JP2968239B2 - X-ray CT system - Google Patents

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. 2. Description of the Related Art A conventional example of an X-ray CT apparatus performing a helical scan includes "application of digital image processing to medical equipment and problems" (a seminar "Digital signal of medical image" organized by the Giken Center). Papers on Processing Techniques and Their Problems in Clinical Applications, "October 26, 1981. Isao Horiba, II42.
-II page 44) (referred to as Conventional Example A), and
-1111738 (referred to as Conventional Example B). Conventional example A
Is a document showing the principle of a spiral scan CT apparatus.
The principle of a spiral scan having two features of rotating the source around the subject and moving the subject in the body axis direction with the rotation is disclosed. Further, Conventional Example A discloses reconstructing data collected by the spiral scan. Thus, the principle of the spiral scan X-ray CT apparatus has been described. A conventional example B discloses a spiral scan X-ray CT apparatus as in the conventional example A. Further, Conventional Example B discloses various methods for reconstructing data from data acquired by spiral scanning and for reducing artifacts. [0004] In each of the conventional examples A and B, there is no specific description of the control mechanism of the X-ray source and the bed on which the subject is mounted when the spiral scan is performed. The conventional example A is of course the principle, but in the conventional example B, the bed continuously moves and the X-ray source rotates around the bed in opposition to the X-ray detector. (Japanese Unexamined Patent Publication (Kokai) No. 59-111538, No. 2).
Page, upper right column, 17 lines to 2 pages, lower left column, 8 lines). Bed moving,
Even in the case of opposing rotation, if each is independently controlled independently, a complicated control sequence is indispensable to realize the actual spiral scan such as when to measure and when to end It is. An object of the present invention is to provide an X-ray CT apparatus capable of easily and reliably performing spiral scan measurement. SUMMARY OF THE INVENTION The present invention provides an X-ray source for generating X-rays, and an X-ray for detecting X-rays emitted from the X-ray source and transmitted through a subject. A detector and a bed on which the subject is mounted and moved in the body axis direction of the subject, and a rotating frame for rotating the X-ray source rotates the X-ray source around the subject, thereby generating an X-ray beam from many angles. In an X-ray CT apparatus that irradiates and scans to obtain helical scan data, stores the helical data, and reconstructs the helical scan data, an arbitrary slice position ( Xn), and reading the stored rotation data for a predetermined area including an address associated with the slice position based on a distance (D) of movement of the bed per rotation of the rotating frame; Slice the spiral data Means for calculating projection data at a large number of angles at the slice position by interpolation processing based on the distance from the position, and means for reconstructing a tomographic image at the slice position from the projection data at a large number of angles. Disclosed is an X-ray CT apparatus provided with the above. Further, the present invention provides an X-ray source for generating X-rays, an X-ray detector for detecting X-rays emitted from the X-ray source and transmitted through the subject, and a subject mounted with the subject. Having a bed that moves in the body axis direction, a rotating frame that rotates the X-ray source rotates around the subject to irradiate and scan the X-ray beam from a number of angles, and scans spiral scan data. Then, in the X-ray CT apparatus for storing and reconstructing the spiral scan data, an arbitrary slice position (X
means for setting n) and associating the stored rotation data with the slice position based on the positional information (Xij) of the subject on the bed in the body axis direction and the projection angle information (βi) of the rotating frame. Means for reading projection data for a plurality of angles at the slice position by reading out a predetermined area including the address to be processed, and performing interpolation processing on the helical data based on the angle difference from the projection angle indicating the slice position. Means for reconstructing a tomographic image at the slice position from projection data at multiple angles.
A line CT apparatus is disclosed. Further, the present invention provides an X-ray generator for generating X-rays.
