Resolution characterization of continuous axial sampling in whole body PET

By acquiring whole body data at a large number of small axial positions, each equal to the transaxial plane separation, one can achieve a significant improvement in image quality. This improvement is attributed to the uniform axial sensitivity achieved by allowing each detector plane measure each axial data point. By moving the bed in a true continuous motion, instead of in discrete steps, one can achieve additional improvements in image quality by eliminating artifacts due to under-sampling in the axial direction. To investigate the properties of the continuous axial sampling, measurements and simulations of an ECAT EXACT HR PET system were performed. The axial resolution of this system is 3.5 mm at the center of the FOV and the axial sampling is approximately 3.1 mm. This system clearly undersamples axially and sampling artifacts were also seen in a hot spot phantom and bar patterns, imaged in the axial direction. By moving the bed continuously and sort the data into smaller bins (<1.6 mm) these sampling artifacts were virtually eliminated. Images acquired at a high sampling frequency had better image contrast and noise characteristics after spatial filtering compared to images with the same total number of counts but acquired at a low spatial frequency.