JP2823531B2 - X-ray CT system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an X-ray CT apparatus for reconstructing a tomographic image of a subject based on data on the X-ray absorption coefficient of the subject obtained by irradiating the subject with X-rays. More particularly, the present invention relates to an X-ray CT apparatus for performing a so-called helical scan for moving a subject in a body axis direction during scanning.

[0002]

2. Description of the Related Art In recent years, as an X-ray CT apparatus, for example, FIG.
As shown in the figure, the couch top 100 on which the subject P is placed is moved in the body axis direction of the subject P, and the X-ray tube 101 is moved.
In addition, there has been proposed an apparatus that performs a so-called helical scan in which the detector 102 is rotated around the subject P. In this case, as shown in FIG. 5, the relative trajectory 103 of the X-ray tube 101 with respect to the subject P draws a helical shape.
An image is reconstructed using the data corresponding to the portion up to as one rotation data, and a slice image (tomographic image) of the subject P can be obtained. Such a helical scan has an advantage that three-dimensional information of the subject P can be obtained in a short time.

However, the slice plane obtained from the data from the point a to the point b as described above is different from the slice plane obtained by a normal scan as shown in FIG. As shown in FIG. 7, the slice planes do not match at the rotation angles of 0 ° and 360 °, and reconstructing an image using these data as they are often causes significant artifacts. For this reason, it has been considered that, for example, data for 360 degrees at the same slice position is obtained by interpolation as described below, and artifacts resulting from data inconsistency due to slice plane displacement are reduced.

[0004] For example, as shown in FIG.
In 03, when creating the interpolating C data points of a given rotational phase of predetermined slice position data d _B data d _A and point B to point A in the same rotational phase as it across the point C To perform interpolation processing. That is, when performing primary interpolation, the distance d between point A and point C and the distance m between point B and point C are used as weighting factors, and the data d of point C is calculated by the following equation.
Create _C.

[0005]

D _C = m × d _A / (l + m) + l × d _B / (l + m) By such interpolation, data corresponding to 360 degrees of an arbitrary slice plane can be obtained, and the artifact of the slice image can be reduced. Can be.

When an image is reconstructed from 360-degree data as shown in FIG. 8, the center E of the 360-degree main data area D is set as the slice center position of these data. In order to obtain a slice image at the position, 180 degrees (1
/ 2 main areas). That is, it is necessary to collect data for at least 180 degrees before and after a desired slice position where a slice image is desired to be obtained. When performing the above-described interpolation, as shown in FIG. 8, it is necessary to collect data in a range in which interpolation areas F and G for obtaining interpolation data are added to both ends of the area D. There is.

[0007] Therefore, when the operator places the subject P, the operator determines a photographing region for which an image is desired to be obtained with respect to the subject P, and then sets the photographing region in the 1/2 main region. Or the object P and the table 10 so that scanning and data collection are performed on a range to which the interpolation area is added.
0 is positioned and set, and a scan area is set. Alternatively, the subject P and the table top are scanned such that a scan is performed in a range in which the table top approaching when the table top 100 starts to move further and the deceleration moving amount when the table top 100 stops are added to the above range. The positioning, installation, and setting of the scan area of the 100 are performed. As a result, the top 1
Since 00 moves at substantially the same speed, more accurate data can be obtained.

[0008]

However, in the case of the above-mentioned prior art, the operator has to carry out the operation for the half main area,
Judging the interpolation area, the top board approaching part and the deceleration movement part,
Since the positioning of the subject P and the top 100 and the setting of the scan area are performed, the operation is complicated, and there is a problem that the positioning of the subject P and the top 100 and the accuracy of the scan area are poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to accurately and simply carry out a half main area, an interpolation area, and a simple operation.
It is an object of the present invention to provide an X-ray CT apparatus capable of scanning a required area including a top board approaching part, a deceleration moving part, and the like.

[0010]

In order to achieve the above object, according to the present invention, a top plate on which a subject is placed is moved in the body axis direction of the subject, and the table is rotated around the subject. In an X-ray CT apparatus that performs a helical scan on the subject by using an X-ray source and reconstructs a tomographic image based on data obtained by the scan, the imaging regions of the subject are adjacent to each other. Divided into different areas
When performing multiple helical scans by using
After the end of the scan for the first area of
Scanning a second area adjacent to the first area
Before performing the step, the tabletop control means for moving the tabletop in the direction opposite to the scanning direction by the interpolation area or further by the tabletop approach amount, and at least overlap the data by the interpolation area Is collected.

