Simulation of left ventricular dyssynchrony using the XCAT phantom

Multi-Harmonic Phase Analysis (MHPA) has been developed to quantify left-ventricular (LV) mechanical dyssynchrony with gated single photon emission tomography (SPECT) myocardial perfusion imaging (MPI). Although MHPA has shown promising clinical results, it needs to be optimized technically. The purpose of this study is to develop a tool to simulate LV mechanical dyssynchrony in gated SPECT MPI using an extended cardiac torso phantom (XCAT). A special version of the XCAT phantom was developed to control regional myocardial wall thickening using more than 300 B-splines points over the LV myocardium and 26 temporal frames over a cardiac cycle. By shifting the regional myocardial wall thickness values in the temporal domain, regional phase delays can be simulated to represent LV mechanical dyssynchrony. Gated SPECT data were created with phase delays of 0°, ±20°, ±40°, and ±60° in the anterior wall for a LV with normal perfusion. The activity maps given by XCAT were submitted to a SPECT simulator to generate gated SPECT projections. The gated SPECT projections were reconstructed and reoriented into gated short-axis images, which were then submitted to MHPA. A correlation of R² = 0.9941 between MHPA measured and simulated regional phase delays was obtained, indicating that MHPA can accurately measure the simulated phase delays. Thus, a simulation tool based on the XCAT phantom has been developed to simulate regional phase delays, which can be accurately measured by MHPA. This tool can offer the opportunities to investigate the relationship between phase delay and myocardial defect, and to optimize MHPA for various factors such as noise and cardiac torsion in future studies.