JP3023201B2 - X-ray computed tomography apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray computed tomography apparatus (hereinafter, referred to as an X-ray CT apparatus) for performing a helical scan using a cone or a pyramidal X-ray beam.

[0002]

2. Description of the Related Art An X-ray CT apparatus is widely used not only for medical purposes but also for industrial purposes as a device for taking a tomographic image of a subject. In particular, in medical use, it occupies an important position as an image diagnostic device. The subject is three-dimensional, but since the X-ray CT apparatus captures (scans) a tomographic image (slice), it is necessary to scan a large number of slices to capture the entire subject. The scanning speed of recent X-ray CT systems is much faster than the earlier ones,
Although the overall photographing time has also been shortened, there is a demand for photographing more quickly. This is because (1) the number of slices to be scanned increases as the CT apparatus becomes important, and (2) in the case of a method called dynamic scan, the movement of the contrast agent injected into the body is photographed. This is because short-time photographing is required. Conventionally, two types of methods have been proposed and put into practical use in order to shorten the photographing time. One is a helical scan method, and the other is a method using a cone beam.

As shown in FIG. 13, a method using a cone beam is such that a cone beam (actually not a cone but a pyramid, but generally called a cone beam) 12 from one X-ray tube 10 is used. Is projected onto a subject (not shown), and projection data obtained from the projection data is stored in an image intensifier or the like.
This is a method of collecting by the dimensional X-ray detector 14. For convenience of the following description, coordinates are determined as shown in FIG. Here, the slice plane is defined by the XY coordinate plane, and the slice thickness direction is defined as the Z axis.

[0005] As shown in FIG. 15, at a certain projection angle (a rotation angle θ with reference to the Y axis in the XY plane) at a certain slice position (a certain z position in the Z direction) in a normal scanning method. The collected projection data is P (z, θ)
And The normal scan method is a method of collecting 360-degree projection data while fixing the scan position, sequentially moving the scan position in the Z direction, and collecting the next 360-degree projection data. Therefore, the projection data P (z, θ) is collected in order from 0 ° to 360 ° for each projection position as shown by (1), (2),... In FIG. In this case, the scan position and the slice position are the same, and the image at that position is reconstructed using 360 ° projection data of one vertical column, which is the same projection position.

Next, the helical scan method will be described.
The projection data collected by this method is expressed as PH (z, θ)
And Since the helical scan changes the scan position z in synchronization with the change in the projection angle θ, the projection data P
H (z, θ) are collected in the order shown in FIG.
In order to reconstruct an image at a certain slice position, one column of 360 ° projection data is required, but in the helical scan method, there is no one column of 360 ° projection data. Therefore, it is necessary to virtually combine the projection data PH (z, θ) in one vertical column. This is generally a method of interpolating two or more pieces of data having different scan positions z at the same projection angle θ. For example, the projection data I indicated by the dashed circle is obtained by interpolating the left and right projection data L and R according to the position in the Z direction.

As is apparent from FIGS. 16 and 17, the helical scan method has a shorter overall scan time than the normal scan method. However, since projection data is interpolated in the slice direction, there is a disadvantage that blurring in the slice thickness direction is large and resolution in the slice direction is poor.

Next, an ordinary scanning method using a cone beam will be described. In the normal scan method and the helical scan method, all the projection data is perpendicular to the Z axis, but in the case of a cone beam, it spreads in the Z axis direction as shown in FIG. Therefore, the scan position z of the projection data differs depending on the position in the X and Y directions. Therefore, the scan position of the projection data is set on the Z axis (x = y = 0).
And this is defined as PC (z, θ). FIG.
As shown in (1), a large number of projection data can be collected simultaneously by using a cone beam. Further, the scan position is fixed while the 360-degree projection data is collected, as in the normal scan method. Therefore, the projection data PC (z,
θ) are collected in the order shown in FIG.

