JPH05309089A - X-ray ct device - Google Patents

Abstract

PURPOSE:To decrease width in the body axis direction required for reconstitution in a spiral scan, and to improve reliability of a reconstituted image by realizing the spiral scan in two directions of a going path and a return path. CONSTITUTION:An X-ray generating device 1 and an X-ray detector 2 rotate continuously on a flat plane determined in advance. In such a state, a bed 3 on which an examinee is laid proceeds at a constant speed. In the processing process, the examinee is exposed by X rays. The exposure is executes by a spiral scan. Transmitting X rays obtained by the spiral scan are detected by the X-ray detector 2 and subjecting to various pre-treatments and A/D conversion by a data collecting circuit 2A, and spiral data SR is obtained. This spiral data SR is stored in a two-dimensional buffer 12 in which arguments (i), (j) are addresses. An interpolating circuit 13 obtains projection data R of a required tomographic surface from the spiral data SR. The obtained projection data R is subjected to burr correction processing and reversal projection processing by a filter correcting circuit 14 and a reversal projection arithmetic circuit 15, respectively, and thereafter, a CRT 16 displays a tomographic image. By executing this operation in the return direction, as well and a reconstituted image is obtained from both of them.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus for performing a spiral scan. A conventional example of an X-ray CT apparatus that has performed a helical scan is "application and problems of digital image processing to medical equipment" (seminar sponsored by Giken Center "Digital signal of medical image"). Paper on "Problems for Processing Technology and Its Clinical Application" October 26, 1981. Yuio Horiba, II 42
-II page 44) (referred to as conventional example A), and JP-A-59-59.
No. 111738 (referred to as Conventional Example B). Conventional example A
Is a document showing the principle of the spiral scan CT apparatus, and X
A principle of a helical scan having two characteristics of rotating a radiation source around a subject and moving the subject in the body axis direction with the rotation is disclosed. Furthermore, the conventional example A discloses that the data collected by this helical scan is reconstructed. Thus, the principle of the helical scan X-ray CT apparatus has been described. Conventional example B discloses a helical scan X-ray CT apparatus similar to conventional example A. Further, Conventional Example B discloses various reconstruction methods and artifact reduction methods from data collected by a helical scan. [0004] In each of the above-mentioned conventional examples, the bed is moved only in one direction. As a result of the movement in only one direction, the projection data necessary for reconstruction is inevitably large in terms of the width in the body axis direction of the subject. Furthermore, if the width in the body axis direction becomes large, there arises a problem in the reliability of the reconstructed image itself. An object of the present invention is to provide an X-ray CT apparatus capable of reducing the width in the body axis direction required for reconstruction in a helical scan and improving the reliability of a reconstructed image. .. According to the present invention, there is provided an X-ray source for generating X-rays, and an X-ray for detecting X-rays transmitted through an object provided facing the X-ray source. A line detector, a patient bed on which a subject is placed and which can be continuously moved on both the forward and backward paths, a data collection means for collecting the detected data, and an image reconstruction means for reconstructing an image from the data. , At least, continuously rotating the X-ray source around the subject, and moving the patient bed continuously in the body axis direction of the subject during the rotating movement. The subject was exposed to X-rays inside, and helical scanning was performed in both directions of reciprocation to reconstruct a tomographic image at an arbitrary slice position. The present invention provides an X-ray source that generates X-rays, an X-ray detector that is provided facing the X-ray source, and that detects X-rays that have passed through the subject, and a forward route and a backward route that carry the subject. At least a continuously movable patient bed, data collection means for collecting detected data, and image reconstruction means for image reconstruction from the data, and the X-ray source surrounding the subject. Continuously and rotationally moving the patient bed in the body axis direction of the subject during the rotational movement,
