Degradation of SPECT image quality due to the presence of I-124 in I-123 iodoamphetamine

The presence of small amounts of I-124 can significantly degrade image resolution on single photon emission CT (SPECT) brain scans performed with I-123 iodoamphetamine. A line source of I-123 iodoamphetamine was prepared and counted for 4 days; line spread functions were generated and the full widths at half-maximum and MTFs were calculated. Energy resolution was also evaluated. Using a three-dimensional phantom with cold spherical lesions, Tc-99m studies could easily resolve spheres 1.9 cm in diameter, while for I-123 imaging with 3%-5% I-124, resolution was reduced to 2.5-cm lesions. The results indicate that small amounts of I-124 can significantly degrade image resolution on SPECT