JP4576980B2 - X-ray imaging device - Google Patents

Description

  The present invention relates to a medical or industrial X-ray imaging apparatus, and more particularly to an X-ray imaging apparatus using an X-ray fluorescence multiplier.

An X-ray imaging apparatus captures an image of X-rays that have passed through a subject. However, in an X-ray imaging apparatus that uses an X-ray fluorescence multiplier, X-rays that have passed through the subject are first subjected to X-ray fluorescence multipliers. Is converted into an optical image of visible light whose brightness has been increased, and this optical image is guided to an optical imaging device such as a TV imaging tube or a CCD camera by an output optical system to obtain a video signal. In general, as shown in Patent Document 1 below, for example, an iris device (a diaphragm device) for adjusting the amount of visible light incident on the optical imaging device is provided in the output optical system. It is also known to provide a control circuit system for controlling the aperture of the iris device as shown in Patent Document 2 below. For example, in a medical X-ray imaging apparatus or the like, the X-ray dose incident on the X-ray fluorescence intensifier tube varies greatly depending on the imaging technique or the condition of the subject, and as a result, the amount of visible light incident on the optical imaging apparatus also changes greatly and remains unchanged. In this case, the dynamic range of the optical imaging apparatus is exceeded, and it is necessary to adjust the incident light quantity of the optical imaging apparatus in order to avoid this and obtain an excellent X-ray image signal.
JP 20004397 A JP 11-88769 A

  By the way, in response to the miniaturization of an image sensor such as a CCD element, the miniaturization of an output optical system (usually composed of a plurality of lenses) that guides an optical image from an X-ray fluorescence multiplier to an optical imaging device has progressed. In addition, the iris device incorporated in this is also downsized. On the other hand, in medical X-ray imaging devices, the degree of change in light quantity is increasing due to diversification of X-ray diagnostic methods, and a smaller minimum aperture diameter is required, and light quantity control for obtaining a finer X-ray image signal. Improvement of accuracy is required.

  However, the mechanical accuracy, rattling, frictional force, electrical control error, etc. of the iris blade have a more significant effect on the performance as the minimum aperture diameter becomes smaller, ensuring the performance such as dimming accuracy and reproducibility of the iris device. Will become difficult. As a result, the cost of each component of the iris device is increased and the performance is deteriorated.

  As an improved method for this, there is known a method in which an ND filter is appropriately inserted in the optical path. However, if such a mechanism is provided, it becomes mechanically complicated and causes a high cost. In addition to the iris device, it is conceivable to insert a filter whose light transmittance changes according to the input voltage in addition to the iris device, but it is similarly complicated and expensive. I can't escape.

  The present invention provides an X-ray image signal that has a simple structure and low manufacturing cost, does not incur substantial light amount loss, has high light amount control performance in an iris device, and can obtain an excellent image quality X-ray image signal. It is an object to provide an imaging device.

In order to achieve the above object, in the X-ray imaging apparatus according to claim 1, an X-ray fluorescence intensifier tube, an output optical system for guiding an output optical image of the X-ray fluorescence intensifier tube, and the output optical system An optical imaging device to which the optical image guided by the optical input device is input, a dimming iris device inserted in the output optical system, and a transmitted light amount reducing film provided at the center of the optical path on the lens surface of the output optical system; Is featured.

According to the first aspect of the present invention, the transmitted light amount reducing film is positioned at the center of the optical path on the lens surface constituting the optical system that guides the output optical image from the X-ray fluorescence multiplier to the optical imaging device. Is provided. For this reason, when the iris device has been narrowed down, the amount of light transmitted by the transmitted light amount reducing film is reduced, which is the same as when the aperture diameter is further narrowed down. That is, the amount of transmitted light can be further reduced without reducing the aperture diameter. Therefore, since it is not necessary to reduce the minimum opening diameter of the iris device, avoid the situation that the mechanical accuracy of the iris blade or the error of the control system has a more significant influence, and at the time of small iris of the iris device Dimming performance can be improved. On the other hand, when the iris of the iris device is close to full open, the transmitted light amount reducing film is provided only in the center of the optical path, so the rate of decrease in the amount of light is small and not causing a problem. Due to the decrease, the light amount deviation between the central portion and the peripheral portion of the optical path can be corrected. Since the transmitted light amount reducing film is only provided on the lens surface, the processing is simple and the manufacturing cost does not increase. Since the transmitted light amount reducing film is provided at the entrance pupil position of the output optical system, the shadow of the transmitted light amount reducing film does not appear in the output image.

