JPS58183145A - Gated scan ct apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a gated scan type OCT apparatus.

[Technical background of the invention and its problems]

Generally, in a CT device, for example, an XIIICT@, an X-ray tube, an X-ray detector, and a
While rotating the body axis over 180°
Since scanning is performed by emitting a beam and collecting transmission data, artifacts corresponding to the scanning time occur when obtaining a tomographic image of an organ that moves significantly, such as the heart.

These artifacts can be reduced by shortening the scan time, but since X-ray CT scans are performed using a mechanical rotation mechanism, each scan requires at least 2 seconds S degrees. However, the pulsation period is 0.9~
For the heart at tO seconds @ degrees, it is impossible to obtain a clear tomographic image of the heart during the diastole or systole by eliminating the artifacts associated with the scanning time. A gated scan type X-ray CT apparatus has been proposed. This focuses on the fact that the heart repeats the same beat periodically.
If the motion state of the heart at a certain time is the phase of the beat, then
The line transmission data was collected by multiple scans, and the data was collected 7
Among the tX-ray transmission data, image reconstruction is performed using the Zj X-ray transmission data corresponding to a predetermined same phase based on the period of the R wave obtained from the electrocardiogram, and a tomographic image of the heart in a constant state corresponding to this predetermined phase is obtained. However, in this gated scanning method, it is essential to scan the same subject multiple times, and in order to obtain high-quality images, it is necessary to increase the number of scans. Increasing the number of scans to 1 for the same subject means that the exposure dose to the subject [by increasing
! 11.The fact that it does not have any negative effect on the subject and causes fear, has become an obstacle to improving the quality of conventional images.7tQ
Purpose of the Invention The present invention has been made in view of the above circumstances, and aims to reduce the exposure dose while performing multiple scans on the same subject in order to obtain high-quality images. [Summary of the Invention] The purpose of the present invention to achieve the above object is to provide a gated scan CT apparatus that can perform the same body movement periodically. The radiographic data of the imaged area is collected over time by exposing the subject, including the specific imaged area, to radiation t at predetermined angles and performing multiple radiation scans. In a gated scan CT system that reconstructs an image based on radiographic data that is in the same phase as the body movement of the imaged area, the first scan of the multiple radiation scans involves The radiographic data tube is collected, and the radiation exposure range is controlled so that in subsequent scans, radiographic data is collected for a limited area centered on the specific imaging area.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained with reference to the drawings.
It is a schematic explanatory diagram of a cr device. In FIGS. 1 and 2, the configuration and function of the device will be explained first. An X-ray data collection unit 1 is connected to an X-ray tube 1α and an
ray detector 1h, and the X-ray tube 1cL and ) A barrel heart is shown, and for convenience of explanation, heart 6a is shown.
is located near the rotation center 4. The collimator 5 in the data acquisition unit 1 rotates together with the X-ray tube 1a, and is provided perpendicularly to the direction of irradiation of X-rays from the Xl1I tube 1eL. Opening position [06, which can limit the X-ray irradiation range by shifting, is an electrocardiogram detector, which detects the electrocardiogram signal of the heart obtained through the electrodes attached to the subject 3. Outputs the beat cycle time. Reference numeral 7 denotes a control device having a function of displacing the position and opening width of the collimator 5 with respect to the X-ray tube 1a based on the operation of an ROI (specific region) indicator 11, which will be described later. Reference numeral 8 denotes a storage device that stores the pulsation cycle time of the electrocardiogram detector 6 and the xIN transmission data detected by the X-ray detector 1h in the data collection si in association with each other.

9 is X-ray transmission data at a predetermined same phase of the pulsation based on the pulsation cycle time stored in the storage device 8 [read out from the storage device 8 and read out xIIi! This is an image reconstruction device that reconstructs an image g1 based on transmission data. is a display that displays images obtained by the image reconstruction device 9. 11 is ROI (7
? g! ! With the ROI indicator, it is possible to specify a specific position and size within the image displayed on the display 1°, and this specified data is input to the control device 7. 0 Furthermore, the control device 7 includes a calculation unit, and the spread angle and deflection angle during X-ray irradiation, which will be described later, are determined based on the specified data specified by the ROI indicator 11. and the opening width of the collimator 5 corresponding to this spread angle and deflection angle.

