Design considerations of small crystal positron camera systems

Positron emission tomography (PET) is an important Nuclear Medicine technique, which is used to determine the spatial distribution of the uptake of administered tracer substances labeled with positron emitting radionuclides. Initially PET was used as an imaging technique. The methodological demands are in this case less severe than when quantitative estimations are attempted. In the latter case it is necessary to make accurate corrections to insure that the estimates are reproducible and unbiased. The most important corrections are those that concern absorption, random and scattered coincidences. A series of LSF studies have been performed in order to investigate the figures of merit of small crystal positron camera systems, as a function of crystal materials and crystal geometry choice. Three crystal materials have been considered - BGO, GSO and BaF2. The experimental results will in a future study be used to validate results from Monte Carlo simulation. Two detector arrays with 5-10 crystals each were used, the number depending on the crystal width. The investigated crystal widths were 2, 4 and 5.5 mm in the BGO case, 6 mm in the GSO case and 6 and 7 mm in the BaF2 case. Only one crystal in the crystal group was mounted on the photomultiplier tube. The others served to give a realistic scatter and crystal penetration environment