Quantification in Positron Emission Mammography (PEM) with planar detectors: Contrast resolution measurements using a custom breast phantom and novel spherical hot-spots

We have previously demonstrated that our Position Emission Mammography-1 (PEM-1) system can successfully detect small (<2 cm diameter) tumors. Images in the current system are judged qualitatively for the presence of focal uptake of F-18- FDG. We are presently taking steps toward quantifying the emission images To this end rye have constructed a breast phantom and developed a novel technique for fabricating very small wall-less radioactive hot-spots. The hot-spots are made by adding F-18-FDG to a 25 mg/cc solution of Agarose in water. The heated solution is poured into spherical molds which are separated upon congealing to yield robust wall-less radioactive hot-spots. The hot-spots were uniform to within 1-5 parts in 100. Less than 01% of the total hot-spot activity leaked into the background in 30 minutes. Contrast resolution experiments have been performed with 12 mm and 16 mm diameter hot-spots in the breast phantom containing water with various amounts of background activity. in both cases the observed contrast values agree well with the ideal values. in the case of the 12 mm hotspot with a 350-650 keV energy window, image contrast differed from the ideal by an average of 11%. The image contrast for 12 mm hot-spot improved by 40% and the number of detected events decreased fry 35 % when the low energy threshold was increased from 300 keV to 450 keV.