Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Patent
1991-02-28
1992-08-11
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
H01J 4702
Patent
active
051381680
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and apparatus for quantitative autoradiography analysis using electron or beta radiation from radionuclides.
A microassay technique for measuring immunological activity has been developed based on the incorporation of radioactive nucleotides into lymphocyte DNA. This allows study of multiple samples of cells taken from patients with a variety of diseases, or from experimental animals. It is not uncommon for several hundred samples per day to require assay of radioactive incorporation into samples which are harvested onto filter discs, often referred to as "dot-blots". The major limitations in the application of this technique result from the requirement to cut individual dot-blots from a multi-sample filter, transfer them to vials, add the hazardous, solvent-based, scintillant counting-fluid to each vial, cap, number and finally effect a radiation count of the individual samples using a scintillation counter. Thus this technique is extremely time consuming and involves the use of hazardous material.
An alternative method involves the use of photographic film for mapping. The principal advantages of this method, namely that photographic film is inexpensive and the spatial resolution obtained is excellent, are outweighed by the disadvantages which are that the technique is relatively insensitive because exposure times are measured in days, only limited quantitation can be obtained and even that involves the use of expensive instruments, and the technique is extremely time consuming.
Thus there is a long-felt need for a method and apparatus for the simultaneous counting of multiple samples on single filters by direct counting of radioactive emissions, so avoiding the shortcomings of the multiple sample handling and the use of the scintillation counting technique, and the photographic technique. Accordingly, this is the objective of the present invention.
The present invention is based on a high-density avalanche chamber (referred to hereinafter as HIDAC) detector first developed for the imaging of positron-emitting radioisotopes. This type of detector has been further developed over the years and one particular development is disclosed in a paper entitled "The High-Density Avalanche Chamber for Position Emission Tomograph" written jointly by the present inventor, A. P. Jeavons, and others and presented at the IEEE Nuclear Science Symposium, Washington DC, United States of America, 20-22 October 1982. The disclosure of this paper is incorporated herein by reference.
The HIDAC detector has been used very successfully in hospitals for the scanning of patients and has to date used X-ray or gamma-ray converters. The HIDAC detector comprises a plurality of converters each comprising a stack of alternate conductive and non-conductive layers, typically of lead and fibreglass, respectively. The converters are "transparent" to the incident radiation by way of being perforated. More specifically, the converters are formed with 1 mm diameter holes arranged in a triangular pattern with centre-to-centre distance of 1.16 mm. The converters may be arranged in pairs to increase sensitivity and each pair has a multi-wire chamber on each side thereof, making four multi-wire chambers in all. Each multi-wire chamber comprises a multi-wire anode inbetween a pair of multi-wire cathodes, with the wires thereof having a 1 mm pitch and with the wires of adjacent pairs of anodes and cathodes being orthogonally arranged to provide X and Y axis detection. The converters and multi-wire chambers are disposed in a gas-tight container through which a gas, for example a mixture of Ne-CO.sub.2, is passed at a pressure slightly above atmospheric pressure. A strong electric field, for example 12 kv/cm, is applied across the converter.
The use of lead in the converters is dictated by the inability of gamma radiation of itself to ionise a gas. Thus the lead is used to arrest incident photons which thus release photoelectrons from the lead which then ionise the gas. The electrons are contained within a given hole
REFERENCES:
patent: 4280075 (1981-07-01), Comby et al.
patent: 4686368 (1987-08-01), Anderson et al.
J. E. Bateman, R. Stephenson, and J. F. Connolly, "MWPC Developments at Rutherford Appleton Laboratory for Medical Imaging", Nuclear Instruments and Methods in Physics Research, vol. A269 (Jun. 1988) pp. 415-424.
A. Jeavons, K. Hood, G. Herlin, C. Parkman, D. Townsend, R. Magnanini, P. Frey and A. Donath, "High-Density Avalanche Chamber for Positron Emission Tomography", IEEE Transactions on Nuclear Science, vol. NS-30, No. 1 (Feb. 1983) pp. 640-645.
Hannaher Constantine
Oxford Positron Systems Limited
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