the present invention. FIG. 3 is a diagram used for explaining a second embodiment of the three-dimensional image reconstruction method according to the present invention. FIG. 4 is a diagram used for explaining the third embodiment of the three-dimensional image reconstruction method according to the present invention. FIG. 5 is a diagram used for explaining the fourth embodiment of the three-dimensional image reconstruction method according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... X-ray CT apparatus, 20 ... Scanner, 22 ... X-ray generator, 24 ... Subject, 26 ... Subject table, 28 ... Subject table moving apparatus, 30 ... Multi-row X-ray detector, 30A, 30B ... X-ray detection element array, 30A ₁ , 30A ₂ ... X-ray detection element, 32 ... scanner body, 34 ... scanner rotation device, 40 ... controller, 42 ... CPU, 44 ... X-ray generation device controller, 46 ... scanner rotation control 48 ... Subject table movement control unit 50 ... Measurement signal A / D conversion unit 52 ... Reconstruction computing unit 54 ... Data display / storage control unit 56 ... Display for image display 58 ... Data recording device Reference numeral 60: Reference image creation unit 62: Three-dimensional image creation unit 64: Operation unit control unit 66: Console 68: Bus

Claims (3)

A detection element array in which a plurality of X-ray detection elements facing each other with the subject interposed therebetween is arranged in the direction of the body axis of the subject. Means for detecting by a multi-row detector comprising a plurality and outputting projection data of a plurality of slices of the subject;
A means for creating a plurality of reference images from the projection data, wherein two consecutive images among the plurality of created reference images are plural so that a part of the projection data as a creation source is common to each other. Means for creating a reference image of
Means for reconstructing a three-dimensional image of the subject from the plurality of reference images;
An X-ray CT apparatus comprising: The means for creating the plurality of reference images from the projection data includes:
Means for reconstructing tomographic images of the plurality of slices from projection data of the plurality of slices;
The means for creating the plurality of reference images from the tomograms of the plurality of slices, wherein two consecutive images of the plurality of reference images have a common part of the tomograms from which they are created. Means for creating the plurality of reference images by repeatedly creating one reference image from tomograms of at least two slices of the tomograms of the plurality of slices;
The X-ray CT apparatus according to claim 1, comprising: A detection element array in which a plurality of X-ray detection elements facing each other with the subject interposed therebetween is arranged in the direction of the body axis of the subject. Detecting with a multi-row detector comprising a plurality, and outputting projection data of a plurality of slices of the subject; and
A step of creating a plurality of reference images from the projection data, wherein two consecutive images of the plurality of created reference images are plural in such a way that a part of the projection data as a creation source is common to each other Creating a reference image of
Reconstructing a three-dimensional image of the subject from the plurality of reference images;
A three-dimensional image reconstruction method for an X-ray CT apparatus, comprising:

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