Minimization of Parallax Error in Dedicated Breast PET

The increase of the detector thickness and the incidence angle of impinging photons permits an enhancement of sensitivity in positron emission tomography (PET) scanners. But also increases the parallax error and leads to a worsening of spatial resolution. Instead of introducing hardware modifications in the readout electronics or in the detector, we propose in this work to model the photon penetration depth in the detector material and to account for this effect during the image reconstruction. The validation of the model was based on experimental measurements with the MAMMI breast dedicated PET. It consists of twelve detector modules of monolithic LYSO scintillators. A point-like source was acquired at several radial positions across the field of view. The performance of the model was analyzed in terms of position accuracy and spatial resolution. Full width at half maximum (FWHM) average improvement values of 1.0 mm (radial), 0.4 mm (tangential), and 0.3 mm (axial) have been measured when the photon penetration depth was taken into account. The use of the model proposed in this work allows us to design PET detectors with improved sensitivity while maintaining the spatial resolution of the scanner.