In vivo diffusion MRI of the human heart using a 300 mT/m gradient system

This work reports for the first time on the implementation and application of cardiac diffusion-weighted MRI on a Connectom MR scanner with a maximum gradient strength of 300 mT/m. It evaluates the benefits of the increased gradient performance for the investigation of the myocardial microstructure.

Cardiac diffusion-weighted imaging (DWI) experiments were performed on 10 healthy volunteers using a spin-echo sequence with up to second- and third-order motion compensation ( $M_2$ and $M_3$ ) and $b=100,\hspace{0.17em}450$ , and 1000 $s/m{m}^2$ (twice the $b_{\max }$ commonly used on clinical scanners). Mean diffusivity (MD), fractional anisotropy (FA), helix angle (HA), and secondary eigenvector angle (E2A) were calculated for b = [100, 450] $s/m{m}^2$ and b = [100, 1000] $s/m{m}^2$ for both $M_2$ and $M_3$ .

The MD values with $M_3$ are slightly higher than with $M_2$ with $\Delta \text{MD}=0.05\pm 0.05[\times 10^{-3}{\text{mm}}^2/s](p=4e-5)$ for $b_{\max }=450s/{\text{mm}}^2$ and $\Delta \text{MD}=0.03\pm 0.03[\times 10^{-3}{\text{mm}}^2/s](p=4e-4)$ for $b_{\max }=1000s/{\text{mm}}^2$ . A reduction in MD is observed by increasing the $b_{\max }$ from 450 to 1000 $s/{\text{mm}}^2$ ( $\Delta \text{MD}=0.06\pm 0.04[\times 10^{-3}{\text{mm}}^2/s](p=1.6e-9)$ for $M_2$ and $\Delta \text{MD}=0.08\pm 0.05[\times 10^{-3}{\text{mm}}^2/s](p=1e-9)$ for $M_3$ ). The difference between FA, E2A, and HA was not significant in different schemes ( $p>0.05$ ).

This work demonstrates cardiac DWI in vivo with higher b-value and higher order of motion compensated diffusion gradient waveforms than is commonly used. Increasing the motion compensation order from $M_2$ to $M_3$ and the maximum b-value from 450 to 1000 $\hspace{0.17em}s/{\text{mm}}^2$ affected the MD values but FA and the angular metrics (HA and E2A) remained unchanged. Our work paves the way for cardiac DWI on the next-generation MR scanners with high-performance gradient systems.