JPH0910203A - X-ray tomography method and x-ray tomography apparatus - Google Patents

Abstract

PURPOSE: To generate high quality images in helical scanning by matching the helical rotation track of one of X-ray detection columns with the other column, adding detected results on the helical rotation track in the matched X-ray detection columns and forming the tomographic images of a testee body. CONSTITUTION: When data addition in the helical scanning is instructed from an operation part, a table moving distance in one rotation is set so as to be equal to slice thickness. Then, detection data are sampled by X-ray detectors 31 and 32, and since the timings of obtaining the detection data at matched positions are shifted for one rotation even though the rotation tracks match for the detection data from the X-ray detectors 31 and 32, one of the detection data is delayed and the timings of the detection data are matched in timing adjustment parts 10c and 10d. The detection data are addition-processed in an addition processing part 10e inside an image reconstitution device 10 and a reconstitution processing part 10f generates image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray tomography method and an X-ray tomography method.
More particularly, the present invention relates to an X-ray tomography method and an X-ray tomography apparatus capable of obtaining a high-quality image.

[0002]

2. Description of the Related Art In an X-ray tomography apparatus, a subject is irradiated with a fan-shaped X-ray beam from an X-ray source, and a plurality of X-rays transmitted through the subject are arranged in accordance with the spread of the fan-shaped X-ray beam. X of a one-dimensional array (detection element)
Measure with a line detection train.

The transmitted X-rays are measured in a plurality of view directions while rotating the X-ray source and the X-ray detection array around the subject. Such measurement of transmitted X-rays is called scan. Then, based on the measurement data of multiple views obtained by the scan,
A tomographic image of the subject is reconstructed.

By the way, the noise contained in the tomographic image obtained by scanning depends only on the X-ray dose (mA · S) if the reconstruction function and slice thickness are constant. That is, noise can be reduced by increasing the X-ray dose. For this purpose, the tube current (mA) should be increased or the scan time (S) should be lengthened.

In this case, the extension of the scan time leads to an increase in artifacts due to the movement of the subject. That is, an artifact occurs due to a contradiction of data due to the movement of the subject between the first angle data and the last angle data of one scan.

Therefore, extending the scan time lengthens the interval between the data acquisition timings and makes it easier for artifacts to occur. Therefore, a plurality of scans are executed at the same position in a short scan time, and the obtained data is added and averaged to realize noise reduction. For example, when data of the same SN ratio is added at a ratio of 1: 1, the noise component of the random phase becomes +3 dB, while the signal component of the same amplitude and the same phase becomes +6 dB. Therefore, the SN ratio can be improved.

[0007]

By the way, as one form of scanning, as described in, for example, Japanese Patent Publication No. 2-60332, scanning is performed a plurality of times while continuously moving the subject in the body axis direction. There is a so-called helical scan in which the above is continuously performed.

In the case of this helical scan, since the scan position is gradually changing, it is theoretically impossible to add the data of the same cross section. The present invention has been made in view of the above points, and an object thereof is to realize an X-ray tomography method and an X-ray tomography apparatus capable of generating a high-quality image in a helical scan.

[0009]

The inventor of the present application has conducted earnest research to improve the problem relating to image quality improvement in the conventional helical scan, and as a result, it is possible to perform noise reduction by adding scan data even in helical scan. The present invention has been completed by newly discovering a method for doing so.

That is, a first aspect of the present invention, which constitutes a means for solving the problems, irradiates a measurement space with X-rays, and transmits a plurality of X-rays that pass through an object placed in the measurement space and are incident. The X-ray detection row of the row detects the X-ray having a predetermined slice thickness while rotating the focal point of the X-ray around the subject at a constant moving speed smaller than the total thickness of the plurality of slice thicknesses in the body axis direction of the subject. By moving the spiral rotation orbit in at least one row of the plurality of X-ray detection rows to match the rotation trajectory of the other row, the detection result on the spiral rotation trajectory in the matched X-ray detection rows Is added to form a tomographic image of the subject, which is an X-ray tomography method.

