Wai-Hoi Wong 1, Hongdi Li 2, Yuxuan Zhang 1, Rocio Ramirez 1, Hossain Baghaei 1, Shaohui An 2, Chao Wang 2, Shitao Liu 2, Yun Dong 2 1 University of Texas MD Anderson Cancer Center, Houston, TX, 2 Shanghai United Imaging Healthcare Co, Shanghai, China. A high-resolution time-of-flight clinical PET detection system using the PMT-quadrant-sharing technology

The PMT-Quadrant-Sharing (PQS) detector block

LYSO is expensive (1/5 the price of gold) The Objective is to get higher sensitivity per cc of LYSO More efficient use of LYSO by increasing the axial field of view while reducing the crystal depth System Design GEANT4 MC simulation But large AFOV increases PMT and electronics cost Use PMT-quadrant-sharing reducing PMT usage by 75% for increasing AFOV cheaply 15mm deep LYSO, 28-cm AFOV

Detector Ring Design To achieve ultrahigh resolution using large PMT to increase AFOV 2.35 x 2.35 mm pitch 38-mm PMT 16 x 16 LYSO block Achieve decoding 256 crystals per PMT usage Adapt PMT-Quad-Sharing blocks to a gapless detector-ring geometry Ring has 24 modules (3 x 7 blocks) 3 blocks in-plane and 7 blocks axial The edge blocks are half-ground to fit the quadrant-sharing PMT

27.6-cm axial FOV A detector module

The “Slab-Sandwich-Slice” (SSS) Detector Production These are 15 sets of inter-slab irregular reflecting masks for a 16 x 16 array to decode 256 crystals / PMT Each reflecting mask can be cut into any shape providing many degrees of freedom to optimize crystal decoding There are 4 sandwich types in this 16 x 16 block

The SSS production method is highly uniform and precise as shown in the decoding map of these 72 detector blocks

We use the 5 th -generation HYPER Pileup-event-recovery front-end electronics Hybrid coincidence

NEMA ResolutionExpectation (mm)Measured (mm) Transaxial (1 cm)≤2.8 mm2.72 Axial (1 cm)≤3.1mm2.76 Trans Radial (10 cm)≤3.3mm3.36 Trans Tangential (10cm)≤3.2mm3.05 Axial (10cm)≤3.6mm2.96 NEMA image resolution measurement Reconstruction algorithm: FBP2D (SSRB) Pixel Size: 0.3 x 0.3 x 1.22

FWHM0 cm4 cm8 cm12 cm16 cm20 cm24 cm28 cm Mid plane P (V) Mid plane P (H) ¼ axis NP (V) ¼ axis NP (H) V: Vertical H: Horizontal PSF reconstructed image resolution (mm)

Average time-of-flight resolution 473 ps (+ 36 ps)

Very fine axial sampling, slice-to-slice separation = 1.22 mm

3 minutes/bed 4 bed positions Oncology

MIP TOF + PSF 2 min/bed, 2 iterations PSF 3 min/bed, 3 iterations TOF + PSF Recon SNR: TOF/PSF 2 min/bed 2 iterations = PSF 3 min/bed 3 iterations  2/3 scan time, faster recon, no loss of detectability SNR = (Signal – Background) / SDBackground See Jakoby, et al, Phys. Med. Biol. 56 TOF + PSF Recon SNR: TOF/PSF 2 min/bed 2 iterations = PSF 3 min/bed 3 iterations  2/3 scan time, faster recon, no loss of detectability SNR = (Signal – Background) / SDBackground See Jakoby, et al, Phys. Med. Biol. 56

Conclusions With PMT-quadrant-sharing Detector design we have developed an ultrahigh resolution TOF PET/CT It has a resolution of 2.8 mm using FBP (1.5 mm using PSF) Large axial FOV 27.6 cm, ultrafine axial sampling of 1.22 mm This large system with ultrahigh resolution uses only 576 PMT (reducing PMT and electronics cost, while increasing reliability) It has 129,024 detectors with a TOF resolution of 473 ps

These developments have been supported by:  NIH-RO1- EB PHS Grant  NIH-RO1- EB PHS Grant  NIH-RO1- EB PHS Grant  Shanghai United Imaging Healthcare Fund