Contributions to depth discrimination gamma-gamma-coincidence methods in scintigraphy.

Two problems in the gamma-gamma-coincidence method for depth discrimination in scintigraphy are discussed. Firstly, the FW (1/e)M of the distribution function of time differences between 'coincident' pulses is calculated to be the optimum resolving time for measurement of true coincidences. Secondly, the improvement of time resolution of such an apparatus by substituting a large volume NaI(TI) crystal by an array of many small ones is analysed. It is shown that such arrays will have no practical advantage since the loss in efficiency is of the same order of magnitude as the gain in time resolution.