JPH08294484A - X-ray ct system - Google Patents

Abstract

PURPOSE: To improve utilization efficiency of data by obtaining projection data at an arbitrary slicing position from those of a projection angle near the slicing position and also at a position opposing that projection angle. CONSTITUTION: A transmitted X-ray obtained from spiral scanning is detected by an X-ray detector 2, so that spiral data are formed through various pre- processing and AD conversion at a data collecting circuit 2A. These spiral data are stored in a two-dimensional buffer 12, which is implemented over the entire measuring range of an examinee. Then, an interpolative circuit 13, after obtaining a projection data of a desired tomographic plane from the spiral data, is treated for correction of out-of-focus image in a filter correcting circuit 14. Successively, the projection data are treated for inverse projection in an inverse projection arithmetic circuit 15, with a tomographic image obtained at position X and displayed on CRT 16. By means of this structure, reconstruction is made possible with the actual data for 180 deg..

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 of digital image processing to medical equipment and its problems" (seminar sponsored by Giken Center "Digital signal of medical image"). Paper on "Problems of 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 a spiral scan CT apparatus, and X
The 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 X-ray CT apparatus by the spiral scan has been described. Conventional example B discloses a helical scan X-ray CT apparatus similar to conventional example A. Furthermore, the conventional example B discloses various reconstruction methods and artifact reduction methods from data acquired by a helical scan. The conventional example A shows the principle of the helical scan X-ray CT apparatus, but does not disclose a specific reconstruction method. The reconstruction method of the conventional example B is
A method of dividing the entire image of the scan range into small elements and reconstructing them at once, for example, two different points S providing 360 °.
Considering ₁ and S _2, and considering the data obtained from one rotation of the X-ray tube from S ₁ to S _2, it is assumed that the fan beam position is fixed at the center of two points S ₁ and S _2. A known method of approximating and reconstructing an image for each plane (US Pat. No. 4,149,247)
No.), is disclosed. Furthermore, the data obtained by two rotations from S ₁ to S ₃ for 720 ° is simply averaged (bundled, that is, superposed) to obtain data for one rotation, and the slice position (S ₂ position) is represented. An example in which the scan data is reconstructed as scan data is disclosed (it is also disclosed that an example of three or more rotations can be played) (referred to as disclosure a). Furthermore, it is disclosed that the same effect can be achieved by independently reconstructing the projection data obtained at each rotation and averaging a plurality of obtained images (referred to as disclosure b) (this disclosure describes each This means that each rotation is independently reconstructed to obtain an image for each rotation, and an averaging is performed among the plurality of images. Therefore, the reconstruction method for independently obtaining for each rotation is: Any one of a is a prerequisite). In the conventional example B, how to divide into small elements, what to reconstruct at once,
There is no description about, and the substance as a reconstruction method is not certain. In the conventional example B, the beam position is fixed at the center of one rotation for reconstruction, and slice setting at any position other than the center is virtually impossible. In the conventional example B, “a” is a simple average example and follows the following equation. P (θ, φ) = {P ₁₂ (θ, φ) + P ₂₃ (θ, φ)} / 2 In the above equation, θ is the X-ray source position (projection angle) and φ is the projection angle θ. It is the channel number (In the publication, P = (θ, φ) ..., but P (θ, φ) = ...
I think it is an error. From the above equation, θ changes (0
Even if (° ≦ θ ≦ 360 °), the simple averaging is always performed and set as P (θ, φ) at the slice position S ₂ . Therefore, the distances p ₁₂ p and pp ₂₃ are not taken into consideration, and there are many errors in the reconstruction data at the slice position p. Here, p is the position of the data P (θ, φ), and p ₁₂ is the data P ₁₂ (θ, φ).
The position of φ), p ₂₃ is the position of P ₂₃ (θ, φ). In the conventional example B, the concept is the same as that of the conventional example B except that the number of rotations is 2 or more, and has the same problem. The conventional example B, b, has the same concept as that of a and has the same problem. Further, one of the artifact reducing methods of the conventional example B is the starting point (θ = 0
The objective is to reduce the artifacts that are expected to occur due to the difference in the data between the angle () and the end point (θ = 360 °). Therefore, the weighted average correction is performed near each of the start point and the end point. This reduction method is an artifact reduction under the reconstruction method of a, b of the conventional example B, and at intermediate positions other than the vicinity of the start point and the end point, respectively, a, b are reconstructed. Take a construction method. All of the reconstructions in the conventional example B are based on the measured data for 360 °. However, if the measured data for 180 ° can be used instead of the measured data for 360 °, the data utilization efficiency will be improved. The object of the present invention is to achieve 3 in a helical scan.
