Design and performance of a portable positron-sensitive surgical probe

Reports the design and performance of a portable positron-sensitive surgical probe. The probe is designed to be sensitive to positrons and insensitive to background gammas including 511 keV. The probe consists of a multi-mode PMT and an 8×8 array of thin 2 mm ×2 mm plastic scintillators coupled 1:1 to GSO crystals. The probe uses three selection criteria to identify positrons. An energy threshold on the plastic signals reduces the false positron signals in the plastic due to background gammas: a second energy threshold on the PMT sum signal greatly reduces background gammas in the GSO. Finally, a timing window accepts only 511 keV gammas from the GSO that arrive within 15 ns of the plastic signals, reducing accidental coincidences to a negligible level. The first application being investigated is sentinel lymph node (SLN) surgery, to identify in real-time the location of SLNs in the axilla with ¹⁸F-FDG uptake, which may indicate metastasis. The authors´ simulations and measurements suggest that the probe´s signal to background ratio in this situation will be high. Preliminary results on the performance of the probe are presented