JPH0522538B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field This invention provides a radiation irradiation means and a two-dimensional radiation detection means that are arranged opposite to each other with a subject in between, and that both are placed at the center of the tomographic plane of the subject. The present invention relates to an improvement in a tomography apparatus that obtains a shadow image of an arbitrary tomographic plane using transmitted radiation by moving symmetrically around a point to blur shadows in areas other than the tomographic plane.

(b) Prior art A tomography apparatus usually has the following features, as shown in Figure 1:
An X-ray tube 1 and a film 2 are placed facing each other with a subject 4 on a table 3 in between, and an The wire tube 1 and the film 2 are made movable, and are configured to be moved symmetrically about the center point O of the tomographic plane 5. Various loci of movement on the surfaces 6 and 7 are adopted, such as a straight line, a circle, an ellipse, a hypocycloidal trajectory, and a spiral trajectory.

Incidentally, in such a parallel plane tomography apparatus, the distance between the X-ray tube 1 and the film 2 changes as the X-ray focal point moves. and,
In film 2, the X-ray intensity changes at a rate of the inverse square of this distance. That is, the X-ray intensity I can be expressed as I=K/{(ar) ² +L ² } where a=L/L ₀ . Here, K is a constant, r is the distance from the normal line passing through the center point O to the X-ray focal point (i.e. radius), L is the distance between surfaces 6 and 7, L ₀
is the distance between surfaces 5 and 6. Therefore, when imaging is performed with the tube voltage of the X-ray tube 1 constant, there is a problem in that the density of the shadow image produced on the film 2 changes moment by moment as the X-ray tube 1 moves.

In order to eliminate this inconvenience, conventional tomography apparatuses that move the X-ray tube 1 and film 2 in one dimension (that is, take a straight trajectory) use mechanisms such as simple harmonic motion (single chord motion). 2-dimensional movement (such as an elliptical orbit, but a circular orbit whose central axis is the normal line passing through the center point of the cross-sectional layer) (excluding the above), a method has been considered in which the X-ray current is electronically controlled by following the position (see Japanese Patent Laid-Open No. 58-20117, etc.). However, the former method is mechanically complicated and cannot be applied to anything other than a straight trajectory. Furthermore, in the latter case, since the tube current (mA) value changes during imaging, it is difficult for the operator to know at what mA the final imaging was performed, and moreover, strict control is difficult due to the characteristics of thermal inertia.

In addition to these, it is possible to correct using the X-ray tube voltage, but to do so, the X-ray tube voltage generator must have a slide autotransformer type structure or a tetrode tube type. However, it is expensive and difficult to use practically.

(C) Purpose This invention is an improved tomography system that can correct changes in radiation intensity due to changes in distance, is relatively inexpensive, sufficiently practical, and can adopt any trajectory. The purpose is to provide equipment.

(d) Configuration In the tomography apparatus of the present invention, the radiation irradiation means and the two-dimensional radiation detection means are arranged opposite to each other with the object in between, and both are symmetrically arranged around the center point above the cross-sectional layer in the object. When moving, the position of the radiation irradiation means or the two-dimensional radiation detection means is detected, the distance between them is determined from this position, and the above movement is performed at a speed inversely proportional to the square of this distance. I have to.

(E) Embodiments In the embodiments shown below, the present invention is applied to a type of tomography apparatus that can employ various trajectories. In order to be able to create various trajectories, it is necessary to combine rotational motion and linear motion, so to express it schematically, as shown in FIG. This means that the linear motion mechanism 9 is held by the rotary motion mechanism 8 that rotates the linear motion mechanism 9. Although not shown in FIG. 2, the film 2 is connected to the X-ray tube 1 via a connecting lever rotatably supported around a center point O (see FIG. 1) as a fulcrum.
When the X-ray tube 1 moves on various orbits such as a spiral orbit, the film 2 moves symmetrically about a point O with respect to the movement of the X-ray tube 1. A mechanism for achieving such relative motion has been commonly used in tomography apparatuses, so its explanation will be omitted.