During the movement of the subject, the subject is exposed to X-rays to cause helical scanning in both directions of reciprocation, and projection at an arbitrary slice position is made by using the data collected in the forward pass and the return pass. Data was obtained, and a tomographic image at an arbitrary slice position was image-reconstructed from the projection data. Further, the present invention provides
An X-ray source that generates X-rays, an X-ray detector that is provided facing the X-ray source, and detects X-rays that have passed through the subject, and a subject that is placed on both the forward and backward paths. At least a continuously movable patient bed, a data collection means for collecting detected data, and an image reconstruction means for reconstructing an image from the data are provided, and the X-ray source is continuously provided in the surrounding of the subject. The patient bed is continuously moved in the body axis direction of the subject during the rotational movement, the subject is exposed to X-rays while the subject is moving, and the patient is rotated in both directions of reciprocation. In an X-ray CT apparatus that is configured to perform a uniform scan, interpolation processing is performed between the data collected on the forward path and the data acquired on the return path to obtain projection data at an arbitrary slice position, and an arbitrary slice is obtained from the projection angle data. It was decided to reconstruct the tomographic image of the position. As a result, it is possible to realize a two-direction spiral scan of the forward path and the backward path, and it is possible to obtain a high-resolution reconstructed image that cannot be obtained only by the forward path from the projection data obtained from it. FIG. 2 is an external view of an RR type CT device.
The X-ray CT apparatus includes an X-ray tube apparatus (X-ray generator) 1,
It comprises an X-ray detector 2, a high voltage generator for an X-ray tube (not shown), and a patient bed 3. The X-ray tube device 1 and the X-ray detector 2 are in a positional relationship of facing each other with the subject on the bed 3 interposed therebetween. Under this opposed positional relationship, the X-ray tube device 1 and the X-ray detector 2 are continuously rotated. Due to the continuous rotation, the high voltage from the high voltage device to the X-ray tube device 1 was supplied via the slip ring. This rotation speed is a constant speed as can be seen from the sine wave locus of FIG. 5 described later. The X-ray tube device 1 and the X-ray detector 2 are integrally mounted on a frame. A slip ring mechanism is attached to the frame (scanner) to supply high voltage. The patient bed 3 can move at a constant speed in a direction (arrow) perpendicular to the plane of rotation of the scanner. Patient bed 3
Of X-rays and X-ray exposure by the X-ray tube apparatus 1
The rotation of and synchronize with each other. By moving and rotating the patient bed and the X-ray tube apparatus 1 at a constant speed determined by each, there is an advantage that the management of the collected data in the spiral scan becomes easy.
If the movement of the patient bed and the rotation of the X-ray tube device 1 are not constant, it is not easy to set the coefficients a and b in the interpolation processing described later, and it is not easy to extract two data having the same projection angle. Now, the scanner is rotated continuously at a high speed on a fixed rotating surface. At this time, the patient bed 3 is inserted into the gantry opening 4 at a constant speed, and scanning is performed within a range including a desired tomographic plane. Scan positioning is performed prior to this scanning. As for the positioning, referring to FIG. 3, the first tomographic plane 6 serving as a reference for starting imaging is set at a distance a from the scanner rotation plane A.
