JP3802650B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a double-density interpolation method and an X-ray CT (Computed Tomography) apparatus, and more specifically, selects data of opposing views sandwiching an image reconstruction position from data collected by helical scanning, and An interpolation method for obtaining interpolation data at an image reconstruction position by interpolation using data, and a double-density interpolation method capable of obtaining interpolation data of double the conventional density and the double-density interpolation method that can be suitably implemented The present invention relates to a line CT apparatus.
[0002]
[Prior art]
FIGS. 4 to 6 are explanatory views showing the principle of acquiring a group of parallel X-ray beam data by controlling the timing of data acquisition in an RR X-ray CT apparatus.
As shown in FIG. 4A, ½ of the fan angle of the X-ray beam (the angle formed by the X-ray beams incident on the detector channels at both ends of the detector 13) is φ, and the detector angle pitch ( The angle formed by the X-ray beam incident on the adjacent detector channel is ψ, the angle of the X-ray tube 11 is 0 °, and the detector channel number is set in the direction opposite to the rotation direction of the X-ray tube 11 and the detector 13. When “1” to “M” are attached, 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 incident on the detector channel “2” is The angle formed with the 0 ° axis A is (φ−ψ).
Next, as shown in FIG. 4B, when the X-ray tube 11 and the detector 13 are rotated by the detector angular pitch ψ, the X-ray beam incident on the detector channel “2” is the 0 ° axis. The angle formed by A is φ, and the angle formed by the X-ray beam incident on the detector channel “3” and the 0 ° axis A is (φ−ψ).
4 (a) and 4 (b), the X-ray beam incident on the first detector channel at the first X-ray tube angle and the detector angle pitch ψ rotated from the first X-ray tube angle. An X-ray beam incident on the second detector channel adjacent to the first detector channel at a second X-ray tube angle in a direction opposite to the rotation direction of the X-ray tube and the detector is a parallel X-ray beam. It turns out that it becomes.
That is, as shown in FIG. 5, every time the X-ray tube 11 and the detector 13 are rotated by the detector angular pitch ψ, the parallel X-ray beam is adjacent in the direction opposite to the rotation direction of the X-ray tube and the detector. It will inject into each detector channel in order.
Therefore, as shown in FIG. 6, if data is acquired in the order of the number of detector channels at every timing when the X-ray tube 11 and the detector 13 are rotated by the detector angular pitch ψ, data of a group of parallel X-ray beams is obtained. Can be obtained.
[0003]
7 to 8 show a group of parallel X-rays parallel to the y-axis when the X-ray tube 11 and the detector 13 are rotated around the z-axis while being moved along the z-axis and scanned helically. It is explanatory drawing which shows the spatial position of a beam.
As shown in FIG. 7, the z-axis positions of the parallel group of parallel X-ray beams are different from each other. When viewed in the + z direction, the X-ray beam is followed by the parallel X-ray beam in the -y direction, and the X-ray beam is followed by the parallel X-ray beam in the + y direction.
Further, as shown in FIG. 8, the x-axis positions of the parallel 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 are alternately displayed. positioned. In FIG. 7 and subsequent figures, the numbers shown at the arrowheads of the respective X-ray beams represent the time order in which data corresponding to the X-ray beams are collected. Such an arrangement of the X-ray beams is called a quarter offset, and is for obtaining a high resolution.
[0004]
Now, as shown in FIG. 9, when the image reconstruction position zg is determined on the z-axis, the opposite view data sandwiching the image reconstruction position zg is selected from the data acquired by the helical scan, and these opposite views are displayed. The interpolation data of the view at the image reconstruction position is obtained by interpolation using the data. As a conventional example of the interpolation method using the opposite view data, there are an interpolation method for obtaining interpolation data from two data (FIG. 10) and an interpolation method for obtaining interpolation data from three data (FIG. 11).
