JP2002102218A - X-ray ct system, operation console, controlling method therefor, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT system capable of reconstituting an X-ray tomographic image of high image quality while securing an advantage of high speed photographing that a helical scan has, by adaptively changing the helical pitch according to a scan position when a series of helical scans are performed in a set scan section. SOLUTION: A processing for imaging two kinds of subject fluoroscopic images is performed (step S1), and a correspondence relation of a scan position and calculated tube current is set based on the subject fluoroscopic images (step S2). The state of fluctuation of a calculated tube current value for adjacent scan positions is measured and a correspondence relation of the scan positions and helical pitch is set by a prescribed threshold decision (step S3). In accordance with the correspondence relation with the set helical pitch, a helical scan is executed while automatically controlling helical pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT (Computerizon) for reconstructing an X-ray tomographic image of a subject by X-ray irradiation.
ed Tomograpy) systems and operation consoles, their control methods and storage media.

[0002]

2. Description of the Related Art In general, an X-ray CT system irradiates an X-ray fan beam from an X-ray tube, which is an X-ray source, to a subject after collimating it at a predetermined irradiation angle (for example, 60 degrees). The collection of projection data obtained by detecting the transmitted X-rays by an X-ray detector having a plurality of (for example, 1000) detection channels over a length depending on the irradiation angle of the X-rays is referred to as an X-ray tube. The X-ray detection unit performs (scans) at a plurality of (for example, 1000) projection angles while rotating around the subject, and reconstructs an X-ray tomographic image based on the projection data at each projection angle.

At present, as a scanning method, the subject is moved in the body axis direction (also referred to as the z-axis direction) in synchronization with the change in the projection angle (that is, the X-ray tube and the X-ray detection unit are moved). A helical scan method that collects projection data (which spirals around the specimen) is known to realize high-speed imaging.

In the case of helical scan, since projection data is collected in a spiral shape, only projection data at a target slice position is collected at one projection angle. Therefore, prior to image reconstruction, it is necessary to interpolate the projection data in the z-axis direction.

By the way, X by the helical scan method
In the X-ray CT system, the slice thickness T at the center of rotation (determined by the width of the X-ray detector in the z-axis direction) and the transport amount S of the subject per scan (collecting 360-degree projection data) Is referred to as a helical pitch (hereinafter, simply referred to as a pitch), and this parameter is generally included in one of the scan condition setting items.
For example, when the slice thickness is 10 mm, and the transport amount of the subject per scan (that is, the transport speed) is 10 mm, the pitch is 10/10 = 1.

[0006] The setting of the pitch is related to the imaging time and the resolution of the obtained tomographic image in the z-axis direction. If the pitch is increased, the photographing time is shortened, but on the other hand, inconsistency is generated in the interpolation data, which causes an artifact. Conversely, if the pitch is reduced, the photographing time becomes longer, but the interpolation accuracy is improved and higher image quality of the reconstructed image can be expected. That is, the pitch is determined in a trade-off relationship between the image quality of the tomographic image required for the imaging target / purpose and the interpolation accuracy.

[0007]

By the way, in the chest, for example, the lungs occupy most of the lungs, so the amount of X-ray attenuation is small, whereas in the abdomen, the amount of X-ray attenuation is large because there are many organs. In addition, in a region where the lung occupies most, since the shape of each organ at each slice position does not change significantly, the variation of the X-ray attenuation at each slice position is also small. However, when moving toward the abdomen, the proportion occupied by the lungs decreases and the proportion occupied by another organ (such as the liver) increases. Therefore, in this region, it can be said that the organ shape at each slice position changes greatly, and the X-ray attenuation at each slice position varies greatly. High resolution in the z-axis direction will be required in a region where the X-ray attenuation amount varies greatly at each slice position, that is, in a region where the shape of each organ greatly changes at each slice position.

However, in the conventional X-ray CT system, only one kind of pitch can be set for a series of helical scans in a set scan section. Therefore, when the set scan section includes a portion where the X-ray attenuation does not relatively change and a portion where the X-ray attenuation greatly changes as described above, the X-ray attenuation greatly changes. The inconsistency of the interpolation grows where
There is a problem that a high resolution in the z-axis direction cannot be secured, and the image quality of the reconstructed image is deteriorated.