The present invention provides an X-ray CT apparatus that can be reconstructed with 180 ° measured data without using 60 ° measured data. SUMMARY OF THE INVENTION The present invention is an X-ray CT apparatus for moving an object mounting bed while rotating an X-ray source to perform a spiral scan measurement. An X-ray CT apparatus is disclosed in which data is obtained from projection data of a projection angle near the slice position and projection data of a projection angle at a position opposite to the projection angle. Further, according to the present invention, in an X-ray CT apparatus for rotating a X-ray source and moving a subject-mounting bed to perform a spiral scan measurement, projection data at an arbitrary slice position is in the vicinity of the slice position. Disclosed is an X-ray CT apparatus which is obtained by interpolating projection data of a projection angle and projection data of a projection angle at a position opposite to the projection angle. 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, an X-ray detector 2, an X-ray tube high voltage generator (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. Based on this facing 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 (rotary 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. Here, as an example of the synchronization, as shown in an example of FIG. 7 described later, the rotational speed of the scanner and the moving speed of the patient bed move at a constant speed in the section between R ₁ and R ₂ , and during this period, In X-rays are exposed one after the other or continuously. Since the three parties are synchronized with each other, scanning by the spiral scan and measurement by the spiral scan become possible. Furthermore,
In order to realize the constant speed rotation of the X-ray scanner and the constant speed movement of the patient bed, control is performed according to a predetermined speed pattern as shown in the drawing. Since the patient bed and the X-ray tube device 1 are synchronously controlled to move and rotate at a constant speed determined by each, there is an advantage that management of collected data in a 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 as shown in FIG. 3 and is scanned within a range including the desired tomographic plane F (that is, the scanning range W ₀ shown in FIG. 3). Here, the scanning range W ₀ is a measurement section (synonymous with an imaging section) required for reconstruction, and the desired tomographic plane F is a slice plane obtained from the scanning range. Various slice planes are set within the width of the tomographic plane F. Here, the slice plane is the slice plane S (X _n ) of FIG.
Is a surface arbitrarily selected, and the reconstructed image is calculated along this surface. In the figure, the scanning range W ₀ is a range defined by B and B ′, and the desired tomographic plane F is a range defined by C and C ′. B is a start point indicating the scan start position of the scan range W ₀ , B'is an end point indicating the scan end position, C is a start point of the desired tomographic plane F, and C'is its end point. Further, a section connecting A and A'is a bed movement section set wider than the scanning range W ₀ , A is a movement start point of the patient bed, and A'is a movement stop point of the patient bed. The section connecting A and B is the time necessary and sufficient for the patient bed to start moving and to move at a constant speed, and the section connecting B'and A'is the time from decelerating to a deceleration stop. Is. Thus, in the scanning range W ₀ , the constant-speed movement of the patient bed is ensured, and the X-ray scanning is also rotated at a constant speed. In this section W ₀ , the CT helical scan measurement can be executed by exposing the X-ray. . The section from the start point B of the scanning range W ₀ to the start point C of the desired tomographic plane F and the section from the end point C ′ of the desired tomographic plane F to the end point B ′ of the scanning range W ₀ are , A data measurement section used for interpolation. By measuring extra data for such interpolation, the desired tomographic plane F
It is possible to obtain a CT tomographic image at. Prior to such scanning, positioning for scanning is performed. For positioning, it is naturally necessary to determine a desired tomographic plane F and a scanning range W ₀ .
It is clear that the desired tomographic plane F and the scanning range W ₀ are uniquely determined, and in practice, either one may be determined. If the scanning range W ₀ is defined, A, B,
The positions C, A ', B', and C'are obtained. So A
As the bed movement start point, B as the constant velocity movement as the start point of the scanning range W ₀ , and C as the start point of the desired tomographic plane F,
Let C ′ be the end point of the desired tomographic plane F and B ′ be the scanning range W.
Positioning is performed so that the end point is ₀ and A ′ is the stop point of the patient bed. After this, the movement of the patient bed is started from the position A. In this way, for positioning, a desired slice plane F or a scanning range W ₀ corresponding to the slice plane is given, and a certain distance a from the starting point C (position 6) of the slice plane F desired. C and A are given so that the position A comes to the position. A
And B, that is, a section of distance (ab) is a section until the scanner and the patient bed have a constant speed. Furthermore, B
It has been described above that the section between C and C is an extra measurement section for obtaining projection data 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 C' (position 7) by the distance b, the X-ray irradiation is stopped, and the patient bed decelerates and stops on the plane A '.
As described above, by moving the patient bed at a constant speed in the scanning range W ₀ during scanning, as seen from the stationary subject, the helicopter is swung during the section of the scanning range W ₀ as shown in FIG. Are scanned in a circular pattern. FIG. 5 shows the trajectory of the one-way scan of the subject of the X-ray tube device at this time. Setting of the above scanning range and A at each position,
The setting of B, C, A ', B', and C ', and the control of the patient bed and the control of the X-ray exposure using this positioning thereafter are performed in FIG. 11 described later. The projection data obtained by the spiral scanning (hereinafter referred to as spiral data) is obtained when the scanner is rotated in the spiral shape 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 ) (where β = 0 ° to 360) on the tomographic plane is obtained.
)) 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 point 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 , the 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) data, 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 _g and X _m , and the projection data at that time is SR (β ₁ ,