In FIGS. 16, 17 and 19, one projection data is indicated by one circle, but the projection angles in the Z-axis direction are not the same. In the case of FIG. 16 and FIG. 17, since all the projection data are perpendicular to the Z axis, the projection data at a projection angle separated by 180 degrees becomes the projection data facing each other as shown in FIG. . On the other hand, in the case of the cone beam, the center of the slice position is the same as in FIG. 20A, but the projection data intersects as the distance from the center increases, as shown in FIG. 20B. This angle increases in proportion to the deviation from the center.

Therefore, X-ray C using a cone beam
Reconstruction in a T device is a mathematically very difficult problem. Therefore, some approximation is performed and reconstruction is performed.
Off-center slices are less accurate.

[0010] The simplest method of reconstructing an X-ray CT apparatus using a cone beam is to assume that the X-ray tube is at a very remote position, and that all projection data of the cone beam is perpendicular to the Z axis. It is to approximate that there is. As a result, the image can be reconstructed by the convolution / back-projection method as in the case of the normal scan. However, this approximation does not provide sufficient accuracy in off-center slices.

As another approximate reconstruction method, reference 1 (LA
Feldkamp, et.al: Practical conebeam algorithm, J.
Opr. Soc. Am. A, 6, pp. 612-619, 1980) is well known. This method is more accurate than the above method, but the reconstruction is complicated,
There are problems that the accuracy differs depending on the slice and that the accuracy is still insufficient.

Thus, in order to shorten the photographing time,
Each of the two types of conventionally proposed methods has advantages and disadvantages, and a method capable of scanning a large number of slices in a short time with a simple configuration and high accuracy has not been realized. A system combining these two methods has been studied, but has not been put to practical use. For example, Reference 2 (Hiroyuki Kudo, Tsuneo Saito, "Reconstruction of 3D CT Image from Conical Beam Projection by Helical Scan", M.
The reconstruction method described in BE88-63, 9-16) assumes that the object is small, and the reconstruction is also complicated and impractical.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned circumstances, and has as its object to provide an X-ray CT apparatus having a simple structure capable of imaging a large number of slices in a short time. It is to be.

Another object of the present invention is to provide a helical scan type X-ray CT apparatus using a cone beam which has high accuracy and whose accuracy does not depend on the slice position.

[0015]

An X-ray CT apparatus according to the present invention comprises: an X-ray source for emitting a fan beam X-ray having a predetermined spread width also in the body axis direction of a subject; X-ray detecting means for detecting X-rays from multiple directions, which are arranged in a two-dimensional manner and which have passed through the subject, and an arbitrary width equal to or smaller than the length of the X-ray detecting means in the body axis direction. Beam width setting means which can be set to the above, driving means for driving the X-ray source or the subject so that the X-ray source draws a spiral trajectory around the subject, and X-ray source or the subject by the driving means Drive amount control means for controlling the drive amount of the laser beam and the spread width set by the beam width setting means in association with each other, and image reconstruction processing is performed by data collected under the control of the drive amount control means to perform a tomographic image. Processing means for obtaining
Beam width setting means focuses on scan time and image quality
Spread width of X-ray according to selection of one of the emphasis modes
Is set .
Here, the beam width setting means is in the scan time emphasis mode.
When is selected, set the beam width wide and
When the mode is selected, the beam width may be set narrow. Ma
The drive amount control means is set by the beam width setting means.
Control so that the drive amount changes in proportion to the size of the spread width
May be. In addition, fanby with a predetermined spread width
Beam depending on the position in the body axis direction
A correction means for correcting the system path length may be further provided.

