JPH04292147A - X-ray ct device - Google Patents

Abstract

PURPOSE:To exactly execute a positioning to a measuring position and an actual measurement by providing a means for setting an image reconstituting position from an inside, and a means for executing a movement to the start of a measuring position of a bed required for a series of measurements from a set position. CONSTITUTION:An operator determines a reconstituting position CC' on a body 22 to be examined, and inputs it to a system control circuit 13. As for the input method, a method for setting the image reconstituting position CC' being a patient's measuring position by a projector installed in a scanner gantry part 100, and there after, fetching automatically a bed position in that case, and an input method executed by a keyboard by using an X-ray projection drawing of a patient of a CT device itself are available. A system control circuit 13 selects a speed pattern of a bed 5 corresponding to a set measuring condition by a table 14, and determines positions A, B, A' and B' by calculation. The bed 3 is moved to an initial position A, moved by a selected speed pattern from the position A, and an X-ray source 1, and exposure of X rays are also controlled by the selected pattern. Based on an address, spiral data is stored in a buffer 12.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention is an X-ray CT system that obtains CT images through helical scanning. The present invention relates to an X-ray CT device that performs positional control to a measurement position.

0002

[Prior Art] Instead of a fixed-subject type X-ray CT device,
A spiral scanning type X-ray CT apparatus, in which the rotation of the X-ray source and the movement of the bed are performed simultaneously, is beginning to be used. With the spiral scanning method, measurement can be completed within one breath-holding period (20 to 30 seconds) of the subject, and because there is less stress on the subject, it is said that good images without unnecessary movement can be obtained. have characteristics. Note that when the amount of movement of the bed is large, the deviation between the measurement start position and the measurement end position becomes large, so that a normal image reconstruction method has a problem in that image artifacts occur.

Conventional examples of such a circular scanning type X-ray CT apparatus include Japanese Patent Application Laid-Open Nos. 59-111738 and 62-87.
There is issue 137. JP-A-59-111738 is a CT
An example is disclosed in which images are obtained by helical scanning. Unexamined Japanese Patent Publication 1986
No.-87137 discloses an example of interpolation according to distance distribution in obtaining projection data for CT image calculation by spiral scanning. Both also provide certain solutions for suppressing the occurrence of image artifacts.

0004

[Problem to be solved by the invention] JP-A-59-1117
No. 38 discloses various techniques for obtaining CT images by helical scanning, but there is no positioning control of the bed position and the X-ray source position. Although JP-A-62-87137 is practical in that it describes an example of interpolation to a vertical tomographic plane (slice plane), it does not describe positioning control of the bed position and the X-ray source position.

[0005] In particular, in the spiral scanning type, measurement is performed while moving the bed, so if the measurement position fails to be determined, the measurement will be performed at an incorrect position that is not the intended image reconstruction position.

[0006] Furthermore, in order to obtain a CT image on one slice plane, projection data for 360° on this slice plane is required, but in spiral scanning, the projection data on this one slice plane is Because the bed is moving, it is essentially impossible to measure 360° projection data on the same fault plane.
The image reconstruction position based on this measurement will be shifted. There is also a method of obtaining 360° projection data using measurement data from the bed positions before and after this slice plane, but in this case, the amount of measurement data required for this reconstruction method must be taken into account. , incorrect positioning causes trouble in calculating a CT image on a desired slice plane.

Furthermore, in spiral scanning, the slice plane must be able to be set arbitrarily, and the bed must be positioned accurately so that a CT image can be obtained on any slice plane. Must.

[0008]Furthermore, the bed position control system may employ various speed patterns, and it is preferable that the bed can be positioned in accordance with these various speed patterns.

The above is only the positioning of the bed, but
Since the radiation source also provides a projection angle, its positioning is important. Furthermore, there are examples in which the rotation of the X-ray source takes various speed patterns, and it is important to control the rotation of the X-ray source in accordance with these various speed patterns.

An object of the present invention is to control the position of the bed and the X-ray source so that measurement can be performed under various X-ray conditions by simply performing positioning similar to the patient positioning method of a conventional X-ray CT apparatus. The present invention provides an X-ray CT apparatus that performs

[0011]

[Means for Solving the Problems] The present invention comprises means for externally setting an image reconstruction position, and means for moving a bed from the set position to a measurement start position necessary for a series of measurements. (Claim 1).

Furthermore, the present invention includes means for externally setting an image reconstruction position, moving the bed from the set position to a measurement start position necessary for a series of measurements, and moving the bed from the start position at a predetermined speed. means for performing spiral measurement at a position including the set position while moving the bed and rotating the X-ray source according to a pattern (Claim 2)
.

According to the present invention, the bed and the X-ray source are controlled so that the image can be reconstructed at the set position simply by externally providing the image reconstruction (slice) position (claim 1).

Furthermore, according to the present invention, by simply providing an image reconstruction position from the outside, the bed is initialized to the movement start position, and the bed and X-ray source are moved from this start position according to a desired speed pattern. and rotation, and measurement is performed from the set position (Claim 2).

