JP3284109B2 - 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 an 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 shooting time has been shortened, there is a demand for faster shooting. 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 system, and the other is a system 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 a cone beam) is supplied from one X-ray tube 10. Projection 12 is projected onto a subject (not shown), and projection data obtained by the projection is used as 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 scanning method is a method of collecting 360-degree projection data while fixing the scanning position, sequentially moving the scanning 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 line 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 drawback that blur in the slice thickness direction is large and resolution in the slice direction is poor.

Next, a normal scanning method using a cone beam will be described. In the ordinary scanning method and the helical scanning method, all projection data are perpendicular to the Z axis, but in the case of a comb beam, they are spread 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 the figure, when using the cone beam, a large number of projection data can be obtained.
Data can be collected at the same time. Further, as in the case of the normal scanning method, the scanning position is fixed while the 360-degree projection data is collected. 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 FIGS. 16 and 17, since all the projection data are perpendicular to the Z axis, the projection data at the projection angles 180 degrees apart face each other as shown in FIG. It becomes projection data. On the other hand, in the case of the cone beam, the center of the slice position is the same as that in FIG. 20A, but as the distance from the center increases, the projection data intersects as shown in FIG. 20B. become. This angle increases in proportion to the deviation from the center.

Therefore, a conventional method using a cone beam is used.
Reconstruction in a scanning X-ray CT apparatus is a very difficult problem mathematically. For this reason, reconstruction is performed by performing some kind of approximation, but accuracy is deteriorated in a slice far from the center.

Normal scanning method using a cone beam
The simplest method of reconstructing the X-ray CT apparatus is to assume that the X-ray tube is at a very remote position and that all projection data of the comb beam is perpendicular to the Z axis. Is to approximate. This allows fan beams instead of cone beams
As with the scan used, the image can be reconstructed by a convolution back-projection method. The premise of this reconstruction is that the X-ray tube is located very far away
Sometimes, the X-ray tube is not far away
In this case, accuracy in a slice away from the center is not sufficient.

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 has higher accuracy than the above method, but has problems such as complicated reconstruction, different accuracy depending on slices, and insufficient accuracy.

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",
The reconstruction method described in MBE88-63, 9-16) assumes that the subject is small,
Reconstruction is also complicated and impractical.

[0013]

[0008] The present invention has been made to address the above-mentioned circumstances, Mijikatoki multiple slices
Aiming to capture images in between and simplify image reconstruction.
Target.

[0014]

Means for Solving the Problems To achieve the above object,
Therefore, the present invention relates to an X-ray computer for performing a helical scan.
In the tomography system, the channel direction and the
X-rays that irradiate an X-ray beam having a spread width in the body axis direction
A source and a detecting element for detecting the X-rays,
And a plurality of X-ray detecting means arranged in the body axis direction.
Helical scan hand that performs the helical scan using
Steps and projections collected by this helical scanning means
Based on the data, the projection data falls in the body axis direction.
Image reconstruction assumed to have been obtained with a normal X-ray beam
Reconstructing means for performing
is there. Here, the reconstructing means performs the helical scan.
From the collected projection data, the desired slice position
Projection data and the projection closest to the desired slice position
Using the data, the image reconstruction at the desired slice position is performed.
You may go. Further, the reconstructing means includes the helical scan.
Out of the projection data collected by the
Detecting elements provided in the body axis direction near the surface
The image at the desired slice position is reproduced using the projection data of
Configuration may be performed. Further, the X-ray source is the helical
The data collected by the can is perpendicular to the body axis direction
Error is reduced by assuming that the beam is obtained with
Even if provided at such a distance from the body axis of the subject
good.