[0016]

According to the X-ray CT apparatus of the present invention, a helical scan is performed using conical X-rays, and normal reconstruction is performed by regarding the cone beam as a beam perpendicular to the slice thickness direction. Thus, scanning of multiple slices can be performed in a short time with a simple configuration, and there is no need to interpolate projection data, but there is no difference in error depending on the slice position, and there is little blur in the slice thickness direction. Is obtained.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the apparatus will be described. First, a helical scan method using a cone beam according to the present invention will be described with reference to FIG. An X-ray tube 10 irradiates a subject 18 with pyramid-shaped X-rays (cone beam) and projects projection data based on the X-rays transmitted through the subject 18 by a two-dimensional X-ray detector 14 such as an image intensifier. collect. The X-ray tube 10 and the two-dimensional detector 14 rotate around the subject 18 about the Z-axis along the body axis of the subject 18, and at each projection angle at a predetermined angle between 0 degrees and 360 degrees. Collect projection data. At that time, in synchronization with the rotation of the X-ray tube 10 and the two-dimensional detector 14,
The couch 16 on which the subject 18 is placed is moved in the Z-axis direction.
In this scan, assuming that the subject 18 is fixed, the X-ray tube 10 moves along a helical (spiral) trajectory as shown in FIG. Therefore, projection data is also collected in a helical shape. In the case of this helical scan method, the feed amount of the bed for a projection angle of 360 degrees is Z
The width of the beam is adjusted in the axial direction (here, the length of the two-dimensional detector in the Z-axis direction).

FIG. 3 is a diagram of the two-dimensional detector 14 as viewed from directly above. When an image intensifier is used as the two-dimensional detector 14, data is sampled and collected for each rectangular area surrounded by the grid shown in FIG. FIG.
In FIG. 15, the vertical direction is the spreading direction of the fan beam shown in FIG. 15, and is generally called the channel direction. The horizontal direction is generally called a slice direction. Therefore, a group of data in the vertical direction in FIG. 3 constitutes one projection data. The sampling pitch in the channel direction is equiangular, and here, one projection data has 512 channels. The projection data near the center is irradiated with X-rays from almost right above, so that the projection data is almost the same as the projection data of the ordinary scan method. The length d in the Z direction of each rectangle is set equal so that sampling is performed at equal intervals in the Z axis direction, that is, in the slice direction.

The projection data collected by the scan according to the present invention will be described. As in the case of using a normal cone beam, the projection data also has a spread in the Z-axis direction as shown in FIG. 17 in this case. Therefore, the scan position z of the projection data differs depending on the position in the X and Y directions. Therefore, here, the scan position of the projection data is set on the Z axis (x =
y = 0), and this is defined as PCH (z, θ). One PCH (z, θ) is set to 1 as in the case of FIG.
As shown by the circles, the projection data PCH (z, θ) is collected in the order shown in FIG.

Consider the case of reconstructing a slice, for example, a slice at zt in FIG. In order to reconstruct this slice, projection data at 360 ° (or 180 ° + fan angle in the case of half scan) at this position is necessary. That is, the projection data of one column in FIG. 4 is collected. However, in fact, 360 rows of vertical columns
Since there is no projection data of the degree, projection data at a position adjacent to zt is collected. These projection data are indicated by black circles in the figure.

Since the projection data collected in this way has the same projection angle in the Z-axis direction, the projection data at a projection angle 180 degrees apart is as shown in FIG. Therefore,
The reconstruction of the projection data is also a very difficult problem mathematically. However, comparing FIG. 5 with FIG. 20B in the case of the conventional method using a cone beam, the following features are obtained. 1) In the case of the present invention shown in FIG. 5, the intersection angle is smaller than that of the conventional example shown in FIG. 2) The intersection angle in FIG. 20B differs depending on the slice position, but in the case of FIG. 5, the distribution of the intersection angle does not depend on the slice position.

Therefore, considering that the X-ray tube 10 is far away from the Z-axis, all projection data is perpendicular to the Z-axis, that is, the cone beam is projected to a beam perpendicular to the slice thickness direction. Error is small even if it is assumed that In this way, an image can be reconstructed by the convolution / back-projection method as in the case of a normal scan.

For this reason, in the following manner, in the helical scan system using a cone beam, the accuracy is high, and the accuracy does not depend on the slice position.
Reconfiguration can be performed. That is, 1) Helical scan is performed using a cone beam to collect projection data.