A second invention constituting means for solving the problem is an X-ray irradiating means for irradiating the measurement space in which the subject is placed with X-rays, and an X-ray in the body axis direction of the subject. X-ray detection means having a plurality of X-ray detection rows and detecting X-rays that pass through a subject and are incident, and at least one of the plurality of X-ray detection rows has the same spiral shape as the other row. Rotation control means for rotating the X-ray focal point in a relatively spiral manner around the subject so that the X-ray focus passes through the same rotation trajectory, and a plurality of X-ray detection rows of the X-ray detection means pass through the same rotation trajectory. The X-ray tomography apparatus further comprises: a tomographic image forming unit that forms a tomographic image of the subject by adding the results detected by the X-ray detection array.

Further, in the third invention constituting the means for solving the problem, the X-ray detection means in the second invention described above is used from the viewpoint that image reconstruction for two kinds of data can be completed at once. Data of the X-ray detection signals detected by the X-ray detection row that passes through the same rotation trajectory in a plurality of X-ray detection rows at the same position are added, and then image reconstruction is performed to form a tomographic image of the subject. It is preferable to be a tomographic image forming means.

A fourth aspect of the present invention, which constitutes a means for solving the problems, is the same as the second aspect of the present invention described above, from the viewpoint of facilitating addition processing. Image reconstruction is performed on each of the data at the same position of the X-ray detection signal detected by the X-ray detection train that passes through the same rotation trajectory in the detection train, and the respective image reconstruction results are added to obtain a tomographic image of the subject. It is preferable that the tomographic image forming means forms a tomographic image.

[0014]

In the first aspect of the invention, the measurement space is irradiated with X-rays, and the X-rays that pass through the subject placed in the measurement space and are incident are detected by a plurality of X-ray detection arrays. At this time, the X-ray focal point of a predetermined slice thickness is moved around the subject at a constant moving speed smaller than the total thickness of the plurality of slice thicknesses in the body axis direction of the subject to rotate in a plurality of rows. It is performed while making the spiral rotation trajectory in at least one row of the X-ray detection row match the rotation trajectory in another row. Then, the detection results on the spiral rotation trajectory in the matched X-ray detection rows are added to form a tomographic image of the subject. As a result,
By adding the detection results on the same trajectory, it is possible to generate a high-quality image in the helical scan.

In the second aspect of the invention, the X-ray focal point is relatively moved around the subject so that at least one of the plurality of X-ray detection rows passes through the same spiral orbit as the other row. And the results detected by the X-ray detection rows that pass through the same rotational trajectory in a plurality of X-ray detection rows are added together to form a tomographic image of the subject. As a result, it becomes possible to generate a high quality image in the helical scan by adding the detection results in the same trajectory.

In the third aspect of the invention, the image reconstruction is performed after the data at the same position of the X-ray detection signals detected by the X-ray detection trains passing through the same rotation orbit in a plurality of X-ray detection trains are added. A tomographic image of the subject is formed. As a result, it becomes possible to generate a high quality image in the helical scan by adding the X-ray detection signals in the same trajectory. Further, the image reconstruction of the two types of data can be done only once.

According to the fourth aspect of the invention, image reconstruction is performed on each of the data at the same position of the X-ray detection signals detected by the X-ray detection trains passing through the same rotational orbit by a plurality of X-ray detection trains. The image reconstruction results are added to form a tomographic image of the subject. As a result, it becomes possible to generate a high quality image in the helical scan by adding the image reconstruction results in the same trajectory. Also, since the images (image data) generated by image reconstruction are added, a general-purpose addition process can be adopted, which is preferable in terms of circuit configuration.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a flowchart showing a processing procedure of a principle X-ray tomography method of the present invention, and FIG. 2 is a radiation (X-ray) CT scanner as an example of an X-ray tomography apparatus for realizing the X-ray tomography method of the present invention. It is a block diagram which shows the whole structure at the time of using. FIG. 3 is a configuration diagram showing a main part configuration around the gantry in FIG.

