Attenuation Correction Methods for Dual Gated Myocardial Perfusion SPECT/CT

Abstract

Dual respirator!y-cardiac gating (DG) method was shown to produce motion-freeze myocardial perfusion SPECT images. However, appropriate attenuation correction (AC) for DG SPECT is yet to be determined. This study aims to evaluate the performance of various attenuation maps for DG cardiac SPECT. We used the 4D Extended Cardiac Torso (XCAT) phantom to simulate a male patient with respiratory cycle of 5 s and respiratory -motion amplitude of 2 cm along the z-axis. The respiratory cycle was divided into 1152 frames which were grouped to 6 respiratory and 8 cardiac phases, i.e., a total of 48 phases. The corresponding attenuation maps were grouped to represent different AC maps: DG CT (DCT), respiratory gated CT (RCT), average CT (ACT), interpolated CT (ICT), HCTs at endinspiration (HCT-in), end-expiration (HCT-ex) and midrespiration (HCT-mid) respectively. The ICT was obtained by interpolation based on the motion vector generated between HCTin and HCT-ex from affine+b-spline image registration. We used an analytical projector to simulate a LEHR collimator with 120 noise-free projections over 180°, which were later reconstructed by OS-EM method using different AC maps respectively. For each cardiac phase, reconstructed images from different respiratory phases were registered to end-expiration and summed to get a registered cardiac image. Polar plots were generated for 8 registered cardiac images and relative difference (RD) was computed for each segment for the 17-segment analysis. For all cardiac phases, the average RD max for AC with ACT, HCT-in, HCT-ex, HCT-mid, RCT and ICT comparing to DCT were 4.09%, 9.24%, 5.04%, 4.02%, 3.22% and 2.85% respectively. Since DCT and RCT are clinically challenging due to the high radiation and implementation complexity, ICT is recommended for AC in DG cardiac SPECT, followed by HCT-mid or HCT-ex, with good accuracy and relative low radiation dose.