Experimental results from the C-SPRINT prototype Compton camera

A Compton camera is being tested for nuclear medicine applications. Our des ign uses a single 3 cm by 3 cm silicon pad detector as the first detector s ystem, and SPRINT, an array of position-sensitive sodium iodide modules, as the second detector. Experimental results with a Tc-99m point source show coincidence energy spectra agreeing with theoretical predictions. The coinc idence energy spectra for both silicon and SPRINT detectors correspond to t he geometry-determined scattering angle range. Recorded energy falls outsid e of strict geometric limits because of Doppler broadening and detector ene rgy resolution effects. The summed energy peak in the initial data run for a Tc-99m source has a FWHM energy resolution of 33 keV, primarily due to en ergy uncertainty in the SPRINT modules. A second data run showed an improve ment to 25 keV in summed energy resolution due to careful calibration of, a nd correction for, significant first and second detector gain nonuniformiti es. Images generated from the second acquired data set result in a backproj ection image resolution of 1.5 cm at a source distance of 10 cm. Analytical and Monte Carlo calculations show a very close agreement of 1.6 cm. Using a list-mode maximum likelihood EM reconstruction algorithm, the image resol ution is improved to 7 mm, although the resolution recovery is at the expen se of increased noise in the image.