Only the front is positioned. The distance a has an allowance until the moving speed of the patient bed becomes constant, and the X-ray pulse is synchronized with the B surface (distance b) where the speed becomes steady after the scanner and the patient bed start rotating and moving. To start the exposure. The distance b in this case is a distance in which extra data must be measured after the start and end of the measurement because projection data is obtained by using interpolation in the direction in which the patient bed moves. When the patient bed reaches the plane B ', which has passed the final slice plane 7 by the distance b, the X-ray irradiation is stopped, and the patient bed decelerates and stops on the plane A'. In this way, by moving the patient bed during the scanning, the scanning is performed in a spiral shape as shown in FIG. FIG. 5 shows a trajectory of the X-ray tube apparatus in this case, which is obtained by one-way scanning of the subject. The projection data obtained by the spiral scanning (hereinafter referred to as spiral data) is obtained when the scanner is spirally rotated around the object to be scanned as shown in FIG. It is equivalent to projection data. The helix data SR is determined by the projection angle β and the position X of the subject in the body axis direction. Here, the position X ₀ at the start of scanning and the distance that the bed (and the subject) moves while the scanner makes one rotation are D. To reconstruct a tomographic image of the slice plane (tomographic plane) S (X _n ) at the object position X _n , projection data R (β, X _n ) (where β = 0 ° to 36)
0 °) is required. Then, projection data R (β, X _n ) of the desired tomographic plane S (X _n ) is obtained from the spiral data SR by interpolation, and an image is reconstructed from the projection data. To obtain a tomographic image, projection data R (β, X _n ) on the tomographic plane (where β = 0 ° to 360)
)) Is required. The spiral data is shown below by a general formula. ## EQU1 ## SR = (β _i , X _j ) where the projection angle β _i is a value in the range of 0 ° ≦ β _i ≦ 360 °, and the position X _j satisfies X ₀ ≦ X _j ≦ X _e . It is an arbitrary turn to do. X ₀ is the scanning start position and X _e is the scanning end position.
The projection angle β _i corresponds to the height of the X-ray tube on the vertical axis in FIG. Therefore, in one-way scanning, X _j
= X _n at the slice plane S (X _n ) at the position X _n , projection data at the projection angle β _i : R (β _i , X _n ) is one rotation before and after X _n (± D) Interval (that is, X _n −D
<X _n <X _n + D), and the projection angle R (β _i , X _n ) from the spiral data of the same projection angle β _i.
Is calculated by interpolation. This interpolation is a two-point linear interpolation, and for example, the projection angle β shown in FIG.
Looking at ₁ , the front and rear positions of X _n , which coincide with the projection angle β ₁ , are X _e and X _m , and the projection data at that time is SR (β ₁ ,
X _e ), SR (β ₁ , X _m ), and the distance b between X _e and X _n is b = X _n −X _e , and the distance a between X _m and X _n is a = X _m −.
Since it is X _n , the interpolation formula is [Equation 3]. ## EQU00003 ## R (β ₁ , X _n ) = {SR (β ₁ , X _e ) × a + SR (β ₁ , X _m ) × b} / (a + b) This process is 0 with X _n fixed. If 360 ° in all directions (all projection angles) where ≤ ≤ β _i ≤ 360 °, position X
_n projection data are obtained. FIG. 1 shows an embodiment of an X-ray CT apparatus for unidirectional scanning. The X-ray CT apparatus includes an X-ray generator 1, an X-ray detector 2, a data acquisition circuit 2A, a buffer memory 12,
The interpolation circuit 13, the filter correction circuit 14, the back projection calculation circuit 15, and the CRT 16 are included. X-ray generator 1 ... Generates a fan-shaped X-ray beam. X-ray detector 2 ... Comprised of a multi-channel detection element for detecting a transmission fan-shaped X-ray beam. Data acquisition circuit 2A ... The detection values of the multi-channel detector 2 are fetched and preamplification, AD conversion, and other processing are performed to obtain spiral projection data SR. Two-dimensional buffer: A buffer having an address of i × j. The spiral projection data SR is stored. That is, the buffer 12 is determined by the projection number i and the scanner rotation speed number (how many rotations) j. Scanner 1
Assuming that the number of projections in rotation is pp and the total number of rotations of the scanner (how many scans) is JC, the parameters of the spiral data SR are obtained by the arguments i and j of this two-dimensional array as follows. Projection angle β _i = β ₀ + (i−1) × Δθ Position X _ij = X ₀ + (j−1) × D + (i−1) × ΔD where, ΔD = 360 ° / Pp ΔD = D / pp. Interpolation circuit 13 ... When the position X _n is designated,
Projection data R in the X _n and (beta _i, X _n) created by interpolation. That is, the spiral projection data SR is converted into the projection data R. Filter correction circuit 14 ... Performs blur correction.