Calculate the opening l1lt and send the calculated data to the collimator 5.
The operation of a gated scano type X@CT apparatus having a configuration of 0 or more in which feedback is provided will be explained with reference to FIG. 3. First, as shown in FIG. 1, the collimator 5 is set so that the entire area of the subject B is exposed to KX-rays, and the
36 around the subject 6 in the direction of arrow A in FIG. 6.
While rotating by 0°, xlI transmission data is collected at each position P1a Pz...PM and the first scan is performed. At this time, the heartbeat cycle time is detected by the electrocardiogram detector 6, and the The cycle time and the X-ray transmission data are stored in the storage device 8 in association with each other. The Xfs transmission data obtained by the first scan is read out from the storage device 8, reconstructed as a tomographic image by the image reconstruction device 19, and displayed on the display 10. This one
Among the reconstructed images of the subject 6 obtained by the same scan, the reconstructed image 1iii of the heart 11g3g is the heart 6-
It is obscured by the pulsation of the Therefore, in the second and subsequent scans, specify the area including the heart 3gt,
The position and width of the opening of the collimator 5 are set so that xIIiI is irradiated only to this designated area. At this time, the settings of the collimator 5 are 1ii on the display 10.
[While watching, operate the ROI indicator 11 to specify the position of the heart 34E on the display 10, and further specify its size. Based on this operation, the control device 7 controls the aperture width and aperture position of the aperture of the collimator 5, and adjusts the aperture width and position of the aperture of the collimator 5 to a location of 1 m x 1 m in accordance with the specified range on the display 10.
! The collimator 5 is set so that the beam is irradiated. In this case, as shown in FIG. 2, if the heart 3a is located near the center of rotation 4, the heart 113α can be included within the irradiation range of radius r around the center of rotation 4.

Therefore, the spread angle α of the X@ exposure required in this case is @
:2 zLn-'' --, (11) Here, R indicates the distance between the focal point position on the X-ray tube 1 and the rotation center 4.

After the collimator 5 is set to achieve the spread angle α determined as described above, the second and subsequent radiation scans are performed. The second and subsequent scans may be performed using the conventionally provided asynchronous gated scan method, or a method in which the scan start time is sequentially delayed with respect to a predetermined phase of the pulsation for each scan (Japanese Patent Application No. 1983). -154865). The above-mentioned second and subsequent scans are performed (K). , . . . The X-ray transmission data of the pH point and the pulsation cycle time corresponding to the X-ray transmission data are stored in the storage device 8. Therefore, the storage device 8 stores the X-ray transmission data of the entire area of the subject 3 obtained in the first scan, and the X-ray transmission data of the designated area including the heart 64 obtained in the second and subsequent scans. The data and the pulsation cycle time corresponding to the X-ray transmission data are stored.

Therefore, when displaying a tomographic glt image at a predetermined same phase of the pulsations in the heart 3g, the same phase of the pulsations obtained by the first and second and subsequent scans is determined based on the periodic time of the pulsation. The X-ray transmission data of the designated area of the subject 30 located in the area is read out from the storage device 8, and the X-ray transmission data of the area other than the designated area of the subject 30 among the X-ray transmission data obtained by the first scan is read out from the storage device 8. Read out 8.

And l! The iigI reconstruction device 9 collects the xH transmission data 'tm of the specified area, and reconstructs multiple images by superimposing this with the xlIil transmission data of the areas other than the specified area, and displays the reconstructed images on the display 1o. By the above-described operation, a clear tomographic image of the subject 3 corresponding to a predetermined phase of the heartbeat 6ε can be obtained.

The case where the heart 3c is located near the center of rotation 4 has been explained above, but next, the second and subsequent scans of M when the heart 6g is set at a position away from the center of rotation 4 [Fig.
Also explained in addition to reference. In FIG. 4, the heart 6a is located at coordinates (x, y) with respect to the center of rotation 4. - N times of X-ray irradiation is performed in - times of scanning, and the
@ Exposure position tPn. P* # Let βxeh* be the deflection angle with respect to the rotation center 4 in X@ exposure at Pz,
X111! ! The spread angle is α1.41%. At this time, the spread angle and deflection angle β at point Ps are calculated by the following equation (2
), (3).