X-ray source and X-ray irradiated from X-ray source and transmitted through subject
An X-ray detector for detecting X-rays, a bed on which the subject is mounted and moved in the body axis direction of the subject, and a rotating frame for rotating the X-ray source rotates around the subject. In an X-ray CT apparatus that scans by irradiating an X-ray beam from a number of angles, obtains spiral scan data, stores the spiral data, and reconstructs the data, Means for setting an arbitrary slice position (Xn) of the subject; and storing the rotation data once stored based on the rotation projection angle (△ θ) of the rotating frame per unit movement distance (△ D) of the bed. Means for reading a predetermined area including an address associated with the slice position, interpolating the helical data and calculating projection data at a large number of angles at the slice position, and Slice position Further comprising a means for reconstructing a tomographic image, which discloses an X-ray CT apparatus according to claim. FIG. 2 is an external view of an RR type CT apparatus. The X-ray CT apparatus includes an X-ray tube device (X-ray generator) 1, 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 apparatus 1 and the X-ray detector 2 are in a positional relationship to face each other with the subject on the bed 3 interposed therebetween. The X-ray tube apparatus 1 and the X-ray detector 2 are continuously rotated under the opposed positional relationship. For continuous rotation, high voltage from the high voltage device to the X-ray tube device 1 was supplied via a slip ring. This rotation speed is a constant speed as can be seen from a 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 high voltage is supplied by attaching a slip ring mechanism to the frame (rotary scanner). The patient bed 3 can move at a constant speed in a direction (arrow) perpendicular to the rotation plane of the scanner. Patient bed 3
Movement and X-ray irradiation by the X-ray tube device 1 and the X-ray tube device 1
Are synchronized with each other. Here, as an example of the synchronization, for example, as shown in the example of FIG. 7 described later, in the section between R ₁ and R ₂ , the rotation speed of the scanner and the moving speed of the patient bed move at a fixed constant speed, respectively, and During this time, it means that X-rays are successively or continuously emitted. With the synchronization of the three parties, the scanning by the spiral scan and the spiral scan measurement can be simply and reliably performed. Furthermore, in order to realize constant rotation of the X-ray scanner and constant movement of the patient bed, control is performed according to a predetermined speed pattern as shown in the figure. Since the patient bed and the X-ray tube apparatus 1 are synchronously controlled and move and rotate at a constant speed determined respectively, there is an advantage that management of acquired data in a spiral scan is facilitated. If the movement of the patient bed and the rotation of the X-ray tube apparatus 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 rotates continuously and 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, it is scanned in the range (i.e. the scanning range W ₀ shown in FIG. 3) containing the desired tomographic plane F. 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 a slice plane S (X _n ) in FIG.
, And a reconstructed image is calculated along this surface. In the figure, the scanning range W ₀ is a range determined by B and B ′, and the desired tomographic plane F is a range determined by C and C ′. B is a starting point which indicates a scanning start position of the scan range W _0, 'end point indicates the scanning end position, the starting point of C is desired tomographic plane F, C' B is at its end point. Furthermore, 'a widely set bed movement section than interval scan range W ₀ connecting the, A movement start point of the patient bed, A' A and A is a movement stopping point of the patient bed. The section connecting A and B is the necessary and sufficient time until the patient bed starts moving and reaches a constant speed, and the section connecting B 'and A' is the time from the constant speed movement to the deceleration and stop. It is. Thus, in the scanning range W ₀ , constant movement of the patient bed is secured, and the X-ray scan is also rotated at a constant speed. In this section W ₀ , CT spiral scan measurement can be performed by exposing X-rays. . [0014] scanning range W ₀ of the starting point B to the starting point C of a desired tomographic plane F section and the desired interval 'from the end point B of the scanning range W _0' end point C of the fault plane F to the , A data measurement section used for interpolation. By measuring extra data for such interpolation, the desired tomographic plane F
CT tomographic image can be obtained. Prior to such scanning, positioning for scanning is performed. For positioning defines a desired tomographic plane F of course, it is necessary to determine the scanning range W _0.
Desired it is clear that is uniquely determined together with the tomographic plane F and the scan range W _0, in practice, it may be determined either one. If the scanning range W ₀ is determined, A, B,
The positions of C, A ', B', and C 'are obtained. So, A
Is the bed movement start point, B is the constant speed movement, B is the start point of the scanning range W ₀ , C is the desired tomographic plane F start point,
Let C 'be the end point of the desired tomographic plane F and B' be the scanning range W
Positioning is performed so that _{0 is} the end point and A ′ is the stop point of the patient bed. Thereafter, the movement of the patient bed is started from the position A. [0016] Thus, the positioning, giving scan range W ₀ corresponding to the desired tomographic plane F or this, relative to the start point of the desired tomographic plane F C (position 6), separated by a distance a C and A are given so that the position A comes to the position where the camera is moved. A
And B, that is, a section of the distance (ab) is a section until the scanner and the patient bed have a constant speed. Further, B
As described above, the section between C and C is an extra measurement section for obtaining projection data using interpolation in the direction in which the patient bed moves. When the patient bed reaches the plane B ', which is a distance b after the final tomographic plane C' (position 7), the X-ray irradiation is stopped, and the patient bed decelerates and stops at the plane A '.
