JPS641140B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an improvement of a tomographic X-ray imaging apparatus. There are two types of tomographic X-ray imaging apparatuses: those of a parallel movement type in which the X-ray tube and film move horizontally, and those of an arc movement type in which they move along an arc. Both of these methods have their advantages and disadvantages,
The former method allows the distance between the X-ray tube focus and the film to be large and the distance between the top plate surface and the film to be small, so it is possible to create cross-sectional images with less geometric blur caused by the size of the focus. An image was obtained;
Although it is superior to the latter method in terms of imaging accuracy, on the other hand, the distance between the X-ray tube focal point and the film changes during parallel movement of the two, and the As the deflection angle of the rod (with respect to the vertical line) increases and the distance increases, the amount of X-rays reaching the film decreases, making it difficult to photograph the subject at a constant density on the film surface. It has its drawbacks. Conventionally, as a countermeasure to eliminate this drawback, the horizontal movement speed of the X-ray tube was increased in the middle of the movement,
A method is used to reduce the deflection angle near both ends where it becomes large. Fig. 1 shows an example of a conventional device using this method, in which a swinging rod 4 is swingably engaged with a support shaft 3 fixed to a base, and a horizontal X-ray tube running guide. 5 and a film button travel guide 6, the X-ray tube 1 and film 2, which are connected via the swing rod 4, are moved horizontally in opposite directions in conjunction with each other. Furthermore, as a means for changing the horizontal movement speed v of the X-ray tube 1 as described above and swinging the swinging rod 4, a drive lever 8 rotated at a constant angular velocity ω is attached to the X-ray tube 1. On the other hand, it is engaged with a vertical guide 7, which is fixed via a holding mechanism, via a sliding body. Therefore, the horizontal movement speed v of the X-ray tube 1 in this case is v=rωsinθ. Here, r is the length of the lever 8. (Although the variable speed drive mechanism is shown above the X-ray tube 1 in the figure for clarity, it is normally provided below.)
The horizontal movement speed v of the ray tube 1 is varied according to a sinusoidal curve to adjust the incident X-ray dose and to perform soft start and soft stop of the X-ray tube 1. Therefore, in preparation for the run-up until the moving speed v reaches a predetermined speed suitable for starting X-ray irradiation, a fairly long preliminary running area is required, so the X-ray tube running guide 5 is long. This has the disadvantage that the apparatus becomes larger and the drive mechanism for changing the horizontal movement speed of the X-ray tube 1 becomes complicated. This invention improves the above-mentioned drawbacks of the conventional parallel movement type tomographic X-ray imaging apparatus that can obtain tomographic images with less geometric blur, and shortens the preliminary travel range required for horizontal movement of the X-ray tube. The present invention provides a tomographic X-ray imaging device in which the length of the X-ray tube travel guide is shortened to reduce the size of the device, and the horizontal movement speed is changed by a simple drive mechanism. This is what we are trying to provide. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a front view schematically showing the main components of this device. This device is almost the same as the conventional device shown in FIG. 1, but the drive lever 8 is engaged with the swinging rod 4 via a sliding member, and the vertical guide 7 also serves as the swinging rod 4 itself. The difference is that The top plate 9 is movable up and down within a certain range, and the axis of the support shaft 3 of the swinging rod 4 can be aligned with the cut surface of the subject to be imaged. Next, the operation of this device will be explained. Now, the distance between the axis of the support shaft 3 and the center of the traveling guide 5 of the X-ray tube 1 is l, the distance between the axis and the center of rotation of the drive lever 8 is a, and the length of the drive lever 8 is R. , let the constant rotational angular velocity be ω, then X
The horizontal movement amount x of the ray tube 1 (focal point of the X-ray tube) is expressed by the following equation. x=l・Rcosθ/a+Rsinθ...(a) Here, θ is the rotation angle of the drive lever 8 with the counterclockwise direction being positive. Therefore, if the moving speed of the focal point in the horizontal direction is V, then V=dx/dt=dx/dθ・dθ/dt=(a+Rsinθ)(-lR
sinθ)−lRcosθ・Rcosθ/(a+Rsinθ) ²・dθ/dt
=-Rl(R+asinθ)/(a+Rsinθ) ²・ω……(Ro
) The maximum velocity (Vmax) in this case occurs when the X-ray tube 1 moves on the vertical line y, that is, when θ=90° in equation (B). Therefore, Vmax=-
Rlω/a+R. Further, V=0 is obtained from equation (b) when the drive lever 8 occupies a rotation angle θ that satisfies sin θ=−R/a. In equation (b), for example, l=
1200mm, a=820mm, R=340mm, ω=π radian/sec, the rotation angle θ for V=0 is -
It is 24°30′. At this time, the swing angle β of the swinging rod 4 with respect to the vertical line y indicated by the two-dot chain line is
Since it is 24°30′, the movement position of the focal point (x) =
1200tan24゜30′=547mm. and from the horizontal position
By rotating the drive lever 8 in the counterclockwise direction shown by the arrow to the symmetrical position from the 24°30' inclined position shown by the two-dot chain line, the swinging rod 4 is moved 24 symmetrically with respect to the vertical line y. It can be made to swing by ゜30′. Table 1 shows the movement position (x) of the focal point of the X-ray tube 1 and its horizontal movement speed V during this swinging movement, (a),
(b) The above values were substituted for l, R, a, and ω in both equations, and the rotation angle θ of the drive lever 8 was used as a parameter to calculate the value.

