Experimental results from the C-SPRINT prototype Compton camera

A Compton camera is being tested for nuclear medicine applications. Our design uses a single 3 cm by 3 cm silicon pad detector as the first detector system, and SPRINT, an array of position-sensitive sodium iodide modules, as the second detector. Experimental results with a ^99mTc point source show coincidence energy spectra agreeing with theoretical predictions. The coincidence energy spectra for both silicon and SPRINT detectors correspond to the geometry-determined scattering angle range. Recorded energy falls outside of strict geometric limits because of Doppler broadening and detector energy resolution effects. The summed energy peak in the initial data run for a ^99mTc source has a FWHM energy resolution of 33 keV, primarily due to energy uncertainty in the SPRINT modules. A second data run showed an improvement to 25 keV in summed energy resolution due to careful calibration of, and correction for, significant first and second detector gain non-uniformities. Images generated from the second acquired data set result in a backprojection 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 resolution is improved to 7 mm, although the resolution recovery is at the expense of increased noise in the image