Evaluation of different multi-pinhole imaging geometries for SPECT imaging of Parkinsonian disorders

Focusing multi-pinhole (MP) collimators are increasingly being used for small animal as well as targeted VOI imaging. We use focused MP collimators to improve the resolution and sensitivity of photons detected from the striatal region of the brain. Simulations were based on activity distributions derived from clinical SPECT images of normal and Parkinson’s Disease patients injected with 99mTc-Trodat. Radioactive counts extracted from the clinical images were mapped onto regions of the Zubal brain phantom for input into the SPECT simulator. Simulated images were then generated modeling single pinhole (SP), nine pinhole (9PH) and 21 pinhole (21PH) collimators attached to one of the heads of a clinical SPECT scanner. The images were reconstructed using OSEM and evaluated after every iteration. The resulting image quality was evaluated using the ideal VOIs from the Zubal phantom for metrics such as contrast to noise ratio (CNR), bias, mean Uptake Ratio and standard error of the mean. In addition, for cross validation an automated feature detection and analysis tool was used for the detection and stratification of the simulated PD images. The CNR for the 9PH and 21PH was observed to increase by 66% and 81% while the corresponding noise levels dropped by 71% and 84%. Similarly the absolute bias was 64%, 28% and 22% for the SP, 9PH and 21PH respectively. Our results showed an improved performance of the MP collimators over the SP collimator configuration. The 21PH case performed well in terms of CNR and absolute bias, while the 9PH case resulted in the most accurate estimate of the true Uptake Ratio. The MP configurations were consistently observed to be superior to the single pinhole. In conclusion, focusing MP collimators were found to give improved quantification and better resolution compared to traditional SPECT acquisitions. The improved CNR enables more refined 3D visualization of the striatum, which could translate to better stratification of Parkinsonain disorders.