JPS6051778B2 - X-ray generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray generator, and particularly to an X-ray generator that can change the electron beam irradiation position on an X-ray generating target, and further transmits the X-rays generated from the target through a microscopic aperture of a pinhole lens. The present invention relates to an X-ray generator which extracts a micro beam as a micro beam.

2. Description of the Related Art In recent years, devices (CT devices) for acquiring tomographic images of objects such as human bodies have been developed and are attracting attention.

In this CT apparatus, an X-ray source and an X-ray detector are moved in parallel or rotationally around an object, so that the object is irradiated with X-rays at many different angles. Figure 1 shows a CT system that uses an X-ray microbeam generator as an X-ray source that scans an electron beam over a target and extracts the X-rays generated from the target through a microscopic aperture of a pinhole lens. ing. In the figure, reference numeral 1 denotes an electron gun, and an accelerated electron beam generated from the electron gun 1 is converged onto an X-ray generation target 2 by a suitable converging lens (not shown). Target 2 1-waist 1f! lmlml! LLμJ and ILI can be changed by deflecting the IZ line. X-rays generated by irradiating the target 2 with an electron beam pass through a small aperture of a pinhole lens 4 to become a microbeam, and are projected onto a subject 5. If the electron beam irradiation position on the target 2 is changed here, the projection direction of the X-ray microbeam passing through the microscopic aperture of the pinhole lens 4 changes, and as a result, the subject 5 is scanned by the X-ray beam. That will happen. The X-rays transmitted through the subject 5 are sent to an X-ray detector 6.
The detection signal is supplied to an electronic computer (not shown) and processed. In this arrangement, an X-ray microbeam generator consisting of an electron gun 1, a target 2, a deflection coil 3, a pinhole lens 4, etc. and an X-ray detector 6 are installed.
When the X-rays are rotated around the subject 5, X-rays are projected onto the subject 5 at many different irradiation angles, and the detector 6 obtains detection data sufficient to obtain a tomographic image. Now, the density resolution or S/N ratio of a tomographic image obtained with the above-mentioned CT apparatus can be improved by increasing the intensity of the X-ray beam irradiated to the subject, that is, by increasing the power of the electron beam irradiated to the target 2. Furthermore, by narrowing the width of the electron beam image on the target 2 seen through the minute aperture of the pinhole lens 4, the spatial and spatial resolution of the image can be increased.

However, when the electron beam power is increased or the width of the electron beam image is narrowed, the temperature of the electron beam irradiated portion of the target 2 increases, resulting in damage to the target. J The present invention has been made in view of the above points, and is capable of increasing the power of an electron beam without damaging the target, increasing the intensity of the X-ray beam projected onto the subject,
Furthermore, the present invention provides an X-ray generating device that can narrow the width of an electron beam image on a target.

In the present invention, the cross-sectional shape of the electron beam irradiated onto the X-ray generating target is elongated, and the target is arranged at an angle with respect to the plane on which the electron beam is deflected.

Figure 2A shows an electron beam FG with a width of b1 and a length of h at a target T1 placed perpendicular to the deflection plane perpendicular to the plane of the paper.
FIG. 2B shows a case where a similar electron beam is irradiated onto a target Tb arranged at an angle θ with respect to the deflection plane. In Figure 2A, target T
The length of the electron beam image on a is h, but in FIG. 2B, the length h'' of the electron beam image on the target Tb is h/Sinθ
becomes. Here, the following relationship approximately holds true for the power P of the electron beam irradiated onto the target. PCX:
) (length of electron beam image) x l (width of electron beam image) As a result,
Comparing the cases of Fig. 2A and Fig. 2B, if θ = 30 figures, h'' = h'', and assuming that the width of the electron beam images in both cases is the same, in the arrangement of Fig. 2B, the electron beam The power can be doubled, and if the X-rays generated from the target are taken out at a small extraction angle, X-rays of high intensity can be obtained.

Furthermore, when irradiating electron beams of the same power in two types of arrangements, the width of the electron beam image can be set to 114 in FIG. 2B. Now, as mentioned above, if the target is placed at an angle with respect to the deflection plane of the electron beam, the target's . High intensity X-rays can be obtained without damage, and the width of the electron beam image on the target can be narrowed, but when scanning the electron beam on this tilted target, the electron beam image seen through the pinhole is It looks like it's leaning towards.

