Impact of Collimator on DaT-SPECT Imaging: Monte Carlo Simulation Study

Aim: The purpose of this study was to assess the impact of the collimator in viewing the dopamine transporter, using 123I ioflupane single-photon emission computed tomography (DaT-SPECT) images utilizing a Monte Carlo simulation. Methods: For the purpose of this study, the Monte Carlo simulation of electrons and photons (MCEP)- SPECT was used. A numerical phantom was created from a real basal ganglia phantom and installed within the code. The specific binding ratios (SBRs) were 5.03 and 2.01 for the background concentration of 7.44 kBq/mL or 7.04 and 3.03 for a background concentration of 5.56 kBq/mL. The simulated images were evaluated using a recovery coefficient (RC). Initially, we simulated the performance of 14 collimators without resolution correction to investigate the impact of the collimator dimension. The effects of two resolution correction methods (collimator broad correction (CBC) and three-dimensional frequency– distance relationship (3D-FDR)) on two reconstruction methods (Ordered-Subsets Expectation Maximization (OSEM) and Filtered back projection (FBP)) was assessed for collimators that demonstrated a better RC value. Results: Five low-energy high-resolution (LEHR) collimators and one medium-energy general-purpose (MEGP) collimator demonstrated superior RC values. These collimators had a high aspect ratio (holelength/hole-diameter). The maximum RC value without resolution correction was 64.9% when the image was reconstructed with OSEM. The RC value improved to 79.7% when the resolution correction of CBC was applied. When the resolution collection was applied, the RCs improved by approximately 1.2 times when compared against those without the resolution correction. In terms of the reconstruction method, the RC obtained using OSEM was statistically insignificant when compared to the RC using FBP. The difference in the RC value with collimators decreased according to resolution correction. Conclusion: The LEHR collimator with a high aspect ratio, and the OSEM with spatial resolution correction were confirmed to be appropriate for DaT-SPECT imaging. In terms of the reconstruction method, CBC was more favourable than FDR.