JPH0767445B2 - X-ray CT system - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

 The present invention relates to an X-ray CT apparatus that performs scanning.

[Prior art]

An example of a conventional X-ray CT apparatus that has been scanned is "Application of digital image processing to medical equipment and problems" (Seminar hosted by the Giken Hoho Center, "Digital signal processing technology for medical images and its clinical application." Paper on "Problems of". Showa 56
October 26, year. Written by Yuuo Horiba. II42 to II42) (referred to as conventional example A) and JP-A-59-111738 (referred to as conventional example B). The conventional example A is a document showing the principle of the scanning CT apparatus, and has two characteristics: rotating the X-ray source around the subject and moving the subject in the body axis direction along with the rotation. The principle of scanning is disclosed. Furthermore, the conventional example A discloses that the data collected by such a scanning is reconstructed. Thus, the principle of the X-ray CT apparatus based on the Raran scan has been described. Conventional example B discloses a scanning X-ray CT apparatus similar to conventional example A. Further, Conventional Example B discloses various reconstruction methods and artifact reduction methods from the data collected by the scanning.

[Problems to be Solved by the Invention]

The conventional example A shows the principle of the scanning 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 one time, for example, two different points S ₁ and S ₂ providing 360 ° are considered, and from S ₁ to S when considering the data obtained in one rotation of the X-ray tube leading to the _2, known for performing image reconstruction for each plane by approximating to that fan beam position is fixed to the center of the S ₁ and S ₂ 2 points Method (USP414
No. 9247) 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 in 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, there is no description about how to divide it into small elements and what to do at one time, 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 ...
(1) In the formula (1), θ is the X-ray source position (projection angle), and φ is the channel number at the projection angle θ (P = (θ, φ) ... However, P (θ, φ) = ...
I think it is an error. From the equation (1), θ changes (0
Even if (° ≤ θ ≤ 360 °), the feature is that 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 the reconstruction data at the slice position p has many errors. Here, p is the data P
The position of (θ, φ), p ₁₂ is the position of the data P ₁₂ (θ, φ), and 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, too, has the same idea as that of a and has the same problem. Furthermore, one of the methods for reducing artifacts in Conventional Example B is to reduce the artifacts that are expected to occur due to the difference in data between the start point (θ = 0 °) and the end point (θ = 360 °). To aim. 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. When reconstructing the data acquired by the spiral scan, the data necessary for the reconstruction must be the data at the same slice position. The idea of Conventional Example B is to uniformly treat data at different slice positions as data at the same slice position. An object of the present invention is not to uniformly treat data at different slice positions as data at the same slice position, but calculate data at the same slice position using data at different slice positions. The present invention provides an X-ray CT apparatus in which the calculated data is used for reconstruction to improve the accuracy of reconstruction in a helical scan. A further object of the present invention is to provide an X-ray CT apparatus that enables reconstruction at an arbitrary slice position in a helical scan and allows free selection at the slice position.

[Means and Actions for Solving the Problems]

The present invention, projection data at any slice position from any continuous data of the data collected by the helical scan,
The interpolation processing is performed for each projection angle, and in the interpolation processing, the X-ray beam data of the projection angle before and after the slice position for each projection angle is interpolated using the distance from the slice position as a parameter. And a second means for reconstructing a tomographic image at the arbitrary slice position by the obtained projection data. As a result, projection data at an arbitrary slice position is obtained by interpolation processing from arbitrary continuous data of data acquired by the helical scan, and a tomographic image at an arbitrary slice position is obtained from the projection data. Incidentally, the interpolation processing includes various kinds of interpolation such as quadratic interpolation as well as linear interpolation as will be described later, and all of these are interpolation using a distance as a parameter. Further, the present invention reconstructs a tomographic image by interpolation from the data obtained by the reciprocating motion of the bed.

