Collimation for Imaging the Myocardium

Line-source response functions and modulation transfer functions (MTFs) were used to compare the resolution obtained with four myocardial-imaging agents: 129Cs, 43K, 13N-ammonia, and 81Rb contamination. When an Anger camera with pinhole collimator was used, the order of decreasing resolution was 129Cs, 43K, 13N, and 81Rb. Two techniques were employed to determine the extent to which spatial resolution could be improved. The first, involving the addition of lateral shielding, improved the MTFs for all the agents studied. The second, which utilized a subtraction mode, gave the best overall results. With the second method the MTF curves for 129Cs and 43K became very similar and were superior to both 81Rb and 13N. Both techniques were found useful in improving the spatial resolution of certain myocardial-imaging agents by reducing or eliminating the effects of penetration of the pinhole collimator walls by high-energy photons.