Introducing a Novel Parallel Hole Collimator: The Theoretical and Monte Carlo Investigations

To assess function of various organs as well as recognize malignancy in its initial stages, single photon emission computed tomography system is employed in which the collimators can obtain the qualified images toward better diagnostic on the lesions and metabolic performance. Although new designs and optimized methods as well as the analytical models have been proposed to improve tradeoff between resolution and sensitivity in the collimators, but opposing behavior of them still remains as one of the major problems associated with the parallel hole collimators (PCs). In this paper, a new design, namely, extended parallel hole collimator (EPC) in which trapezoidal denticles are added upon the collimator septa at the detector side, has been proposed to improve performance of the PCs. Two PCs as PC
₃₅
and PC
₄₁
with hole sizes of 1.5 mm and hole lengths of 35 and 41 mm, respectively, are considered for comparison and investigation of the EPC performance. Theory and Monte Carlo simulations have been carried out to evaluate some of its related parameters such as sensitivity, resolution, and contrast. To reconstruct the tomographic images of Jaszczak phantom, the maximum-likelihood expectation maximization algorithm is chosen. The results have been indicated that the EPC has increased the amount of sensitivity as 10.2% compared to the PCs at the same resolution, and decreased the penetrating ratio as well as produced the tomographic images with lower noise coefficient (NC%), and improved contrast to noise ratio. Finally, it is found that the EPC may obtain the qualified images.