Comparison of imaging characteristics of Xe-133 and Xe-127 for use in dynamic brain SPECT: a Monte Carlo investigation

The aim of the study was to determine the degree of improvement obtained by using Xe-127 as the imaging agent compared to Xe-133 for rCBF SPECT. The SIMIND Monte Carlo code was used to simulate projections of gray and white matter at a ratio of 4:1 using a realistic voxelized anthropomorphic brain phantom. Xe-133 and Xe-127 were simulated using high-sensitivity and medium-energy collimators respectively. Data were acquired into 64 projections of 128×128 matrix size. A Tc-99m HMPAO study was simulated as reference. Contrast calculations yielded values of 2.1:1, 1.8:1, and 1.3:1 between gray and white matter for Tc-99m, Xe-127, and Xe-133 respectively. A normalized profile through a transverse mid-brain slice demonstrates the improvement in resolution with Xe-127 compared to Xe-133. The difference in resolution between Tc-99m and Xe-127 are less pronounced. Further investigation is needed to study the noise characteristics of both Xenon isotopes for clinical rCBF studies. With Xe-127 and an optimized medium-energy high-resolution fan-beam collimator, it is likely that a notable increase in quantitative accuracy of rCBF estimation can be realized