The present invention has been made in view of such a problem, and when performing a series of helical scans in a set scan section, a helical scan is adaptively changed in accordance with a scan position. It is an object of the present invention to provide an X-ray CT system and an operation console capable of reconstructing a high-quality X-ray tomographic image while securing the advantage of high-speed imaging, a control method thereof, and a storage medium.

[0010]

To achieve the above object, for example, an X-ray CT system according to the present invention has the following arrangement. That is, a helical scan is performed to collect projection data while moving the subject in the body axis direction in synchronization with a change in the projection angle when irradiating the subject with X-rays generated from the X-ray tube. An X-ray CT system for reconstructing a tomographic image of the subject based on the collected projection data, wherein a fluoroscopic image capturing unit captures a perspective image of the subject from a plurality of projection angles orthogonal to the body axis of the subject. Determining means for determining a control value of the transport speed at each scan position based on each of the subject fluoroscopic images captured by the fluoroscopic image capturing means; and the transport at each scan position determined by the determining means. Scan control means for performing a helical scan according to a speed control value.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Configuration) FIG. 1 is a block diagram of an X-ray CT system according to an embodiment. As shown in the figure, the system includes a gantry apparatus 100 in which an X-ray detection mechanism for integrally irradiating an X-ray to a subject and detecting X-rays transmitted through the subject is integrated, and various operations performed on the gantry apparatus 100. It is configured by an operation console 200 that performs settings and reconstructs and displays an X-ray tomographic image based on data output from the gantry device 100.

The gantry device 100 has the following configuration, including the main controller 1 that controls the entire system.

Reference numeral 2 denotes an interface for communicating with the operation console 200. Reference numeral 3 denotes a transport of a subject (patient) lying on the table 12 (in a direction perpendicular to the drawing, that is,
a gantry having a cavity for the
Inside, an X-ray tube 4 (controlled by an X-ray tube controller 5) as an X-ray source, a collimator 6 having a slit for defining an X-ray irradiation range, and an X-ray irradiation range of the collimator 6 Is provided with a motor 7a which is a motor for adjusting the slit width. The driving of the motor 7a is controlled by the collimator controller 7.

The gantry 3 has an X-ray detector 8 for detecting X-rays transmitted through the subject, and a data collector 9 for collecting projection data obtained from transmitted X-rays obtained by the X-ray detector 8. Also have. The X-ray detection unit 8 may use a multi-detector provided with a plurality of detector arrays that detect X-ray beams adjacent to each other in the transport direction of the subject, or a single-row detector array. It may use a single detector in the array.

The X-ray tube 4 and the collimator 6 and the X-ray detector 8 are provided at positions opposing each other with the hollow portion therebetween, that is, with the subject interposed therebetween, and the gantry is maintained in a state where the relationship is maintained. 3. This rotation is performed by a rotation motor 10 driven by a drive signal from a motor controller 11.
The table 12 on which the subject is placed is transported in the z-axis direction, and is driven by a table motor 13.

The main controller 1 analyzes various commands received via the interface 2 and, based on the analysis, the X-ray tube controller 5, the collimator controller 7, the motor controller 11, the table motor controller 14, and the data collection unit. Various control signals are output to the unit 9. The main controller 1 also performs a process of transmitting the projection data collected by the data collection unit 9 to the operation console 200 via the interface 2.

The operation console 200 is a so-called workstation, and as shown, a CPU 51 for controlling the entire apparatus, a boot program and a BIOS.
, And a RAM 53 functioning as a main storage device.

The HDD 54 is a hard disk drive in which an OS, a diagnostic program for giving various instructions to the gantry device 100 and reconstructing an X-ray tomographic image based on data received from the gantry device 100 are stored. Have been. The diagnostic program includes a scan control processing program described later. The VRAM 55 is a memory for expanding the image data to be displayed.
6 can be displayed. 57 and 58 are a keyboard and a mouse for performing various settings. An interface 59 communicates with the gantry device 100.