2) The position of the projection data in the Z direction is defined as the position where the projection data crosses the Z axis, and the projection data at the same position as the slice position and the adjacent position among all the projection data is defined as the projection angle 0. Gather about 360 degrees. 3) Convolution backprojection of each collected projection data, assuming that the projection data is perpendicular to the Z axis.

A first embodiment of the present invention based on such a principle will be described. FIG. 6 is a system block diagram according to the embodiment of the present invention. Here, a case where the present invention is applied to a so-called third-generation X-ray CT apparatus, and an embodiment in which an image is reconstructed using 360-degree projection data will be described. The output of the two-dimensional detector 14 is supplied to the storage device 20. The storage device 20 includes a raw data storage unit 20a, an edited raw data storage unit 20b, and a reconstructed image storage unit 20c.
Having. Data in the storage device 20 is supplied to the reconfiguration device 24 via the bus line 22. The output of the reconstructing device 24 is stored in the reconstructed image storage unit 20c and displayed on the image display device 26. A central processing unit (CPU) 28 for performing overall control is connected to the bus line 22. C
An operation console 30 for setting scanning conditions as appropriate by the operator is connected to the PU 28. Here, console 3
0 designates a beam width in the Z-axis direction and the total number of scans in addition to the scan conditions set by a normal X-ray CT apparatus in order to instruct a cone beam helical scan. However, unlike a normal helical scan, it is not necessary to specify the feed speed of the bed because it is linked to the beam width in the Z-axis direction.

The CPU 28 controls the X-ray generator 32 including the X-ray tube 10, the bed 16 and the two-dimensional X-ray detector 14 to perform a cone beam helical scan. X-ray generator 3
Reference numeral 2 denotes a body axis direction (Z axis) of the subject in combination with the two-dimensional X-ray detector 14 while irradiating the subject with a cone beam X-ray.
Rotate about the center of rotation. The two-dimensional X-ray detector 14 converts the X-ray projection data transmitted through the subject into digital values and stores the digital values in the first raw data storage unit 20a of the storage device 20. The projection data is sampled as described above with reference to FIG.

The couch 16 moves in the Z-axis direction in synchronization with the rotation of the X-ray generator 32 and the two-dimensional X-ray detector 14. The moving speed is set so that the bed 16 is moved by the beam width in the Z-axis direction for one rotation of the X-ray generator 32 and the two-dimensional X-ray detector 14.

When the projection data of 360 degrees or more is collected in the raw data storage unit 20a, editing of the raw data (selection of projection data used for reconstructing a certain slice) and image reconstruction are performed in the following procedure. Do.

As shown in FIG. 3, the width of the projection beam on the Z axis in the Z direction (the length of the two-dimensional detector in the Z direction in the embodiment) is L, the sampling interval of the projection data in the Z direction is d, Let N = L / d. Further, as shown in FIG. 4, when the interval between the projection angles of the projection data is h, and the number of projections per rotation is M, M = 360 / h. S is the total number of scans
If N (this is specified by the operator) and the total number of projections is MM, then MM = M × SN.

Let M / N be a parameter RMN. RMN
Is generally a very large number, so here 3 ≦ R
MN. Here, RMN is an integer. However, even when the RMN is not an integer, it can be implemented in substantially the same manner as the embodiment.

In FIG. 4, since one vertical column is a slice position, one vertical column of projection data is necessary. However, there is a case where there is no projection data, so that projection data of an adjacent position is selected as shown by a black circle.

Here, an image that can be reconstructed (the number of slices)
Is GN, as can be seen from FIG. 4, GN = N ×
(SN-1). Also, the position of the first slice is Z
= 0.

The number of projections (and collected) up to the present is set as a parameter MC. MC is a two-dimensional X-ray detector 1
4 is updated each time the storage unit 1 stores N pieces of projection data of one projection. This update is performed separately and separately from the flowchart below.