【Example】

FIG. 2 is an external view of the 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.
Consists of 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 in FIG. 5 described later. The X-ray tube device 1 and the X-ray detector 2 were integrally mounted on the 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. The X-ray irradiation of the patient bed 3 by the X-ray tube device 1 and the rotation of the X-ray tube device 1 are synchronized with each other. By moving and rotating the patient bed and the X-ray tube device 1 at a constant speed determined by each, there is an advantage that the management of 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 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, and scanning is performed within a range including a desired tomographic plane. Scanning positioning is performed prior to this scanning. As for the positioning, as shown in FIG. 3, the first tomographic plane 6 serving as a reference for starting imaging is positioned a certain distance a from the scanner rotation plane A. The distance a has a margin 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. Start the bombing of. 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. The patient bed has passed the final tomographic plane 7 by a distance b. B '
When it reaches the plane, the X-ray irradiation is stopped, the patient bed decelerates and stops at the A'plane. In this way, by moving the patient bed during scanning, the scanning is performed in a spiral shape as shown in FIG. The trajectory of the X-ray tube apparatus with respect to the subject at this time is shown in FIG. The projection data obtained by the spiral scanning (hereinafter referred to as spiral data) is, as shown in FIG. 4, the projection data obtained when the scanner object is rotated and rotated in the spiral shape. Are equivalent. The spiral data SR is determined by the projection angle β and the position X in the body axis direction of the subject. Here, the position at the start of scanning is X ₀ , and the distance that the bed (and the subject) moves while the scanner makes one rotation is D. To reconstruct a tomographic image of the slice plane (tomographic plane) S (X _n ) at the object position X _n , the projection data R
(Β, X _n ) (where β = 0 ° to 360 °) is required.
The present invention is characterized in that projection data R (β, X _n ) of a desired tomographic plane S (X _n ) is obtained from the helical 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 ) (where β = 0 ° to 360 °) on the tomographic plane may be obtained. The spiral data is shown below by a general formula. SR = (β _i , X _j ) ... (1) However, the projection angle β _i is a value in the range of 0 ° ≦ β _i ≦ 360 °, and the position X _j is X ₀ ≦ X _j ≦ X _e . It is an arbitrary point to be satisfied. 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, the projection data R (β _i , X _n ) ... (2) at the projection angle β _i at the slice plane S (X _n ) at the position X _n where X _j = X _n is one revolution before and after X _n. Minute (± D) interval (ie, X _n −D <
Data of X _n <X _n + D) is used, and the projection angle R (β _i , X _n ) is obtained by interpolation from the spiral data of the same projection angle β _i . This interpolation is a two-point linear interpolation, and for example, the projection angle β ₁ shown in FIG.
In matching the projection angle beta _1, before and after the position of the X _n is X _g, an X _m, the projection data at that time _{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 , X _m
Since the distance a from X _n is a = X _m −X _n , the interpolation formula is (3)
Becomes R (β ₁ , X _n ) = {SR (β ₁ , X _g ) × a + SR (β ₁ , X _m ) × b} / (a + b) (3) With this process fixed at X _n , 0 ° ≤ β ₁ ≤ 360 ° 3
If it is performed in all directions of 60 ° (all projection angles), the projection data at the position X _n can be obtained. FIG. 12 shows a comparative example between the case where projection data is obtained by the interpolation processing of the present embodiment and the case where projection data is obtained by the simple averaging processing according to Conventional Example B. Slice plane S at position X _n
In order to obtain a tomographic image at (X _n ), in the conventional example B, the projection angle (X-ray tube height) along the slice plane S (X _n ) does not occur, but a constant inclination downward to the right in the figure. Line (simple averaging processing line). For example, when P ₁ and P ₂ are given to obtain the projection data at the position q ₁ , since p ₁ q ₁ = q ₁ P ₂ = d, the simple mean value is just the projection data at the q ₁ position. is there. But P ₃
In order to obtain the projection data at the position q ₂ given P and P ₄ , the simple averaging method results in the projection data at the position q ₃ instead of the position q ₂ . That is, in the simple averaging method, the projection data at the position along the simple averaging processing line in FIG. 12 is obtained. On the other hand, in the present embodiment, in order to obtain the projection data at the position q ₁ by giving P ₁ and P ₂ , since P ₁ q ₁ = q ₁ P ₂ = d, the projection data obtained by the complementary tube processing Is the data at position q ₁ . But,
