  Intraoperative Gamma Probe (IPG) remains the current gold standard modality
for sentinel lymph node identification and tumor removal in cancer patients.
However, even alongside the optical dyes they do not meet with <5% false
negative rates (FNR) requirement, a key metric suggested by the American
Society of Clinical Oncology (ASCO). We are aiming to reduce FNR by using time
of flight (TOF) PET detector technology in the limited angle geometry system by
using only two detector buckets in coincidence, where one small-area detector
is placed above the patient and the other with larger detection-area, placed
just under the patient bed. For proof of concept, we used two Hamamatsu TOF PET
detector modules (C13500-4075YC-12) featuring 12x12 array of 4.2x4.2x20 mm3 LFS
crystal pixels, one-one coupled to silicon photomultiplier (SiPM) pixels.
Detector coincidence timing resolution (CTR) measured 271 ps FWHM for the whole
detector. We 3D printed lesion phantom containing spheres with 2-10 mm in
diameter, representing lymph nodes, and placed it inside a 10-liter warm
background water phantom. Experimental results show that with sub-minute data
acquisition, 6 mm diameter spheres can be identified in the image when a lesion
phantom with 10:1 activity ratio to background is used. Simulation results are
in good agreement with the experimental data, by resolving 6 mm diameters
lesions with 60 seconds acquisition time, in 25 cm deep background water
phantom with 10:1 activity ratio. The image quality improves as the CTR
improves in the simulation, and with decreasing background water phantom depth
or lesion to background activity ratio, in the experiment. With the results
presented here we conclude that limited angle TOF PET detector is a major step
forward for intraoperative applications in that, improved lesion detectability
is beyond what the conventional Gamma- and NIR-based probes could achieve.