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an X-ray CT apparatus according to the present invention. Each component is as follows. X-ray tube device (X-ray source) 1
...Generates a fan-shaped X-ray beam continuously or intermittently. X-ray detector 2...located opposite to the X-ray tube device 1, and is a multi-channel detector. Gantry opening 4...
There is a measurement space inside through which X-rays pass, and measurement can be performed by inserting a subject into the opening 4. Scanner body (
Scanner gantry section) 100...This is a device that rotates the X-ray tube device 1 and the X-ray detector 2 while facing each other. Each point on the rotation can be expressed by a projection angle, and this projection angle can be associated with a projection angle number of 1 to pp for one rotation of 0° to 360°.

Bed 3: A device on which a subject 32 is placed and moved forward or backward toward the gantry opening 4. This movement of the bed 3 is performed continuously, and during this movement, X-rays are emitted from the X-ray tube device 1 continuously or intermittently. In this way, the subject 32 is subjected to a spiral scan. Data acquisition circuit 2A: Captures transmitted X-ray signals detected by the X-ray detector 2 corresponding to channels, performs AD conversion, and converts them into data. Since this data is obtained by spiral scanning, it will be referred to as spiral data SR. Two-dimensional buffer 12: A memory that is addressed by the rotation number j of the X-ray tube device 1 and the projection angle number i of the X-ray tube device 1, and stores helical data. The rotation number j is the number of rotations of 360°, and if the distance that the bed 3 travels during one rotation is D, then at the rotation number j, the bed is
It exists in position D. Therefore, j is also a parameter indicating the bed position. The projection angle number i is 360
The position of the X-ray tube device 1 corresponding to the measurement position during one rotation of ° (
angle). If the moving distance of the bed in one projection angle pitch of the X-ray tube device is ΔD, then the bed position X at the address (j, i) is: X=j×D+i×ΔD…(1
). In this two-dimensional buffer 12, all the spiral data measured within the spiral scanning section are stored at the corresponding address (j, i
). Further, the X-ray detector 2 is of a multi-channel type, and requires a parameter called a channel number k in addition to the address (j, i). Therefore, to be precise, an address consists of three parameters (j, i, k).

Projection data forming circuit 15: Creates projection data for a CT image on an arbitrary slice plane from the spiral data in the two-dimensional buffer 12. CT on any slice plane
To obtain an image, projection data for a projection angle of 360 degrees (projection data for a half scan of 180 degrees) on the slice plane is required. In order to obtain this 360° projection data, it is necessary to
Various methods described in No. 7137 can be employed. For example, Japanese Patent Application Laid-Open No. 62-87137 uses a method of calculating 360° projection data by interpolation from the spiral data before and after the slice plane. This interpolation method can also be adopted in this embodiment. Filter correction circuit 16: Performs spatial filtering processing for blur removal and enhancement processing. It is conventionally known. Back projection calculation circuit 17... From the projection data after spatial filtering, C
Obtain T image data. It is conventionally known. Display section 18
...The results of gradation processing of CT image data are displayed as a CT image. System control circuit 13: Controls the position of the scanner unit 100 and bed 3, controls X-ray exposure, and controls measurement. This system control circuit 13 is the central part of the present invention, and takes in the "measurement position" instructed by the operator from the outside, and performs position control and exposure control so that the actual spiral scan can be performed at this measurement position. Control (including measurement control). Measurement parameter table 14: A memory that stores speed patterns, measurement conditions, etc. of the bed 3 and the X-ray tube device 1. This table 14 is also one of the features of the present invention. Note that even if this table is not provided, it may be latched in the control circuit 13.

The above is the configuration of FIG. 1 and the functions of each component. Next, the measurement position control of this embodiment will be described in detail using FIGS. 2 and 3.

FIG. 2 shows examples of various patterns, (a) is an example of the rotation pattern of the X-ray source, (b) is an example of the bed movement speed pattern, and (c) is an example of the X-ray irradiation timing (ON/OF).
It is a figure showing F). FIG. 3 is a diagram showing the movement range of the bed, the imaging range, and the image reconstruction range when the tomographic target is a human head.

According to the bed movement speed pattern shown in FIG. 2B, the tomographic plane A is the bed movement start position, and the tomographic plane A' is the bed movement stop position. Fault plane B reaches a constant velocity state, and fault plane B' ends its constant velocity state. According to this velocity pattern, the bed advances at a constant acceleration in section AB, and reaches a constant velocity at the position of plane B. Speed up, this is B
Bed position control is performed so that the bed continues to 'plane', decelerates at a constant acceleration from B' to A', and stops at A'. There are various other speed patterns, but any speed pattern can be realized using a servo motor or the like.

Similarly to the bed movement speed pattern, the scanner rotational speed pattern shown in (a) of FIG. Eggplant. In addition, in FIGS. 2A and 2B, dotted lines indicate various movement start timings, rotations, and movement speed pattern examples. In this way, various combinations are possible in measurement.

In (c) of FIG. 2, OFF means that X-rays are not irradiated, and ON means that it is a section in which X-rays are irradiated. In this ON section, either continuous exposure or intermittent exposure is adopted.