Such movement of the X-ray tube 1 is performed by motors 14 and 17, respectively, incorporated in a control system as shown in FIG. The motor 14 drives the rotary motion mechanism 8, and the motor 17 drives the linear motion mechanism 9. In the control system shown in Fig. 3, 11
is a setting section that selects and sets arbitrary trajectory conditions. Motor control information regarding various trajectories is stored in advance in the main control unit 12, and motor control information can be specified from among these control information according to set orbit conditions or other external conditions. motor control information is modified according to the trajectory newly set in the setting unit 11, and each of the two motors 14 and 17 is simultaneously controlled using this control information to form a specific trajectory. Control commands to do this are issued by the main controller 12 in response to operating signals that provide commands to start and stop movement. This control command is given to the motor controllers 13 and 16 at the same time, and the rotational and radial movements are controlled simultaneously. At this time, the actual rotational speeds of the motors 14 and 17 are detected by the rotational speed detection sections 15 and 18, respectively, and fed back to the motor control sections 13 and 16, respectively. Drive signals are supplied from the motor control units 13 and 16 to the motors 14 and 17, respectively, so that the motors 14 and 17 match. Reference numeral 19 is a coordinate position detecting section, and the motor 1
The coordinate position of the X-ray tube 1 in motion is calculated from the signals obtained by detecting the actual rotational speeds of the X-ray tubes 4 and 17. Radius r from the position thus determined (see Figure 1)
Based on this value of r, the main control unit 12 performs an operation to obtain the square of the distance given as a function of r, that is, {(ar) ² +L ² }, and calculates the square of the distance, which is inversely proportional to the square of this distance. The rotational speeds of the motors 14 and 17 are determined and commands are issued so as to obtain a moving speed of the X-ray tube 1.

Therefore, in this way, the moving speed of the X-ray tube 1 changes in inverse proportion to the square of the distance from the X-ray tube 1 to the film 2, and when the distance is large, the X-ray intensity reaching the film 2 is small. When the distance is small and the X-ray intensity is high, the exposure speed is slow (that is, the exposure time is shortened), so the amount of X-rays irradiated to the film 2 is always constant.

Although the parallel plane type has been mainly described above, an arc movement type in which the moving surfaces of the X-ray tube 1 and the film 2 are spherical surfaces centered on the center O can be similarly applied. However, in the arc movement method, the distance between the X-ray tube 1 and the film 2 does not change, so in a spiral trajectory, the movement is not constant angular velocity but constant velocity.

(f) Effects According to this invention, the distance between the radiation irradiation means and the two-dimensional radiation detection means is determined, and the
Since these movements are controlled to be performed at a speed inversely proportional to the multiplication factor, it is possible to correct the intensity of radiation incident on the radiation irradiation means, which changes with the change in the distance described above. Moreover, since this is done by improving the control system, it can be realized at a relatively low cost and is quite practical in this respect. Furthermore, because of this improvement in the control system, the irradiation radiation dose can be made uniform no matter what arbitrary trajectory is adopted.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the operation of the tomography apparatus, FIG. 2 is a perspective view schematically showing the movement mechanism of the tomography apparatus according to an embodiment of the present invention, and FIG. 3 is the same embodiment. FIG. DESCRIPTION OF SYMBOLS 1... X-ray tube, 2... Film, 3... Table, 4... Subject, 5... Tomographic plane, 8... Rotational movement mechanism, 9... Linear movement mechanism, 11... Setting section,
12... Main control section, 13, 16... Motor control section, 14, 17... Motor, 15, 18... Motor rotational speed detection section, 19... Coordinate position detection section.

Claims (1)

[Claims] 1. A radiation irradiation means for irradiating a subject with radiation, a two-dimensional radiation detection means arranged opposite to the radiation irradiation means with the subject in between so that the radiation transmitted through the subject is incident, and the radiation irradiation means a moving means for moving the two-dimensional radiation detecting means symmetrically about a center point on a tomographic plane set in the subject; a means for detecting the position of the radiation emitting means or the two-dimensional radiation detecting means; The radiation irradiation means and 2
Find the distance to the dimensional radiation detection means and calculate this distance by 2
The above radiation irradiation means and 2 at a speed inversely proportional to the
A tomography apparatus comprising a control means for moving a dimensional radiation detection means.