Design of a collimator for breast-specific gamma imaging and assessment of NEC rate for a pet scanner using Monte Carlo simulations and response surface methodology

This thesis is composed of two studies that demonstrate the implementation of Monte Carlo (MC) simulations and response surface methodology (RSM) to specific problems in planar and tomographic nuclear medicine imaging. In the first study, the collimator of a planar small field-of-view continuous crystal breast specific gamma camera is optimized by maximizing the lesion contrast-to-noise ratio (CNR) with respect to hole diameter, septal thickness and hole length. This study demonstrated that the pairwise interaction effects of the collimator parameters play a key role in determining the set of optimal parameter. As a result of optimization, a considerable improvement of up to 73% in CNR with respect to the reference collimators is achieved. Moreover, the critical region for detectability shifted towards the direction of smaller lesion diameter and lower tumor-to-background ratio. Another conclusion of the study is that the optimizer adapts itself to the spatial resolution/sensitivity trade-off as the lesion depth changes. Based on these findings, we conclude that the advantages obtained with this approach may lead to an advancement in collimator design. Whereas, the second study is involved with the positron emission tomography (PET) camera performance based on the noise-equivalent-count rate (NECR). In this part, the effect of lower energy threshold (LET) and coincidence time window (CTW) on NECR is investigated over a range of activities. Our findings showed that both LET and CTW showed significant linear and quadratic effects. Moreover, the evidence of presence of interaction among parameters makes this approach superior in comparison to conventional one-variable-at-a-time assessment techniques. Through an in-depth literature review, the proposed approach is also shown to be useful for a range of cameras for both human and animal use, as well as organ-specific and time-of-flight PET scanners.