Device for the Recording and Reproduction of X-Ray Pictures

The invention relates to a device for the recording and reproduction of X-ray pictures, employing a layer of amorphous selenium which is disposed in a suitable housing.

To improve the picture quality and contrast of a recording of X-ray pictures, in comparison to the conventional photographic plates, it is already known to utilize the so-called "xero-radiography" process in which the X-rays hit a layer of amorphous selenium having a high dark resistance which is already charged prior to the exposure. The X-ray quanta produce high-speed photo-electrons in the selenium which, in turn, produce electron-hole pairs, as result of which a breaking down of charge occurs. Such layer is developed by dusting with a cloud of powder, for example, consisting of toner particles, whereupon the toner image is transferred by an electric field to an applied paper and is fixed by suitable thermal treatment.

It will be apparent from such a complicated development process that only low image production rates can be achieved and a radioscopic process in the form of series investigations is out of the question.

The invention has as its objective, the production of a device for the recording and reproduction of X-ray pictures with high contrast, by means of which high image rates can be achieved, whereby the device is also suitable for radioscopic series investigations.

This objective is realized in the invention, in conjunction with the use of a layer of amorphous selenium disposed in such a housing, by the provision of a thermoplastic layer at one side of the selenium layer, with an electrode being disposed on the free surface of the opposite side of such layer. Preferably, an additional dielectric reflector is disposed between the thermoplastic layer and the selenium layer.

In a specific exemplary embodiment, an additional movable corona-charge electrode is provided which is disposed to enable charging of the free surface of the thermoplastic layer when desired, to provide even greater sensitivity.

For effecting a read-out of a recorded structure in accordance with the invention, a schlieren or phase-contrast optics may be provided, disposed to receive reflected optical radiation impacting the recorded structure, a partially transmissive reflector being disposed between the optics and the recorded structure for directing optical radiation on such structure while at the same time, permitting radiation reflected from such structure to pass through the reflector to the optics.

Referring to the drawings, in which like reference characters indicate like or corresponding elements:

FIG. 1 is a semi-diagrammatic figure schematically illustrating a device in accordance with the invention during recording thereof; and

FIG. 2 is a similar figure illustrating the use during reproduction of a recorded structure in accordance with the invention.

Referring to FIG. 1, the reference numeral 1 designates the X-rays which are to be recorded and which have passed through an object 2. Disposed in a housing 3 is a layer 5 of amorphous selenium having a thickness, for example, of 150 to 300.mu. and having a high dark resistance of over 10.sup.15 ohm/cm. Disposed on the upper surface of the selenium layer, as viewed in FIG. 1, is an electrode, while disposed at the opposite side of the selenium layer is a dielectric layer 6 which is interposed between a thermoplastic layer 7 and the selenium layer 5. Also disposed in the housing 3 adjacent the thermoplastic layer 7 is a movable corona-charge electrode 8, by means of which the exterior free surface of the thermoplastic layer 7 can be provided with a surface charge.

Prior to the exposure of the photo-conductive selenium layer with the X-rays, the thermoplastic layer 7 is suitably charged to a few kV, after which the selenium layer is exposed to the X-rays. Each X-ray quantum produces in the selenium a high-speed photo-electron which in turn produces an electron-hole pair, whereby, as a result of the charge flow produced in the selenium, the voltage across the thermoplastic layer increases following exposure to the X-rays 1. The charge distribution arising in the selenium layer 5 produces a corresponding, locally variable voltage distribution in the thermoplastic layer 7 so that during the development of the thermoplastic film a surface relief 9, as illustrated in FIG. 2, is formed. Such development of the thermoplastic layer can be achieved in known manner, for example, by means of the heatable electrode 4 or by infra-red radiation following which the surface relief 9 is fixed by cooling.

In order to increase the sensitivity of the arrangement, during the heating of the thermoplastic layer 7, the electrode 4 can be connected to a high voltage, whereby the thermoplastic layer is disposed in a field of approximately 100V/.mu..

In order to further increase the sensitivity, the phase relief produced on the thermoplastic layer can be subsequently reinforced or strengthened, for example, by again charging the thermoplastic layer with the corona-charge, followed by a further development with heat.

Read-out of the X-ray pictures, taken in accordance with the invention, is schematically illustrated in FIG. 2, in which the surface relief 9 is read out by means of an optical radiation 12 directed upon the surface relief 9, for example by means of a partially transmissive reflector 10. Following impacting of the radiation upon the surface 9, it is reflected, with such reflected radiation passing through the reflector 10 and into a schlieren or phase-contrast optics 11 from which it is projected upon a suitable screen 13.

As the X-ray information often is of a very low frequency, and the degree of deformation of the thermoplastic material dependent upon the layer thickness-at higher frequencies, advantageously a grid may be produced on the thermoplastic layer, prior to the exposure thereof with the X-rays, for example by the interference of two laser beams and the subsequent development of the thermoplastic film. Thus, after the exposure to the X-rays and the heating, not only does the surface relief produced by the X-rays arise but also a phase relief produced by the grid structure. As a result of this multiplication of the X-ray picture with a high frequency grid structure, the sensitivity and thus the signal-to-noise ratio of the process can be improved. During read-out, the grid structure can be very easily removed by means of a filter in the schlieren or phase-contrast optics. Another possibility of effecting application of a suitable grid structure, resides in the disposition of an absorption grid for X-rays, i.e., a plate coated with gold, in the X-ray path, ahead of the electrode 4.

The present invention thus enables the recording and reproduction of X-ray pictures of particularly high contrast and in a rapid and economical manner.

Having thus described our invention it will be obvious that although various minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent granted hereon all such modifications as reasonably, and properly come within the scope of our contribution to the art.