(Processing) The configuration of the X-ray CT system in the embodiment is generally as described above. Subsequently, an outline of the scan control processing in the X-ray CT system having such a configuration will be described with reference to the flowchart of FIG. The program corresponding to this flowchart is the operation console 2
00, which is stored in the RAM 53 after power-on and executed by the CPU 51.

First, in step S1, the subject is laid on the table 12, and then a scout scan is performed. Scout scan means that the X-ray tube 4 and the X-ray detector 8 are not rotated and fixed at a fixed projection angle, and the table 12 on which the subject is placed is gradually conveyed while continuously transporting the X-rays. One fluoroscopic image of the subject is obtained from the projection data thus obtained.

Here, as shown in FIG. 3, the X-ray tube 4 is positioned at a projection angle of 0 ° just above the subject (under the control of the motor controller 11), and a first scout scan is performed. Projection angle 9 at which tube 4 hits right beside subject
A second scout scan positioned at 0 degrees is performed and 2 scout scans are performed.
Obtain different types of fluoroscopic images of the subject.

Note that the scout scan condition setting and execution command are set on a setting screen 400 as shown in FIG. 4, for example.
(Displayed on the CRT 56 of the operation console 200). As shown in the figure, in a scout scan setting field, a start position and an end position of a scout scan with respect to a predetermined reference position, a tube voltage and a tube current applied to the X-ray tube 4, and a projection angle can be set. In order to obtain the above two types of subject fluoroscopic images,
After inputting the projection angle “0” in the scout scan setting field, the user presses a start button 402 for executing a scout scan to execute the first scout scan. continue,
Similarly, after inputting the projection angle “90” in the scout scan setting field, the user presses the start button 402 to execute the second scout scan. Of course, conversely, the second scout scan may be performed first, or a mode for automatically and continuously performing the first and second scout scans may be provided.

As a result, as shown in FIG.
The upper fluoroscopic image of the subject can be obtained.

By the way, as described above, for example, in the chest, the lung occupies a large part, so that the amount of X-ray attenuation is small, whereas in the abdomen, there are many organs, so that the amount of X-ray attenuation is large. In addition, the physiques of the subjects also differ from one another.

When a scan is performed, the S / N ratio of the projection data at a portion having a large X-ray attenuation may be lower than that at a portion having a small X-ray attenuation. To cope with this, if the scan is performed with a large X-ray dose, a good S / N ratio can be obtained irrespective of the site, but it should be avoided because the radiation is more than necessary.

To solve such a problem, X
A so-called Auto mA that automatically controls a tube current value applied to the X-ray tube 4 for determining a dose according to a scan position of a subject.
The technique is known. By using this technique, it is possible to set an appropriate X-ray dose according to the part of the subject having a different amount of X-ray attenuation, and to suppress unnecessary exposure and obtain a favorable S /
A tomographic image having N can be obtained.

In the embodiment, the Auto mA technology is used. Therefore, the CPU 21 calculates Auto mA in step S2. Specifically, step S1
The body width and body thickness information at each scan position of the subject are obtained using the two types of projection data obtained in the above. In general, the cross section of the subject is not circular, but rather close to an ellipse. Accordingly, noise is calculated by calculating the ellipticity at each slice position based on the above body width / body thickness information and calculating the cross-sectional area of the slice plane at each slice position based on the amount of X-ray attenuation. The tube current for each slice position is calculated so as to be within a predetermined range. FIG. 6 is a graph showing an example of the correspondence between the scan position and the calculated tube current. The correspondence between the scan position and the calculated tube current shown in this graph is
It is created in the RAM 53 as an Auto mA table 53a.

The configuration of the Auto mA table 53a is as shown in FIG. 7, and describes a combination of a scan position (unit: mm) with respect to a predetermined reference position and a tube current value (unit: mA) at the scan position. Have been.

When the Auto mA table 53a is created in this way, the process proceeds to step S3.