First, the overall structure when an X-ray CT scanner is used will be described with reference to FIGS. 2 and 3. The gantry 1 is a mechanical portion of the X-ray CT, and causes the X-ray tube 2 and the detector 3 to mechanically or electrically perform operations according to various scanning methods around the subject. The table 4 is fed into the gantry 1 with the subject 5 placed thereon. At this time, the tilt of the gantry 1 and the movement of the table 4 are controlled by the table / gantry controller 6. Further, the X-ray tube 2 is controlled by the control of the X-ray tube drive generation control device 7 to rotate / stop and generate / pause X-rays. The table / gantry control device 6 and a system control device, which will be described later, constitute rotation control means.

The detector 3 rotates around the subject 5 integrally with the X-ray tube 2 under the control of the detector driving device 8. X
The X-ray transmitted through the subject 5 by the irradiation of the ray tube 2 is detected by the detector 3
The data is collected by the data collection device 9.
The collected data is transferred to the image reconstruction device 10.
The image reconstruction device 10 reconstructs the image of the input data, displays the image data on the display device 11, and simultaneously stores the image data in the data storage device 12.

It should be noted that this detector 3 has X, as shown in FIG.
The line detectors 31 and 32 are composed of two X-ray detection lines. The data detected by the X-ray detectors 31 and 32 are collected by the DAS 9a and DAS 9b.

The image data stored in the data storage device 12 is read out to form a projection image described below in the X-ray tomography device 13, and the projection image is displayed on the display device 11.

Here, the image reconstructing apparatus 10, which is a characteristic part of the present invention, has a data addition function, as will be described later. The operation unit 14 is an input means for inputting various instructions, and the system control unit 15 controls the entire apparatus according to various instructions from the operation unit 14 and a predetermined operation program.

In addition to the mechanical rotation of the X-ray tube 2 and the detector 3 as described above, it is also possible to electronically rotate the irradiation and the detection by using means provided in advance over the entire circumference. There is something to do. This embodiment will be described using a device that mechanically rotates.

Next, an X-ray tomography method performed by the above-mentioned X-ray tomography apparatus will be described with reference to the flowchart of FIG. [Initial setting] In this initial setting, there are a normal helical scan setting and a setting for performing data addition in the helical scan, which is a feature of this embodiment.

In the case of a normal helical scan, in the above-mentioned apparatus equipped with two rows of X-ray detectors, the table moving distance in one rotation is twice the slice thickness, as shown by the spiral rotation trajectory in FIG. I am trying to become. The arrow shown above the spiral rotation track in FIG. 4 indicates the movement distance of the table in one rotation.

By doing so, there is an advantage that scanning can be performed at high speed. In the present embodiment, when there is an instruction to add data in the helical scan from the operation unit 14, the table moving distance (table interval) in one rotation is set even when the X-ray detectors of two rows are provided. It is set to be equal to the slice thickness (step 1 in FIG. 1).

When the helical scan is performed with the gantry tilted, the slice thickness of the X-ray detector in the tilted state and the table movement distance per rotation are set to be equal.

Further, the system control unit 15 includes an operating unit 14
A scan plan is prepared based on the values input from and various parameters are determined. [Scan execution] A scan is executed based on the parameters set by the initial setting (step 2 in FIG. 1). In the above-mentioned initial setting, since the table moving distance (table interval) in one rotation is set to be equal to the slice thickness, as shown in the schematic diagram of FIG.
In the rotation trajectories of the X-ray detectors of the rows, the rotation trajectories of the respective rows are completely overlapped.

[Separation and collection of image data] Detector 31
And 32, the detection data are collected (steps 3 and 4 in FIG. 1), and sensitivity correction and various processes according to the characteristics of each detector are executed as preprocessing (step 4 in FIG. 1). This preprocessing is performed by the preprocessing units 10a and 10b inside the image reconstructing apparatus 10, respectively.