According to the above configuration, when the helical scan is performed a plurality of times, the first scan is completed after the first scan is completed.
Before performing the second scan in the same direction as the scan, the top control unit moves the top in the direction opposite to the scan direction by the interpolation area or further by the top approach, and only by the interpolation area. By performing the data collection in an overlapped manner, the extra scan is reliably performed by the interpolation area at the joint between the scans, and the interpolation data is obtained. Therefore, the interpolation can be performed without trouble even at the joint portion of each scan, and the occurrence of artifacts can be prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described below with reference to the drawings. FIG. 1 shows an X-ray C according to the present invention.
It is a block diagram which shows the structure of an example of T apparatus roughly.
In FIG. 1, an X-ray CT apparatus 1 is provided with a scanner unit 2 that scans a subject P. The scanner unit 2 places the subject P thereon, and moves the subject P in the body axis direction (arrow a). , B direction), an X-ray tube 4 for irradiating the subject P with X-rays, and a detector 5 for detecting X-rays transmitted through the subject P. I have. The top 3 is driven by a top driving circuit 6, and the top driving circuit 6 is controlled by a top control unit 7. Thus, the top 3 moves in a predetermined direction by a predetermined distance.

When imaging the subject P, the top 3 on which the subject P is mounted is moved in the body axis direction of the subject P,
By rotating the X-ray tube 4 and the detector 5 around the body axis of the subject P, a helical scan is performed such that the relative trajectory of the X-ray tube 4 with respect to the subject P draws a spiral shape. Detector 5
Is output to an image reconstructing unit 9 via a data collection circuit 8, and the image reconstructing unit 9 reconstructs an image based on the data, and then outputs a video having the reconstructed image as a content. The signal is sent to a display means 10 such as a CRT display, and a slice image (tomographic image) of the subject P is displayed on the display means 10.
Are displayed. The data collection circuit 8 is controlled by the data collection control means 11 so that the data collection circuit 8 collects only data obtained from a predetermined range of the subject P.

When scanning the subject P,
First, the operator sets an imaging region in which an image is desired to be obtained for the subject P, and places the subject P on the top 3 so that the end of the set imaging region on the scan start side is the scan start position. I do. Further, the information of the set photographing area is input to the input unit 12.
Enter by. In response, the top control unit 7 and the data collection control unit 11 move the top 3 via the top driving circuit 6 and the data collection circuit 8, respectively, as described later.
Control the scope of data collection.

The control of the movement of the top 3 will be described.
Before the start of the scan, as shown in FIG. 2, an imaging region J is set for the subject P, and when the end K of the imaging region J is arranged at the scan start position, the scan start side end In K, a 1/2 main area for obtaining data for 180 degrees and an interpolation area for obtaining interpolation data (180
The top 3 is moved such that the position N obtained by adding the sum area L of the degrees and the top M for starting the movement of the top 3 to the scan start position.

At the time of scanning, the area R of the sum of the 主 main area and the interpolation area, similar to the area L, and the tabletop 3 are stopped at the scan end side Q of the imaging area J. The top board 3 is moved so that scanning is performed up to the position T to which the deceleration movement S is added. That is, before the start of the scan, the top 3 moves in the direction opposite to the scan direction by an amount corresponding to the addition of the areas L and M. At the time of scanning, the top 3 moves the distance from the position N to the position T in the scan direction. Go to

On the other hand, the data is collected so that the data is collected in a range obtained by adding the above-mentioned regions L and R to the photographing region J, that is, at the time of scanning from the position U to the position W in FIG. The data collection control means 11 controls the data collection circuit 8 so that only the collected data is collected.
Control. The collected data of the imaging region J, the １ ／ main region, and the interpolation region are sent to the image reconstructing unit 9,
After the interpolation processing as described in the conventional example is performed, a slice image at a desired slice position is reconstructed.