Thus, by constant speed moves at a scan range W ₀ during scanning the patient's bed, as viewed from the subject at rest, during the interval of the scanning range W ₀ as shown in FIG. 4 (b) Nira旋Is scanned. FIG. 5 shows the trajectory of the X-ray tube apparatus at this time by one-way scanning of the subject. The above-described setting of the scanning range and the A,
The setting of B, C, A ', B', and C ', and the control of the patient bed and the control of the X-ray irradiation using the positioning are performed in FIG. 11 described later. Projection data obtained by helical scanning (hereinafter referred to as helical data) is obtained when a scanner is helically rotated around an object and scanned, as shown in FIG. It is equivalent to projection data. The spiral 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 during one rotation of the scanner are D. To reconstruct a tomographic image of a slice plane (tomographic plane) S (X _n ) at the subject position X _n , projection data R (β, X _n ) (where β = 0 ゜ −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. In order to obtain a tomographic image, projection data R (β, X _n ) on the tomographic plane (where β = 0６０360
I) can be obtained. The spiral data is represented by the following general formula. 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 Is any one point. X ₀ is the scanning start position, the X _e is a scan end position.
The projection angle β _i corresponds to the X-ray tube height on the vertical axis in FIG. Therefore, in the one-way scan, X _j
= R _n (X _i ) at the projection angle β _i on the slice plane S (X _n ) at the position X _{n at} the position X _n is R (β _i , X _n ) for one rotation before and after X _n (± D) (Ie, X _n −D
<X _n <X _n + D section) and the projection angle R (β _i , X _n ) from the spiral data of the same projection angle β _i
Is obtained by interpolation. This interpolation is a two-point linear interpolation, for example, the projection angle β shown in FIG.
_{In FIG. 1} , the front and rear positions of X _n that match 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 equation is (Equation 3). R (β ₁ , X _n ) = ｛SR (β ₁ , X _g ) × a +
SR (β ₁ , X _m ) × b｝ / (a + b) If this processing is performed in all directions (all projection angles) of 360 ° 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 one-way scanning. The X-ray CT apparatus includes an X-ray generator 1,
X-ray detector 2, data acquisition circuit 2A, buffer memory 1
2. It comprises an interpolation circuit 13, a filter correction circuit 14, a back projection operation circuit 15, and a CRT 16. X-ray generator 1 generates a fan-shaped X-ray beam. X-ray detector 2 is composed of a multi-channel detection element for detecting a transmission fan-shaped X-ray beam. Data collection circuit 2A: fetches the detection values of the multi-channel detector 2 and performs processing such as preamplification and AD conversion to obtain spiral projection data SR. Two-dimensional buffer: a buffer having an address i × j. The helical projection data SR is stored. That is, the buffer 12 is determined by the projection number i and the scanner rotation number (number of 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 as follows by the arguments i and j of the two-dimensional array. ## EQU4 ## 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 _Xn is designated,
Projection data R in the X _n and (beta _i, X _n) created by interpolation. That is, the helical projection data SR is converted into projection data R. Filter correction circuit 14 performs blur correction.
The filter function is determined by the details of the blur correction. Back-projection operation circuit 15 Back-projects the output of the filter correction circuit 14 after filtering. Thereby, a tomographic image is obtained. CRT16 ... 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. In the process of moving forward, the X-ray
The line is exposed. This irradiation is performed by helical scanning. The transmitted X-ray obtained by helical scanning is
The data is detected by the X-ray detector 2 and subjected to various preprocessing and AD conversion by the data acquisition circuit 2A. Thus, spiral data SR
Get. The spiral data SR is stored in the two-dimensional buffer 12 having the addresses of the arguments i and j. Similarly, spiral data SR is 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 projection data R of a desired tomographic plane from the spiral data SR. That is, to identify the desired tomographic plane by specifying the position X _n, projected at the position X _n data R
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, 6 is obtained. Therefore, the projection data R (i,
X _n ) can be obtained by the following equation. 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 back-projected by the back-projection operation circuit 15 to obtain a tomographic image at the position _Xn . CRT1
6 displays a tomographic image. An embodiment of the present invention in which a reciprocating bidirectional scan is performed in place of the above-described one-way scan, and a reconstructed image is obtained from the scan by an interpolation process will be described. The patient bed is moved not only in one direction but also in the opposite direction, and is scanned from plane B to plane B 'in FIG. At this time, if the scanning is performed so that the trajectory 9 of the forward movement (forward direction) and the trajectory 8 of the backward movement (reverse direction) intersect, the subject is scanned as shown in FIG. FIG. 7A shows a case where only one tomographic image is obtained.
