Continuous bed motion in TOF PET: Finer planar sampling and axial image resolution

Abstract

The impact upon axial image resolution for the TOFPET portion of TOF-PET/CT (time-of-flight positron emission tomography / computed tomography) via continuous bed motion (CBM) due to finer axial/planar sampling in the projection space is examined. We try a 1.6x finer axial sampling pitch in the rebinning step (0.125cm instead of 0.2cm) and show a (slight) 6.5% improvement in full-width-half-maximum axial image resolution (0.447cm instead of 0.448cm) as a result. A 21M event count CBM TOF-PET list-mode study of an F-18 point source placed 1cm radially off from field-of-view (FOV) center was performed on a Siemens 4-Ring Biograph mCT Flow. For this single TOF-PET study, the raw, 64-bit detector-pair coincidence-event list-mode data was recorded. Also for this study, the bed moved horizontally at a constant speed of 1mm/sec with a horizontal bed position reporting (i.e. list-mode tag packets) resolution of 0.05cm. Due to a post-acquisition processing step which added bed position tag packets to the list-mode file, the reported resolution for bed position was effectively extended to 0.001cm via simple linear interpolation. It is noted that this 1.6x finer pitch sampling results in correspondingly larger projection-space data sets - data sets which take longer to reconstruct. It is also noted that such high-counting statistics for each small region of interest in the PET FOV are typically impractical and unobtainable in a normal clinical setting. The significance for clinical use is discussed.