Myofiber strain in healthy humans using DENSE and cDTI

Purpose: Myofiber strain, E-ff, is a mechanistically relevant metric of cardiac cell shortening and is expected to be spatially uniform in healthy populations, making it a prime candidate for the evaluation of local cardiomyocyte contractility. In this study, a new, efficient pipeline was proposed to combine microstructural cDTI and functional DENSE data in order to estimate E-ff in vivo. Methods: Thirty healthy volunteers were scanned with three long-axis (LA) and three short-axis (SA) DENSE slices using 2D displacement encoding and one SA slice of cDTI. The total acquisition time was 11 minutes +/- 3 minutes across volunteers. The pipeline first generates 3D SA displacements from all DENSE slices which are then combined with cDTI data to generate a cine of myofiber orientations and compute E-ff. The precision of the post-processing pipeline was assessed using a computational phantom study. Transmural myofiber strain was compared to circumferential strain, E-cc, in healthy volunteers using a Wilcoxon sign rank test. Results: In vivo, computed E-ff was found uniform transmurally compared to E-cc (-0.14[-0.15, -0.12] vs -0.18 [-0.20, -0.16], P<.001, -0.14 [-0.16, -0.12] vs -0.16 [-0.17, -0.13], P<.001 and -0.14 [-0.16, -0.12] vs E-cc_(C) -0.14 [-0.15, -0.11], P=.002, E-ff_(C) vs E-cc_(C) in the endo, mid, and epi layers, respectively). Conclusion: We demonstrate that it is possible to measure in vivo myofiber strain in a healthy human population in 10 minutes per subject. Myofiber strain was observed to be spatially uniform in healthy volunteers making it a potential biomarker for the evaluation of local cardiomyocyte contractility in assessing cardiovascular dysfunction.