JPS59183737A - S-r type x-ray ct apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an S-R type X-ray CT apparatus.

[Technical background of the invention and its problems]

The S-R type XmCT device has a plurality of detectors arranged in a circular or arc shape, and emits fan beam-shaped X-rays while rotating on a circular or arc-shaped orbit while facing the detectors. The detector is configured to reconstruct a tomographic image using data output from the detector and display the tomographic image.

Compared to other types of X-ray CT apparatuses, the conventional SR type X-ray CT apparatus requires a large amount of data and a long image reconstruction processing time in relation to the spatial resolution that can be obtained. The reason is as follows. ■It would be good to significantly increase the number of detectors to improve spatial resolution, but increasing the number of detectors poses manufacturing and processing difficulties. To understand this, the method of extending the spatial frequency response of the image reconstruction algorithm to the high frequency range is
Usually adopted. Since data sampling is performed every fixed rotation angle Δθ of the X-ray tube, the above method corresponds to reducing Δθ. Then, even if the number of detectors is not increased, the amount of data for the S-R type X-ray CT system will be, for example, 1.5 million points versus 300,000 points compared to the R-g type X-ray CT system. The amount of data is huge. ■The S-R type X-ray CT device rearranges the collected data (source fan data) into data (detector fan data) about the detector fan beam with the detector as the key to the fan, and converts the said detector fan data into image reconstruction processing using the convolution-pack projection method. The number of detector fan beams is equal to the number of detectors, and the processing time for condelusion and backprojection is proportional to the number of detector fan beams. On the other hand, R-R type X-ray C
T device] 8g: uses the source fan data to
I? Image reconstruction processing is performed using the IJ knee-john-back projection method, but the number of source fan data is relatively small because the number of fan beams does not have a significant effect on spatial resolution. Therefore, if the spatial resolution is the same, S-R type
l'111 Number of detector fans and R-R of JICT device
The number of source fans for type XQ CT equipment is, for example, 1.
088 to 400. As described above, the large number of detector fans is also a factor in prolonging the total image reconstruction processing time in the S-R type X-ray CT apparatus.

As described above, the S-R type X-gland CT apparatus 4 has the following features in order to deal with the increase in data amount and the lengthening of the reconstruction processing time.
First, having a huge storage capacity requires media such as magnetic disks, magnetic tapes, and 1% speed data processing equipment, resulting in higher prices for the entire equipment and longer time periods for inspecting objects. It is inviting

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide an SR type X-ray CT apparatus that reduces the amount of data and shortens the image +4 configuration processing time.

[Summary of the invention]

The outline of the present invention for achieving the above object is to detect an X-ray tube that emits Xi Mitsuan beams while rotating around the subject, and an X-ray fan beam arranged on the circumference or in an arc. In a 5-Rfi X-ray CT apparatus, which has at least a plurality of X-ray detectors capable of performing The present invention is characterized in that it includes an interpolation means that performs averaging processing on the data output from the L detector, and reconstructs the fault edge using the data obtained by performing the averaging processing.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an S-R type X-ray CT apparatus which is an embodiment of the present invention, FIG. 2 is a block diagram showing the functions of the computer in FIG. 1, and FIG.
FIG. 2 is a flowchart showing the processing procedure performed by the computer in FIG. 1 of Book J; FIG.

(5) As shown in FIG. 1, S-R is an embodiment of the present invention.
The type X-ray CT apparatus has a plurality of X-ray detectors 1 arranged on a circumference, and is moved along a circular orbit while facing the X-ray detector 1, and X-ray tube 4 that irradiates the Xi Mitsuan beam toward the subject 2 located at the
A group of data obtained by the X-win fan beam, which collects data output from the gantry 5 and the X-ray detector 1, and sets the X-ray 1 radiation position as the delivery woman. A data collection device 6 that outputs the data as data, a computer 7 having function implementation means described below, a storage means such as a magnetic disk 8 for writing and extracting the data of each building, and instructing the computer 7 to operate. The interpolation detector fan data transferred via the operation console 9 which outputs all the command signals to be outputted and the computer 7 is controlled. An image reconstruction device 1o that performs image reconstruction processing according to the solution-pack pronoection method, an image display device 11 that optically displays the tomographic image reconstructed by the image reconstruction device 10, and a tUTJ'4 self-X-ray A high voltage generator 12 that applies a full high voltage to the X-ray tube 4 at a predetermined timing in order to irradiate the X-ray fan (6) beam 3 from 'u4; It has a system control device 13 that controls the operation timing.

