A Monte Carlo Simulation Study of Optimization for Collimator in a Pixelated SPECT Camera

Objective

To investigate the influence of collimator hole shape, size, and material on the performance of the high-resolution SPECT camera to find the optimal collimator design using the GEANT4 application for the tomographic emission Monte Carlo platform.

Methods and Materials

The geometry of the dual head camera equipped with a pixelated CsI(Na) crystal, lead hexagonal-hole collimator, and two flat-panel H8500 position-sensitive photomultipliers were accurately described in the GEANT4 application for the tomographic emission. The basic features of the scanner were calculated by using 2 mCi ^99mTc sources.

Results

The simulated average spatial resolutions of lead hexagonal-, square-, and round-hole collimators were 2.68, 2.96, and 3.06 mm at 2.5 cm from the collimator surface, respectively. The sensitivity of the lead hexagonal-hole collimator was 10.86% and 18.84%, greater than that of the square and round holes, respectively, on the collimator surface. The measured averages of spatial resolution using gold were 16.14%, 11.39%, and 5.1% better than those of lead, tantalum, and tungsten hexagonal-hole collimators, respectively, at 2.5 cm from the collimator. The sensitivities of the tungsten, gold, tantalum, depleted uranium, and lead hexagonal-hole collimators were 0.74, 0.48, 1.127, 0.32, and 1.38 cps/μCi on the collimator surface, respectively.

Conclusions

The hexagonal-hole collimator was preferred over the square- and round-hole collimators because of the optimum sensitivity and spatial resolution offered by its regular arrangement of apertures. Also, the lower-absorption and stopping-power materials such as lead revealed relatively better characteristics at specific sensitivity, whereas higher-absorption materials such as gold showed the best spatial resolution. The collimator with finer hole size had the superior spatial resolution and less sensitivity than larger holes.