FIG. 3 shows an example of head tomography when the bed movement speed pattern of FIG. 2(b) is adopted. A, A', B, and B' in FIG. 3 are symbols having the same meaning as the speed pattern example in FIG. 2 (b). The AA' section is the movement range of the bed, and the BB' section is the imaging range. Within the bed movement range AA', the AB section and A'B' section are as follows:
Since the vehicle was not moving at a constant speed, it was set as a section in which photography was not performed, and only the constant speed moving section of section BB' was set as a true photographing section. Here, the imaging section is a section in which X-rays are irradiated.

[0024] The photographing section is not the image reconstruction range. Since the bed advances by D during one scan of the spiral measurement, the original image reconstruction position shifts by D/2. Furthermore, when calculation is performed by interpolation between adjacent scan data as an image reconstruction calculation method, there is a further shift by this interpolation area. Therefore, the range in which 360° worth of projection data for final image reconstruction can be obtained is set to a narrower range than the BB' interval, and this set range is the image reconstruction range (CC' interval).
It is.

Based on the above preconditions, the processing procedure of this embodiment will be described below. (1) The operator determines the reconstruction position on the subject and inputs this to the system control circuit 13. The input method is to set the image reconstruction position, which is the measurement position of the patient, using a floodlight (not shown) installed in the scanner gantry section 100, and then automatically import the bed position at that time before starting the measurement, or to use the X-ray CT device. There is an input method using a keyboard (or input using a mouse cursor) using an X-ray projection image of the patient. Here, the image reconstruction range refers to the CC' section in FIG. That is, the operator determines the image reconstruction range of the subject and inputs so that a CT image can be obtained within this range.

(2) The system control circuit 13 selects a bed speed pattern from the table 14 that corresponds to the measurement conditions set by the operator, and performs accurate measurement at the measurement position based on the positional relationship with the subject 32. A, B, B' as possible,
Each position of A' is determined by calculation.

(3), position A is the initial value of the bed,
First, move the bed to this position. The bed is then moved from position A according to the selected speed pattern. At the same time, the rotation of the X-ray source is also controlled according to the selected rotational speed pattern. The exposure of X-rays is also controlled according to (c) in FIG. In this way, the positional relationship with the subject 32 as shown in FIG. 3 is ensured, and the CC' interval can be provided as the image reconstruction range.

(4) The reconstructed position, which is the measurement position, is an example of a range, but the size of this range depends on the purpose of measurement, such as how many slice positions there are and where they should be located.
If you want to obtain projection data for 360° of one slice plane by interpolation as in JP-A No. 62-87137, the size of the interpolation target section (for example, distance D, or D/2 for half scan), etc. It also depends on the processing method. There is also a method of automatically setting the range depending on the measurement purpose and processing method. Alternatively, instead of the range, the center position of the range, the start point, and the end point of the range may be given.

(5) The system control circuit 13 can control the bed 3 and the scanner section 100 in accordance with the control contents given in the procedure described above, thereby making it possible to make the movements as shown in FIG. 3. And the address (j, i,
Store the spiral data in the buffer 12 under k). After storing this data, select and read the helical data of the CC' section from among the helical data, and interpolate the projection data of 360° (or 180°, other examples are possible) on the slice plane. Find it by etc. CT image data is obtained by reconstruction from this projection data. These processes are as described in the explanation of FIG.

Although the present invention has been described as an example of the R-R method, it can also be applied to CT apparatuses of other generations.

[0031]

Effects of the Invention In spiral scanning, a deviation essentially occurs between the image reconstruction plane position (slice plane) and the measurement position, making it difficult to determine the measurement position of the subject. By knowing the speed pattern, etc. in advance, positioning to the measurement position and actual measurement can now be performed accurately simply by setting the measurement position from the outside.

[Brief explanation of drawings]

FIG. 1 is an embodiment diagram of the present invention.

FIG. 2 is a diagram showing various pattern examples of the present invention.

FIG. 3 is a diagram showing an example of application of the present invention to a subject.

[Explanation of symbols]

1. X-ray tube device (X-ray source) 2 Multi-channel X-ray detector 3 Bed 12 2-dimensional buffer 13 System control circuit 14 Measurement parameter table 15 Projection data formation circuit

Claims (2)

[Claims] Claim 1: The rotation of the X-ray source and the movement of the bed on which the subject is placed are performed mutually to perform a spiral scan on the subject, and when the measurement is performed by this spiral scan, arbitrary information can be obtained from the rotation data. In an X-ray CT apparatus that obtains tomographic images in a slice plane, means for externally setting an image reconstruction position, means for moving a bed from the set position to a measurement start position necessary for a series of measurements, and more. An X-ray CT device consisting of [Claim 2] The rotation of the X-ray source and the movement of the bed on which the subject is placed are mutually performed to perform a helical scan on the subject, and when the measurement is performed by this helical scan, arbitrary information can be obtained from the rotary data. In an X-ray CT apparatus that obtains tomographic images in a slice plane, a means for externally setting an image reconstruction position, a means for moving a bed from the set position to a measurement start position necessary for a series of measurements, and An X-ray CT apparatus comprising means for performing spiral measurement at a position including the set position while moving a bed and rotating an X-ray source according to a predetermined speed pattern from a starting position.