Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1995-05-12
1997-05-20
Allen, Stephone
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250207, 2504861, 313525, H01J 4014
Patent
active
056314590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to devices producing images by the effect of excitation of a luminescent screen. It relates more particularly (but not exclusively) to the cathodoluminescent screens of radiological image intensifier tubes (called RII tube for short).
Taking the case of RII tubes for example, these tubes are used mainly in medical imaging, that is to say in the context of radiodiagnosis, where they produce a visible image which conveys the radiological image of a patient.
2. Discussion of Background
FIG. 1 diagrammatically shows conventional radiodiagnosis equipment. This equipment includes a source SX of X-rays delivering radiation RX to which a patient P is exposed.
On the other side of the patient P, that is to say opposite the source SX, the X radiation carrying a radiological image is picked up by an RII tube.
The RII tube generally comprises a vacuum enclosure 2 closed at one end by an entry window FE through which the X radiation penetrates. This X radiation then encounters an entry screen EE, the function of which is to translate the intensity of the X radiation incident at each point of its surface into a number of electrons (not represented).
To this end, the entry screen EE generally comprises a scintillator SC associated with a photocathode PhC.
The scintillator converts the X radiation into visible photons which are themselves converted into electrons by the photocathode.
A set of electrodes DE accelerates these electrons and focuses them onto a cathodoluminescent screen called exit screen ES. The exit screen ES is arranged in proximity to an exit window FS or exit wall situated at the second end of the RII tube, opposite the entry window FE.
The impact of the electrons on the cathodoluminescent screen ES makes it possible to reconstitute the image (amplified in terms of brightness) which, at the outset, was formed on the surface of the photocathode PhC of the entry screen.
The exit window FS is a transparent component generally made of glass (or possibly also consisting of an optical-fibre device), which can be made, for example, from a component fixed onto the envelope of the enclosure 2, or may even constitute a part of this envelope. The exit window FS carries the cathodoluminescent screen ES which, in general, consists of a layer of phosphor material. Under these conditions, the image, in visible light, formed by the cathodoluminescent screen ES is visible from outside the RII tube, through the exit window FS.
The image delivered by the cathodoluminescent exit screen ES is generally viewed via an optical device DO, arranged outside the RII tube, centred, for example, on a longitudinal axis 5 of the RII tube, around which axis the cathodoluminescent screen ES is also centred.
This image may possibly be distributed by the optical device Do, on the one hand, towards various image detectors, such as, for example, cinematographic and photographic imaging cameras marked 6, 7, respectively, arranged on either side of the optical device Do on a second axis 8 perpendicular to the axis 5 of the tube, and, on the other hand, towards an image detector consisting of a television imaging camera CT.
The television camera CT is linked to a visual display device DV capable, in "direct" mode, of displaying the image which is delivered in the form of electrical signals by the television camera CT (in the case of radioscopy). In the example represented, the camera CT is also linked to a signal acquisition and processing device ATS which can store and process the signals, in digital form, relating to the image (in the case of digital radiography) and possibly correct the image displayed by the visual display device DV.
Equipment like that shown in FIG. 1 is currently used successively in fluoroscopy or radioscopy mode, and in digital radiography mode. However, these two modes pose different problems.
In the case of digital radiography, the doses of X-rays are often significant (and the duration of application of the radiation is very short (a few mil
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Allen Stephone
Thomson Tubes Electroniques
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