Influence of collimator hole dimensions on parallel and cone-beam brain SPECT

This study assesses the influence of collimator hole dimensions on the accuracy of brain SPECT. To this end, four low energy, parallel hole (PH) collimators and four low energy, half cone beam (CB) collimators with different hole dimensions were simulated. The simulated projection data were representative of Ultra High Resolution (UHR), High Resolution (HR), Medium Resolution (MR), and General Purpose (GP) collimators. Reconstruction was performed with the Ordered Subsets Expectation Maximization (OS-FM) algorithm with and without correction for the camera response (CRC and NCRC, respectively). The distance-dependent blurring kernel used in CRC matched the blurring used in the simulations. Image accuracy was assessed by calculating contrast-to-noise ratios (CTN) in a phantom containing cold spheres and by calculating Mean Squared Errors (MSE) between the true 3D Hoffman brain phantom and its reconstructions. For the accuracy of PH collimators, results indicate that when NCRC is applied, the UHR collimator results in better CTN ratios and lower MSE than the collimators with lower resolution. However, when CRC is applied, the GP collimator outperforms the higher resolution collimators. For the CB collimators, the low resolution collimators (GP and MR) result in the best CTN ratios and the lowest MSE, regardless if CRC is applied.