DOI Encoding PET

Small-animal PET scanners have not reached the highest sensitivity and spatial resolution that is achievable, largely due to an unfavorable trade-off between resolution and efficiency in most detector designs. Our objective is to develop high resolution, high sensitivity depth-encoding detectors for in vivo molecular imaging with PET based on position-sensitive avalanche photodiode (PSAPD) technology, fololowed by construction of a high spatial resolution and high resolution uniformity prototype scanner for small-animal imaging based on the PSAPD/LSO detector modules. PSAPDs offer several attractive features including low density readout (event location is encoded in just four signal outputs), thin cross-section (enabling dual-ended read out of scintillator arrays to provide depth of interaction information) and high quantum efficiency. Preliminary data has clearly demonstrated the ability of these devices to resolve arrays of 1x1 mm cross-section LSO crystals and to provide a 2 mm depth of interaction resolution with 20 mm thick detectors. We are seeking to develop and optimize PSAPD detectors suitable for incorporation into a high resolution, high sensitivity small-animal PET scanner.

[LSO array]

7x7 LSO array, Crystal size: 0.92x0.92x20 mm³, Pitch: 1 mm

Specifically, we are performing experiments which will address the minimum resolvable LSO crystal size as a function of PSAPD surface area and temperature, the effect of different PSAPD read out schemes, depth of interaction resolution as a function of crystal length, size, and surface treatment, and the stability of PSAPDs as a function of time, bias voltage and temperature. A complete evaluation of PSAPD/LSO PET detectors will include measurements of flood histograms, individual crystal energy spectra, depth of interaction resolution, timing resolution and intrinsic spatial resolution. Quantitive comparison will be made to LSO detectors based on position sensitive photomultiplier tubes (the technology currently used in most small-animal PET systems). Finally, a simple single detector ring small-animal PET scanner will be developed using the optimized PSAPD/LSO detectors as a proof of concept. Electronics, data acquisition and image reconstruction algorithms will be developed for the PET system with depth of interaction capability. Based on these results, the performance (in terms of spatial resolution and sensitivity) of a multi-ring small-animal PET system built from these detector modules will be predicted and compared with available commercial small-animal PET scanners.

[DOI module]
One module for dual ended readout of an LSO array.
Two PSAPDs are shown, with five charge sensitive preamps
on each readout board. Connection cables are not shown.

slides from 2006 IEEE NSS/MIC conference (San Diego, CA)