Validation of ultrasound detection of transmural myofiber orientation in excised human ventricular myocardium

OBJECTIVE: Current methods for in vivo detection of the transmural myofiber orientation in ventricular myocardium rely on long scans (>15 minutes) with diffusion magnetic resonance imaging (DMRI), limiting the use of myofiber orientation as an imaging biomarker. Backscatter Tensor Imaging (BTI) is an emerging ultrasound (US) imaging technique that can detect myofiber orientation with high spatial and temporal resolution, and it may be integrated into existing clinical ultrasound scanners. Here we demonstrate, for the first time, validation of BTI in excised human LV and RV ventricular myocardium. METHODS: BTI was performed on two LV and two RV human myocardium samples with a rotational scan of an 18 MHz linear array. Validation was performed by comparison with ground truth histological sectioning. RESULTS: US- and histology-derived fiber orientation were in good agreement. Root-mean-square error was 10.3° and correlation was 0.88. One sample of RV myocardium did not exhibit fiber organization, so that neither BTI nor histology could identify a fiber orientation. CONCLUSION: BTI can accurately estimate the transmural fiber orientation in excised human myocardium. Challenges for translation of BTI and development of fiber orientation as an imaging biomarker include adoption of fully-populated matrix ultrasound arrays for real-time volume imaging, and degradation of BTI performance resulting from ultrasound aberration in transthoracic echocardiography.