[Timing Adjustment] As shown in FIG.
The detection data from the X-ray detectors 31 and 32 have the same rotational trajectory. However, since the timing at which the detection data at the coincident position can be obtained is deviated by one rotation, the timing adjustment units 10c and 10d delay at least one of the detection data to make the timings of the detection data coincide (step 6 in FIG. 1). ).

[Data addition] The detection data at the same position is subjected to addition processing by the addition processing unit 10e in the image reconstructing apparatus 10 by timing adjustment (step 7 in FIG. 1). By such addition processing, noise reduction is executed and the SN ratio of the detected data is improved.

[Image Reconstruction] The reconstruction processing unit 10f in the image reconstruction apparatus 10 executes image reconstruction on the detection data collected and subjected to the addition processing after the timing adjustment to generate image data ( 1 step 8).

Since it is the detection data obtained by the helical scan, it is possible to generate any number of image data at any angle. [Display and Storage] If necessary, the image data generated by the image reconstruction is displayed on the display device 11 and stored in the data storage device 12 (step 9 in FIG. 1).

By performing the above steps, in the X-ray tomography apparatus having the two rows of X-ray detectors 31 and 32, even when the helical scan is executed, a high quality image is obtained by the addition processing. It will be possible to obtain. Further, since the image reconstruction is executed after adding the detection data, the image reconstruction can be performed once for the two types of detection data, so that the processing time and the processing circuit are not complicated.

In the above description, the X-ray detectors 3 in two rows are used.
Although the rotation trajectories of 1 and 32 are made to coincide with each other, for example, even in an apparatus having three or more rows of X-ray detectors, high quality images are similarly obtained by addition and image reconstruction. be able to.

FIG. 6 is an explanatory view schematically showing the degree of overlap of the rotational trajectories in the above description. One of the two rows of X-ray detectors is the rotational trajectory of the other detector in the forward and backward rotation. Regarding coincidence, overlapping portions are indicated by hatching in the same direction.

Here, FIG. 7 shows the case where three rows of X-ray detectors are used, and when the respective X-ray detectors are considered to rotate forward and backward, the rotation trajectories coincide with each other.
In this case, it can be realized by setting the table movement distance (table interval) in one rotation to be equal to the slice thickness. By doing so, it becomes possible to obtain a higher quality image.

In the case of FIG. 6, the data addition cannot be performed because the overlap does not occur at each one of the rotation start and the rotation end. Therefore, the detection data of this part is discarded.

Further, in the case of FIG. 7, sufficient overlap cannot be obtained by each two rotations of rotation start and rotation end. Therefore, the detection data of this part is discarded. FIG. 8 is a flowchart showing another example of the processing procedure of the X-ray tomography method, which corresponds to FIG. Further, FIG. 9 is a configuration diagram showing a configuration of an apparatus for executing the procedure of FIG.
This corresponds to FIG.

In the case of the processing procedure of FIG. 1, the timing is adjusted at the stage of the detected data collected and subjected to the pre-processing, the data addition processing is executed, and then the image reconstruction processing is executed. In the processing procedure shown in FIG. 8, the image reconstruction processing is executed by the reconstruction processing units 10g and 10h for each detected data (step 7 in FIG. 8), and the respective image data obtained by the reconstruction is added. The addition processing is performed by the unit 10i (step 8 in FIG. 8).

Also by doing so, a high quality image with an improved SN ratio can be obtained. In this case, timing adjustment (step 6 in FIG. 8) is data addition (step 8 in FIG. 8).
Before the image reconstruction, it may be before or after the image reconstruction.

With this processing procedure, the data addition (step 8 in FIG. 8) of the addition processing unit 10i can be executed at the image data stage. Therefore, a general-purpose image processing program or processing circuit should be used. This has the advantage that the structure of the device can be simplified.