The projection data at the position q ₂ has different distances as P ₃ q ₂ = d ₁ and q ₂ P ₄ = d _2, and the projection data obtained by performing the interpolation process using this d ₁ and d ₂ is the position. q ₂ Thus, according to this embodiment, it is possible to obtain the projection data of the projection angle along the vertical interpolation processing line of the slice plane S (X _n ). The conventional example B is characterized in that it becomes a processing line in the lower right direction, and the projection data on this processing line is used as the projection data for reconstruction. When the processing line itself according to the conventional example B is treated as the one obtained by the interpolation processing line of the present embodiment, the vertical line hardly matches the data on the interpolation processing line, and only one point (q ₁ It is conceivable that the reconstructed image of the tomographic image on the slice plane S (X _n ) has a large error. On the other hand, when the projection data along the simple averaging processing line in the conventional example B is reconstructed assuming that it is obtained on the processing line, the simple averaging is performed instead of the tomographic image at one slice position. This means that an average tomographic image within the width W of the processing line in the X direction is obtained. In any case, the example of the present invention recognizes the slice position X _n ,
The projection data for 0 ° to 360 ° completely along the slice plane S (X _n ) can be obtained by interpolation. Therefore, the tomographic image obtained by the reconstruction is also a tomographic image along S (X _n ). Further, in the present embodiment, the slice position X _n may be any arbitrary position. This is because, at any arbitrary position, the projection data before and after the same projection angle can be obtained by the interpolation process to obtain the projection data as the arbitrary slice plane. In Conventional Example B, although not clear, the tomographic image at a fixed position along each cycle (every 360 °) is calculated as shown in FIG. 12, and the position is limited by the cycle unit on the spiral scan. However, it seems that a tomographic image at any arbitrary position cannot be calculated (see FIG. 2 of Conventional Example B and its description). An embodiment of the X-ray CT apparatus of the present invention is shown in FIG. The X-ray CT device includes an X-ray generator 1, an X-ray detector 2 and a data acquisition circuit.
2A, buffer memory 12, interpolation circuit 13, filter correction circuit
14, a back projection calculation circuit 15, and a CRT 16. 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 12 ... A buffer having an address of i × j. The spiral projection data SR is stored. That is, the buffer 12 has a projection number i and a scanner rotation number (how many rotations).
determined by j. Furthermore, the number of projections in one rotation of the scanner is pp, and the total number of rotations of the scanner (how many scans) is JC.
Then, 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
(4) However, Δθ = 360 ° / PP ΔD = D / PP (5) When the interpolation circuit 13 ... position X _n is specified, created by interpolating projection data R in X _n (beta _i, X _n). 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. Backprojection arithmetic circuit 15 ... Backprojects the filtered output of the filter correction circuit 14. 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 moves forward at a constant speed. X on the subject in the process of moving forward
X-rays from the ray generator 1 are emitted. This exposure is performed by spiral scanning. The transmitted X-ray obtained by the spiral scan is detected by the X-ray detector 2 and subjected to various kinds of preprocessing and AD conversion by the data acquisition circuit 2A. Thus, the spiral data SR is obtained. This spiral data SR has arguments i, j
Is stored in the two-dimensional buffer 12 whose address is. Similarly, the spiral data SR is obtained over the entire measurement range of the subject,
Store 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 (i, X _n ) at the position X _n is created. Specifically, as is clear from the equations (4) and (5), 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. It becomes the relationship of the figure. Therefore,
The projection data R (i, X _n ) can be obtained by the following formula. R (i, X _n ) = {SR (i, m) × a + SR (i, m + 1) × b} / (a + b) ...
(6) Next, the obtained projection data R (i, X _n ) is subjected to 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 . CRT16 displays a tomographic image. still,
Although the same projection angle i is used for the interpolation, it goes without saying that other neighboring angles may be included in addition to the same projection angle i. Another embodiment 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, the locus 9 of forward movement and the locus 8 of backward movement
When the scanning is performed so as to intersect with each other, the subject is scanned as shown in FIG. Seventh case when only one tomographic image is obtained
This will be described with reference to FIGS. FIG. 7A shows the scanner rotation speed 16, the patient bed movement speed 17 and the X-ray pulse 18.