[0005]
In the interpolation method shown in FIG. 10, data P1 (i, j) on one side (−z direction side) of the image reconstruction position zg and the X-ray beam path of the data P1 (i, j) are used as one direction. The data P2 (i ′, j ′) on the other side (+ z direction side) of the image reconstruction position zg having an offset on the side (−x direction side) is selected as the opposing view, and the data P1 (i , j), P2 (i ′, j ′), the interpolation data PP (i, j) is obtained from the weighted average. That is,
PP (i, j) = w1 (i, j) .P1 (i, j) + (1-w1 (i, j)). P2 (i ', j')
w1 (i, j) = (zg-z (i ', j')) / (z (i, j) -z (i ', j'))
z (i, j) is the z-axis position of the data P1 (i, j),
z (i ′, j ′) is the z-axis position of the data P2 (i ′, j ′). Here, i and i ′ represent view numbers, and j and j ′ represent detector channel numbers assigned to the detector channels.
[0006]
On the other hand, in the interpolation method shown in FIG. 11, data P1 (i, j) on one side (−z direction side) of the image reconstruction position zg and the X-ray beam path of the data P1 (i, j) are used as references. Data P2 (i ′, j ′) on the other side (+ z direction side) of the image reconstruction position zg having an offset on one direction side (−x direction side) and an image having an offset on the other direction side (+ x direction side) The data P2 (i ′ + 1, j ′) on the other side (+ z direction side) of the reconstruction position zg is selected as an opposite view, and the average of the two data on the other side (+ z direction side) of the image reconstruction position zg Data P2 (i ′ + 1/2, j ′) is obtained, and the average data P2 (i ′ + 1/2, j ′) and data P1 on one side (−z direction side) of the image reconstruction position zg are obtained. Interpolated data PP (i, j) is obtained from the weighted average of (i, j). That is,
PP (i, j) = w1 (i, j) .P1 (i, j) + (1-w1 (i, j)). P2 (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 the z-axis position of the data P2 (i ′ + 1, j ′).
[0007]
[Problems to be solved by the invention]
In the conventional interpolation method described above, the density of the obtained interpolation data PP (i, j) is the same as that of one side of the opposite data, and data collected by the quarter offset method is not used to obtain high resolution. There is a problem.
SUMMARY OF THE INVENTION An object of the present invention is to provide a double-density interpolation method and an X-ray CT apparatus that can obtain interpolation data with double the conventional density and can obtain high resolution by using data collected by the quarter offset method. Is to provide.
[0008]
[Means for Solving the Problems]
In the first aspect, the present invention collects data by helical scanning, selects a set of opposing views sandwiching the image reconstruction plane at the image reconstruction position from the data, and uses the opposing view data. An interpolation method for obtaining interpolation data in the image reconstruction plane by interpolation, wherein an offset is introduced between the opposing view data along a transverse application axis set in a direction transverse to the X-ray beam irradiation direction. In such a case, interpolation on one direction side of the transverse coordinate axis in the image reconstruction plane is performed using one opposite view data and offset data on one direction side of the transverse coordinate axis in the other opposite view data corresponding thereto. In addition to obtaining the data, the offset of the transverse coordinate axis in the other direction in the one opposing view data and the other opposing view data corresponding thereto. 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 Todeta.
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 X-ray beam path of the data P1 (i, j) are set in one direction. 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 As the opposite view. Then, based on the load average of the data P1 (i, j) on one side of the image reconstruction position zg and the data P2 (i ′, j ′) on the other side of the image reconstruction position zg having an offset in the one direction side. Then, interpolation data PP (ii, j) having a 1/2 offset in one direction is obtained. Further, according to the load 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 side, 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 the data P1 (i, j),
z (i ′, j ′) is the z-axis position of the data P2 (i ′, j ′),
z (i ′ + 1, j ′) is the z-axis position of the data P2 (i ′ + 1, j ′). Therefore, interpolation data having double the density of the conventional method can be obtained, and high resolution can be obtained by utilizing data collected by the quarter offset method.
