Performance Characterization of a Miniature, High Sensitivity Gamma Ray Camera

A compact, hand-held gamma camera with excellent intrinsic and extrinsic performance has been developed for the rapid identification and localization of sentinel lymph nodes during the surgical staging of cancer. The camera comprises a 5×5 cm² field of view NaI (Tl) pixellated crystal array, a high sensitivity lead (2.0 cm thick) hexagonal parallel-hole collimator, a position sensitive photomultiplier tube (PSPMT), and a novel highly multiplexed electrical readout. The intrinsic energy resolution (12.1±2.0%) at 140 keV including edge crystals, extrinsic sensitivity (5 cps/μCi from 1-5 cm with a 24% energy window) and extrinsic spatial resolution (1.81±0.1 mm at 0.6 cm) facilitate rapid identification of a radioactive node. Using a node phantom we performed an ideal observer study to estimate the detectability of small spheres in the range of 3 mm to 8 mm with different exposure times. With a 5 seconds exposure the camera can detect a 3 mm diameter sphere at a depth of 3.6 cm containing 1 μCi of Tc-99m within a cold background, and a 4 mm diameter sphere containing 2 μCi at 2.6 cm depth within a warm background (>10:1 contrast) with a 5 second exposure duration.