A novel Concept for Prostate Dedicated PET scanner: A 4-layered Detector with Depth of Interaction and Time of Flight Capabilities

With the emergence of organ-specific PET scanners with smaller gantry size and non-cylindrical geometries, the need for specific PET detectors with high sensitivity and resolution is becoming more highlighted. Implementation of depth of interaction (DOI) and time of flight (TOF) capabilities in the detector appears to be the key solution for the simultaneous improvement of resolution and sensitivity. In this work, we introduce a 4-layer detector tower with a dual-sided readout scheme enabling DOI andTOF capabilities. The detector has dimensions of $18 \times 18 \times 30$ mm and is configured with 4 layers of eight $2.05 \times 4.4 \times 30 \mathrm{~mm}$ Lutetium Fine Silicate (LFS) crystals. Two arrays of 16 strip Multi-Pixel Photon Counters (MPPCs) are attached to opposite sides of the detector, so that each crystal is read by 8 MPPCs (4 from each side). An in-house manufactured flood source, placed between two identical detectors, was used to calibrate energy, time, linearity, and later to evaluate the coincidence time resolution (CTR). The spatial resolution was measured using slit illumination of the detectors (${\lt}1 \mathrm{~mm}$ width). The detector showed excellent uniformity with less than 7% non-uniformity. The energy resolution was 87 keV (17%) full-width at half-maximum (FWHM) at 511 keV. The resulting CTRfor tower vs tower was 189 picoseconds, improved to 170 ps for layer vs layer. The DOI resolution and the resolution along the crystal pixelation are similar to the pitch of the crystals (4.5 and 2.25 mm, respectively). The resolution within the 30 mm elongation of the crystals was 4.7 mm FWHM. The this detector showed precise timing andspatial resolution, along with high sensitivity due to its 4-layer structure, making the proposed concept a potential candidate for organ-specific and noncylindrical geometry scanners.