Use of systematic surface roughing to enhance the spatial resolution of the dual-ended readout of axially-oriented 100 mm long LYSO crystals.

In this work we explored the effects of using systematic band patterns of surface roughing to modulate the light transport in a dual-ended readout detector for PET imaging that uses 100 mm long LYSO crystals oriented in the axial direction. The long surfaces of 3 × 2 × 100 mm³ LYSO crystals, initially polished on all sides, were systematically roughed in a band pattern with 0.8 mm bands of roughed surface spaced at 5 mm increments over the central 8 cm of the crystal length. Cases of one to four surfaces of the crystal roughed with this pattern were explored. Two configurations of bands were examined for the opposite surfaces of the crystals: (i) bands created in the same axial location (coinciding bands) and (ii) band locations interleaved (interleaving bands). Each crystal was then wrapped in Teflon and read out at both ends using position sensitive photomultiplier tubes (PSPMTs). An electronically collimated 511 keV photon beam was oriented perpendicular to the long direction of the crystal and data acquired at discrete locations along the crystal length. The ratio of the two PMT signals was used to find the axial position of interaction and axial-positioning resolution in the light sharing direction of the dual-ended readout detector while their sum was used to determine the light output and energy resolution. The axial-positioning resolution corrected for the beam width improved from an average of 8.7 mm FWHM with no surface treatment to 5.9, 3.9 or 3.4 mm FWHM for coinciding band patterns on one, two or four surfaces, respectively. The banding patterns resulted in degraded energy resolution, with a decrease from 11.1% FWHM for the untreated crystal to 12.0%, 13.5% and 13.6% for the patterns on one, two and four surfaces, respectively. When the axial-positioning resolution is corrected for the beam width, we estimated the best resolution for the case of four banded surfaces to be 3.4 mm FWHM in this study. The same axial-positioning resolution was obtained when interleaving bands were created on only two opposite surfaces with a better energy resolution of 12.2%.