In step S3, first, by referring to the Auto mA table 53a obtained in step S2, the X-ray of the part at each scan position is determined based on the fluctuation of the calculated tube current value when the scan position is moved. Estimate the variation of the attenuation.

As is clear from the above description, a relatively large tube current value is calculated by the Auto mA at the scan position where the X-ray attenuation is large, and a relatively small tube current value is calculated at the scan position where the X-ray attenuation is small. Is calculated.

Therefore, if the calculated tube current value fluctuates greatly between adjacent scan positions, the scan position becomes X
It can be guessed that this is a site where the variation of the linear attenuation is large, that is, a site where the shape of each organ at each slice position changes greatly. In such a portion, a high resolution in the z-axis direction will be required, so that the pitch is set to be small.

Conversely, if the fluctuation of the calculated tube current value is small at adjacent scan positions, the scan position is a site where the fluctuation of the X-ray attenuation is small, that is, the shape of each organ at each slice position is largely changed. It can be guessed that there is no such part. In such a part, a high resolution in the z-axis direction will not be required, so that it is possible to shorten the photographing time by setting a large pitch.

In the embodiment, the variance σ of the calculated tube current value with respect to the adjacent scan position is obtained in order to estimate the variation of the X-ray attenuation of the site at each scan position. FIG. 8A shows an example of the variance σ of the calculated tube current value with respect to the adjacent scan position calculated from the relationship between the scan position and the calculated tube current value (the relationship obtained in step S1) as shown in FIG. (B).

Then, a threshold value th for the variance σ is set (see FIG. 4B), and a threshold value determination is performed for each scan position. At a scan position having a variance equal to or larger than the threshold th, the pitch is set to a predetermined small value (for example,
5), and the pitch is set to a predetermined large value (for example, 4.0) at a scan position having a variance less than the threshold value. FIG. 3C is a graph showing the result of the threshold value determination. The correspondence between the scan position and the pitch shown in this graph is obtained as RA table as the pitch table 53b.
Created in M53.

The configuration of the pitch table 53b is as shown in FIG. 9, in which a scan position (unit: mm) with respect to a predetermined reference position and a combination of pitches at the scan position are described.

When the pitch table 53b is created in this way, the process proceeds to step S4, where a scan plan is made. This scan plan is generally performed by inputting items such as a scan start position, an end position, and a slice thickness on a scan plan screen displayed on the CRT 56. The set scan conditions are created and stored in the RAM 53 as a scan condition setting file 53c.

After the above processing, scanning is performed according to the Auto mA table 53a, the pitch table 53b, and the scanning conditions stored in the RAM 53.

In step S5, it is determined whether or not a scan start instruction has been issued based on the input from the keyboard 57 or the mouse 58.

When a scan start instruction is given, the process proceeds to step S6, in which the table motor 13 is driven to transport the table 12 on which the subject lies, to the initial scan position based on the set scan start position.

Then, the process proceeds to a step S7 to execute a scan. Specifically, it is as follows.

First, the calculated tube current value and the pitch corresponding to the initial scan position are read from the Auto mA table 53a and the pitch table 53b, respectively. The pitch is converted into a transport amount of the table 12 per scan corresponding to the transport speed of the subject by multiplying the slice thickness T at the rotation center of the gantry 3. Then, a scan start command is transmitted to the gantry device 100 using necessary information in the set scan conditions, including the calculated tube current value and the transport amount, as parameters.

The main controller 1 of the gantry apparatus 100 starts the scanning operation in response to this command. In this case, in particular, the main controller 1 sends the calculated tube current value received as a parameter to the X-ray tube 4 so that Scanning is performed after controlling the tube controller 5 and controlling the table motor controller 13 so that the table 12 is transported at a transport speed that realizes the received transport amount.

When one scan is completed, in step S8,
The scan is repeated until it is determined that the end of the scan section has been reached. At this time, the main controller 1
While sequentially reading the calculated tube current value and the pitch corresponding to the subsequent scan position from the Auto mA table 53a and the pitch table 53b in the M53, the scan is performed while controlling the X-ray tube controller 5 and the table motor controller 13 accordingly. Will continue.

