Screen for converting X-rays into light photons

Details Screen for converting X-rays into light photons Screen for converting X-rays into light photons

2002-02-28

2004-05-18

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiation responsive nonelectric signalling

Luminescent device

Reexamination Certificate

active

06737656

ABSTRACT:

TECHNICAL FIELD AND STATE OF THE PRIOR ART
The invention concerns a screen for converting X-rays into light photons.
The invention also concerns a screen panel for converting X-rays into light photons as well as a radiological device comprising such a conversion screen.
The invention applies to fields that use the conversion of X-rays into light photons such as, for example, the field of medical radiology or the filed of non-destructive testing of nuclear waste storage packages.
In the field of medical radiology, a screen for converting X-rays into light photons is associated with the means for emitting X-rays and the means for acquiring and displaying an image in order to make a radiology device.
According to the known art, a radiology device comprises an X-ray generator associated with an X-ray tube, a support (on which a patient or an object is placed), and a radiographic film. A flow of X-rays is emitted by the X-ray tube. This flow of X-rays is attenuated by the patient or the object. The residual flow that is transmitted through the patient or the object is measured by the radiographic film. There is then an interaction between the non-attenuated X photons and the radiographic film.
In the field of medical imaging, large size conversion screens are often required. For example, screens of 43 cm×43 cm are necessary to achieve “wide field” acquisitions such as pulmonary radiographs, and screens of 80 cm×60 cm are necessary for non-destructive testing.
Apart from their large size, conversion screens used in medical imaging must be as precise and have as high a performance as possible, in other words they must provide the largest number of light photons possible, for each X photon interacting with the screen.
According to the known art, such screens comprise a rigid panel (a metal sheet or a glass sheet) that is covered, on one face, by a layer of scintillating material such as gadolinium oxysulphide or cesium iodide (CsI), which ensures that the X-rays are converted into visible light. The metal sheet or glass sheet ensures that the conversion screen is rigid. Such a conversion screen in then placed in the radiological device in such a way as to ensure that the light from the X radiant image can be emitted towards the digital sensor.
This type of technology does not enable large size screens with high performance to be made. In fact, for large size screens, for example screens with dimensions greater than or equal to 40 cm×40 cm, flexion occurs in the centre of the screen.
In the event where, for example, the optics used make it necessary to have a fixed focal distance and a field depth whose precision must reach more or less 100 microns at the screen level, the slightest mechanical deformation then causes the captured image to be blurred.
The deformations in the screen may be partially corrected by increasing the thickness of the panel but then the panel absorbs part of the X-rays and the image resolution is considerably deteriorated.
In the event where a glass panel is used, another disadvantage is the presence of multiple internal light reflections within the panel, and these reflections also disrupt the proper operation of the device.
The invention does not have these disadvantages.
DESCRIPTION OF THE INVENTION
In fact, the invention concerns a screen panel for converting X-rays into light photons. The panel comprises a rigid foam plate, a first layer of composite material located on one face of the rigid foam plate and a second layer of composite material located on the other face of the rigid foam plate, parallel to the first face.
The assembly comprising the first layer of composite material, the rigid foam plate and the second layer of composite material provides a solution to the problem of making large size screens. In fact, this assembly enables a very rigid panel, in terms of deformation, to be made and which only slightly attenuates X-rays. The foam itself is rigid and does not contribute to the reduction in tension or in plating the screen. The foam plate acts as a mechanical support between the layers of composite material that surround it and thus ensures the whole panel assembly has very good rigidity. The foam has the advantage of being only slightly attenuating to X-rays and having a homogeneous structure vis á vis the X-rays.
The invention also concerns a screen for converting X-rays into light photons comprising a panel and an active layer for the conversion of the X-rays into light photons deposited on one face of the panel. The panel is a panel according to the invention.
The invention also concerns a radiological device comprising a screen for converting X-rays into light photons, whereby the conversion screen is a screen according to the invention.
According to the invention, the deformations in the screen are advantageously compatible with the precision of the field depth of the optical devices used.


REFERENCES:
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patent: 5274864 (1994-01-01), Morgan
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patent: 5519229 (1996-05-01), Verbeke et al.
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patent: 0 919 859 (1999-06-01), None
Patent Abstracts of Japan, JP 63-313100, Dec. 21, 1988.

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