This will be described with reference to (b). FIG. 7A is a time chart showing the relationship among the scanner rotational speed 16, the patient bed moving speed 17, and the X-ray pulse 18. From FIG. 7 (b), a scan 9 of 180 ° (or more) necessary for obtaining one tomographic image is performed in the forward direction, and the movement of the patient bed and the X-ray scan are performed until the scanner is further rotated by 180 °. After stopping the irradiation and shifting the phase by 180 ° (in this way, the trajectory in the forward direction and the trajectory in the reverse direction intersect), a scan 8 of 180 ° (or more) is performed in the reverse direction. The trajectory 9 of the X-ray tube apparatus with respect to the subject is as shown in FIG. However, the broken line indicates the movement of the patient bed.
It indicates that the scanner is rotating only after stopping the exposure. When scanning is performed in this manner, projection data is obtained by interpolating 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. In the one-way scan, the error caused by the interpolation is the same on any tomographic plane. However, in the two-way scan, the plane including the intersection and perpendicular to the bed moving direction has the least 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 the projection of the trajectory from the side. The tomographic plane 19 in FIG. 7B corresponds to the plane S in FIG. To obtain a 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
Reference numeral 1 denotes forward data, and P2 denotes projection data at the time of backward movement.
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)
j)) / 2 i = 1, 2,... CN CN: total number of channels j = 1, 2,... NP NP: total number of views When this processing is performed for 0 ≦ β ≦ 180 °, projection data of the first half of the half scan is obtained. 1 obtained
If one tomographic image is obtained from the projection data for 80 °, and this data is subjected to blur correction and back-projection, a desired tomographic image can be obtained. FIG. 9 shows the bidirectional scan in FIG.
The corresponding diagram is shown. The horizontal axis indicates the sample position of the object in the body axis direction of the spiral data, and the vertical axis indicates the projection number. Compare with FIG. To slice position X _n in FIG. 6, to obtain a reconstructed image of two loci L ₁ and L ₂ Metropolitan on both sides. 9, to obtain a reconstructed image from the locus L ₃ on both sides L ₄ Prefecture. L
₁ and the L ₂ are completely separated on either side of the position X _n, greater its body axis direction width. That is, in order to obtain a reconstructed image, it is necessary to obtain the reconstructed image by interpolation from the position in the body axis direction where the width is large. 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, reconstruction can be performed with data at a position closer to the slice position _Xn . As a result, the reliability of the reconstructed image increases. Although one tomographic image is obtained from the 180-degree projection data obtained in the above embodiment, a method of obtaining 360-degree projection data and obtaining a tomographic image will be described as another embodiment. . In FIG. 10, 360 ° scanning is required in both forward and reverse directions to obtain 360 ° projection data. Assuming that the range of the second embodiment is 0 ° to 180 °,
In the present embodiment, scanning is required in the range of -90 ° to 280 °. The first half scan is obtained in the same manner as in the first embodiment, and the second half scan is performed in Q1 and Q2 shown in FIG.
Is obtained in the same manner, and 1 is obtained from the total projection data obtained.
One tomographic image can be reconstructed. However, in the second embodiment, when obtaining the second half scan, the projection data used for interpolation is far away from the distance, and the error due to the interpolation becomes larger than when obtaining the first half scan. I have to think. However, the error is small compared to the one-way scan. FIG. 11 shows a control system diagram of the present invention. The X-ray control unit 101 controls the high voltage generator 110 to generate a high voltage. This is so-called X-ray irradiation control. The rotating frame control unit 102 is an X-ray tube device (X-ray generator)
In addition to control for continuously rotating the X-ray detector and the X-ray detector in opposition, control taking into account the projection angle is also 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
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 controller 10
Synchronize 3. More specifically, in each embodiment, the slice position specified in advance is given by: X _n = X _s +3 (D / 4) + n (D / 2) where n = 0, 1 , 2,3, so that the ...., to determine the scanning start position X _s. However,
D is determined by the bed moving speed and the rotating speed of the rotating frame. In addition, the position X _e at the end of the forward scan and the projection angle θ _e are stored, and the start position of the backward scan is X _e and the start projection angle is θ _e + 180 °.