The computer 7 has a writing/reading means 7A, a data rearrangement means 7B, and
It is composed of an interpolation calculation means 7C and a transfer means 7D.

(2) The writing/adjusting means 7A writes the source fan data outputted from the data storage unit 6 and the interpolation detector fan gutter (described later) outputted from the interpolation calculation means 7C to the full magnetic disk 8. , controls reading out of the source fan data written on the magnetic disk 8 by the data rearrangement means 7B and the interpolation calculation means 7CK.

The data 14 arrangement means 7B rearranges the source fan data read out from the magnetic disk 8 through the arranging/reading means 7A ft, for example, as shown in FIG. A fan-shaped fan with the key point of the fan! Reorganize the Ronoexion data into 6 detector fan data. In addition, in FIG. 4, fo t f
l+... indicates the X-ray irradiation position of the X-ray tube 4.

The interpolation calculation means 7C reads out the detector fan data outputted from the data rearrangement means 7B and written on the magnetic disk 8 via the write/read means 78 again via the write/read means 7Ai, and reads out the detector fan data output from the data rearrangement means 7B and writes it into the adjacent magnetic disk. Detector fan data is bundled and averaged to 1/2 or less for interpolation. The interpolation process in the interpolation calculation means 7C will be described in detail below. For convenience of explanation, it is assumed that two adjacent detector fan data are bundled and averaged.

As shown in FIG. 5, the X-ray irradiation position fo of the X-ray tube 4 is
=f* The central angle of . . . is Δθ, data is collected every Δθ, and the central angle of the arranged X-ray detectors 1 is ΔV. Therefore, the number of X-ray detectors l arranged is 2π/Δda. The position of each X-ray detector l is 2 mΔF and 2 mΔF with respect to the reference position do.
m+1)Δ'r. Then, the position of the X-ray detector is obtained by interpolating the position of all the fans. Note that m is an integer of 0, 1.2, . . . .

The number of discrete data that constitutes the detector fan data is N
(integer) number. This N is the X-ray tube 4 and X-ray detector 1
('FDD), the distance 1171t between the X-ray tube 4 and the center of the imaging area: (FCD), is a constant determined by the imaging area and Δθ. Each of the N pieces of data constituting the detector fan whose split is the 2mth (or 2m+1st) X-ray detector position is =0, 1, 2.
, . . . This is data collected at (N-1). This data 6D(2m,k) [or D(2m+1.k
)). Now, W = 2 mΔW and '-(2m
+1) It can be calculated using the interpolated detector fan data iP formula, which requires the virtual X-ray detector position (9) at the midpoint of ΔF.

For all the detector fans, the interpolation calculation means 7C
According to the first equation, interpolation calculations are performed from m-0 to m=7-1.

Furthermore, the interpolation calculation means 7C transfers the interpolated detector fan data obtained by the calculation between t+IA to the magnetic disk 8 via the writing/reading means 7A, and does not output (discard) the detector fan data used for the interpolation calculation. ).

The transfer means 7D reads out the interpolated detector fan data written on the magnetic disk 8 in 1m order via the writing/extraction means 7A and transfers it to the fore-portrait image reconstruction device 10.
configured to transfer to.

In the present invention, the transfer means 7D is omitted, and the interpolated detector fan data written on the magnetic disk 8 is immediately transferred to the image reconstruction device 1o by the annotation/reading means (10) 7A. It may also be read out.

Next, the operation of the above configuration will be explained along with the flow shown in the third diagram.

As shown in FIGS. 1 and 5, the X-ray tube 4 rotates on its circumferential orbit and emits an X-ray fan beam 3 toward the subject 2 at each X-ray irradiation position forf, . Exposure. The X-ray fan beam 3 that has passed through the subject 2 is detected by the X-ray detector 1, and the data output from the X-ray detector 1 is collected by the data collection device 6. The data acquisition device 6 detects each X-ray irradiation position fo.

A data group υ such as a plurality of data outputted from a plurality of X-ray detectors 1 into which an X-ray fan beam irradiated by fl... is incident is collected together and used as source fan data. The source fan data of 2 ga θ are sequentially outputted to the computer 7 as follows.

