An LSO BLOCK detector for PET using an avalanche photodiode array

Abstract

A Block detector, consisting of a four by four array of lutetium oxyorthosilicate (LSO) scintillator crystals coupled to a two by two avalanche photodiode (APD) array was built and tested. The detector block was 8.5 by 8.5 by 10 millimeters so that the crystals were on 2.13 millimeter centers. The APD array has an active area of approximately 9 by 9 millimeters divided into four diodes of 4.5 by 4.5 millimeters each. A standard reach-through process was used to fabricate the diodes. Each of the sixteen crystals in the block was easily identified. The average FWHM of the peaks in ratio space was 4% of full scale. The average energy resolution was 16.2% for 511 keV gamma rays. A single LSO crystal coupled to an APD and put in time coincidence with a plastic detector produced a time coincidence of 1.9 nanoseconds FWHM.