JPH02257941A - Radiation amount regulator in radiation imaging device - Google Patents

Abstract

PURPOSE:To control exposure compensation with high responsive property and accuracy to provide a sharp picture with wide latitude by driving a throttle member for regulating a radiation amount with a galvanometer type drive device. CONSTITUTION:A radiation screening member 2 formed on the radiation side of a radiation source 1 with a laterally long opening 2a is provided to be moved in the direction orthogonal to the longitudinal direction for forming a fan beam FB. A plurality of throttle members 3 movable integrally with said member 2 and connected with rotary shafts 5 of galvanometer type drive devices 4 are provided, and the throttle member 3 is disposed adjacent every region of longitudinally divided opening 2a with each rotary shaft 5 being directed in the directions orthogonal to the longitudinal direction of the opening 2a. The throttle members 3 are disposed staggered at such intervals that the fan beam FB can be almost screened when the throttle members 3 are fully closed. The fan beam FB is radiated to the human body 6 so that the picture taking and recording corresponding to the radiation amount passing through the opening 2a are carried out on an imaging surface 7. The radiation amount is detected by a detector 8 and the passed radiation amount is regulated by changing the opening area so that the radiation amount reaching the image taking surface 7 falls within an approximately fixed range.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a radiation dose adjustment device for exposure compensation in a radiation (generally X-ray) imaging device.

<Prior Art> A radiation imaging device generally uses an X-ray tube as a radiation source, and detects and records the radiation dose from the radiation source that has passed through an irradiated object, such as an X-ray film or stimulable fluorescence. It is composed of a means for capturing and recording images of the body, etc.

By the way, in chest imaging using an X-ray imaging apparatus used for medical purposes, for example, there is a problem in that the anatomical thickness shows large fluctuations due to differences in thickness and radiation absorption in the imaging area.

That is, thicker areas are underexposed and, for example, the density when output to film is too low (too much), while thinner areas are overexposed and too dark, resulting in a decrease in latitude.

For this purpose, an aperture is provided in front of the radiation source, and a diaphragm member is moved in and out to variably control the aperture area for each region divided in the longitudinal direction, and the radiation beam obtained by passing through the aperture is It performs scanning that moves in the longitudinal direction and the perpendicular direction and projects the image onto the object while capturing and recording the image on the imaging surface installed behind the object, while a detector is installed to detect the radiation dose of each part on the imaging surface. There is a structure in which the amount of aperture by the aperture member is controlled so as to obtain an appropriate amount of exposure based on the detection signal from the detector (see Japanese Patent Application Laid-Open No. 129034/1984, etc.).

<Problems to be Solved by the Invention> Incidentally, in such a radiation imaging device, since the aperture control is performed while scanning the radiation beam, it is necessary to perform the aperture control with good responsiveness to the detection signal from the detector. .

However, in conventional devices, the aperture area is controlled by sliding the diaphragm member in a direction across the aperture, but this does not necessarily allow responsive control.

The present invention has been made in view of these conventional problems, and an object of the present invention is to provide a radiation imaging device that solves the above-mentioned problems by having a configuration in which the aperture member can be driven and controlled with good responsiveness to obtain an appropriate amount of exposure. With the goal.

Therefore, the present invention provides a radiation shielding member having an aperture for generating a radiation beam between a radiation source and a subject, and also provides a radiation shielding member connected to a galvanometer drive device to be rotatably driven. A plurality of diaphragm members are arranged to face the opening and adjust the amount of radiation passing through the aperture.

Further, the configuration may include a vibration means for vibrating the aperture member.

<Operation> Each diaphragm member is rotationally driven by a galvanometer-type drive device based on a detection signal of the radiation dose on the imaging surface, and the amount of radiation passing through is adjusted, thereby obtaining an image with proper exposure compensation.

Further, by providing the vibrating means, the disparity between the portions through which radiation easily passes and the portions through which it is difficult to pass is suppressed, and it is possible to prevent striped patterns from occurring in imaging.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 1 showing the configuration of one embodiment, a radiation shielding member 2 having a horizontally long opening 2a is provided on the irradiation side of a radiation source (generally an X-ray tube) 1, and this radiation shielding member 2 is connected in the longitudinal direction. By moving in the right angle direction, a fan beam FB is generated.

