Improvements in photomultiplier and TV camera tubes for nuclear medicine

Electro-optic devices such as photomultiplier tubes or TV camera tubes are used in nuclear medicine applications directly or indirectly as sensors of scintillations resulting from excitation of phosphor or scintillators by x- or γ-rays. Ideally, a detector would provide 100 percent quantum efficiency, have a read-out mechanism whose noise does not obscure the response from a single photon, and have a response time sufficiently short so as not to degrade the scintillation pulse. Photomultiplier tubes have been improved in quantum efficienctly and in response time. Photomultiplier tubes have been improved in quantum efficiency and in response time. Photocathodes, however, do not run better than 20 to 30 percent quantum efficiency. Response times can be less than 1 ns so that for the detection of ordinary scintillations, this is more than adequate. Vidicon camera tubes utilize photoconductive type sensors which can have essentially 100 percent quantum efficiency in parts of the spectrum. Unfortunately the read out mechanism introduces lag and noise so that the inherent photoconductor quantum efficiency cannot be fully realized. Recently developed silicon intensifier target (SIT) camera tubes provide a read out mechanism which overcomes much of the amplifier limitation inherent in vidicons, but again, the primary sensor is a photocathode so that 100 percent quantum efficiency is not achieved. SIT tubes are capable, however, of detecting remarkably low level light images with a minimum of lag