The filter function depends on the content of the blur correction. Back-projection arithmetic circuit 15 ... Back-projects the filtered output of the filter correction circuit 14. Thereby, a tomographic image is obtained. CRT 16 ... Displays a tomographic image. The operation will be described. The X-ray generator 1 and the X-ray detector 2 are continuously rotating on a predetermined plane. In this state, the bed 3 on which the subject is placed advances at a constant speed. The X-ray from the X-ray generator 1 is applied to the subject during the forward movement.
The line is exposed. This exposure is performed by spiral scanning. The transmitted X-rays obtained by spiral scanning are
It is detected by the X-ray detector 2, and various pre-processing and AD conversion are performed by the data acquisition circuit 2A. Thus, the spiral data SR
To get The spiral data SR is stored in the two-dimensional buffer 12 having the arguments i and j as addresses. The spiral data SR is similarly obtained over the entire measurement range of the subject and stored in the two-dimensional buffer 12. After the spiral data is filled in the two-dimensional buffer 12, the interpolation circuit 13 obtains the projection data R of the desired tomographic plane from the spiral data SR. That is, the position X _n is specified to specify the desired tomographic plane, and the projection data R at the position X _n is specified.
Create (i, X _n ). Specifically, as is clear from [Equation 4] and [Equation 5], when the horizontal axis represents the sample position of the spiral data SR in the body axis direction of the subject and the vertical axis represents the projection number i, There are 6 relationships. Therefore, the projection data R (i,
X _n ) can be obtained by the following formula. R (i, X _n ) = {SR (i, J1) × a + SR (i, J1 + 1) × b} / (a + b) Next, the obtained projection data R (i, X _n). )
Undergoes blur correction processing in the filter correction circuit 14. The projection data after the blur correction processing is backprojected by the backprojection calculation circuit 15 to obtain a tomographic image at the position X _n . CRT1
6 displays a tomographic image. According to the present invention, reciprocal bidirectional scanning is performed in place of the above-mentioned unidirectional scanning, and a reconstructed image is obtained from the reciprocating bidirectional scanning. Examples of the present invention will be described. The patient bed is moved not only in one direction but also in the opposite direction to scan from plane B to plane B'in FIG. At this time, if the scanning is performed so that the trajectory 9 of the forward direction (forward direction) movement and the trajectory 8 of the backward direction (reverse direction) intersect, the subject will see FIG.
Scanning is performed as shown in (b). A case where only one tomographic image is obtained will be described with reference to FIGS. FIG. 7A is a time chart showing the relationship among the scanner rotation speed 16, the patient bed movement speed 17 and the X-ray pulse 18. From FIG. 7B, the scan 9 of 180 ° (or more) necessary for obtaining one tomographic image is performed in the forward direction, and the patient bed is moved and the X-ray is scanned until the scanner further rotates 180 °. After stopping the exposure and shifting the phase by 180 ° (so that the trajectory in the forward direction intersects with the trajectory in the reverse direction), when scanning 8 at 180 ° (or more) in the reverse direction is performed, The locus 9 of the X-ray tube device with respect to the subject is as shown in FIG. However, the broken line shows the movement of the patient bed.
Indicates that only the scanner is rotating after the exposure is stopped. When scanning is performed in this manner, projection data is obtained by interpolation of projection data when the patient bed is moving in the forward direction and projection data when the patient bed is moving in the reverse direction. Further, in the unidirectional scan, the error due to interpolation was the same on all tomographic planes, but in the bidirectional scan, the error due to interpolation was smallest in the plane including the intersection and perpendicular to the bed movement direction. Therefore, when the scanning shown in FIG. 7B is performed, the tomographic plane 19 is obtained. In FIG. 8, (a) is from above, (b) is from above.
Is the projection of the trajectory from the side. The tomographic plane 19 in FIG. 7B corresponds to the plane S in FIG. In order to obtain the tomographic image of the surface S, projection data on the surface S may be obtained. Therefore,
Consider projection data P1 and P2 having the same projection angle β. P
1 is projection data when moving forward, and P2 is projection data when moving backward.
