JPH10314161A - Double density interpolation method and x-ray ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the interpolation data of the density doubled from before. SOLUTION: By the weighted average of the data Pi(i, j) of one opposing view from the view point of an image reconstitution position and the other opposing view data P2(i', j') at the image reconstitution position offset to one direction side with a crossing coordinate axis set so as to cross the irradiation direction of the X-ray beam of the data P1(i, j) as a reference, the interpolation data PP(ii, j) on one direction side of the crossing coordinate axis are obtained. Also, by the weighted average of the data P1(i, j) and the other opposing view data P2(i'+1,j') of the image reconstitution position offset to the other direction side of the crossing coordinate axis of the data P1(i, j), the interpolation data PP(ii+1, j) on the other direction side are obtained. Thus, the data gathered by a quarter offset system are utilized and the high definition images of a high resolution are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a double density interpolation method and an X-ray CT (Computed Tomography) apparatus.
More specifically, there is provided an interpolation method in which data of an opposite view sandwiching an image reconstruction position is selected from data collected by helical scan, and interpolation data at the image reconstruction position is obtained by interpolation using the data of the opposite view. Further, the present invention relates to a double-density interpolation method capable of obtaining double-density interpolation data and a X-ray CT apparatus capable of suitably implementing the double-density interpolation method.

[0002]

2. Description of the Related Art FIGS. 4 to 6 are explanatory diagrams showing the principle of acquiring data of a group of parallel X-ray beams by controlling data acquisition timing in an RR type X-ray CT apparatus. . As shown in FIG. 4A, 1/2 of the fan angle of the X-ray beam (the angle between the X-ray beams incident on the detector channels at both ends of the detector 13) is φ,
The detector angular pitch (the angle formed by the X-ray beams incident on the adjacent detector channels) is ψ, the angle of the X-ray tube 11 is 0 °, and the rotation direction of the X-ray tube 11 and the detector 13 is opposite to the rotation direction. When the detector channel numbers are assigned from “1” to “M”, the angle between the X-ray beam incident on the detector channel “1” and the 0 ° axis A is φ, and the X-ray beam is incident on the detector channel “2”. The angle that the X-ray beam makes with the 0 ° axis A is (φ−ψ). Next, as shown in FIG.
When the X-ray tube 11 and the detector 13 are rotated by the detector angle pitch ψ, the angle between the X-ray beam incident on the detector channel “2” and the 0 ° axis A is φ, and the detector channel “3” is formed. The angle formed by the X-ray beam incident on "" with the 0 ° axis A is (φ-ψ). From FIG. 4A and FIG. 4B, the first
An X-ray beam incident on a first detector channel at an X-ray tube angle of
The X-ray beam incident on the second detector channel adjacent to the first detector channel in the direction opposite to the rotation direction of the X-ray tube and the detector at the second X-ray tube angle rotated only by It turns out that it becomes an X-ray beam. That is, as shown in FIG. 5, each time the X-ray tube 11 and the detector 13 are rotated by the detector angle pitch ψ, the parallel X-ray beam is adjacent to the X-ray tube and the detector in the opposite direction. To each detector channel in turn. Therefore, as shown in FIG. 6, if the data is acquired in the order of the number of the detector channel at each timing when the X-ray tube 11 and the detector 13 are rotated by the detector angle pitch ψ, the data of the group of parallel X-ray beams can be obtained. Can be obtained.

FIGS. 7 and 8 show a group of groups parallel to the y-axis when the helical scan is performed by moving the X-ray tube 11 and the detector 13 along the z-axis while rotating the x-ray tube 11 and the detector 13 around the z-axis in the xyz space. It is explanatory drawing which shows the spatial position of a parallel X-ray beam. As shown in FIG. 7, the z-axis positions of a group of parallel parallel X-ray beams are different from each other. Looking at the + z direction, the X-ray beam is followed by a parallel X-ray beam in the −y direction, and then the X-ray beam is followed by a parallel X-ray beam in the + y direction. As shown in FIG. 8, the x-axis positions of a group of parallel X-ray beams are different from each other. When viewed from the -x direction to the + x direction, a parallel X-ray beam whose X-ray beam irradiation direction is the -y direction and a parallel X-ray beam whose X-ray beam irradiation direction is the + y direction alternately. positioned. In the drawings after FIG. 7, the numbers indicated by the arrowheads of the respective X-ray beams indicate the time order in which data corresponding to the X-ray beam is collected. X like this
The arrangement of the line beam is a quarter offset
fset) to obtain high resolution.

[0005] As shown in FIG. 9, when an image reconstruction position zg is determined on the z-axis, data of an opposite view sandwiching the image reconstruction position zg is selected from data acquired by helical scanning. Interpolation using the data of the opposite view is performed to obtain interpolation data of the view at the image reconstruction position. Conventional examples of the interpolation method using the data of the opposite view include an interpolation method of obtaining interpolation data from two data (FIG. 10) and an interpolation method of obtaining interpolation data from three data (FIG. 11).

