Evaluation of the Spatial Resolution Improvement of the MicroPET R4 Scanner with a Wobbling Bed

The MicroPET R4 scanner was designed for imaging small rodents like mice and rats. In many cases its spatial resolution is not good enough to perform the required task. We have implemented an eccentric motion (commonly referred to as wobbling) which is applied to the bed during scanning. The bed can wobble with a period of 8-15 seconds and a variable radius between 0.25 and 1.75 mm in 0.25 mm steps. The program which histograms the list-mode data was re-written to increase the spatial sampling by incorporating the wobble position in the sinograms. The corrections for the dwell time, apparent crystal location, and crystal-pair efficiency are applied within the program. A series of scans was performed to decide on the optimum wobble radius; it was found to be 1.50 mm. Another series of scans was performed during which a source was moved 0.25 mm between scans with and without the optimal wobble motion. The peak-to-valley ratio between two Na-22 point sources 4.0 mm apart improved from 1.75 in the conventional mode to 2.26 during wobbled scans applying a ramp filter. The bed wobbling mechanism could be added to the microPET R4 or P4 scanners without any major change and without compromising any imaging modes. The improved spatial resolution may represent a cost-effective upgrade to a trade in and purchase of the newer higher performance scanner.