Control the system. Here, looking at (Equation 8) with respect to the reciprocating motion, it is as follows from FIG. The intersection of the forward and backward sample points is (D /
2) It occurs at intervals. In order to obtain the data at the X _n point by interpolation, sample data before and after the X _n point and between (D / 2) are required. When X _n −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, the valid for _{X n -X s = 3 (D} / 4) and subsequent ones. Here, X _n −X _s = (D / 4) is n = −1
In this case, X _n −X _s = 3 (D / 4) corresponds to n = 0. In the third generation (RR type) CT apparatus, as an algorithm for reconstructing a tomographic image from projection data, a direct method for backprojecting the detected fan beam data as it is, and a parallel beam for the fan beam data are used. Arrangement method of back projection after converting to data is known, but the present invention can be applied to various applications such as rotary scan and electronic scanning type using cone beam, regardless of those algorithms and generations. It is effective. Further, as an interpolation method, in addition to linear interpolation, 2
Next-order, third-order, and other higher-order interpolation (for several slices) is also possible. According to the present invention, synchronous control of the rotary scanner and the bed can be achieved, and spiral scan measurement can be performed easily.
It can be executed reliably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an embodiment of a CT apparatus according to the present invention. FIG. 2 is an external view of an RR type CT apparatus. FIG. 3 is an explanatory diagram of one-way scanning. FIG. 4 is an explanatory diagram of one-way scanning and two-way scanning. FIG. 5 is a diagram illustrating a relationship 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 trajectory according to the embodiment of the present invention. FIG. 8 is a diagram showing a trajectory according to the embodiment of the present invention. FIG. 9 is a diagram illustrating a relationship 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. [Description of Signs] 1 X-ray tube device 2 X-ray detector

Claims (1)

(57) [Claims] An X-ray source for generating X-rays, an X-ray detector for detecting X-rays radiated from the X-ray source and transmitted through the subject, and a body mounted with the subject in a body axis direction of the subject A rotating frame for rotating the X-ray source, which rotates around the subject to irradiate and scan X-ray beams from a number of angles to obtain spiral scan data, Means for setting an arbitrary slice position (Xn) of the subject within a range in which the helical scan data is obtained, in an X-ray CT apparatus for storing and reconstructing the helical data; When the stored data is stored based on the moving distance (D) of the bed, the spiral data is read out for a predetermined area including an address associated with the slice position, and the spiral data is interpolated based on the distance from the slice position. And the slice position An X-ray CT apparatus comprising: means for calculating projection data at a plurality of angles; and means for reconstructing a tomographic image at the slice position from the projection data at a plurality of angles. 2. An X-ray source for generating X-rays, an X-ray detector for detecting X-rays radiated from the X-ray source and transmitted through the subject, and a body mounted with the subject in a body axis direction of the subject A rotating frame for rotating the X-ray source, which rotates around the subject to irradiate and scan X-ray beams from a number of angles to obtain spiral scan data, In an X-ray CT apparatus for storing and reconstructing rotation scan data,
Means for setting an arbitrary slice position (Xn) of the subject within the range in which the spiral scan data is obtained; position information (Xij) in the body axis direction of the subject on the bed; and projection angle information of the rotating frame When the stored spiral data is read based on (βi) for a predetermined area including an address associated with the slice position, the spiral data is subjected to an interpolation process based on an angle difference from a projection angle indicating the slice position. Means for calculating projection data at a large number of angles at the slice position, and means for reconstructing a tomographic image at the slice position from the projection data at a large number of angles. apparatus. 3. An X-ray source for generating X-rays, an X-ray detector for detecting X-rays emitted from the X-ray source and transmitted through the subject, and a body mounted with the subject in a body axis direction of the subject A rotating frame for rotating the X-ray source, which rotates around the subject to irradiate and scan X-ray beams from a number of angles to obtain spiral scan data, Means for setting an arbitrary slice position (Xn) of the subject within a range in which the helical scan data is obtained, and an X-ray CT apparatus for storing and reconstructing the helical data; ), The stored spiral data is read out for a predetermined area including an address corresponding to the slice position when the stored spiral data is stored based on the projected angle of rotation (Δθ) of the rotating frame. Multiple angle projections of the position Data calculating means, and means for reconstructing a tomographic image at the slice position from the projection data at many angles.
Line CT device.