Evaluation of Respiratory Gating Schemes for Cardiac SPECT Using a Population of Phantoms

Respiratory gating was proposed to reduce motion blur in cardiac SPECT. This study aims to evaluate 3 respiratory gating methods for cardiac SPECT. We used a population of 4D XCAT phantoms to simulate 10 patients injected with Tc-99m-MIBI, 6 with normal heart and 4 with heart defects. Phantoms varied in gender, body size, heart size, activity distribution and breathing pattern. For each phantom, 3 respiratory cycles were divided into 288 frames which were grouped to 6 gates with: (1) equal amplitude gating (AG); (2) amplitude gating with equal counts (CG) and (3) equal time gating (TG). Average activity and attenuation maps in each gate represented gated SPECT and CT. The end-expiratory and end-inspiratory phases were used as references. One hundred and twenty noise-free projections were generated from RAO to LPO using an analytical LEHR projector and reconstructed by OS-EM with 200 updates, using gated CT for attenuation correction. Reconstructed images in each gate were registered to referenced images using affine+bspline method, then averaged and reoriented to generate short-axis images and polar plots. Relative difference (RD) of the average image intensity was computed at each segment in 17-segment analysis based on the references. For all phantoms, the maximum RD_ALL of AG, CG and TG were 7.41 ± 4.45%, 7.10 ± 3.58% and 12.33 ± 3.80% when registered to end-expiration and 6.38 ± 2.68%, 7.22 ± 3.97% and 13.73 ± 4.95% when registered to end-inspiration. We conclude that the amplitude based methods (AG and CG) shows better performance in motion reduction.