In step S7 described above,
Since the projection data collected by the data collection unit 9 by scanning is transferred to the operation console 200, the CP
U51 performs image reconstruction processing to create a tomographic image, and C51
Display on RT56.

As described above, in the case of the helical scan, the projection data at the target slice position is collected only at one projection angle. It is necessary to interpolate in the direction. As an interpolation method, basically, a known technique such as a 360-degree interpolation method and a counter beam interpolation method can be used. However, in the interpolation calculation in the embodiment, the pitch is handled as a pitch P (z) using the scan position z as a variable.

Further, in the image reconstruction processing, in order to keep the slice thickness of the tomographic image constant, it is possible to optimize the data range and the weighting coefficient used according to the pitch P (z).

In the above-described embodiment, the pitch is set in two stages based on the threshold value determination for each scan position with respect to the variance σ of the calculated tube current value for the adjacent scan position (FIG. 8 (c)). )), But the variance σ
The pitch may be changed continuously according to (z). For example, P (z) = f (σ (z)) = A / σ + B (where
A and B are constants) and the pitch can be set.

As described above, in the conventional X-ray CT system, only one kind of pitch can be set for a series of helical scans in the set scan section. For example, by preliminarily estimating the variation in the amount of X-ray attenuation of a part at each scan position, an optimal pitch was set for each scan position, and the pitch was automatically controlled during the scan. A high-quality X-ray tomographic image can be reconstructed without losing the advantage of high-speed imaging.

Most of the control of the X-ray CT system in the embodiment is performed on the operation console 200. Since the configuration itself of the operation console 200 can be realized by a general-purpose information processing device (workstation, personal computer, or the like), it is also possible to install software in the device and realize the configuration.

That is, an object of the present invention is to supply a storage medium (or a recording medium) in which program codes of software for realizing the functions of the above-described embodiments are recorded to a system or an apparatus, and to provide a computer (a computer) of the system or the apparatus. Alternatively, the present invention can also be realized by a CPU or an MPU) reading and executing a program code stored in a storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code.
And the like perform part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the above-described flowchart (shown in FIG. 2).

As a storage medium for storing such a program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, C
D-ROM, magnetic tape, nonvolatile memory card, R
OM or the like can be used. Further, it may be downloaded via a medium such as a network (for example, the Internet).

[0055]

As described above, according to the present invention,
When performing a series of helical scans in a set scan section, the helical pitch is adaptively changed according to the scan position, thereby securing the advantage of high-speed imaging possessed by the helical scan while maintaining high-quality X-ray tomographic images. X-ray CT system and operation console capable of reconstructing the same, a control method thereof, and a storage medium can be provided.

[Brief description of the drawings]

FIG. 1 is a block configuration diagram of an X-ray CT system according to an embodiment.

FIG. 2 is a flowchart illustrating a scan control process according to the embodiment.

FIG. 3 is a diagram for explaining a scout scan process in the embodiment.

FIG. 4 is a diagram showing an example of a display screen for setting and executing a scout scan in the embodiment.

FIG. 5 is a diagram illustrating an example of a subject fluoroscopic image according to the embodiment.

FIG. 6 is a diagram illustrating an example of a correspondence relationship between a scan position obtained by Auto mA and a calculated tube current in the embodiment.

FIG. 7 is a diagram illustrating an example of an Auto mA table according to the embodiment.

FIG. 8 is a diagram for explaining a process of determining a correspondence between a scan position and a helical pitch.

FIG. 9 is a diagram illustrating an example of an Auto mA table according to the embodiment.