Figure 3 shows an electron beam (line segment GF) perpendicular to the plane S. The target surface T is arranged at an angle θ with respect to the plane S.
The image of the electron beam on the target surface T of the line segment GF is BC. The image BC on this target has an angle ψ like IJ when viewed from the pinhole P side.
It looks tilted. Such an inclination of the electron beam image on the target as viewed from the pinhole has substantially the same effect as widening the width of the electron beam image, and is not preferable. In the present invention, the electron beam with an elongated cross-sectional shape has the following characteristics for the deflection plane of the electron beam:
It is tilted at a certain angle and irradiated onto the target. Here, the case where there is no inclination of the electron beam image on the target as seen from the pinhole when the electron beam is tilted at a certain angle with respect to the deflection plane will be considered based on FIG. 4. In FIG. 4, an elongated electron beam FG having a length h is tilted by ψ with respect to a direction perpendicular to the plane of deflection of the electron beam. This electron beam! The component weight for the surface is ``.

Such an electron beam is irradiated onto a target surface T tilted by θ with respect to the deflection plane, and the component of the electron beam image on the target parallel to the deflection plane is indicated by AB in the figure. Component AB of the electron beam image has no inclination when viewed from the center point P of the pinhole.
Note that the portion H in the figure shows the relationship when the target is viewed from a direction perpendicular to the deflection plane of the electron beam. The following equation is derived from the relationship shown in FIG. From the above two equations.

Furthermore, the box can be approximately expressed as follows ■−
Therefore, the following relational expression is obtained.

The above equation can be further rewritten as follows.

If the target is tilted at an angle of 0 so as to satisfy equation (4), the tilt of the electron beam image seen from the pinhole side will disappear.

As is clear from equation (4), if the electron beam is deflected,
The angles α and β change accordingly, but the angles α and β
If the inclination angle θ of the target is changed locally according to changes in This results in an extremely narrow image. FIG. 5 shows an embodiment of the present invention, in which reference numeral 11 denotes an electron beam source capable of generating an electron beam with an elongated cross-section.

The elongated electron beam generated by the electron beam source 11 is deflected by an electrostatic deflector 12 to which a deflection signal is supplied from an appropriate deflection signal generation circuit (not shown), and is irradiated onto an X-ray generation target 13. . X-rays generated by irradiating the target 13 with an electron beam are extracted through a minute aperture 15 of a pinhole lens 14 and projected toward a subject (not shown). Here, the target 13 is arranged at an angle with respect to the deflection plane of the electron beam, and the angle of the inclination is as follows:
They differ from place to place so that the above-mentioned equation (4) is substantially satisfied. As a result, the electron beam image on the target seen through the minute aperture 15 of the pinhole lens 14 has no inclination, and a narrow X-ray beam is projected onto the object. The present invention has been described in detail above, but in the present invention, an X-ray generating target is irradiated with an electron beam having an elongated cross section, and the target is arranged at an angle with respect to the deflection plane of the electron beam. Since the power of the electron beam can be increased and the width of the electron beam image on the target can be narrowed, if the X-ray generator according to the present invention is used in a CT device, it is possible to obtain a tomographic image with extremely high resolution. I can do it.

In the above-mentioned embodiment, an electron beam source that generates an elongated electron beam is used; however, an appropriate electron beam source may be used to form an elongated electron beam using an astigmatism device, and the target may be irradiated with the elongated electron beam. good.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional apparatus for obtaining an X-ray tomographic image, and FIG. 2 is a diagram showing a target arranged perpendicularly to the deflection plane of the electron beam and a target arranged at an angle to the deflection plane. FIG. 3 is a diagram showing an electron beam image on the target seen from the pinhole position, FIG. 4 is a diagram for explaining the principle of the present invention,
FIG. 5 is a diagram showing an embodiment of the present invention. 11... Electron beam source, 12... Deflector,
13...X-ray generation target, 14...pinhole lenses.

Claims (1)

[Claims] 1. An electron beam with an elongated cross section is irradiated onto an X-ray generation target, and the X-rays generated from the target are taken out through the opening of a pinhole lens, and the electron beam is deflected to determine the electron beam irradiation position on the target. In the X-ray generator configured to be variable, the electron beam irradiation surface of the target is arranged to be inclined with respect to the electron beam deflection surface,
An X-ray generator characterized in that the angle of inclination varies depending on the deflection angle of the electron beam.