[0009]
In a second aspect, the present invention is an X-ray CT apparatus that collects data by helical scanning and obtains interpolated data in the image reconstruction plane using a set of opposing view data sandwiching the image reconstruction plane. When an offset is introduced between the set of opposing view data along a transverse coordinate axis set in a direction transverse to the X-ray beam irradiation direction, the data obtained from the helical scan is selected from the data obtained by the helical scan. The image reconstruction plane is sandwiched between the data selection means for selecting a pair of opposing view data, one opposing view data, and offset data on one side of the transverse coordinate axis in the other opposing view data corresponding thereto. The interpolation data in one direction side of the transverse coordinate axis is obtained in the image reconstruction plane using the one opposing view data and the other corresponding to this Interpolation calculation means for obtaining interpolation data on the other direction side of the transverse coordinate axis in the image reconstruction plane using offset data on the other direction side of the transverse coordinate axis in the opposed view data, An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the second aspect, the double-density interpolation method according to the first aspect can be suitably implemented.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.
[0011]
FIG. 1 is a block diagram of an X-ray CT apparatus according to an embodiment of the present invention.
The X-ray CT apparatus 100 includes an operation console 1, a table device 8, and a scanning gantry 9.
The operation console 1 includes an input device 2 that receives an operator's instructions and information, a central processing unit 3 that performs data collection processing, interpolation processing, image reconstruction processing, and the like, and a control signal and the like on the table device 8 and scanning. A control interface 4 that outputs to the gantry 9, a data collection buffer 5 that collects data acquired by the scanning gantry 9, a CRT 6 that displays images and data, and a storage device 7 that stores programs and data are provided. .
The table device 8 moves the cradle 8c carrying the subject (scanned person) 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, a detector 13, a data collection unit 14, and a rotation controller that rotates an X-ray tube and the like around the body axis of the subject. 15.
Instead of or in addition to moving the subject by the table device 8, the scanning gantry 9 may be moved in the z direction.
[0012]
FIG. 2 is a flowchart of a processing procedure in which the X-ray CT apparatus 100 collects data by helical scanning 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, For each of a plurality of shooting positions, view raw data d (i, j) corresponding to the shooting position is collected.
In step S2, parallel X-ray beam projection data P (i, j) is obtained by fan / para conversion and preprocessing.
[0013]
In step S3, interpolation data PP (ii, j) for all views at the image reconstruction position zg is obtained by double density interpolation. That is, as shown in FIGS. 3A and 3B, a group of parallel X-ray beams parallel to the y-axis will be described as an example. Data P1 (-z direction side) data P1 (-) of the image reconstruction position zg i, j) and data on the other side (+ z direction side) of the image reconstruction position zg having an offset on one direction side (−x direction side) with reference to the X-ray beam path of the data P1 (i, j). P2 (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 opposed to each other. Choose as. The data P1 (i, j) on one side (−z direction side) of the image reconstruction position zg and the other side (+ z) of the image reconstruction position zg having an offset on the one direction side (−x direction side). Interpolated data PP (ii, j) having a ½ offset on one direction side (−x direction side) is obtained by a weighted average of the data P2 (i ′, j ′) on the direction side). Further, the data P1 (i, j) and 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). Interpolation data PP (ii + 1, j) having a 1/2 offset on the other direction side (+ x direction side) is obtained by the weighted 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 the data P1 (i, j),
z (i ′, j ′) is the z-axis position of the data P2 (i ′, j ′),
z (i ′ + 1, j ′) is the z-axis position of the data P2 (i ′ + 1, j ′). Therefore, as shown in FIGS. 3A and 3B, the density of the interpolation data PP (ii, j) obtained on the image reconstruction plane is double the density of one side of the opposing data.
[0014]
Returning to Fig. 2, in step S4, the interpolation data PP (ii, j) is equally spaced to obtain the equally spaced projection data PP '(ii ", j). As shown in (b), since the distances from the image reconstruction plane of the X-ray beam corresponding to each facing view are not equal, the interpolation data PP (ii, j) is not evenly spaced. This is because it is necessary to correct.
