To develop cardiac magnetic resonance elastography (MRE) for noninvasively measuring left ventricular (LV) pressure
Material and Methods:
The anterior chest wall of 8 healthy volunteers was vibrated by 24.3-Hz acoustic waves for stimulating oscillating shear deformation in myocardium and adjacent blood. The induced motion was recorded by an electrocardiogram-gated, vibration-synchronized and segmented gradient-recalled echo MRE sequence acquiring 360 phase-contrast wave images with a temporal resolution of 5.16 milliseconds in the short-axis view during controlled breathing. Relative changes in wave amplitudes served as a measure of LV pressure
variation during the cardiac cycle. MRE pressure
data were combined with LV volumes obtained from segmentation of 3D cine-steady-state free precession data sets.
Shear wave amplitudes decreased from diastole to systole, which reflects the dynamics of myocardial shear modulus
variations during the cardiac cycle. Assuming spherical shear stress, a linear relationship between myocardial stiffness and LV pressure
was derived. The MRE-measured pressure
was plotted as a function of LV volumes. Characteristic P-V cycles displayed an isovolumetric increase in pressure
during early systole, whereas less pronounced volume
conservation was observed in early diastole. Mean cardiac P-V work in all volunteers was 0.85 ± 0.11 J.
In vivo cardiac MRE is a noninvasive method for measuring pressure
-related heart function determined by shear modulus
variations in the LV wall. This is the first noninvasive mechanical test of cardiac work in the human heart and is potentially useful for assessing pathologies associated with increased myocardial stiffness such as diastolic dysfunction.