Preliminary study for the development of a tweezers-type coincidence detector for tumor detection

We have conducted a preliminary study for development of a tweezer-type coincidence detector for tumor detection in procedures such as FDG-guided surgery. The detector consists of a pair of LSO scintillators, optical fibers, a pair of photo-multiplier tubes (PMTs), and a coincidence circuit. Because the LSO scintillators are located on the tips of tweezers, a target organ such as a lymph node or the colon can be positioned between them. The size of a single LSO was 3.7 mm×3.7 mm×10 mm, and the scintillation photons are transferred to the PMTs via 2-mm-diameter, 1-m long optical fibers. The results show that the light loss due to the fiber was significant but there was sufficient light to observe the photo-peak of the 511-keV gamma photons. Sensitivity response function perpendicular to the detector has a full-width at half-maximum (FWHM) of 2.5 mm, while that parallel to the detector has a FWHM of 5.5 mm. Background counts due to the natural radioisotope in 176Lu can be observed when the distance between these two scintillators is small. Results also show that the absolute sensitivity was 0.057% at the center of the detector when the two LSOs were 10 mm apart and that the optical fiber was insensitive to bending up to a radius of 10 cm. From these results, we conclude that the proposed tweezers-type coincidence detector could be some interest for tumor detection using FDG, such as that in radio-guided surgery.