[Table] In the speed curve V shown in Figure 3, the horizontal axis shows the focus movement position, and the vertical axis shows the horizontal movement speed of the focus (the maximum speed is 100
The figures in Table 1 are plotted in terms of % (expressed as %). When the swing angle β of the swinging rod 4 becomes 22°30′,
When the exposure of the beam tube 1 is started, the moving position of the focal point at that time is x=497 mm, so from FIG. 3, the moving speed V of the focal point at that position corresponds to about 60% of Vmax. If the distance between the center of the support shaft 3 and the film 2 is l', the distance between the focal point of the X-ray tube 1 and the film (Rocus Film Distance), the so-called FFD length, is approximately (l + l')/cosβ, and the deflection The FFD when the angle β = 22°30′ is approximately 1.08 of that when the deflection angle β = 0.
It's double. As a result of the experiment, the horizontal movement speed V of the focal point when the flow angle β of the swinging rod 4 is 22°30'.
However, if the deflection angle β of the rocking rod 4, which becomes shorter with FFD, is about 60% of the velocity (Vmax) when it becomes 0°, the X-ray dose received by the film surface during tomography at both deflection angles will be approximately This invention was made because of the fact that, in the conventional mechanism shown in Fig. 1, if the above condition is to be satisfied, the maximum horizontal movement speed of the focus in this case is Vmax = rω. Therefore, the rotational angle position θ of the drive lever 8 where this 60% speed can be obtained is 0.6rω=
From rωsinθ, θ=36°50′, and when the drive lever 8 occupies this rotation angle position, the swing angle β of the swinging rod 4 must be 22°30′. Therefore
rcos36゜50′=ltan22゜30′, and this l
If the length of is 1200mm as mentioned above, then r=1200
tan22゜30′/cos36゜50′=621mm. Table 2 uses these values to calculate the focal point movement position (x) and its horizontal movement speed V (expressed as a percentage with the maximum speed as 100%) in the conventional device using the rotation angle θ of the drive lever 8 as a parameter. It is something that

