A study of depth of interaction measurement using bent optical fibers [in PET scanner]

Depth-of-interaction (DOI) measurement is an important capability for a detector suitable for use in a small PET scanner designed for breast imaging or small animal imaging. We have investigated a different scheme to determine DOI by using a position-sensitive photomultiplier tube (PS-PMT) at one end of an LSO (Lu₂SiO₅) crystal array for positioning and timing, and a single-channel PMT (SC-PMT) connected to the other end through bent optical fibers, with the ratio of the two signals being used to determine the DOI. The main advantages of this approach are that both the PS-PMT and the SC-PMT can provide high signal-to-noise ratio (SNR) outputs (improving DOI resolution), and that the necessary technology is available with easy readout electronics. Therefore, the design permits a relatively simple and practical solution to measure DOI while still maintaining good detector performance. We have successfully bent optical fibers, with a light loss due to fiber bending of less than 12% for bending angles from 90° to 130° and for a radius of curvature from 2 to 10 mm. Preliminary measurements for a detector with 2×2×21 mm³ LSO scintillators and a Hamamatsu R5900-C8 PS-PMT reveal good DOI measurement capability with this design, with the measured DOI resolution ranging from 4.2 to 6 mm. It also provides excellent crystal identification and coincidence timing performance. The attenuation and scattering effects introduced by using optical fibers were also studied