Compact gamma-ray probe for breast imaging based on a 5-inch PSPMT and a single NaI crystal scintillator

Scintimammography is a promising technique for breast cancer detection. Scintimammography uses radiotracer containing 99m Tc that emits 140 keV gamma photons. We developed a small field of view gamma ray imaging probe called IRIS. A possible application of this probe is scintimammography. IRIS is composed by a single NaI(T1) scintillator coupled to a 5 inch round PSPMT. In order to optimize compromise between resolution and detection efficiency, we developed a Monte Carlo code modeling light transport in NaI crystals. The thickness of the scintillator (4 mm) was optimized for 99m Tc imaging. We also designed a high-resolution collimator with a 35 mm thickness and 1.7 mm hole diameter. Detection efficiency of the crystal is 65 % at 140 keV. IRIS shows a 2.5 mm global spatial resolution in contact. Energy and spatial corrections allow a ± 5 % uniformity and an energy resolution better than 10 % at 140 keV. IRIS has a 10 cm field of view and a 13 cm external diameter at the entrance face. The small size of the detector head allows placing the detector close to the breast, improving global spatial resolution. The high-resolution gamma ray imaging probe IRIS shows physical characteristics well suited for 99m Tc breast imaging.