Fig. 17

Illustration of strain computation using the Harmonic Phase (HARP) tool on tagged CMR images (a–d) and from feature tracking on cine CMR images (e–h). In HARP, first a semi-automated frequency analysis of the tagged CMR image (a) is performed to identify the harmonic peaks in each of the tag directions (b), filters are then applied to isolate the peaks and obtain the corresponding phase maps from which Eulerian strain maps (c) can be computed. Subplot (d) shows the strain curve at the mid-ventricular level for an asymptomatic volunteer obtained based on tracking of the user-defined mesh (a). In feature tracking of cine CMR images, endo- and epicardial contours are drawn at end-diastole (e) or end-systole (g). A characteristic pixel pattern in the order of a few millimeters squared is identified as a template. The software then tries to discern a similar pattern in the subsequent frame from which displacement of the pixels is computed (f). This is repeated through the entire cycle to obtain displacement from which strain is computed. Subplot (h) shows the strain curve at the mid-ventricular level computed from feature tracking. The tagged and cine CMR images and the strain curves were from the same participant