According to the present invention, the channel direction and the test
Irradiates an X-ray beam that has a spread width in the body axis direction of the body
The X-ray source and the detector that detects X-rays
And X-ray detecting means arranged in the body axis direction.
Perform a helical scan and collect by helical scan.
Using the projection data obtained, the projection data is
Image reconstruction assumed to have been obtained with a vertical X-ray beam
So you can shoot many slices in a short time
And can simplify image reconstruction.
You. In the reconstruction means, helical scan
Projection of desired slice position from collected projection data
Data and the nearest projection data to the desired slice position
To perform image reconstruction at the desired slice position
Scans the X-ray source with data collected by helical scan.
Data was obtained with an X-ray beam perpendicular to the body axis direction.
Away from the body axis of the subject so that the error is reduced.
If it is provided, the image can be reconstructed with high accuracy,
An image of high quality can be obtained.

[0016]

[0017]

[0018]

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an X-ray CT apparatus according to the present invention will be described below with reference to the drawings. 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 pyramidal X-rays (cone beam), and projects projection data based on the X-rays transmitted through the subject 18 into a two-dimensional X-ray detector such as an image intensifier. Collect at 14. The X-ray tube 10 and the two-dimensional detector 14 are arranged along the Z axis of the subject 18.
The projection data is rotated about the subject 18 around the axis, and the projection data is collected at each projection angle at a predetermined angle between 0 ° and 360 °. At that time, the bed 16 on which the subject 18 is placed is moved in the Z-axis direction in synchronization with the rotation of the X-ray tube 10 and the two-dimensional detector 14. 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 manner. In the case of this helical scan system, the amount of feed of the bed for a projection angle of 360 degrees is adjusted to the spread width of the beam in the Z-axis direction (here, the length of the two-dimensional detector in the Z-axis direction). .

FIG. 3 is a view 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 in this case also has a spread 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, 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, it is necessary to project 360 ° (or 180 ° + fan angle in the case of half scan) projection data at this position. The projection data of the position, 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 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 manner 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,
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. is there.

1) In the case of the present invention shown in FIG. 5, FIG.
The intersection angle is smaller than in 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 the projection data is perpendicular to the Z-axis, ie, the cone beam is 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 the 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 by 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 at the same position as the slice position and the adjacent position among all the projection data Data is collected for projection angles 0-360 degrees.

3) Assuming that the projection data is perpendicular to the Z axis, convolution backprojection is performed on each of the collected projection data.

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 stored in the storage device 2
0 is supplied. The storage device 20 includes a raw data storage unit 20
a, an edited raw data storage unit 20b and a reconstructed image storage unit 20c. The data of the storage device 20 is the bus line 2
2 to the reconstruction device 24. Reconstruction device 2
The output of No. 4 is stored in the reconstructed image storage unit 20 c 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. The console 28 is connected to the CPU 28 for the operator to set the scanning conditions as appropriate. Here, in order to instruct a comb beam / helical scan, the console 30 sets the beam width in the Z-axis direction and the scan conditions in addition to those set by a normal X-ray CT apparatus. Also specify the total number of scans. 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 comb 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 projection data of the X-ray transmitted through the subject into digital values and stores the digital values in the first raw data storage section 20a of the storage device 20. The projection data is sampled as described above in 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, the raw data is edited (selection of projection data used for reconstructing a certain slice) in the following procedure. , And image reconstruction.

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, and the projection data is sampled in the Z direction. The interval is d, and N = L / d. As shown in FIG. 4, the interval between the projection angles of the projection data is h, and the number of projections per rotation is M
Then, M = 360 / h. The total number of scans is SN (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 in the embodiment.

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

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 times of projection (and collection) performed so far is set as a parameter MC. MC is a two-dimensional X-ray detector 1
4 is updated each time N pieces of projection data of one projection are stored in the storage unit 1. This updating is performed independently in a part different from the following flowchart.

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, Step # 1000
Then, necessary data is initialized. The data to be initialized will be described later. In step # 2000, the raw data storage unit 20
The M projection data necessary for reconstructing the Gi-th slice are selectively read out from the raw data PCH (m, n) in a, and these are read as edited raw data GCH (Gi , G
m) is written in the edited data storage unit 22b. The details will be described later.

In step # 3000, the reconstructing device 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.