As described above, in this embodiment, the system automatically sets the moving area and the data collection area of the top 3 only by setting and instructing the photographing area J by the operator. By operation, the scanning is performed with high accuracy and in a necessary area by adding the 領域 main area, the interpolation area, the top board approaching part, and the deceleration movement part to the photographing area J. Data can be collected from a range only. Therefore, the burden on the operator is reduced, and data necessary for slice image creation and interpolation processing can be obtained by an easy operation.
It is possible to prevent the setting of the photographing area from being erroneous and, consequently, from photographing the wrong area.

In the above embodiment, when the set photographing area J is large and it is necessary to perform a plurality of helical scans, as shown in FIG. The top 3 is moved in the direction opposite to the scanning direction by an area Y obtained by adding a / 2 main area (180 degrees), a correction area for obtaining correction data, and a top board approaching area, The next scan may be started from the position Z. Here, the correction is a data correction for reducing data inconsistency caused by a displacement of a slice position on the subject P due to body movement. In this case, in the area Y, data is collected so as to overlap with the previous scan area by the half main area and the correction area. This ensures that extra scanning is performed at the seam between scans by the interpolation area, the correction area, and the top board advance, and the interpolation data and correction data necessary for interpolation and correction are obtained. Therefore, interpolation can be performed without any trouble at the seam of the scan, and correction can be performed to reduce data inconsistency due to body motion, thereby reducing the occurrence of artifacts. In addition, the main region may be overlapped by a preset amount in consideration of the movement of the target portion due to respiratory movement or the like.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made. For example, in the above-described embodiment, an example is given in which scanning is performed on an area obtained by adding all of the shooting area to the 主 main area, the interpolation area, the top board approaching area, and the deceleration movement area. The scanning may be performed on an area to which only the 主 main area is added or an area to which an interpolation area is further added. In these cases, the scan area and the data collection area match.

In the above embodiment, the third generation X
In the present invention, the fourth generation X-ray C
It is also applicable to T devices. Further, in an X-ray CT apparatus that performs a half scan, the present invention can be applied to a case where data of one rotation is obtained by scanning 180 degrees + fan angle.

[0022]

The X-ray CT apparatus according to the present invention has the above-described configuration and operation. The operator can set an imaging region in which an image is desired to be obtained by simply setting an imaging region to obtain an image. Scanning can be performed on a necessary area including the board approach and deceleration movement, and accurate data can be collected from only the necessary range. Therefore, the operation is easy,
The burden on the operator is reduced, and data necessary for slice image creation and interpolation processing can be reliably obtained by an easy operation, so that an erroneous setting of an imaging area, and furthermore, imaging of an incorrect area can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a configuration of an X-ray CT apparatus according to an example of the present invention.

FIG. 2 is an explanatory diagram showing a scan area in the example shown in FIG.

FIG. 3 is an explanatory diagram showing a scan area in the example shown in FIG. 1;

FIG. 4 is a diagram showing a part of a conventional X-ray CT apparatus.

FIG. 5 is a diagram showing a relative trajectory of an X-ray tube with respect to a subject in a conventional example.

FIG. 6 is a diagram showing a slice plane obtained by an X-ray CT apparatus.

FIG. 7 is an explanatory diagram for explaining an interpolation process in a helical scan.

FIG. 8 is an explanatory diagram for explaining an interpolation process in a helical scan.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 2 Scanner part 3 Bed top 4 X-ray tube 5 Detector 6 Top drive circuit 7 Top control means 8 Data acquisition circuit 9 Image reconstruction part 10 Display means J Imaging area L, R 1/2 The area of the sum of the main area and the interpolation area M Top board approach S S Deceleration P

Claims (1)

(57) [Claims] 1. A top plate on which a subject is placed is moved in the body axis direction of the subject, and a spiral scan is performed on the subject by an X-ray source rotating around the subject. In an X-ray CT apparatus that reconstructs a tomographic image based on data obtained by this scan, an imaging region of a subject is divided into a plurality of different regions adjacent to each other.
When performing multiple helical scans by splitting
After the end of the scan for the first of the regions
The second region adjacent to the first region.
Before performing the scan, the table control means for moving the table by the interpolation area, or further, by the approach of the table in the direction opposite to the scanning direction, so that the table overlaps at least by the interpolation area. An X-ray CT apparatus characterized in that data is collected by using an X-ray CT apparatus.