Parallax correction in PET using depth of interaction information

The authors investigate the restoration of radial resolution for transaxially off-center sources in a PET ring detector configuration using directly measured depth of interaction (DOI) information. Lutetium oxyorthosilicate (LSO) crystals are coupled to a photodetector along the radial dimension of the PET ring configuration. Four millimeter wide crystals are segmented into 4 mm and 10 mm lengths in the radial dimension and optically isolated so that scintillation light is localized to the radial extent of the segment, giving 4 mm and 10 mm DOI resolution. The authors also segmented 2 mm wide crystals into 10 mm lengths. This DOI technique is unambiguous but not practical for a multi-ring PET scanner. The objective here is to quantify the intrinsic radial resolution as a function of position within the FOV and DOI resolution. The degradation in radial resolution across 75% of the field of view was reduced by 45% (50%) with DOI resolution equal to one-half (one-third) the crystal length. Improved resolution via narrower crystals was overshadowed by DOI effects at ⩾50% off-center positions in 30 mm deep crystals with 10 mm of FOI resolution. Computer simulated images that incorporate 10 mm and 15 mm DOI in 30 mm crystals show improved resolution uniformity over a system without DOI