High Resolution Computed Tomography of Positron Emitters

High resolution computed transaxial tomography has been performed on phantoms containing positron-emitting isotopes. The imaging system consisted of two opposing groups of eight NaI(T1) crystals 8 mm × 30 mm × 50 mm deep and the phantoms were rotated to measure coincident events along 8960 projection integrals as they would be measured by a 280 crystal ring system now under construction. The spatial resolution in the reconstructed images is 7.5 mm FWHM at the center of the ring and approximately 11 mm FWHM at a radius of 10 cm. We present measurements of imaging and background rates under various operating conditions. Based on these measurements, the full 280 crystal system will image 10,000 events per sec with 400 ¿Ci in a section 1 cm thick and 20 cm in diameter. We show that 1.5 million events are sufficient to reliably image 3.5 mm hot spots with 14 mm center-to-center spacing and isolated 9 mm diameter cold spots in phantoms 15-20 cm in diameter.