The projection data P on the surface S is obtained from P1 and P2.
If the linear interpolation is used for the projection data P (i, j), P (i, j) = (P1 (i, j) + P2 (i, j)) / 2 i = 1, 2, ... CN CN: Total number of channels j = 1, 2, ... NP NP: Total number of views. When this process is performed for 0 ≦ β ≦ 180 °, the projection data of the first half half scan is obtained. Got 1
A desired tomographic image can be obtained by obtaining one tomographic image from the projection data for 80 °, blur-correcting this data, and performing back projection. Incidentally, FIG. 9 shows FIG. 6 in this bidirectional scan.
The corresponding figure is shown. The horizontal axis represents the sample position of the spiral data in the body axis direction of the subject, and the vertical axis represents the projection number. Contrast with FIG. In FIG. 6, the reconstructed image is obtained from the _two loci L ₁ and L ₂ on both sides of the slice position X _n . In FIG. 9, a reconstructed image is obtained from the trajectories L ₃ and L ₄ on both sides thereof. L
₁ and L ₂ are completely separated on both sides of the position X _n , and their width in the body axis direction is also large. That is, in order to obtain the reconstructed image, it is necessary to obtain it by interpolation from the position in the body axis direction having a large width. On the other hand, in FIG. 9, the locus L ₃ and L4 cross with X _n, is small body axis direction of the width of the L ₃ and L _4. That is, the reconstruction can be performed with the data at a position closer to the slice position X _n . As a result, the reliability of the reconstructed image is increased. In the above embodiment, one tomographic image is obtained from the obtained 180 ° projection data, but as another embodiment, a method of obtaining 360 ° projection data and obtaining a tomographic image will be described. In FIG. 10, in order to obtain projection data for 360 °, it is necessary to scan 360 ° in both forward and backward directions.
Assuming that the range of the second embodiment is 0 ° to 180 °, scanning is required within the range of -90 ° to 280 ° in this embodiment. The first half of the half scan is obtained in the same manner as the first embodiment, and the second half of the half scan is obtained by similarly obtaining Q ( _n ) from Q1 ( _n ) and Q2 ( _n ) shown in FIG. One tomographic image can be reconstructed from all projection data. However, in the second embodiment, when the latter half scanning is obtained, the projection data used for interpolation are distant from each other in terms of distance, and the error due to interpolation becomes larger than in the case of obtaining the first half scanning. There must be. However, the error is smaller than that in the unidirectional scan. FIG. 11 shows a control system diagram of the present invention. The X-ray controller 101 controls the high voltage generator 110 to generate a high voltage. This is so-called X-ray exposure control. The rotating frame control unit 102 is an X-ray tube device (X-ray generator).
Not only the control of continuously rotating the X-ray detector and the X-ray detector opposite to each other, but also the control in consideration of the projection angle is possible, and the projection angle can be arbitrarily controlled. The bed movement control unit 103 controls the bed movement direction and speed. However, the speed is constant during scanning. The synchronization device 100 in the system control unit is
Using the position information from the bed position detector 113 and the projection angle information from the projection angle detector 114, the X-ray controller 10
1, rotating frame controller 102, bed movement control unit 10
Synchronize 3. [0032] More specifically, in each embodiment, so that the previously designated slice position is [Equation 8] _{X (n) = X s +3} (D / 4) + (D / 2) n, scan Determine the starting position X _s . However,
D is determined by the bed moving speed and the rotating speed of the rotating frame. Further, the position X _e at the end of the forward scanning and the projection angle θ _e are stored, so that the backward scanning start position is X _e and the starting projection angle is θ _e + 180 °.
