A Compton camera for nuclear medicine applications using In-113m

Theoretical studies show our prototype Compton camera, C-SPRINT, matches th e Tc-99m performance of clinically available mechanically collimated system s if an advantage in sensitivity of similar to 45 can be achieved. Imaging at higher energies substantially reduces the required sensitivity advantage . At similar to 400 keV, our Compton camera system needs only five times th e raw count rate of a mechanically collimated system imaging at 99mTc energ y to reach the performance "break even" point. We analyze our C-SPRINT syst em performance for the isotope In-113m(391.7 keV), and compare it to a coll imated system imaging Tc-99m. In-113m has been used in nuclear medicine app lications in the past, and can potentially be used to label many of the sam e radiopharmaceuticals as Tc-99m, In order to fully compare the two systems , their relative sensitivities are combined with the relative amount of use ful gamma rays that escape the object being imaged (the patient) for the sa me patient radiation dose. Results for uniformly distributed sources show t hat for equal lifetime radiation dose, the ratio of useful Tc-99m to In-113 m gamma rays is 1.59. For a point source of activity centered inside the el lipsoid, the useful ratio decreases to 1.33. These fractions scale up the r equired raw sensitivity advantage to yield a required sensitivity advantage of 5 - 8. Monte Carlo simulations have shown that a raw sensitivity advant age of 25 can be achieved by improving C-SPRINT geometry and using a larger volume of silicon detectors. We conclude that gains of 3-5 in noise equiva lent sensitivity are achievable when imaging In-113m with our Compton camer a relative to a collimated system imaging Tc-99m. (C) 1999 Elsevier Science B.V. All rights reserved.