In FIG. 4, the numbers of N pieces of projection data collected in one projection are 1, 2,... N from the left. Assuming that the projection number is m and the projection data number is n, each projection data in FIG. 4 can be represented as PCH (m, n).

The raw data edited for image reconstruction is stored in the edited data storage section 22b of the storage device 20. This edited raw data is represented by GCH (Gi, Gm). Here, Gi is a slice (image) number, and Gi = 1 to G
N. Gm is a projection data number, and Gm =
1 to M.

FIG. 7 is a flowchart showing the main operation procedure of this embodiment. First, in step # 1000,
Initialize necessary data. The data to be initialized will be described later. At step # 2000, M pieces of projection data necessary for reconstructing the Gi-th slice are selectively read from the raw data PCH (m, n) in the raw data storage unit 20a, and these are read after editing. Raw data GCH (Gi, Gm)
Is written in the edit data storage unit 22b. The details will be described later.

In step # 3000, the reconstruction unit 24 reconstructs the Gi-th slice. Reconstruction is performed by a convolution back-projection method. The projection data used for reconstruction is GCH (Gi, G
m) (here, Gm = 1 to M).

In step # 4000, the Gi-th slice is stored in the reconstructed image storage unit 20c of the storage device 20. At this time, the slice position z is also stored. Step # 5
000, the Gi-th slice is displayed on the image display device 26. In step # 6000, z ← z + d is set in order to update the slice position. Step # 7000
Therefore, Gi ← Gi + 1 is set in order to update the slice number.

At step # 8000, it is determined whether or not Gi ≦ GN to determine whether or not processing of all slices has been completed. If yes, the process returns to step # 2000 to perform the processing for the next slice. If no, that is, if Gi> GN, the processing for all slices has been completed, and the operation ends.

FIG. 8 is a flowchart showing details of the initialization in step # 1000 of FIG. Step #
At 1100, to initialize the position of the slice, z =
Set to 0. In step # 1200, Gi = 1 is set to initialize the slice number. Step # 1300
To convert the raw data PCH (M + 1, 1) to the edited data GCH
Mz = M + 1 to set as (1,1). In step # 1400, nz = 1 is set, and the initialization ends.

FIG. 9 is a flowchart showing details of editing of raw data in step # 2000 of FIG. In step # 2100, initialization necessary for editing this slice is performed. The data to be initialized will be described later. Step # 2
At 200, a determination is made as to whether m ≦ MC to determine whether the acquisition of the required projection data has been completed. If yes, the next step # 2400 is immediately executed. If no, that is, if m> MC, step #
After waiting for a predetermined time in 2300, the next step # 2400
Execute This is because the present embodiment employs a method of editing the projection data and reconstructing the image in parallel with the scanning so that the image can be viewed quickly, so that the editing and the image reconstruction are faster than the scanning speed. In this case, the collection of the projection data may not be in time. In this embodiment, the projection data may be edited and the image may be reconstructed after the scan is completed. In this case, however, these steps # 220
0 and # 2300 are unnecessary.

In step # 2400, the raw data storage unit 2
The projection data PCH (m, n) of 0a is written into the edited data storage unit 20b as the projection data GCH (Gi, Gm) edited for reconstruction. Thereby, the projection data of the black circle shown in FIG. 4 is selected. In step # 2500, m,
Update n. The details will be described later. In step # 2600, Gm ← Gm + 1 is set. Step # 27
At 00, it is determined whether or not Gm ≦ M to determine whether it is necessary to continue editing. If yes, return to step # 2200. If no, step # 28
At 00, mz and nz are updated, and editing of the raw data is completed. This will be described later in detail.

FIG. 10 is a flowchart showing details of the initialization in step # 2100 of FIG. In step # 2110, Gm = 1 is set to initialize the projection data number Gm of GCH (Gi, Gm). Step #
At 2120, m ← mz is set. In step # 2130,
Let n ← nz. In step # 2140, ｛(RMN +
1) The integer part of / 2} is set to r, and the initialization ends.