In 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 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, it is determined whether or not m ≦ MC in order to determine whether or not acquisition of necessary 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 edits projection data in parallel with scanning so that the image can be viewed quickly.
Since the method of image reconstruction is adopted, if the editing and image reconstruction are faster than the scan speed, the collection of projection data may not be in time. To wait. In this embodiment, the projection data may be edited and the image may be reconstructed after the scan is completed.
00 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 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, n ← nz is set.
In step # 2140, the integer part of {(RMN + 1) / 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 the present embodiment, helical scanning is performed using a cone beam to collect projection data, and the position of the projection data in the Z direction is determined by the projection data. Is defined as the position where the data crosses the Z-axis, and the projection data at the same position as the slice position and the adjacent position is collected from all the projection data at the projection angle of 0 to 360 degrees. Each projection data collected is assumed to be perpendicular to the Z axis.
The slice is reconstructed by convolution and back projection of the data. For this reason, in the helical scan method using a cone beam, reconstruction can be performed with high accuracy and without the accuracy depending on the slice position. Therefore, a simple configuration of X can capture a large number of slices in a short time.
A line CT apparatus is provided.

The present invention is not limited to the above-described embodiment, but can be implemented with various modifications. Hereinafter, modified examples will be described.

In the above embodiment, the convolution is performed in the real space, but 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 is
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.

As for the interval of the projection data in the channel and the slice direction, the channel direction may be at the same angle and the slice direction may be at the same interval as in this embodiment, both may be at the same angle, or both may be at the same interval. It may be.

In the embodiment, the beam spread width in the Z-axis direction is set to match the length of the two-dimensional detector in the Z-axis direction.
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. With such a narrow setting, the influence of the cone angle of the X-ray beam is reduced even at the slice position farthest from the center, and as a result, a high-quality image can be obtained.

Although the embodiment has been described with respect to a so-called third generation CT, the same can be applied to a so-called fourth generation CT.

In the embodiment, the projection data for reconstructing one image is 360 degrees. However, even if one image is reconstructed using projection data of 180 degrees + fan angle. Good.

In the embodiment, all the images are reconstructed. However, 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. Alternatively, only the editing is performed in parallel with the scanning and the reconstruction is performed. It may be performed after scanning is completed.

In the embodiment, the collected projection data is stored once and edited, but the collected projection data is edited from the beginning and directly stored as the reconstructed projection data. You may do so.

[0065]

According to the present invention, as described above,
The ability to shoot several slices in a short time
Furthermore, image reconstruction can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a helical scan using a cone beam in an 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 inclinations of opposed projection data according to the embodiment;

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

FIG. 7 is a flowchart showing a main operation procedure according to 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 the inclination of opposed projection data 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.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 6/00-6/14

Claims (4)

(57) [Claims] An X-ray computer for performing a helical scan
In a data tomography apparatus, there is a spread width in the channel direction and the body axis direction of the subject.
X-ray source for irradiating an X-ray beam, and detecting the X-ray
A plurality of detection elements are provided in the channel direction and the body axis direction.
The helical scan using the X-ray detecting means
Helical scanning means for performing scanning, and projection data collected by the helical scanning means.
Based on the projection data in a direction perpendicular to the body axis direction.
To perform image reconstruction assumed to have been obtained with the X-ray beam of
X-ray computed tomography, characterized by comprising a constituting unit, a
apparatus. 2. The helical scanner according to claim 1 , wherein
Out of the projection data collected by the
Position projection data and the nearest
The image reconstruction at the desired slice position is performed using the projection data.
2. The X-ray computer according to claim 1, wherein
Data tomography equipment. 3. The helical scanner according to claim 2 , wherein
Out of the projection data collected by the
Detecting elements provided in the body axis direction near the surface
The image at the desired slice position is reproduced using the projection data of
3. The configuration according to claim 1, wherein the configuration is performed.
X-ray computed tomography apparatus. 4. The method according to claim 1, wherein the X-ray source is used for the helical scan.
X-rays that are collected in the direction perpendicular to the body axis direction
Distance that minimizes errors assuming that the beam was obtained
Characterized in that it is provided separately from the body axis of the subject.
The X-ray according to any one of claims 1 to 3,
Computer tomography equipment.