  Next, an X-ray imaging apparatus embodying the present invention will be described with reference to the drawings.

  FIG. 1 is an overall schematic view of a medical X-ray imaging apparatus according to an embodiment of the present invention. As shown in FIG. 1, X-rays are irradiated from an X-ray tube 11 toward a subject (subject) 10, and X-rays transmitted through the subject 10 enter an X-ray fluorescence multiplier tube 12. This X-ray fluorescence intensifier tube 12 multiplies incident X-rays and converts them into visible light, and an X-ray transmission image is output as an optical image from its output phosphor screen. This optical image is guided to the TV camera 14 through the output optical system 13. The TV camera 14 is an imaging tube or a CCD camera that captures an optical image, and the output optical system 13 includes an objective lens 15 for condensing and re-imaging the output optical image on the imaging surface of the TV camera 14. A TV lens 16 is provided and a TV lens iris 17 is provided. A translucent film 18 is provided on the surface of the TV lens 16 by vapor deposition or pasting.

  FIG. 2 shows an enlarged view of the TV lens 16 and the TV lens iris 17. Moreover, the front view seen from the left direction of this FIG. 2 becomes like FIG. The TV lens iris 17 includes a plurality of (here, five) iris blades 19 and a blade driving mechanism 20 that moves the iris blades 19. The size of the polygonal (pentagonal) opening when the iris blades 19 are moved. Can be changed. The translucent film 18 is provided on the surface of the TV lens 16 so as to occupy a part of the center of the optical path.

  The positions on the optical axis of the iris blade 19 and the translucent film 18 are the entrance pupil positions. The TV lens 16 (which is the same with the objective lens 15) is actually configured by combining a large number of lenses, and therefore the lens placed at a position corresponding to the entrance pupil position among the multiple lenses. A translucent film 18 is formed on the surface. In this embodiment, the area of the translucent film 18 is 1/16 of the effective opening area when the TV lens iris 17 is opened to the maximum. The light transmittance of the translucent film 18 was 25%.

  Here, assuming that the semi-transparent film 18 is not provided, assuming that the F-number at the minimum aperture of the TV lens iris 17 is 11, the translucent film 18 reduces the light to 25%. This is the same as when the opening diameter is half the opening diameter, and the F-number is 22. That is, the aperture can be reduced to F22 without changing the size of the aperture diameter of the TV lens iris 17 at the minimum aperture.

  As described above, the amount of light can be further reduced without changing the size of the aperture diameter of the TV lens iris 17 at the time of the minimum stop, so that the light amount control accuracy when the amount of light is small is improved. This is for the following reason. In general, the control accuracy of the iris opening diameter becomes worse as the opening diameter becomes smaller. Mainly, the accuracy of the mechanical position of the iris blade 19 with respect to the opening diameter increases (the backlash due to the play of the iris blade 19 increases in comparison with the opening diameter), and the control system for controlling the drive mechanism 20 of the iris blade 19 This is because the error increases with respect to the aperture diameter. Therefore, if the amount of light can be reduced without reducing the iris opening diameter, the light amount control accuracy when the amount of light is small is improved.

  When the aperture diameter of the TV lens iris 17 is twice as large as the aperture diameter at the time of the minimum aperture (that is, when the aperture diameter is set to F11), the aperture is opened more than that when the size is equal to the size of the semitransparent film 18. Sometimes, light rays that do not pass through the translucent film 18 enter the TV camera 14. Conversely, in this example, when the aperture is opened from F11, the light in the center of the optical path is reduced by the semitransparent film 18. However, at the maximum aperture, the translucent film 18 having a light transmittance of 25% only occupies 1/16 of the effective aperture area, so the light attenuation rate is 1/64, that is, a loss of light amount of 2% or less. In terms of the F value, only 0.125 is darkened. Therefore, the loss of light due to the provision of the semitransparent film 18 is so small that it can be ignored.

  Rather, here, it is noted that when the aperture is opened from F11, the light at the center of the optical path is reduced by the semi-transparent film 18, so that the difference in light quantity between the center of the optical path and the peripheral part can be corrected. Should. In general, in a lens system, the amount of light at the center of the lens is greater than the amount of light at the periphery, so that the uneven distribution of the amount of light can be corrected and the image quality can be improved. Therefore, it is possible to obtain a video signal with excellent image quality from the TV camera 14 while expanding the control range of the amount of light incident on the TV camera 14 from the X-ray fluorescence multiplier 12 in a direction in which the light amount is small.