Is a time chart showing the relationship. From Fig. 7 (b), the scan 9 of 180 ° (or more) required to obtain one tomographic image is performed in the forward direction, and the patient bed is moved / X-rayed until the scanner further rotates 180 °. After stopping the explosive shots and shifting the phase by 180 ° (this causes the forward and backward trajectories to intersect), scan 180 in the opposite direction (or more) The locus 9 of the X-ray tube device for the subject is as shown in FIG. However, the broken line portion indicates that only the scanner is rotating after the movement of the patient bed and the X-ray exposure are 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. Also,
In the first embodiment, the error due to the interpolation is the same on any tomographic plane, but in the second embodiment, the error due to the interpolation is the smallest in the plane including the intersection point and perpendicular to the bed moving direction. Therefore, when the scanning shown in FIG. 7B is performed, the tomographic plane 19 is obtained. In FIG. 8, (a) is the projection of the trajectory from above and (b) is the projection of the trajectory from the side. The tomographic plane 19 in FIG. 7 (b) 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. P1 is forward, P2
Is projection data at the time of backward movement. Surface P from P1 and P2
The projection data P above is obtained. Projection data P (i, j)
If linear interpolation is used, P (i, j) = (P1 (i, j) + P2 (i, j)) / 2 (7) i = 1,2, ... CN CN: Total number of channels j = 1,2,… NP NP: Total number of views. If this process is performed for 0 ≦ β ≦ 180 °,
The projection data of the first half scan is obtained. A desired tomographic image can be obtained by obtaining one tomographic image from the obtained projection data for 180 °, defocusing the data, and performing back projection. Incidentally, FIG. 9 shows a view corresponding to FIG. 6 in the second embodiment. 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. In the second embodiment, one tomographic image is obtained from the obtained projection data of 180 °, but as a third embodiment, a method of obtaining projection data of 360 ° and obtaining a tomographic image will be described. In Fig. 10, in order to obtain 360 ° projection data, both forward and reverse directions are required.
A 60 ° scan is required. The range of Example 2 is 0 ° to 180
.Degree., Scanning in the range of -90.degree. To 280.degree. Is required in the third embodiment. The first half scanning is obtained in the same manner as in the second embodiment, and the second half scanning is Q1 (n), Q2 shown in FIG.
Similarly, Q (n) is obtained from (n), and one tomographic image can be reconstructed from all the obtained projection data. However, in the third embodiment, when obtaining the latter half scanning, it is necessary to consider that 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 when obtaining the first half scanning. . FIG. 11 shows a control system diagram of the present invention. X-ray controller 101
Controls the high voltage generator 110 to generate a high voltage. This is so-called X-ray bombardment control. The rotating frame control unit 102 can perform not only control for continuously rotating the X-ray tube device (X-ray generator) and the X-ray detector facing each other but also control in consideration of the projection angle. You can control. 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 uses the position information from the bed position detector 113 and the projection angle information from the projection angle detector 114 to determine the X-ray control unit 101 and the rotary frame controller 10.
2. The bed movement control unit 103 is synchronized. Specifically, in each example, pre-specified slice position _{X n = X s +3 (D} / 4) + n (D / 2) ...... (8) where n = 0, 1, 2, 3 The scanning start position X _s is determined so that However, D
Is determined by the bed moving speed and the rotating speed of the rotating frame. The position at the end of forward scanning
X _e and the projection angle θ _e are 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, regarding the reciprocating motion of the equation 8, it is as follows from what is shown in FIG. The intersections of the forward sampling points and the backward sampling points occur at (D / 2) intervals. To obtain the data at X _n points by interpolation, use (D / 2) before and after X _n points.
Need sample data in between. 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, it is valid for X _n −X _s = 3 (D / 4) and later. Where X _n −X _s = (D / 4) is n = −1
Then, X _n −X _s = 3 (D / 4) corresponds to n = 0. 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 directly back-projected, and fan-shaped beam data are converted into parallel beam data. Arrangement method of backprojecting is known after that, but the present invention can be applied to various applications such as optical scanning and electronic scanning if a cone beam is used regardless of the algorithm or generation, and the effect is exerted. To do. Furthermore, as the interpolation method, in addition to linear interpolation, high-order interpolation such as quadratic or cubic (several slices) is also possible.