In addition, a plurality of aperture members 3 made of a lead plate that move together with the radiation shielding member 2 are connected to a rotating shaft 5 of a galvanometer-type drive device 4, and each rotating shaft 5 is connected to the longitudinal axis of the opening 2a. The diaphragm member 3 is opened in the direction perpendicular to the opening 2.
It is arranged so as to face each area divided in the longitudinal direction of a.

The diaphragm members 3 can freely open and close the apertures 2a by their respective rotations, and are disposed with their positions shifted in the radiation irradiation direction at intervals that are sufficient to substantially block the fan beam FB when fully opened.

The fan beam FB is irradiated onto the object (human body) 6,
An image is taken and recorded on an imaging surface 7 such as a screen/film provided behind the object 6 in accordance with the amount of radiation that has passed through the opening 2a.

In addition, in the case of screen/film, the radiation is the phosphor N(
It is irradiated onto a fluorescent screen) and converted into visible light, which is then exposed to a film coated with a silver salt photosensitive material. However, the imaging surface 7 uses a method in which image information is accumulated using a primary phosphor detector, scanned and retrieved by a semi-11C laser, and this digital image information is stored in an external memory so that it can be reproduced on a CRT. It may be of.

Further, a detector 8 is provided to detect the radiation dose of each part on the imaging surface 7, and thereby the fan beam FB
The detector 8 detects the radiation dose of each part on the line that is irradiated, and the driving device 5 controls each aperture member 3 so that the radiation dose reaching the imaging surface 7 for each part is within a substantially constant range. The amount of radiation passing through is adjusted by driving and changing the aperture area.

Furthermore, pie break 9 serves as a vibrating means for vibrating horizontally with a predetermined swing width while moving each aperture member 3 and radiation shielding member 2 together in the vertical direction for scanning.
is connected to the side wall of the frame 10 that holds the radiation shielding member 2 and the drive device 5 together.

FIG. 2 shows an outline of the structure of the galvanometer drive device 4. As shown in FIG.

The amount of rotation of the rotating shaft 5 is controlled by the magnitude of the current applied to the coil of the magnet driver 41, and the amount of rotation is detected by a position sensor 42 attached to one end of the rotating shaft 5. A detection voltage corresponding to the amount of rotation from the position sensor 42 is input to one side input terminal of a differential amplifier 43, and an aperture member driven by this drive device 4 is connected to the + side input terminal of the differential amplifier 43. A detection signal (voltage) from a detector 8 that detects the amount of radiation passing through the attachment site 3 is input.

For example, the radiation dose detected by the detector 8 is larger than the radiation wAil corresponding to the reference exposure dose (
small), a voltage difference is generated between the detection signal voltage corresponding to the current position of the aperture member 3 and the magnet driver 4
1 changes, the diaphragm member 3 rotates in the closing direction (opening direction), and the amount of radiation passing through (irradiation) decreases (increases).

As a result, a radiation dose corresponding to the anatomical thickness is irradiated, and the degree of exposure of each region is controlled to be maintained appropriately.

The galvanometer-type drive device 5 has drive characteristics that are extremely responsive to detection signals, and therefore, by using the drive device 5 to control opening and closing of the diaphragm member 3, Highly accurate exposure compensation control can be performed, and imaging with a wide latitude can be obtained.

Furthermore, the scanning speed can be increased by improving the responsiveness, which leads to reducing the influence on imaging of fast-moving objects such as the heart.

On the other hand, when the rotating shaft 5 is arranged perpendicularly to the longitudinal direction of the opening 2a as in this embodiment, the radiation passes through the portion close to the rotating shaft 5 when viewed from the front of the opening 2a until the aperture member 3 is nearly fully opened. On the other hand, as the distance from the rotating shaft 5 increases, the minimum opening degree of the aperture member 3 through which radiation passes becomes smaller. In other words,
The vicinity of the rotation axis 5 has a non-uniform characteristic in which there are fewer opportunities for radiation to pass through (the farther away from the rotation axis 5, the more opportunities for radiation to pass through).Therefore, if left as is, a striped pattern extending in the scanning direction will appear in the image. There is a tendency to cause
In this embodiment, by scanning the diaphragm member 3 while vibrating it in the longitudinal direction of the aperture 2a with the pipe rake 9, the radiation passing characteristics are made uniform in the longitudinal direction of the aperture 2a, and the occurrence of striped patterns in imaging can be effectively prevented. It can be prevented. In this case, the amplitude of the vibration is approximately the distance from the rotation axis to the side end surface of the aperture member, that is, the width of the aperture 2a of the aperture member in the longitudinal direction.
higher than that (preferably an integral multiple), and the frequency of vibration is
It is preferable to set the size to a size that can prevent the occurrence of striped patterns depending on the scanning speed.

