An investigation of partial volume effect and partial volume correction in small animal positron emission tomography (PET) of the rat brain

Partial volume correction (PVC) has been successfully applied to human PET data, where a range of methods has been used including the use of anatomical side information. The rat brain is expected to have low variability for animals of similar weight, thus making it possible to delineate volumes of interest (VOIs) on a stereotaxic atlas [1]. The aims of this study were to investigate the magnitude of partial volume effect (PVE) in small animal PET for different regions in the rat brain and to evaluate the performance of PVC based on the geometric transfer matrix method (GTM) [2] using anatomical regions drawn on a stereotaxic atlas. PVE estimates in terms of activity retention in each region and spill-over between regions were calculated by convolving each region with a measured spatially invariant point spread function. PVC was tested on dynamic microPET studies of the dopaminergic D2 receptor radioligand ¹¹C-Raclopride which were simulated using PET SORTEO, a Monte Carlo based PET simulator [3]. The kinetics of striatum and remaining brain were simulated based on the simplified reference tissue model [4] using the cerebellum as the reference tissue. A significant amount of PVE is present in microPET rat brain studies with recovery of true VOI concentration being between 52% and 20%. In the simulated ¹¹C-Raclopride study the uncorrected time activity curves showed up to 55% reduction in measured activity concentration and a bias in binding potential of up to −36%. Good activity recovery and improvement of binding potential estimation was achieved with PVC (−0.26% to −4.36% bias). We conclude that PVE has a substantial influence on rat brain studies and PVC should be used to improve quantitative accuracy. PVC using the adapted GTM method shows promising results.