As described above in detail with reference to the embodiments, the measurement space is irradiated with X-rays, and the X-rays transmitted through the subject placed in the measurement space and incident on the measurement space are arranged in a plurality of X-ray detection arrays. The focal point of the X-ray having a predetermined slice thickness is rotated around the subject at a constant moving speed smaller than the total thickness of the plurality of slice thicknesses in the body axis direction of the subject, and the plurality of rows are detected. Of the X-ray detection row of at least one of the X-ray detection rows and the spiral rotation trajectory of the other row,
According to the X-ray tomography method, which is characterized in that the detection results on the spiral rotation trajectory in the coincident X-ray detection rows are added to form a tomographic image of the subject, a high-quality image in helical scanning is obtained. Can be generated.

The X-ray tube 2 for irradiating the measurement space in which the subject is placed with X-rays and the plurality of X-ray detection lines in the body axis direction of the subject are transmitted through the subject and are incident. X-ray detector 3 for detecting the X-rays to be detected, and the X-ray focus is focused so that at least one of the plurality of X-ray detection rows passes through the same spiral orbit as the other one. The results detected by the rotation control means 6 and 15 that relatively spirally rotate around the sample and the X-ray detection array that passes through the same rotation trajectory by the plurality of X-ray detection arrays of the X-ray detector are added. According to the X-ray tomography apparatus characterized by including the image reconstruction apparatus 10 that forms a tomographic image of the subject, it is possible to generate a high-quality image in the helical scan.

Further, the addition processing unit 10e adds the data at the same position of the X-ray detection signal detected by the X-ray detection train passing through the same rotation trajectory in the plurality of X-ray detection trains of the X-ray detector.
Also, an X-ray tomography apparatus characterized by including an image reconstruction apparatus 10 for performing image reconstruction by the reconstruction processing unit 10f to form a tomographic image of a subject,
It is possible to generate a high quality image in the helical scan. In this case, since the image reconstruction is performed after the addition, the image reconstruction processing for two types of detection data only has to be performed once, and the processing content and circuit configuration do not become complicated.

Then, the X detected by the X-ray detection array passing through the same rotation orbit in the plurality of X-ray detection arrays of the X-ray detector.
Image reconstruction is performed by the reconstruction processing units 10g and 10h for each of the data at the same position of the line detection signal,
An X-ray tomography apparatus including: an image reconstruction apparatus 10 that forms a tomographic image of a subject by adding the respective image reconstruction results in an addition processing unit 10i.
It is possible to generate a high quality image in the helical scan. In this case, since each image is reconstructed to generate image data and then the addition is performed, a general-purpose processing program or processing circuit can be used as the addition processing.

[0048]

As described in detail above, in the X-ray tomography method, the measurement space is irradiated with X-rays and a plurality of rows of X-rays are transmitted through the subject placed in the measurement space and are incident. Detected by the X-ray detection column of X, and while moving the focus of X-rays of a predetermined slice thickness around the subject, moves in the body axis direction of the subject at a constant moving speed smaller than the total thickness of the plurality of slice thicknesses. Then, the spiral rotation orbit in at least one row of the plurality of X-ray detection rows is performed while matching it with the rotation trajectory of the other row, and the detection on the spiral rotation orbit in the matched X-ray detection row is performed. According to the first invention in which the results are added to form a tomographic image of the subject, it is possible to generate a high-quality image with an improved SN ratio in the helical scan by adding the detection results in the same trajectory. .

Further, in the X-ray tomography apparatus, the X-ray focus is set on the subject so that at least one row of the plurality of X-ray detection rows passes through the same spiral orbit as the other rows. A second aspect of the present invention in which a tomographic image of a subject is formed by rotating the surroundings in a relatively spiral shape and adding the results detected by the X-ray detection rows that pass through the same rotational orbit by a plurality of X-ray detection rows. According to this, it becomes possible to generate a high-quality image with an improved SN ratio in the helical scan by adding the detection results in the same trajectory.

