Heart

We developed bSSFP-MRE based on the idea of fractional motion encoding for measuring in vivo heart stiffness. Details are given in Rump et. al 2007 [1]. So far we are able to detect externally induced shear waves in the interventricular septum (IVS). Using cine bSSFP-MRI it was found that the IVS largely remains within the image plane throughout the entire heart cycle. The position of the IVS at the start and the end of each fractional MRE image acquisition is shown in the figure below. The consecutively acquired phase difference images are shown as animations to visualize the transverse wave propagating from the apex towards the aortic valve. The maximum deflection amplitude was estimated at 40  microns (without accounting for phase shifts due to the imaging gradients). Without vibrations, no phase signal was obtained after subtracting the phase images. The animations were assembled from 16 frames displaying a calculated increment of 1/8p of the propagating wave phase. The septum is shown without surrounding tissue from a perspective view of 30° in-plane rotation and a 15° latitude tilt. The file names ‘phase1.gif’, ‘phase2.gif’, ‘phase3.gif’ and ‘phase4.gif’ correspond to the time resolution during the cardiac cycle shown in figs. 5 and 8 of [1]. A comparison of the IVS-vibrations indicates differences in the appearance of the waves at different cardiac phases. [1] Rump et al. MRM, 57, 388-395, 2007