PARALLAX CORRECTION IN PET USING DEPTH OF INTERACTION INFORMATION

We investigate the restoration of radial resolution for transaxially o ff-center sources in a PET ring detector configuration using directly measured depth of interaction (DOI) information. Lutetium oxyorthosili cate (LSO) crystals are coupled to a photodetector along the radial di mension of the PET ring configuration. Four millimeter wide crystals a re segmented into 4mm and 10mm lengths in the radial dimension and opt ically isolated so that scintillation light is localized to the radial extent of the segment, giving 4 mm and 10 mm DOI resolution. We also segmented 2mm wide crystals into 10mm lengths. This DOI technique is u nambiguous but not practical for a multi-ring PET scanner. The objecti ve here is to quantify the intrinsic radial resolution as a function o f position within the FOV and DOI resolution. The degradation in radia l 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 effe cts at greater than or equal to 5-% off-center positions in 30mm deep crystals with 10mm of DOI resolution. Computer simulated images that i ncorporate 10 mm and 15 mm DOI in 30 mm crystals show improved resolut ion uniformity over a. system without DOI.