Further, after the data at the same position of the X-ray detection signals detected by the X-ray detection trains that pass through the same rotational trajectory in a plurality of X-ray detection trains are added, image reconstruction is performed to obtain a tomographic image of the subject. According to the third aspect of the invention, it is possible to generate a high-quality image in which the SN ratio is improved in the helical scan by adding the X-ray detection signals in the same trajectory. Then, in this case, the image reconstruction need only be performed once for the two types of detection data, and therefore the processing and circuit configuration do not become complicated.

Then, image reconstruction is carried out for each of the data at the same position of the X-ray detection signals detected by the X-ray detection trains that pass through the same rotation trajectory in the plurality of X-ray detection trains, and the respective image reconstruction results are obtained. According to the fourth invention in which the tomographic image of the subject is formed by adding the image reconstruction results (image data) in the same trajectory, a high-quality image in which the SN ratio is improved in the helical scan is generated. It will be possible. Then, in this case, since the addition may be performed on the normal image data, the addition processing becomes easy.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing example of an X-ray tomography method according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram showing a configuration of an X-ray CT using the X-ray tomography apparatus according to an embodiment of the present invention.

FIG. 3 is a configuration block diagram showing a configuration of a main part of an X-ray CT using the X-ray tomography apparatus according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a general rotational orbit of a helical scan.

FIG. 5 is an explanatory diagram showing a state of a rotation trajectory of a helical scan according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram that schematically shows a basic example of the degree of overlap of rotational trajectories.

FIG. 7 is an explanatory diagram schematically showing another example of the overlapping degree of the rotation tracks.

FIG. 8 is a flowchart showing a processing example of an X-ray tomography method according to another embodiment of the present invention.

FIG. 9 is a configuration block diagram showing a configuration of a main part of an X-ray CT using an X-ray tomography apparatus according to another embodiment of the present invention.

[Explanation of symbols]

 1 gantry 2 X-ray tube 3 detector 4 table 5 subject 6 table / gantry controller 7 X-ray tube drive generation controller 8 detector driver 9 data collection device 10 image reconstruction device 11 display device 12 data storage device 13 X-ray tomography apparatus 14 Operation unit

Claims (4)

[Claims] 1. An X-ray irradiating a measurement space, and X-rays which pass through a subject placed in the measurement space and are incident thereon are detected by a plurality of X-ray detection lines, and an X-ray having a predetermined slice thickness is detected. At least one of the plurality of X-ray detection columns is moved by rotating the line focus around the subject at a constant moving speed in the body axis direction of the subject that is smaller than the total thickness of the plurality of slices. The spiral rotation orbit in is matched with the rotation trajectory in another row, and the detection results on the spiral rotation trajectory in the matched X-ray detection row are added to form a tomographic image of the subject. X-ray tomography method. 2. An X-ray irradiating means for irradiating a measurement space in which a subject is placed with X-rays, and a plurality of X-ray detection rows in the body axis direction of the subject, which are transmitted through the subject to be incident. X-ray detecting means for detecting X-rays, and the X-ray focal point so that at least one of the plurality of X-ray detecting rows passes through the same spiral rotation trajectory as the other row. The object detected by adding the results detected by the rotation control means for relatively spirally rotating around the object and the X-ray detection array passing through the same rotational trajectory by the plurality of X-ray detection arrays of the X-ray detection means. An X-ray tomography apparatus comprising: a tomographic image forming unit that forms a tomographic image of the. 3. The tomographic image forming means adds the data at the same position of the X-ray detection signals detected by the X-ray detection rows passing through the same rotation trajectory in the plurality of X-ray detection rows of the X-ray detection means. The X-ray tomography apparatus according to claim 2, wherein the image reconstruction is performed after that, and a tomographic image of the subject is formed. 4. The tomographic image forming means includes a plurality of X-ray detection rows of the X-ray detection means, each of which has X-ray detection signals detected by an X-ray detection row passing through the same rotational orbit at the same position. The X-ray tomography apparatus according to claim 2, wherein the image reconstruction is performed in step S3, and the respective image reconstruction results are added to form a tomographic image of the subject.