X _g ), SR (β ₁ , X _m ), and the distance b between X _g and X _n is b = X _n −X _g , 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). ## EQU3 ## R (β ₁ , X _n ) = {SR (β ₁ , X _g ) × a +
SR (β ₁ , X _m ) × b} / (a + b) If this process is performed in all 360 ° directions (all projection angles) of 0 ° ≦ β _i ≦ 360 ° with X _n fixed, the 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 collection 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
When 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, Δθ = 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
The data is detected by the X-ray detector 2 and subjected to various types of preprocessing and AD conversion by the data acquisition circuit 2A. Thus, the spiral data SR
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 in the body axis direction of the subject of the spiral data SR 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. ## EQU6 ## R (i, X _n ) = {SR (i, m) × a + SR
(I, m + 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. An embodiment of the present invention will be described in which a reciprocal bidirectional scan is performed instead of the above unidirectional scan, and a reconstructed image is obtained from the reciprocal bidirectional scan by interpolation processing. 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 scanning is performed so that the trajectory 9 of the forward (forward) movement and the trajectory 8 of the backward (reverse) movement intersect, the subject is scanned as shown in FIG. 4B. 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 pausing the exposure and shifting the phase by 180 ° (so that the trajectory in the forward direction intersects with the trajectory in the reverse direction), the scan 8 of 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 indicates movement of the patient bed.
Indicates that only the scanner is rotating after the exposure is stopped. In the case of such scanning, the projection data is obtained by interpolation of the projection data when the patient bed is moving in the forward direction and the projection data when the patient bed is moving in the reverse direction. Further, in the unidirectional scan, the error due to the interpolation was the same in all tomographic planes, but in the bidirectional scan, the error due to the interpolation includes the intersection point and is perpendicular to the bed moving direction has the smallest error due to the interpolation. 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 the projection data when moving forward, and P2 is the projection data when moving backward.
The projection data P on the surface S is obtained from P1 and P2.
If 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 for the first half scanning 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, a 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 scanning is obtained in the same manner as in the first embodiment, and the second half scanning is similarly obtained from Q1 and Q2 shown in FIG. 10A, and one tomographic image is obtained from all the obtained projection data. Can be reconfigured. 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 the interpolation is larger than that in the case of obtaining the first half scanning. There must be. However, the error is smaller than that in the one-way scanning. 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 facing 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. Specifically, in each embodiment, the slice position designated in advance is as follows: X _n = X _s +3 (D / 4) + n (D / 2) where n = 0, 1, The scanning start position X _s is determined so that it becomes 2, 3, ... 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
Is stored, and the system is controlled so that the backward scanning start position is X _e and the starting projection angle is θ _e + 180 °. Here, looking at (Equation 8) with respect to reciprocating motion, it is as follows from what is shown in FIG. The intersections of the forward direction sampling points and the backward direction sampling points occur at (D / 2) intervals. In order to obtain the data at the point _Xn by interpolation, sample data before and after the point _{Xn and} between (D / 2) are required. X _n
When −X _s = (D / 4), the data in the area from X _s to X _n is insufficient (only half), so the interpolation data is insufficient and image reconstruction cannot be performed. Therefore, X _n −X _s =
3 (D / 4) and later are effective. here,
X _n −X _s = (D / 4) means that when n = −1, X _n −X _s =
3 (D / 4) corresponds to n = 0. In the third-generation (RR system) CT apparatus, an algorithm for reconstructing a tomographic image from projection data is a direct method in which the detected fan-shaped beam data is back-projected as it is, and a fan-shaped beam data in parallel beam. Arrangement method and the like of converting back to data and then backprojecting is 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. Be effective. Further, as the interpolation method, in addition to linear interpolation, 2
Higher-order interpolation (several slices) such as second-order, third-order, etc. is also possible. According to the present invention, it is possible to reconstruct an image by utilizing opposite data in a helical scan.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an embodiment 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 relationship diagram between a position and a projection number 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 Codes] 1 X-ray tube device 2 X-ray detector

Claims (1)

What is claimed is: 1. In an X-ray CT apparatus for rotating a X-ray source and moving a subject mounting bed to perform a spiral scan measurement,
An X-ray CT apparatus in which projection data at an arbitrary slice position is obtained from projection data at a projection angle near the slice position and projection data at a projection angle at a position opposite to the projection angle. [2] In the X-ray CT apparatus that performs the spiral scan measurement by moving the subject mounting bed while rotating the X-ray source,
The projection data at an arbitrary slice position is obtained by interpolating projection data of a projection angle near the slice position and projection data of a projection angle at a position opposite to the projection angle.