Contrast recovery of hyperfixation in SPECT: interest of fan beam collimators

The influence of the collimator on the contrast recovery of hyperfixation was studied in SPECT. With a dual headed SPECT system, three parallel collimators sets and 2 fan beam collimators sets were tested with a Jaszczak's phantom. The 6 spheres of the phantom were filled with /sup 99m/Tc and 4 background levels were successively obtained progressively by filling the cylinder of the phantom providing 4 hyperfixation level. The effect of the angular and projection matrix sampling were tested. Using ANOVA, the authors demonstrated higher contrast recovery of hyperfixation when using fan beam collimators. Moreover, this experimental study shows that when using fan beam collimators it is preferable to acquire 64 projections rather than 128 for a chosen fixed acquisition time.