[Table] The speed curve v in FIG. 3 is a plot of the values in Table 2. When performing tomographic X-ray photography with this device, the height of the top plate 9 is adjusted according to the cut surface of the subject to be imaged, and the drive motor is rotated to move the drive lever 8.
Rotate clockwise and stop at the position indicated by the two-dot chain line. At this time, the swing angle β of the swinging rod 4 with respect to the vertical line y is 24°30' in this embodiment.
Next, the drive motor is rotated in the opposite direction to that described above, so that the swing angle β of the swinging rod becomes 22°30′, and as described above, when the horizontal movement speed V of the X-ray tube 1 reaches 0.6Vmax, Start the exposure of wire tube 1, and move the swinging rod 4.
passes through the vertical line y, and the deflection angle β on the left side becomes
When the temperature reaches 22°30′, stop the exposure of X-ray tube 1,
The drive motor is stopped when the deflection angle β reaches 24°30′. In this embodiment, as mentioned above, the deflection angle β
is 24°30' on both sides of the vertical line y, the rotation angle θ of the drive lever 8 is -
24°30' or 180°+24°30', and as shown in Table 1, the horizontal movement speed V of the X-ray tube 1 becomes 0, so a slow start and a slow stop are performed. During this time, the film 2 loaded in the butt key is moved to the X-ray tube by the movement of the swinging rod 4.
It moves horizontally in the opposite direction along the Butsky traveling guide 6, and the object present on the cut surface of the subject to be imaged on the film surface is selectively imaged as a clear shadow by irradiation with X-rays. . In this case, the degree of change in the amount of X-rays reaching the film 2 is small, and the subject can be photographed at a constant density on the film surface. In the tomography, as shown by the focal point horizontal movement speed curve V in Fig. 3, it soft starts from speed 0, passes through the preliminary travel area A, reaches a predetermined speed (60% of Vmax) at point _x0 , and then moves to Y. Radiation exposure started,
The X-ray irradiation ends at the −x ₀ point, which is symmetrical to the x ₀ point, and after passing through the stop preparation travel area A', the speed becomes 0 and a resoft stop occurs. In similar imaging using a conventional device, the X-ray irradiation area C is the same as that of this device, but its preliminary travel area B and stop preparation travel area B' are both larger than that of this device. That is, in this device, the X-ray tube running guide 5 can be shortened by the length of (B-A)+(B'-A')=2(B-A). As is clear from the above description, in the tomographic X-ray imaging apparatus according to the present invention, the length of the traveling guide of the X-ray tube can be shortened compared to conventional apparatuses, and accordingly, the In addition to being able to reduce the size of the X-ray tube, the swinging rod also serves as a guide for the drive lever in the speed change (drive) mechanism for the horizontal movement speed of the X-ray tube, so the drive device has a simple mechanism. be able to.

[Brief explanation of drawings]

FIG. 1 is a schematic front view of the main components of a conventional tomographic X-ray imaging device, FIG. 2 is a similar front view of the device according to the present invention, and FIG. 3 is a diagram showing the differences between the conventional device and the device according to the present invention. X-ray tube (focal point of the X-ray tube)
FIG. 3 is a diagram showing the relationship between the amount of movement and the horizontal movement speed thereof. 1... X-ray tube, 2... Film, 3... Support shaft, 3'... Sliding body, 4... Rocking rod, 5... Running guide for X-ray tube, 6... Running guide for film button key. , 8... Drive lever, A, B... Preliminary running area, A', B'... Stop preparation running area, C... X-ray exposure area, V... Horizontal movement speed of the X-ray tube of this device (velocity curve), v... horizontal movement velocity (velocity curve) of the X-ray tube of the conventional device.

Claims (1)

[Claims] 1. A swinging rod that is movably engaged with a support shaft fixed to a base, and a horizontal X-ray tube running guide and a film butt key running guide are connected via the swinging stick. In a parallel movement type tomographic X-ray imaging apparatus in which an X-ray tube and a film are horizontally moved in conjunction with each other in opposite directions, a drive having a rotation center vertically above the axis of the support shaft. A lever is provided, the lever is engaged with the swinging rod through a sliding body between the X-ray tube and the film, and the swinging rod is caused to swing by driving the drive lever to rotate. A tomographic X-ray imaging device characterized by: