Only one tool exists to perform in-vivo, human non-invasive assessment of the myocardium at the microstructural level, namely diffusion tensor (DT) cardiac magnetic resonance (CMR). DT-CMR quantifies water diffusion in the myocardium, which is constrained by the myocardial micro-architecture. This talk examines potential clinical applications of DT-CMR.
This talk focuses on nascent clinical aspects of DT-CMR on which there is little published data. I will not review the extraordinary work in physics which underlies this technique, which has been published over the last few decades, as this will be covered by others. I will cover a validation paper published by our group in 2017 in detail, and recent in-vivo human work where there is potential clinical impact.
By way of introduction, only one tool exists to perform in-vivo, human non-invasive assessment of the myocardium at the microstructural level, namely diffusion tensor (DT) cardiac magnetic resonance (CMR). DT-CMR quantifies water diffusion in the myocardium, which is constrained by the myocardial micro-architecture. Diffusion aligned to the orientation of cardiomyocytes is greater than the diffusion in the perpendicular directions, and therefore yields information on cardiomyocyte organisation. The diffusion pattern can be visualised in 3D as an ellipsoid which can be described by a mathematical tensor, described by a set of mutually perpendicular eigenvectors E1, E2, and E3.
We have published robust histological validation [Nielles-Vallespin 2017] that shows E1 is aligned with cardiomyocyte orientation, and together with E2 defines the sheetlet orientation (groups of cardiomyocytes ~6 thick separated by shear planes). Rotation and shear of the sheetlets during cardiac contraction is the predominant mechanism of left ventricular longitudinal shortening and radial thickening.
We have shown in-vivo impairment in sheetlet rotation with aberrant systolic & diastolic in hypertrophic & dilated cardiomyopathy respectively [Nielles-Vallespin 2017, Ferreira 2014]]. Aberrant myocardial architecture is also evident in congenital heart disease [Khalique 2018b] and myocardial infarction [Kung 2018]. There is also potential in this new technology in heart failure [Khalique 2018b]. However, although it is at a very early clinical stage, DT-CMR is already yielding considerable new insights into the functioning of the normal heart, bridging the gulf between the understanding of contraction of single cardiomyocytes at the microscopic level, and the contraction seen with clinical imaging techniques at the macroscopic level.
Nielles-Vallespin S, Khalique Z, Ferreira PF, de Silva R, Scott AD, Kilner P, McGill LA, Giannakidis A, Gatehouse PD, Ennis D, Aliotta E, Al-Khalil M, Kellman P, Mazilu D, Balaban RS, Firmin DN, Arai AE, Pennell DJ. Assessment of myocardial microstructural dynamics by in vivo diffusion tensor cardiac magnetic resonance. J Am Coll Cardiol 2017; 69: 661-76.
Ferreira PF, Kilner PJ, McGill LA, Nielles-Vallespin S, Scott AD, Ho SY, McCarthy KP, Haba MM, Ismail TF, Gatehouse PD, de Silva R, Lyon AR, Prasad SK, Firmin DN, Pennell DJ. In vivo cardiovascular magnetic resonance diffusion tensor imaging shows evidence of abnormal myocardial laminar orientations and mobility in hypertrophic cardiomyopathy. J Cardiovasc Magn Reson 2014; 16: 87.
Khalique Z, Ferreira PF, Scott AD, Nielles-Vallespin S, Kilner PJ, Kutys R, Romero M, Arai AE, Firmin DN, Pennell DJ. Deranged myocyte microstructure in situs inversus totalis demonstrated by diffusion tensor cardiac magnetic resonance. JACC Cardiovasc Imaging 2018; 11: 1360-2.
Kung GL, Vaseghi M, Gahm JK, Shevtsov J, Garfinkel A, Shivkumar K, Ennis DB. Microstructural infarct border zone remodeling in the post-infarct swine heart measured by diffusion tensor MRI. Front Physiol 2018; 9: 826.
Khalique Z, Ferreira PF, Scott AD, Nielles-Vallespin S, Wage R, Firmin DN, Pennell DJ. Diffusion tensor cardiovascular magnetic resonance of microstructural recovery in dilated cardiomyopathy. JACC Cardiovasc Imaging. 2018; 11: 1548-50.