FIG. 11 is a flowchart showing the details of updating m and n in step # 2500 of FIG. In step # 2510, m ← m + 1 is set, and in step # 25
At 20, it is assumed that r ← r + 1. In step # 2530, r
It is determined whether or not ≦ RMN. If yes, complete the renewal. If no, in step # 2540, r = 1
In step # 2550, n ← n−1 is set, and in step # 2560, it is determined whether n> 0. If yes, complete the renewal. If no, step # 25
70, n = N, and in step # 2580, m ← m−
M, and the update ends. Thereby, the projection data of the black circle shown in FIG. 4 is selected.

FIG. 12 is a flowchart showing the details of updating mz and nz in step # 2800 of FIG. In step # 2810, nz ← nz + 1 is set, and in step # 2820, it is determined whether nz ≦ N. If yes, complete the renewal. If no, step #
At 2830, nz = 1 is set, and at step # 2840, m
Set z ← mz + M, and end the update.

As described above, according to this embodiment,
Perform helical scan using a cone beam, collect projection data, define the position of the projection data in the Z direction as the position where the projection data crosses the Z axis, and from the entire projection data, the same position as the slice position, and Slices are reconstructed by collecting projection data at adjacent positions for projection angles 0 to 360 degrees, assuming that the projection data is perpendicular to the Z axis, and performing convolution / backprojection on each of the collected projection data. I do. For this reason, in the helical scan method using a cone beam, the accuracy is high, and the accuracy does not depend on the slice position.
Reconfiguration can be performed. Therefore, an X-ray C having a simple configuration capable of imaging a large number of slices in a short time.
A T device is provided. The present invention is not limited to the above-described embodiment, and can be implemented with various modifications. Hereinafter, modified examples will be described. Although the above-described embodiment assumes that the convolution is performed in the real space, the convolution may be performed in the frequency space.

For projection data that is not perpendicular to the Z axis,
Before the convolution, the correction may be performed in advance according to the angle of the projection data with respect to the Z axis. The correction may be performed by any method, but the method described in Document 1 may be employed.

The two-dimensional detector for detecting X-rays
An intensifier may be used, a multi-channel xenon detector may be arranged in plurals, or a solid-state detector, a semiconductor detector and the like may be two-dimensionally arranged.

The channels in the projection data and the intervals in the slice direction are set such that the channel directions are equiangular as in this embodiment.
The slice directions may be at equal intervals, both may be at equal angles, or both may be at equal intervals.

According to the beam spreading width in the Z-axis direction in the embodiment ,
Furthermore, if the spread width is reduced, a more accurate image can be obtained. In that case, it is necessary to reduce the feed amount of the bed for the projection angle of 360 degrees according to the spread width of the beam in the Z-axis direction. Alternatively, the width of the beam in the Z-axis direction may be set in a stepwise manner so that the beam width can be selected in accordance with the scanning time and image quality requirements. That is, the width of the beam is set wide when importance is placed on the short scanning time, and the width of the beam is set narrow when importance is placed on the image quality. If you set it so narrow, from the center
Influence of cone angle of X-ray beam even at the farthest slice position
Which results in higher quality images.
You. Although the embodiment has been described with respect to a so-called third-generation CT, the present invention can be similarly implemented with a so-called fourth-generation CT. In the embodiment, the projection data for reconstructing one image is 360 degrees, but one image may be reconstructed using projection data of 180 degrees + fan angle. In the embodiment, all the images are reconstructed, but only an arbitrary desired image may be reconstructed.

In the embodiment, the editing and the reconstruction are performed in parallel with the scanning. However, the editing and the reconstruction may be performed after the scanning is completed, or the editing and the reconstruction may be performed in parallel with the scanning. It may be performed after scanning is completed.

In the embodiment, the collected projection data is stored once and edited. However, the collected projection data may be edited from the beginning and stored directly as reconstructed projection data.

