A study of depth of interaction measurement using bent optical fibers

Depth of interaction (DOI) measurement is an important capability for a det ector suitable for use in a small PET scanner designed for breast imaging o r small animal imaging. We have investigated a different scheme to determin e DOI by using a position sensitive PMT (PS-PMT) at one: end of an LSO crys tal array for positioning and timing, and a single channel PMT connected to the other end through bent optical fibers with the ratio of the two signal s to determine DOI. The main advantage of this approach is that both the PS -PMT and PMT can provide high signal-to-noise ratio outputs (improving DOI resolution) and that the necessary technology is available with easy readou t electronics. Therefore, the design permits a relatively simple and practi cal solution to measure DOI while still maintaining good detector performan ce. We have successfully bent optical fibers, with a light loss due to fibe r bending less than 12% for bending angles from 90 to 130 degrees and for a radius of curvature from 2 to 10 mm. Preliminary measurements for a detect or with 2x2x21 mm(3) LSO scintillators and a Hamamatsu R5900-C8 PS-PMT reve al good DOI measurement capability with this design, with the measured DOI resolution ranging from 4.2 to 6 mm. It also provides excellent crystal ide ntification and coincidence timing performance. The attenuation and scatter effects introduced by using optical fibers were also studied.