High sensitivity collimators for brain SPECT

In SPECT imaging, converging collimators are known to increase the photon detection efficiency compared to conventional parallel-hole collimators. A converging half-cone-beam (HCB) collimator is especially suitable for human brain SPECT, allowing close positioning of the detector to the patient’s head, while avoiding truncation of the caudal portions of the brain. In this study, we simulated and assessed modified HCB collimators for further gain in photon detection efficiency with the same spatial resolution. Using Monte Carlo simulation, we modeled an astigmatic HCB collimator with axial and transaxial convergence in two orthogonal focal lines. This kind of astigmatic collimation allows utilization of the whole detector field of view, thus increasing the efficiency of the collimator. We also simulated a spatially-variable-focusing (SVF) HCB collimator, which has a set of axial and transaxial focal lines, and may offer a dramatic increase of efficiency for certain regions of the brain without truncating the rest of the brain. Both astigmatic and SVF HCB collimators offer the potential for improved brain SPECT.