I−0 in BoI, βtFi equations (2) and (3), respectively.
Oa% and β, which are found by substituting as θ, are both θ
Since it is expressed as a function of , each point P, , ? ,...
・For each position at pH: 7 Manual force of meter 5 → 0 @ Magnetic amount required to displace the angle and deflection angle [To minimize it, both the angle of spread α and angle of deflection β must be displaced is desirable, but one simple method here is to use the deflection angle β
A method will be described in which the spread angle α is kept constant by controlling only the irradiation angle at each irradiation position. Generally, since R (distance between focal position and center of rotation 4) > X, Y (coordinates of the heart), the blur hardly changes. Therefore, if we calculate the maximum value of %”+2) using formula (2), “”” = “”' ”
-A"+X"+ Y"-2R-MarIX, Yl)・
(4) Therefore, if the maximum spread) angle deflection αxf is set before the start of the second scan, only the deflection angle β need be controlled via the entire control device 7.

Next, the simplest method in this embodiment will be explained. As is clear from FIG. 4, the farthest distance between the heart 6α and the center of rotation 4 is J-hyx+r (5). The maximum spread angle αwuxx of X-rays passing through this point is as follows. If this maximum divergence angle a'max f is used, it is not necessary to constantly control the deflection angle. Therefore, it is sufficient to simply set the maximum spread angle αMLaJ in equation (6) before starting the second scan, and thereafter scan in the same manner as in the conventional gated scan method. Generally, the heart 3a is the object 3
Since the radiation dose is located near the center of Needless to say, it includes. In the above embodiments, a sixth generation CT device is described, and the skin is a fourth generation CT device.
It goes without saying that the same method can be applied to the next generation CT apparatus as well. Furthermore, the object to be imaged by this gated scan method is not limited to the heart, but can also be applied to rapidly moving parts within the subject, such as the respiratory tract and pulsating parts.

〔Effect of the invention〕

As explained above, according to the present invention, in the first scan, X-rays are irradiated to the entire area of the subject at the imaging site,
After that, in the reconstructed image obtained in the first scan, areas that could not be clearly defined due to movement are specified and pressure is applied to perform radiation scanning only on those areas, while other areas with no movement are initially scanned. Since this data is used, it is possible to provide a gated scan CT apparatus that can obtain clear reconstructed images and reduce the exposure dose to the subject.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show an embodiment of the present invention.
A schematic explanatory diagram of the HCR device! Figure I3 is a schematic explanatory diagram for explaining scanning when the specific imaging region is located at the center of rotation, and Figure 4 is a detailed schematic explanation for explaining scanning when the specific imaging region is located away from the center of rotation. It is a diagram. 1...Data collection unit, 1α...X-ray tube, 1h.
... X-ray inspection device, 6... Subject, 6α... Heart, 4... Center of rotation, 5... Collimator, ,
6... Electrocardiogram detector, 7... Control device, 8...
Storage device, 9... Image reconstruction device, 10...
Display, 11...ROI indicator, α...
- Spread angle, β... Deflection angle. Agent Patent Attorney Kensuke Chika (and 1 other person) No.
1 Figure 2 Figure 3 Figure Δ Figure 11 8

Claims (1)

[Scope of Claims] A radiation scanning tube is performed multiple times by irradiating radiation at every predetermined angle to a subject including a specific imaging region in which the same body movement is periodically repeated Km. [In a gated e-scan CR device that collects radiographic data over time and performs image reconstruction based on the radiographic data that is in the same phase as the body movement of the imaging site among the collected radiographic data, the plurality of Of the multiple radiation scans, the first scan collects radiographic data for the entire area of the subject, and the subsequent scans collect radiographic data for a limited area centered on the specific imaging area. A gated scan CT apparatus characterized in that the radiation exposure range is controlled as described above.