In the interpolation method shown in FIG. 10, data P1 (i, j) on one side (−z direction side) of the image reconstruction position zg is
Data P2 (i ', j) on the other side (+ z direction side) of the image reconstruction position zg having an offset on one side (-x direction side) with respect to the X-ray beam path of the data P1 (i, j). ') Is selected as the opposing view, and the interpolation data PP is calculated by the weighted average of the data P1 (i, j) and P2 (i', j ') of the opposing views.
Find (i, j). That is, PP (i, j) = w1 (i, j) · P1 (i, j) + (1−w1 (i, j)) · P
2 (i ′, j ′) w1 (i, j) = (zg−z (i ′, j ′)) / (z (i, j) −z (i ′,
j ')) z (i, j) is the z-axis position of data P1 (i, j), and z (i', j ') is the z-axis position of data P2 (i', j '). Here, i and i 'represent the view numbers, and j and j' represent the detector channel numbers assigned to the detector channels.

On the other hand, in the interpolation method shown in FIG. 11, data P1 (i, i) on one side (−z direction side) of the image reconstruction position zg.
j) and data P2 on the other side (+ z direction side) of the image reconstruction position zg having an offset on one side (−x direction side) with respect to the X-ray beam path of the data P1 (i, j).
(i ', j') and data P2 (i '+ 1, j') on the other side (+ z direction side) of the image reconstruction position zg having an offset on the other direction side (+ x direction side) are selected as opposed views. Then, the average data P2 (i '+ 1/2, j') of the two data on the other side (+ z direction side) of the image reconstruction position zg is obtained, and the average data P2
(i ′ + 1/2, j ′) and one side of the image reconstruction position zg (−z
The interpolation data PP (i, j) is obtained by the weighted average of the data P1 (i, j) on the (direction side). That is, PP (i, j) = w1 (i, j) · P1 (i, j) + (1−w1 (i, j)) · P
2 (i '+ 1/2, j') w1 (i, j) = (zg-z (i '+ 1/2, j')) / (z (i, j) -z
(i '+ 1/2, j')) P2 (i '+ 1/2, j') = (P2 (i ', j') + P2 (i '+ 1, j')) / 2 z (i '+ 1/2, j') = (z (i ', j') + z (i '+ 1, j')) / 2 z (i '+ 1, j') is data P2 (i '+ 1) , j ′).

[0007]

In the above-mentioned conventional interpolation method, the density of the obtained interpolation data PP (i, j) is the same as that of one side of the opposite data, and the quarter offset method is used to obtain high resolution. There is a problem that the collected data is not used. Therefore, an object of the present invention is to provide a double-density interpolation method and a double-density interpolation method capable of obtaining interpolation data having twice the density of the conventional one and obtaining high resolution by utilizing data collected by the quarter offset method.
An object of the present invention is to provide a line CT apparatus.

[0008]

According to a first aspect of the present invention, data is collected by helical scan and a set of opposed views sandwiching an image reconstruction plane at an image reconstruction position is selected from the data. An interpolation method for obtaining interpolation data in the image reconstruction plane by interpolation using the facing view data, wherein the facing view is set along a transverse petition axis set in a direction transverse to the X-ray beam irradiation direction. When an offset is introduced between the data, one of the opposite view data and the corresponding offset data on the one side of the transverse coordinate axis in the other opposite view data are used in the image reconstruction plane. Interpolation data in one direction side of the transverse coordinate axis is obtained, and the one opposed view data and the corresponding opposed view data in the other opposed view data are determined. Providing double density interpolation method characterized by obtaining the interpolation data in the other direction of the transverse axis on the image reconstruction plane by using the offset data in the other direction side of the cross-sectional axes. In the double-density interpolation method according to the first aspect, the data P1 (i, j) on one side of the image reconstruction position zg and the data P1 (i, j) in one direction with reference to the X-ray beam path of the data P1 (i, j). Data P2 (i ', j') on the other side of the image reconstruction position zg with an offset and data P2 (i '+ 1, j') on the other side of the image reconstruction position zg with an offset in the other direction Is selected as the facing view. Then, the data P1 (i, i, i) on one side of the image reconstruction position zg.
j) and the weighted average of the data P2 (i ', j') on the other side of the image reconstruction position zg having an offset on one side,
Interpolated data PP (i
i, j). In addition, by the weighted average of the data P1 (i, j) and the data P2 (i ′ + 1, j ′) on the other side of the image reconstruction position zg having an offset in the other direction, 1 / Interpolation data PP (ii + 1, j) having an offset of 2 is obtained. That is, PP (ii, j) = w1 (i, j) · P1 (i, j) + (1−w1 (i, j)) ·
P2 (i ', j') PP (ii + 1, j) = w2 (i, j) P1 (i, j) + (1-w2 (i, j))
P2 (i '+ 1, j') w1 (i, j) = (zg-z (i ', j')) / (z (i, j) -z (i ',
j ′)) w2 (i, j) = (zg−z (i ′ + 1, j ′)) / (z (i, j) −z (i ′ +
1, j ')) z (i, j) is the z-axis position of data P1 (i, j), z (i', j ') is the z-axis position of data P2 (i', j '), z ( i '+ 1, j') is the data P2 (i '+
1, j '). Therefore, interpolation data having twice the density of the conventional interpolation data can be obtained, and high resolution can be obtained by utilizing data collected by the quarter offset method.

