Analysis of human myocardial dynamics using virtual markers based on magnetic resonance imaging

Myocardial dynamics are three-dimensional (3D) and time-varying. Cineradiography of surgically implanted makers in animals or patients is accurate for assessing these events, but this invasive method potentially alters myocardial motion. The aim of the study was to quantify myocardial motion using magnetic resonance imaging (MRI) and hence to provide a non-invasive approach to characterize 3D myocardial dynamics.

Myocardial motion was quantified in ten normal volunteers by tracking the Lagrangian motion of individual points (i.e. virtual markers), based on time-resolved 3D phase-contrast MRI data and Fourier tracking. Nine points in the myocardium were tracked over the entire cardiac cycle, allowing a wire frame model to be generated and systolic and diastolic events identified.

Radius of curvature of the left ventricular (LV) wall was calculated from the virtual markers; the ratio between the anterior-posterior (AP) and septal-lateral (SL) walls in the LV shows an oval shape of the apical short axis plane at end systole (ES) and more circular at end diastole (ED). The AP/SL ratio for the basal plane shows an oval shape at ES and ED. We found that the rotation of the basal plane in ES was less compared to the apical plane [-2.0 +/- 2.2 versus 4.1 +/- 2.6 degrees (P<0.005)]. The apical plane rotated counter clock wise as viewed from the apex.

This new non-invasive tool, despite current limitations in temporal and spatial resolution, may provide a comprehensive set of virtual myocardial markers throughout the entire LV without the confounding effects introduced by surgical implantation.