In the computer 7, as shown in FIGS. 2 and 3, the source fan data sequentially sent to the writing/reading means 7A is written onto the magnetic disk 8. Next, the writing/reading means 7A sequentially reads out the source fan data once written into the magnetic disk 8 to the data rearranging means 7B. Data rearrangement means 7
B converts 2π/Δθ source fan data into 2π/ΔP detector fan data consisting of N discrete data with the X-ray detector position d as the key point of the fan, as shown in FIG. Then, 2π/Δp pieces of detector fan data are written to the magnetic disk 8 via the writing/reading means 7A. Next, the writing/reading means 7A reads out 2π/ΔV pieces of detector fan data to the interpolation calculation means 7c. The interpolation calculation means 7C calculates the adjacent detector fan data D(2m, k) and D(2m+
1. k), the X-ray detector position d is determined as shown in FIG.
Interpolated detector fan data p(2m+;pk) with the midpoint between 2rn and 62m+1 as the key point of the fan is calculated according to the first equation. This interpolation calculation is performed using the detector fan data D (
2m, k) and D(2m+1, k), so to speak, is calculated as an arithmetic mean. The obtained interpolated detector fan data is N pieces of data θ(2m + 2
+k) is a different data group.

N-1 θ(2m+-, 1c) = ((π-completedΔθ+ to Δθ+2
mΔV)=π−NgaΔθ+toΔθ+(2m+−!−)Δ
f2 (2) The obtained interpolated detector fan data is written to the magnetic disk 8 via the writing/reading means 7A. At this time, the writing/reading means 7A does not transfer the detector fan data used for the interpolation process to the magnetic disk 8, but discards the detector fan data. The interpolated detector fan data written on the magnetic disk 8 is read out by the writing/reading means 7A and transferred to the image reconstruction device 10 by the transfer means 7D. The image reconstruction device 10 reconstructs a tomographic image of the subject based on the transferred interpolated detector fan data. The reconstructed tomographic image is displayed on the image display device 11.

(]3) As mentioned above, by performing interpolation processing in the computer 7, interpolated detector fan data, which is the remainder of the number of side detector fan data, is obtained, and the image is reconstructed using this interpolated detector fan data. , image reconstruction processing time can be significantly reduced. In other words, it is possible to speed up image reconstruction.

Note that even if the amount of data is occasionally reduced due to interpolation processing, the spatial resolution of the obtained tomographic image is hardly impaired. This is illustrated below.

First, since Δθ and ΔV are generally small amounts of copying, k
=0.1.2. , (N-1), D(2
m.

The intersection points XI, ..., Xn of the virtual X-ray beams of k) and D(2m+1.k) are the center of field of view y and the virtual X-ray detector position, as shown in Figure 8. d: 7m + d
It is located on the circumference with 2m+j as both ends of the diameter. In addition, in FIG. 8, 14 indicates a circle in which a plurality of X-ray detectors 1 are arranged, and 15 indicates a circle in which a plurality of X-ray detectors 1 are arranged.
The circumferential orbit in which the ray tube 4 rotates is shown, and 16 indicates the imaging area by the X-ray fan beam 3.

(14) At the visual field center y, since data that intersect at that position are selected and combined, no blurring of the image occurs due to interpolation processing. The same applies to other intersection points. Blurring due to interpolation processing occurs in spatial frequency components orthogonal to the X-ray beam. Such a gap is proportional to the distance between the newly generated virtual X-ray beam shown by the broken line and the truly measured X-ray beam shown by the solid line in FIG. This distance is measured in the direction perpendicular to the virtual x-ray beam. Therefore, in FIG. 8, it can be easily inferred that the influence of the interpolation process is greatest in the vicinity of point a. Assuming that N is an odd number for the sake of simplicity, R is the radius of the imaging area 16, as shown by the solid line at point a. Therefore, the new virtual data resulting from the interpolation process is not what was truly measured at that position, but rather
The sum of the measurements at positions offset by 1 will be used.

Therefore, in general, the following holds true.

The function P(x) distributed in the direction X is Fourier transformed, and its spatial frequency component FU'') is determined according to the third equation.

A function Pl(
The Fourier transform of x)=P(x-t) is υ according to the transition theorem.
It can be expressed by the fourth equation.

F+C/'')-FV)e-'''-=(4) Similarly, by shifting by -t, the Fourier transform of F2(x)=P(x+t) can be expressed by Equation 5.

F2(f) −FCf)e”' −・・・−−(
5) Now, the function P(x) is not measured, what is actually measured is Pt(x) and P 2 (x). From this, interpolation is performed to obtain the average value of Pt(x) and F2(X) for P(x). This estimated value yt, r, -1[. −z2
πft i2πft] FV)2+0 -cns 2rtft -FQQ -...
= (6) That is, a filter of cos2πft is applied to the true spatial frequency component F(g). Fig. 8R Since the spatial frequency component is the average value calculated from the data measured at points shifted by 10 - ΔT and 17 ΔW, a filter called cos2πf (di ΔF) is applied. There used to be.