  For example, in a medical X-ray imaging apparatus, the X-ray exposure conditions are different for each imaging technique, and in a technique that performs continuous fluoroscopy, a low dose of X-rays is exposed from the X-ray tube 11 for a long time. In a technique such as imaging or DSA, X-ray exposure with a large dose is performed for a short time. In the former technique, since the X-ray dose incident on the X-ray fluorescence intensifier tube 12 is small, the amount of visible light output from the X-ray fluorescence intensifier 12 is also reduced proportionally. In this case, since the amount of light incident on the TV lens 16 is small, it is necessary to bring the TV lens iris 17 close to being open in order to secure the amount of light necessary for the TV camera 14. In this way, when the aperture is opened, the light quantity loss due to the translucent film 18 can be a problem, but the effect of the loss is small as described above.

  In the latter method of performing X-ray exposure with a large dose, the X-ray dose incident on the X-ray fluorescence intensifier tube 12 in a short time becomes very large and the output visible light amount increases, so that the TV lens iris is increased. 17 needs to be in a state where the aperture is reduced to the minimum aperture side. However, since the light can be attenuated by the semitransparent film 18 as described above, the aperture diameter of the TV lens iris 17 does not need to be reduced so much. The control accuracy of the opening diameter is improved.

  In either of these cases, fine adjustment of the aperture of the TV lens iris 17 is required in accordance with the body shape of the subject. In particular, since the accuracy of controlling the aperture diameter is improved on the minimum aperture side, this fine adjustment is required. Adjustment can be easily performed with high accuracy.

  The translucent film 18 is provided at the entrance pupil position in the optical axis direction as described above. Therefore, even when the TV lens iris 17 is opened from F11, the translucent film 18 is partially shaded on the image. Never appear. However, when the iris opening diameter becomes smaller and approaches the semi-transparent film 18, the area ratio of the semi-transparent film 18 occupying the opening diameter increases rapidly, so that the amount of light decreases rapidly. In other words, in this example, the light amount control characteristic is steep in the aperture region close to F11 and opened from F11. Therefore, it is conceivable to provide the translucent film 18 at a position offset from the entrance pupil position in the optical axis direction. By doing so, the boundary of the semitransparent film 18 becomes optically ambiguous in relation to the position of the end of the iris blade 19 of the TV lens iris 17, so that it becomes equal to the gradation provided to the semitransparent film 18. The steep light amount control characteristic can be relaxed.

  The translucent film 18 can be formed on the lens surface by vapor deposition, coating, sticking, or the like, similarly to other lens surface treatments. Therefore, the translucent film 18 can be formed at a low cost without increasing the number of processing steps.

  In addition, the semitransparent film 18 basically reduces the transmitted light, and is not limited to the light transmittance of 25% as described above. A film having a light transmittance of 0%, that is, a completely black non-transmissive film may be used. When such an impervious film is used, when the iris aperture diameter becomes smaller and approaches the size of the film, the change in the amount of light becomes steeper than that of the translucent film. Processing is generally easier than a translucent film and can be manufactured at a lower cost.

  Needless to say, the specific structure and the like can be variously changed without departing from the spirit of the present invention.

  According to the X-ray imaging apparatus of the present invention, although it can be manufactured at a low cost with a simple configuration, there is substantially no loss of light quantity when the dimming iris device is opened at a low X-ray dose. The light quantity control accuracy can be improved when the dimming iris device is narrowed down under a large dose.

1 is a block diagram schematically showing an entire X-ray imaging apparatus according to an embodiment of the present invention. The typical side view which expands and shows only the part of TV lens iris and TV lens in the Example. The typical front view which looked at FIG. 2 from the left direction.

Explanation of symbols

10 ... Subject 11 ... X-ray tube 12 ... X-ray fluorescence multiplier 13 ... Output optical system 14 ... TV camera 15 ... Object lens 16 ... TV lens 17 ... TV lens iris 18 ... half Transparent film 19 ... Iris blade 20 ... Blade drive mechanism

Claims (1)

An X-ray fluorescence intensifier tube, an output optical system for guiding an output optical image of the X-ray fluorescence intensifier tube, an optical imaging device to which an optical image guided by the output optical system is input, and the output optical system And a dimming iris device inserted therein and a transmitted light amount reducing film provided at the center of the optical path on the lens surface of the output optical system, and the transmitted light amount reducing film is provided at an entrance pupil position of the output optical system. An X-ray imaging apparatus.

Images