Radiant energy – Invisible radiant energy responsive electric signalling – With radiant energy source
Reexamination Certificate
1998-09-03
2001-05-08
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With radiant energy source
C250S370090
Reexamination Certificate
active
06229147
ABSTRACT:
This invention relates to the field of autoradiography.
Film autoradiography, wherein radiological grade X-ray film is used to record two dimensional spatial beta-radioactivity patterns, is a standard procedure in bio-medical research. The sample may be present as a thin tissue section or dried electrophoresis gel, such as is used in DNA ‘fingerprinting’ techniques. Film autoradiography offers considerable advantages, such as ready availability, low capital cost, very high intrinsic spatial resolution, but balanced against these advantages are some serious disadvantages, principally the very long exposure times—days, weeks or even months—required to produce a developable image. The long exposure times are a direct result of the very low activity typically present per image feature (an image feature being, for example, a discrete band in a DNA sequence). Further disadvantages associated with the use of film are the non-linear response and limited dynamic range associated therewith, and also the fact that post-processing (e.g. microdensitometry) is required in order to produce quantitative data on radioisotope uptake.
In order to alleviate the aforementioned disadvantages, a number of electronic position sensitive detectors have been employed in place of X-ray film. These techniques are:
i) Multiwire and other forms of gas proportional counters;
ii) Photoelectric image intensifiers, for instance comprising a scintillator layer, fibre optic faceplate, S20 optical photocathode and microchannel plate gain stage;
iii) Photostimulable phosphors or “Image Plates”;
iv) Fibre-optic coupled cooled CCDs.
However, each of these techniques suffers from significant drawbacks. Techniques i)-iii) have large associated capital costs. Gas counters offer spatial resolutions of the order of 1 mm and are virtually unable to detect tritium (
3
H) since the low energy
3
H betas (endpoint energy 18.6 KeV) cannot penetrate the counter window. Tritium detection by image intensifier, image plates and CCD arrangements is generally inefficient because of the small optical signal developed in the input layer. Often a fibre-optic demagnifying taper or lens is required to reduce the desired working field approximately (100 cm
2
area) to the very much smaller active area of the output sensor resulting in further loss of signal. The optical transmission of a 5:1 taper is at most a few percent.
The present invention overcomes the abovementioned problems by employing a low noise microchannel plate detector to perform autoradiography.
According to a first aspect of the invention there is provided a detector for autoradiography, the detector comprising a substantially radioisotope free microchannel plate (MCP) detector, the dimensions of the active area of said detector being substantially comparable with, or greater than, the working field of the autoradiography sample, and MCP signal collection means.
The dark count of the MCP detector may be less than 0.15 counts.cm
−2
.s
−1
.
The MCP detector may comprise potassium and rubidium free glass.
The MCP detector body parts may comprise PCTFE.
The MCP detector may be shielded against background gamma rays.
The detector may further comprise a resistive anode readout element.
The front plate of the MCP detector may be held at, or substantially at, ground potential.
The detector may measure beta particles emitted by tritium.
According to a second aspect of the invention there is provided a method for performing autoradiography comprising the steps of:
providing an autoradiography sample; and
measuring beta particles emitted by radioisotopes within said sample with a substantially radioisotope free MCP detector, the dimensions of the active area of said detector being substantially comparable with, or greater than, the working field of the autoradiography sample, and MCP signal collection means.
REFERENCES:
patent: 5475225 (1995-12-01), Stettner
Fraser George William
Lees John Ernest
Gunter, Jr. Charles D.
Ham Seungsook
Hanig Richard
University of Leicester
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