[0053]

As described above, according to the present invention, a helical scan is performed using cone-shaped X-rays, and a cone beam is regarded as a beam perpendicular to the slice thickness direction, and ordinary reconstruction is performed. By doing so, a large number of slices can be photographed in a short time with a simple configuration, and there is no need to interpolate projection data. An X-ray CT apparatus having a simple configuration capable of obtaining an image with few images is provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a helical scan using a cone beam in one embodiment of an X-ray CT apparatus according to the present invention.

FIG. 2 is a diagram illustrating a helical scan.

FIG. 3 is a diagram showing a two-dimensional X-ray detector used in one embodiment.

FIG. 4 is a diagram showing a collection order of projection data in one embodiment.

FIG. 5 is a diagram showing an intersection angle of projection data at a projection angle of 180 degrees apart in one embodiment.

FIG. 6 is a system block diagram showing the configuration of one embodiment.

FIG. 7 is a flowchart showing a main operation procedure of the embodiment.

FIG. 8 is a flowchart showing details of an initialization process in FIG. 7;

FIG. 9 is a flowchart showing details of raw data editing processing in FIG. 7;

FIG. 10 is a flowchart showing details of an initialization process in FIG. 9;

FIG. 11 is a flowchart showing details of a process of updating m and n in FIG. 9;

FIG. 12 is a flowchart showing details of an update process of mz and nz in FIG. 9;

FIG. 13 is a view for explaining a cone beam.

FIG. 14 is a diagram showing a coordinate system in the X-ray CT apparatus.

FIG. 15 is a diagram illustrating a projection angle.

FIG. 16 is a diagram showing an acquisition order of projection data in a conventional X-ray CT apparatus of a normal scan system.

FIG. 17 is a diagram showing an acquisition order of projection data in a conventional helical scan type X-ray CT apparatus.

FIG. 18 is a diagram showing a relationship between a projection angle and a projection position in a conventional X-ray CT apparatus using a cone beam.

FIG. 19 is a diagram showing a collection order of projection data in a conventional X-ray CT apparatus using a cone beam.

FIG. 20 is a diagram showing an intersection angle of projection data at projection angles separated by 180 degrees in a conventional example.

[Explanation of symbols]

10 X-ray tube, 14 two-dimensional X-ray detector, 16 bed
18 subject, 20 storage device, 24 reconstruction device, 2
6. Display device, 28 CPU, 32 X-ray generator.

Claims (4)

(57) [Claims] An X-ray source for radiating a fan beam X-ray having a predetermined spread width also in the body axis direction of the subject to the subject, and a detection element are two-dimensionally arranged. X-ray detection means for detecting X-rays from multiple directions transmitted through the sample; beam width setting means capable of setting the spread width to any length equal to or less than the length of the X-ray detection means in the body axis direction; Driving means for driving the X-ray source or the subject so that the X-ray source draws a spiral trajectory around the subject; driving amount of the X-ray source or the subject by the driving means and setting of the beam width Driving amount control means for controlling the spread width set by the means in association with the processing means, and processing means for obtaining a tomographic image by performing image reconstruction processing based on data collected under the control of the driving amount control means. comprising, the beam width setting means, scan Time and image quality
Spread width of X-ray according to selection of one of the emphasis modes
X-ray computed tomography apparatus which is characterized in that those but is set. 2. The apparatus according to claim 1, wherein said beam width setting means includes a scan time.
When the priority mode is selected, set the beam width wide and
Set narrow beam width when quality mode is selected
2. The X-ray computed tomography apparatus according to claim 1, wherein
Place. 3. The apparatus according to claim 2, wherein the driving amount control means includes a beam width setting unit.
Drive in proportion to the size of the spread width set by the
Claim 1 wherein the momentum is controlled to change.
An X-ray computed tomography apparatus according to claim 2. 4. A fanby having said predetermined spread width.
Different X-rays depending on the position in the body axis direction
Further comprising a correcting means for correcting the path length of the camera.
An X-ray computer according to any one of claims 1 to 3.
Tomography equipment.