In a second aspect, the present invention provides an X-ray CT system for acquiring data by helical scan and obtaining interpolation data in the image reconstruction plane using a set of facing view data sandwiching the image reconstruction plane. An apparatus, wherein an offset is introduced between the pair of opposed view data along a transverse coordinate axis set in a direction transverse to the X-ray beam irradiation direction, the data obtained by the helical scan. Data selection means for selecting a set of opposed view data that sandwiches the image reconstruction plane from among them; one opposed view data and a corresponding offset data in one direction side of the transverse coordinate axis in the other opposed view data; In the image reconstruction plane, interpolation data in one direction side of the transverse coordinate axis is obtained using evening, and the one of the opposite view data evening and the And interpolating means for obtaining interpolation data in the other direction of the transverse coordinate axis in the image reconstruction plane using offset data in the other direction of the transverse coordinate axis in the corresponding opposite view data. An X-ray CT apparatus is provided. The X-ray CT apparatus according to the second aspect can suitably implement the double density interpolation method according to the first aspect.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this.

FIG. 1 is a block diagram of an X-ray CT apparatus according to one embodiment of the present invention. This X-ray CT apparatus 100
Is provided with an operation console 1, a table device 8, and a scanning gantry 9. The operation console 1 includes an input device 2 for receiving instructions and information from an operator, a central processing unit 3 for executing data collection processing, interpolation processing, image reconstruction processing, and the like, and a table apparatus 8 for scanning control signals and the like. It comprises a control interface 4 for outputting to the gantry 9, a data collection buffer 5 for collecting data acquired by the scanning gantry 9, a CRT 6 for displaying images and data, and a storage device 7 for storing programs and data. .
The table device 8 moves the cradle 8c on which the subject (the person to be scanned) is placed in the z direction by the movement controller 8a. The scanning gantry 9 includes an X-ray controller 10, an X-ray tube 11, a collimator 12, and a detector 1
3, a data acquisition unit 14, and a rotation controller 15 for rotating an X-ray tube or the like around the body axis of the subject. The scanning gantry 9 may be used instead of or in addition to moving the subject by the table device 8.
May be moved in the z direction.

FIG. 2 is a flowchart of a processing procedure in which the X-ray CT apparatus 100 collects data by helical scan and generates an image. In step S1, raw data d (i, j) is collected by helical scanning. That is, the X-ray tube 11, the collimator 12, and the detector 13 are rotated, and the subject (or the X-ray tube 11, the collimator 12, and the detector 13) is linearly moved along the z-axis. Raw data d (i, j) of a view corresponding to each of a plurality of shooting positions is collected. In step S2, projection data P (i, j) of the parallel X-ray beam is obtained by fan / para conversion and preprocessing.

In step S3, the interpolation data PP (i) of all the views at the image reconstruction position zg by the double density interpolation.
i, j). That is, as shown in FIGS. 3A and 3B, taking a group of parallel X-ray beams parallel to the y-axis as an example, data P1 (-z direction) on one side (−z direction side) of the image reconstruction position zg. i, j) and X of the data P1 (i, j)
The data P2 (i ', j') on the other side (+ z direction side) of the image reconstruction position zg having an offset on one side (-x direction side) with respect to the line beam path and the other side (+ x direction side) ), The data P2 (i '+ 1, j') on the other side (+ z direction side) of the image reconstruction position zg having an offset is selected as the opposite view. Then, the data P1 (i, j) on one side (−z direction side) of the image reconstruction position zg and the image reconstruction position zg having an offset on the one direction side (−x direction side).
Of the data P2 (i ', j') on the other side (+ z-direction side) is obtained as interpolation data PP (ii, j) having a half offset on one side (-x-direction side). . Also, the data P2 (i '+ 1, j') on the other side (+ z direction side) of the image reconstruction position zg having an offset on the other direction side (+ x direction side) with the data P1 (i, j). Interpolation data PP (ii + 1, j) having an offset of 1/2 on the other direction side (+ x direction side) is obtained by the load average. That is, PP (ii, j) = w1 (i, j) · P1 (i, j) + (1−w1 (i, j)) ·
P2 (i ', j') PP (ii + 1, j) = w2 (i, j) P1 (i, j) + (1-w2 (i, j))
P2 (i '+ 1, j') w1 (i, j) = (zg-z (i ', j')) / (z (i, j) -z (i ',
j ′)) w2 (i, j) = (zg−z (i ′ + 1, j ′)) / (z (i, j) −z (i ′ +
1, j ')) z (i, j) is the z-axis position of data P1 (i, j), z (i', j ') is the z-axis position of data P2 (i', j '), z ( i '+ 1, j') is the data P2 (i '+
1, j '). Therefore, (a) and (b) of FIG.
As shown in the figure, the interpolation data PP obtained on the image reconstruction plane
The density of (ii, j) is twice the density of one side of the facing data.