Furthermore, as is clear from the above-mentioned function, scanning accompanied by such vibration has the effect of suppressing the occurrence of striped patterns when a gap is created when the diaphragm member is fully closed, so it can be suppressed by vibration alone. In some cases, the throttle members may be arranged in a line with a slight gap when fully closed to achieve compactness.

FIG. 3 shows a second embodiment of the invention.

That is, in this embodiment, the connecting body of the diaphragm member 3 and the drive device 4, which is constructed in the same manner as in the first embodiment, is arranged so that the rotating shaft 5 is parallel to the longitudinal direction of the opening 2a and in the width direction of the opening 2a. The opening 2a can be opened and closed freely by rotation of the rotating shaft 5, and the opening 2a is installed at intervals that do not create a gap when viewed from the front of the opening 2a when it is fully closed. . The other configurations are the same as in the first embodiment.

In this embodiment as well, the galvanometer type drive device 4 can perform highly responsive and highly accurate exposure compensation control.

In addition, in this arrangement, the radiation transmission characteristics are the same in the longitudinal direction of the aperture 2a of the aperture member 3, and differ depending on the distance from the rotation axis 5 in the direction perpendicular to the longitudinal direction. Since scanning is performed while moving, it is possible to avoid the occurrence of striped patterns due to radiation transmission characteristics. Therefore, it becomes possible to omit the vibration means. However, if there is a gap between adjacent diaphragm members or if they overlap, and a striped pattern is produced in the imaging of this part, it is sufficient to provide a vibrating means to vibrate in the longitudinal direction of the aperture 2a. In this case, in order to achieve sufficient uniformity of the radiation passing characteristics, it is appropriate that the oscillation width be equal to or larger than the longitudinal length of the aperture 2a of the diaphragm member 3.

In addition, instead of providing such a vibration means, if the detection signal is electrically corrected on the detector side, or if the captured image is displayed on a monitor screen, the generation of striped patterns can be avoided by electrically correcting the reproduction of the captured image screen. In some cases, it may be possible to suppress the

In addition, in the embodiment described above, the horizontally elongated radiation beam is moved and scanned in the vertical direction, but these mechanisms can be rotated by 90 inches to move and scan the vertically elongated radiation beam in the left and right directions. Of course, it is possible.

It can also be applied to systems that irradiate a weak radiation beam once with a detector or stimulable phosphor, and then correct and control the irradiation amount during actual imaging based on the detected value of the amount of radiation transmitted. Even in this case, responsiveness can be improved. Similarly, the scanning speed can be increased by

<Effects of the Invention> As explained above, according to the present invention, by configuring the aperture member for adjusting the radiation dose to be driven by a galvanometer-type drive device, highly responsive and highly accurate exposure compensation control can be performed. , clear imaging with wide latitude can be obtained.

Further, by providing a vibrating means or devising the arrangement of the diaphragm member and the drive device, it is possible to make the radiation passage characteristics uniform and prevent the occurrence of striped patterns in the image.

[Brief explanation of drawings]

In FIG. 1, (A) is a plan view showing the overall configuration of the first embodiment of the present invention, FIG. 1(B) is an enlarged plan view of the main part of the same embodiment, and FIG. Figure (B) is viewed from the radiation irradiation direction, Figure 2 is a diagram showing an outline of the circuit configuration of the galvanometer type drive device used in the above embodiment, and Figure 3 is
FIG. 7 is a diagram of main parts of the second embodiment as viewed from the radiation irradiation direction. 1... Radiation source 2... Radiation blocking member 2a
...Opening 3...Lead plate 4...Drive device
5... Rotation axis 6... Target 7... Imaging surface 8... Detector 9... Vibrator Figure 1 (8) a Figure 1 (C)

Claims (2)

[Claims] (1) A radiation blocking member having an aperture that generates a radiation beam is provided between the radiation source and the subject, and a plurality of diaphragm members connected to a galvanometer drive device and rotationally driven are provided in the aperture. 1. A radiation dose adjustment device for a radiation imaging apparatus, characterized in that the radiation dose adjustment device is configured to adjust the amount of radiation passing through the radiation imaging device. (2) The radiation dose adjusting device in a radiation imaging apparatus according to claim 1, characterized in that the device includes a vibrating means for vibrating the aperture member.