Experimental study for an intraoperative probe for 18F imaging with a silicon pixel detector

Using a silicon pixel detector we have developed an imaging probe for intraoperative detection of tumor masses labeled with 18F-Fluorodeoxyglucose (18FDG) positron emitting radiotracer. The design goal is high efficiency for positron detection from tumor tissue and high rejection of the γ-ray background (511 keV annihilation quanta), coupled to imaging capabilities with submillimeter resolution. In this paper, we report on initial tests of the detector unit (linearity, sensitivity, spatial resolution, γ to β+ ratio), based on a room temperature silicon pixel detector (300 μm thick, ∼2 cm2 sensitive area) with 256×256 pixels of 55 μm pitch, coupled to the Medipix2 readout circuit. The laboratory tests carried out using 18FDG droplets showed counting linearity in the range 37–37,000 Bq, a sensitivity for (γ+β+) of 0.35 cps/Bq, an intrinsic spatial resolution of 230±5 μm with the source in contact with the detector, and a ratio γ/β+ of about 2% due to annihilation quanta.