18F, 11C and 68Ga in small animal PET imaging. Evaluation of partial volume correction methods

The partial volume effect (PVE) significantly affects quantitative accuracy in PET. In this study we used a micro-hollow sphere phantom filled with 18F, 11C or 68Ga to evaluate different partial volume correction methods (PVC). Additionally, phantom data were applied on rat brain scans to evaluate PVC methods on in vivo datasets.

The four spheres (7.81, 6.17, 5.02, 3.90 mm inner diameter) and the background region were filled to give sphere-to-background (sph/bg) activity ratios of 20 : 1, 10 : 1, 5 : 1 and 2 : 1. Two different acquisition and reconstruction protocols and three radionuclides were evaluated using a small animal PET scanner. From the obtained images the recovery coefficients (RC) and contrast recovery coefficients (CRC) for the different sph/bg ratios were calculated. Three methods for PVC were evaluated: a RC based, a CRC based and a volume of interest (VOI) based method. The most suitable PVC methods were applied to in vivo rat brain data.

RCs were shown to be dependent on the radionuclide used, with the highest values for 18F, followed by 11C and 68Ga. The calculated mean CRCs were generally lower than the corresponding mean RCs. Application of the different PVC methods to rat brain data led to a strong increase in time-activity curves for the smallest brain region (entorhinal cortex), whereas the lowest increase was obtained for the largest brain region (cerebellum).

This study was able to show the importance and impact of PVE and the limitations of several PVC methods when performing quantitative measurements in small structures.