Second order motion compensated spin-echo diffusion tensor imaging of the human heart

First and second order MC diffusion encoding gradients were incorporated into a cardiac triggered single-shot SE sequence (Figure 1). Imaging was performed on a 1.5T Philips Achieva system (Philips Healthcare, Best, The Netherlands) equipped with gradients delivering 80mT/m@100mT/m/ms. Five healthy volunteers were imaged with navigator-gating during free-breathing with the following parameters: resolution: 2.2×2.2mm², slice thickness: 6mm, local-look FOV: 230×98mm², TR/TE: 1R-R/83ms, two slices (apex/base). Fat suppression was incorporated by spectral-spatial excitation. Three orthogonal diffusion encoding directions (b=450s/mm², 8 averages) were applied at trigger delays ranging from 45ms to peak systole (steps of 10ms). Ten diffusion directions (10 averages, TR: 2R-R) were acquired in an additional session at 38%/47%/56%/66%/75% peak systole. The mean diffusivity (MD) was calculated as function of trigger delay and used as measure for the sensitivity to bulk motion. Helix angles were calculated upon tensor reconstruction.

MD as function of trigger delay is shown in Figure 2a). Second order MC diffusion encoding yielded an applicable trigger delay range of 15-81% (apical) and 15-77% (basal) of peak systole. For first order MC, the corresponding trigger delay windows were only 30-57% (apical) and 27-56% (basal). Figure 2b) shows a time series of helix angle maps (basal) and the transmural angle histograms (apical/basal) c).