Here, assume an SR type X-ray CT apparatus having the following specifications.

X-ray detector 1200 pieces Δ'/' 5.2mra
d.

FCD 700 + FD0 1800mmX
Line focal point Approximate to infinitesimal MTF (Modulation Transfer Function), assuming Δθ is sufficiently smaller than ΔW, (
17) Approximately expressed by Equation 7, this cutoff frequency is 0
．． 45 tine-pair/mm, and its profile is shown in FIG. On the other hand, if the effective field of view radius is 160wn and one interpolated detector fan data is created from two detector fan data as in the above example, the worst blur can be expressed by the filter function of equation 8, and its profile is as shown in Figure 10.

F(f) - Bunch (πfFtΔv/) One bunch (0,832πf) ・・・・・・・・・(8)
In this way, F(f) sufficiently exceeds the MTF due to the width of the X-ray detection aperture. Therefore, even though the amount of data required for image reconstruction processing has been halved, the spatial resolution obtained is not significantly impaired.

(18) Although one embodiment of the present invention has been described above in detail, this invention is not limited to the above embodiment, and may be implemented with appropriate modifications within the scope of the gist of the invention. It goes without saying that you can do it.

As a second embodiment, the interpolation calculating means may be configured to calculate one piece of interpolated detector fan data from three or more pieces of detector fan data. If this is done, the amount of data used for image reconstruction can be further reduced, although the spatial resolution will be sacrificed a little. In addition, three detector fan data D (3m, k
), D(3m+1°k), D(3m+2.k), interpolation detector fan data P(3m+1°k)
, k) are calculated according to Equation 9.

P(3m+1.k)=H(D(3m,k)+D(3m+
1. k) 10D (3m+2.k))・・・・・・・・・(
9) In this case, the deviation due to the interpolation process is expressed by Equation 10.

FtJ)-1(1+2Fish(2πfRΔF))...
(1) As a third embodiment, the interpolation calculation means is configured to directly interpolate source fan data to calculate interpolated source fan data. In the third embodiment, the re-arranging means is omitted and the image reconstruction process is performed using the obtained interpolation source fan data, and the image reconstruction process is performed while reducing the number of times due to the interpolation process. The amount of data required can be reduced.

〔Effect of the invention〕

According to this invention, it is possible to reduce the amount of data required for image reconstruction to less than the difference, thereby reducing image reconstruction processing time while preventing image deterioration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an S-R type X-ray CT apparatus which is an embodiment of the present invention, FIG. 2 is a block diagram showing the functions of the computer shown in FIG. 1, and FIG. 3 is a block diagram showing the functions of the computer shown in FIG. FIG. 4 is an explanatory diagram showing a detector fan that provides detector fan data; FIG. 5 is an explanatory diagram showing the relationship between the X-ray detector position and the X-ray exposure position; Figure 6 is an explanatory diagram showing a detector fan made up of X-ray beams that provides each data that constitutes the detector fan data, and Figure 7 shows a detector fan beam that provides adjacent detector fan data and a detector fan beam that provides interpolated detector fan data. FIG. 8 is an explanatory diagram for calculating the deke caused by interpolation processing, and FIG. 9 is an explanatory diagram showing the MTF when reconstructing an image using detector fan data.
It is a characteristic diagram showing the profile of. DESCRIPTION OF SYMBOLS 1... X-ray detector, 2... Subject, 3... X-ray fan beam, 4... X-ray tube, 7... Interpolation calculation means,
10... Image reconstruction device. (21)

Claims (2)

[Claims] (1) An X-ray beam that emits an X-ray fan beam while rotating around the subject, and an X-ray beam arranged on the circumference or in an arc.
Multiple X-ray detectors capable of detecting ray fan beams and X?
In an S-R type X-ray CT apparatus having at least an image reconstruction device g that reconstructs a tomographic image of a subject based on data output from an fM detector, data output from an X-ray detector. An S-R type X-ray CT apparatus characterized in that it is equipped with an interpolation means for performing averaging processing, and reconstructs a tomographic image using data obtained by performing the averaging processing. (2) The data to be subjected to averaging processing is obtained by rearranging the data output from the XB1 detector using a detector fan beam that requires 1 h of X-ray detector position (
The S-R type X according to claim 1, characterized in that it is determined by actually measured adjacent detector fan data
wCT device.