In step S5, the equidistant projection data PP ′ (ii ″, j) is subjected to filtered back projection to reconstruct an image. The equidistant projection data PP ′ (ii ″, j) is the conventional one. Due to the double density, the image becomes higher definition than before.
[0015]
According to the X-ray CT apparatus 100 described above, since the interpolation data PP (ii, j) can be obtained at a conventional double density, it is possible to obtain a high resolution image using data collected by the quarter offset method. I can do it.
[0016]
【The invention's effect】
According to the double-density interpolation method and the X-ray CT apparatus of the present invention, interpolation data having a double density can be obtained, and high-resolution high-definition images can be obtained by using data collected by the quarter offset method. I can do it.
[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 scanning 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 X-ray beams are parallel to each other.
FIG. 5 is an explanatory diagram showing a relationship between a rotation angle of an X-ray tube and a detector capable of acquiring a group of parallel beam data and a detector channel;
FIG. 6 is an explanatory diagram showing a relationship between a rotation angle of an X-ray tube and a detector capable of acquiring a group of parallel beam data and a detector channel number to be sampled.
FIG. 7 is an explanatory diagram showing spatial positions on the z-axis of a group of parallel beams.
FIG. 8 is an explanatory diagram showing spatial positions 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 the spatial density of an example of conventional interpolation data.
FIG. 11 is an explanatory diagram showing the spatial density of another example of conventional interpolation data.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 X-ray CT apparatus 1 Operation console 3 Central processing unit 8 Table apparatus 9 Scanning gantry 11 X-ray tube 13 Detector

Claims (2)

An X-ray CT apparatus that collects data by helical scanning and obtains interpolation data in the image reconstruction plane using a set of opposing view data sandwiching the image reconstruction plane,
The image reconstruction from the data obtained by the helical scan when an offset is introduced between the set of opposing view data along a transverse coordinate axis set in a direction transverse to the X-ray beam irradiation direction. Data selection means for selecting a set of opposing view data across the surface;
Interpolation data on one direction side of the transverse coordinate axis is obtained in the image reconstruction plane using one opposite view data and offset data on one direction side of the transverse coordinate axis in the other opposite view data corresponding thereto. And interpolating on the other direction side of the transverse coordinate axis in the image reconstruction plane using 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. Interpolation calculation means for obtaining data;
An equal interval means for obtaining equal interval projection data by equalizing the interpolation data;
An X-ray CT apparatus comprising image reconstruction means for reconstructing an image using the equally spaced projection data. The X-ray CT apparatus according to claim 1,
The data selection means uses data P1 (i, j) on one side of the image reconstruction position zg and data P1 (i) when i and i 'are view numbers and j and j' are detector channel numbers. , j) with respect to the X-ray beam path of the image reconstruction position zg having an offset in one direction and the image reconstruction position zg having an offset in the other direction. Select the other side data P2 (i ′ + 1, j ′) as the opposite view,
The interpolating means outputs data P1 (i, j) on one side of the image reconstruction position zg and data P2 (i ′, j ′) on the other side of the image reconstruction position zg having an offset in the one direction side. The interpolated data PP (ii, j) having a ½ offset in one direction is obtained by the load average represented by the following equation, and the offset is obtained in the data P1 (i, j) and the other direction. Interpolated data PP (ii +) having an offset of ½ on the other direction side by a weighted average represented by the following equation with data P2 (i ′ + 1, j ′) on the other side of a certain image reconstruction position zg 1, j) to obtain X-ray CT apparatus.
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'))
here,
z (i, j) is the z-axis position of the data P1 (i, j),
z (i ′, j ′) is the z-axis position of the data P2 (i ′, j ′),
z (i ′ + 1, j ′) represents the z-axis position of the data P2 (i ′ + 1, j ′).

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