【The invention's effect】

According to the present invention, spiral scanning can be performed simply by moving the patient bed, and high-speed continuous scanning becomes possible. Further, with respect to the data collected by the spiral scan, accurate projection data can be obtained by interpolation processing using continuous data before and after the arbitrary slice position. Further, the slice position can be anywhere, and the tomographic image can be freely generated at the arbitrary position.

[Brief description of drawings]

FIG. 1 is an embodiment view of a CT apparatus of the present invention, FIG. 2 is an external view of an RR type CT apparatus, FIG. 3 is an explanatory view of continuous scanning of the present invention, FIGS. ) Is an explanatory view of spiral scanning according to the present invention, FIG. 5 is a relationship diagram between rotational position and spiral data in the present invention, FIG. 6 is a relationship diagram between position and projection number, and FIG. 7 (a). , (B) and FIGS. 8 (a) and (b) are explanatory views of the second embodiment of the present invention, FIG. 9 is a relationship diagram between the position and the projection number in the second embodiment, and FIG. (A) and (B) are explanatory views of the third embodiment of the present invention, and FIG. 11 is a control system diagram of the present invention,
FIG. 12 is a comparative example diagram of the conventional example and this example. 1 ... X-ray tube device, 2 ... X-ray detector.

Claims (4)

[Claims] 1. 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 can be continuously moved. A patient bed, a data collecting means for collecting the detected data, and an image reconstructing means for reconstructing an image from the data, and the X-ray source is continuously rotated around the subject, The X-ray is configured to continuously move the patient bed in the body axis direction of the subject during the rotational movement and irradiate the subject with X-rays during the movement of the subject to perform spiral scanning. In the CT device, a large number of projection data at arbitrary slice positions from any continuous data of the collected data is obtained by interpolation processing for each projection angle, and in this interpolation processing, for each projection angle, Same or near projection angle before and after the slice position First means for obtaining projection data by performing an interpolation operation on the X-ray beam data using the distance from the slice position as a parameter, and a tomographic image at the arbitrary slice position is reconstructed by the obtained projection data. An X-ray CT apparatus comprising the second means for constituting and the second means. 2. The X-ray CT apparatus according to claim 1, wherein the patient bed and the X-ray source are controlled for uniform velocity motion. 3. The X-ray CT apparatus according to claim 1, wherein the patient bed is controlled to reciprocate. 4. 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 can be continuously moved. A patient bed, a data collecting means for collecting the detected data, and an image reconstructing means for reconstructing an image from the data, and the X-ray source is continuously rotated around the subject, The X-ray is configured to continuously move the patient bed in the body axis direction of the subject during the rotational movement and irradiate the subject with X-rays during the movement of the subject to perform spiral scanning. In the CT device, projection data at an arbitrary slice position is obtained from any continuous data of the collected data by interpolation processing for each projection angle, and in this interpolation processing, the projection data is calculated for each projection angle. X-ray beam data with projection angles before and after the slice position First means for obtaining projection data by performing linear interpolation calculation using the distance from this slice position as a parameter, and the tomographic image at the arbitrary slice position is reconstructed by the obtained projection data. An X-ray CT apparatus comprising the second means.