Continued on the front page (72) Inventor Tetsuya Horiuchi 127 G-Yokogawa Medical System Co., Ltd. 4-7 Asahigaoka, Hino-shi, Tokyo F-term (reference) 4C093 AA22 BA10 CA04 CA34 FA18 FA36 FA56 FA59 FD09 FD11

Claims (7)

[Claims] 1. A method of transmitting projection data at a predetermined transport speed in a body axis direction of a subject in synchronization with a change in a projection angle when irradiating the subject with X-rays generated from an X-ray tube. An X-ray CT system for performing a helical scan to be collected and reconstructing a tomographic image of the subject based on the collected projection data, wherein the X-ray CT system includes a plurality of projection angles orthogonal to a body axis of the subject. Perspective image capturing means for capturing an image; determining means for determining the control value of the transport speed at each scan position based on each subject fluoroscopic image captured by the perspective image capturing means; Scanning control means for performing a helical scan in accordance with the control value of the transport speed at each of the set scan positions. 2. The apparatus according to claim 1, wherein the determining unit calculates a tube current value to be applied to the X-ray tube for each scan position based on each of the subject fluoroscopic images captured by the fluoroscopic image capturing unit. 2. The X-ray CT according to claim 1, wherein a control value of the transport speed at each scan position is determined based on a change in a tube current value calculated for each position.
system. 3. The X-ray CT system according to claim 2, wherein the fluctuation of the calculated tube current value is evaluated by a variance of the calculated tube current values at adjacent scan positions. 4. A helical scan for acquiring projection data while moving the subject in the body axis direction in synchronization with a change in the projection angle when irradiating the subject with X-rays generated from the X-ray tube. A method of controlling an X-ray CT system for reconstructing a tomographic image of the subject based on the collected projection data, comprising: transmitting a fluoroscopic image of the subject from a plurality of projection angles orthogonal to a body axis of the subject. A perspective image capturing step of capturing an image; a determining step of determining a control value of the transport speed at each scan position based on each of the subject perspective images captured in the perspective image capturing step; A scan control step of performing helical scan according to the control value of the transport speed at each scan position. 5. A helical scan for acquiring projection data while moving the subject in the body axis direction in synchronization with a change in the projection angle when irradiating the subject with X-rays generated from the X-ray tube. An operation console of the gantry device for performing, wherein: first instruction means for instructing to capture a fluoroscopic image of the subject from a plurality of projection angles orthogonal to the body axis of the subject; and Determining means for determining a control value of the transport speed at each scan position based on each of the subject fluoroscopic images transferred from the gantry device; and a control value of the transport speed at each scan position determined by the determiner Instruction means for causing the gantry device to perform a helical scan according to the following, and based on the projection data transferred from the gantry device by the second instruction means. Serial X-ray CT system operating console, characterized in that it comprises an image reconstruction means for reconstructing a tomographic image of the subject, the. 6. A helical scan for acquiring projection data while moving the subject in the body axis direction in synchronization with a change in the projection angle when irradiating the subject with X-rays generated from the X-ray tube. A method for controlling an operation console of a gantry device, comprising: a first instruction step of instructing to capture a fluoroscopic image of a subject from a plurality of projection angles orthogonal to a body axis of the subject; Determining a control value of the transport speed at each scan position based on each subject fluoroscopic image transferred from the gantry device, and the transport speed at each scan position determined in the determination process A second instruction step for causing the gantry apparatus to perform a helical scan in accordance with the control value of the gantry apparatus; and the projection data transferred from the gantry apparatus by the second instruction step. Control method for the operation console of the X-ray CT system characterized by having an image reconstruction step of reconstructing a tomographic image of the object based. 7. A helical scan for acquiring projection data while moving the subject in the body axis direction in synchronization with a change in the projection angle when irradiating the subject with X-rays generated from the X-ray tube. A storage medium for storing a program code for an operation console of a gantry apparatus to be executed, wherein a program for a first instruction step for instructing to capture a fluoroscopic image of a subject from a plurality of projection angles orthogonal to a body axis of the subject. A program code for a determining step of determining the control value of the transport speed at each scan position based on each of the subject fluoroscopic images transferred from the gantry device by the first instruction step; A program for a second instruction step for causing the gantry apparatus to perform a helical scan according to the control value of the transport speed at each scan position determined in the step And a program code of an image reconstruction step of reconstructing a tomographic image of the subject based on the projection data transferred from the gantry device by the second instruction step. Storage media.