Control the system. In the third-generation (RR system) CT apparatus, as an algorithm for reconstructing a tomographic image from projection data, a direct method in which the detected fan-shaped beam data is back-projected as it is and a fan-shaped beam data in a parallel beam are used. Arrangement method of converting back to data and then back-projecting are known, but the present invention does not depend on those algorithms or generations, and if a cone beam is used, various applications such as optical scanning and electronic scanning can be applied. Exert an effect. Further, as the interpolation method, in addition to linear interpolation, 2
Higher-order interpolation (several slices) such as second-order and third-order is also possible. According to the present invention, spiral scanning can be performed in both directions of reciprocation, and high-speed continuous scanning can be performed. Further, it becomes possible to obtain accurate projection data by interpolation processing using relatively close continuous data before and after the arbitrary slice position with respect to the data collected by the spiral scan in both directions. The reliability of the reconstructed image can be improved. Furthermore, the slice position is
It is possible anywhere, and tomographic images can be freely generated at any position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an embodiment diagram of a CT device of the present invention. FIG. 2 is an external view of an RR type CT device. FIG. 3 is an explanatory diagram of unidirectional scanning. FIG. 4 is an explanatory diagram of unidirectional scanning and bidirectional scanning. FIG. 5 is a relationship diagram between a rotational position and spiral data. FIG. 6 is a relationship diagram between a position and a projection number. FIG. 7 is a diagram showing a time chart and a locus in the embodiment of the invention. FIG. 8 is a diagram showing a locus in the example of the present invention. FIG. 9 is a diagram showing the relationship between positions and projection numbers in bidirectional scanning according to the present invention. FIG. 10 is an explanatory diagram of another embodiment of the present invention. FIG. 11 is a system configuration diagram of the present invention. [Explanation of reference numerals] 1 X-ray tube device 2 X-ray detector

Claims (1)

What is claimed is: 1. An X-ray source that generates X-rays, an X-ray detector that is provided opposite to the X-ray source, that detects X-rays that have passed through the object, and an object to be placed. The X-ray source includes at least a patient bed that can be continuously moved on both the outward path and the return path, a data collection unit that collects detected data, and an image reconstruction unit that reconstructs an image from the data. Is continuously rotated around the subject, the patient bed is continuously moved in the body axis direction of the subject during the rotational movement, and the subject is exposed to X-rays during movement of the subject. An X-ray CT apparatus characterized by irradiating and performing spiral scanning in both directions of reciprocation to reconstruct a tomographic image at an arbitrary slice position. [2] An X-ray source that generates X-rays, an X-ray detector that is provided facing the X-ray source, and that detects X-rays that have passed through the subject, and a forward and return route with the subject placed on the detector. Each of them has at least a continuously movable patient bed, a data collection unit for collecting the detected data, and an image reconstruction unit for reconstructing an image from the data, and the X-ray source surrounds the subject. The patient bed is continuously moved in the body axis direction of the subject during the rotational movement, and the subject is exposed to X-rays during the movement of the subject, and both directions of reciprocation are performed. A helical scan is performed, projection data at an arbitrary slice position is obtained by using the data collected on the forward path and the data collected on the return path, and a tomographic image at an arbitrary slice position is image-reconstructed from the projection data. X-ray CT apparatus characterized by: [3] An X-ray source that generates X-rays, an X-ray detector that is provided to face the X-ray source, and that detects X-rays that have passed through the subject, Each of them has at least a continuously movable patient bed, a data collection unit for collecting the detected data, and an image reconstruction unit for reconstructing an image from the data, and the X-ray source surrounds the subject. The patient bed is continuously moved in the body axis direction of the subject during the rotational movement, and the subject is exposed to X-rays during the movement of the subject, and both directions of reciprocation are performed. In an X-ray CT apparatus that is designed to perform a spiral scan, interpolation processing is performed between the data collected on the forward path and the data acquired on the return path to obtain projection data at an arbitrary slice position, and from the projection data, Characterized by image reconstruction of tomographic images at arbitrary slice positions X-ray CT device.