Performance of collimators used for tomographic imaging of I-123 contaminated with I-124.

Iodine-123 prepared from the 124Te(p,2n)123I reaction is contaminated with between 3% to 5% I-124 when imaging is performed. The effects of such a mixture were evaluated for medium-energy and low energy general-purpose collimators on a commercially available rotating gamma camera equipped to perform tomography. The planar sensitivity for I-123 was less for the general-purpose collimator, varying between 0.84 and 0.85 in water relative to that measured for the medium energy-collimator. Counts due to scattering or septal penetration of I-124 photons were greater for the general-purpose collimator (36%) than for the medium-energy collimator (15%). Evaluation of the higher-frequency components of the modulation transfer functions confirmed that the low-energy general-purpose collimator is expected to offer significantly more contrast information at frequencies above 0.21 cycles/cm. This is expected to contribute to image quality when studies are performed with collimators of similar design.