2, at step S4, the interpolation data PP (ii, j) is subjected to equal-interval processing to obtain equal-interval projection data PP '(ii ", j). As shown in FIG. 3B, since the distances of the X-ray beams corresponding to the respective opposing views from the image reconstruction plane are not equal, the interpolation data PP (ii, j) are not equally spaced. In step S5, the equally-spaced projection data PP '(ii ", j) is subjected to filtered back projection to reconstruct an image. This image has higher definition than before because the equally-spaced projection data PP '(ii ", j) has twice the density as before.

According to the X-ray CT apparatus 100 described above, the interpolation data PP (ii, j) can be obtained at the conventional double density, so that a high-resolution image can be obtained by utilizing the data collected by the quarter offset method. Can be obtained.

[0016]

The double density interpolation method and X-ray CT of the present invention
According to the apparatus, interpolation data having twice the density of the conventional interpolation data can be obtained, and a high-resolution high-definition image can be obtained by utilizing data collected by the quarter offset method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart of a processing procedure for acquiring raw data by helical scan and generating an image.

FIG. 3 is an explanatory diagram showing a spatial density of interpolation data according to the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a rotation angle of an X-ray tube and a detector and a detector channel when an X-ray beam is parallel.

FIG. 5 is an explanatory diagram showing a relationship between a detector channel and a rotation angle of an X-ray tube and a detector capable of acquiring data of a group of parallel beams.

FIG. 6 is an explanatory diagram showing a relationship between an X-ray tube capable of acquiring data of a group of parallel beams, a rotation angle of a detector, and a detector channel number for sampling.

FIG. 7 is an explanatory diagram showing a spatial position on the z-axis of a group of parallel beams.

FIG. 8 is an explanatory diagram showing a spatial position on the x-axis of a group of parallel beams.

FIG. 9 is an explanatory diagram showing a spatial position on the z-axis of a parallel beam and an image reconstruction position.

FIG. 10 is an explanatory diagram showing a spatial density of an example of conventional interpolation data.

FIG. 11 is an explanatory diagram showing a spatial density of another example of conventional interpolation data.

[Explanation of symbols]

 Reference Signs List 100 X-ray CT apparatus 1 Operation console 3 Central processing unit 8 Table device 9 Scanning gantry 11 X-ray tube 13 Detector

Claims (2)

[Claims] 1. Data is collected by helical scan, a set of opposed views sandwiching an image reconstruction plane at an image reconstruction position is selected from the data, and the image reconstruction is performed by interpolation using the opposed view data. An interpolating method for obtaining interpolated data in a configuration plane, wherein an offset is introduced between the opposed view data along a transverse petition axis set in a direction transverse to the X-ray beam irradiation direction. Using the opposite view data and the corresponding offset data on the other side of the transverse coordinate axis in the other opposite view data to obtain interpolation data on the one side of the transverse coordinate axis in the image reconstruction plane, The one opposite view data and the offset data on the other direction side of the transverse coordinate axis in the other opposite view data corresponding thereto. Double density interpolation method and obtaining the interpolation data in the other direction of the transverse axis on the image reconstruction plane with. 2. An X-ray CT apparatus which collects data by helical scan and obtains interpolation data in the image reconstruction plane using a set of facing view data sandwiching the image reconstruction plane, the apparatus comprising: When an offset is introduced between the pair of opposed view data along a transverse coordinate axis set in a direction transverse to the irradiation direction, the image reconstruction plane is extracted from the data obtained by the helical scan. Data selection means for selecting a pair of opposite view data, one of the opposite view data, and the corresponding offset data on the one side of the transverse coordinate axis in the other opposite view data, and the image reproduction is performed. Interpolation data in one direction of the transverse coordinate axis is obtained in the configuration plane, and the one opposed view data and the other opposed view corresponding thereto are obtained. Interpolating means for obtaining interpolation data in the other direction of the transverse coordinate axis in the image reconstruction plane using offset data in the other direction of the transverse coordinate axis in the data. X-ray CT device.