Myocardial Elastography – Comparison to Results Using MR Cardiac Tagging

MRI cardiac tagging has been established as the gold standard in assessing intramyocardial displacement and strain. Yet, despite the high imaging quality of cardiac MRI, tagging techniques are limited by low spatial and temporal resolution. It has been recently shown that axial displacement and strain could be estimated and utilizing Bscan ultrasonography [1]. We compared and correlated intramyocardial displacement data from B-scan ultrasound images and cardiac MRI in seven normal human subjects. Subjects were first imaged in a 4-chamber view using an Agilent/PMS 5500 system with a 1.8/3.6 MHz probe and at 38 Hz frame rate, and then scanned using a Philips 1.5T Intera system and a CSPAMM tagging sequence. A singlecardiac-cycle tagging loop was generated combining data from 15 cardiac cycles. Incremental axial and lateral, displacement and strain estimates along the interventricular septum between successive frames were obtained using 2D crosscorrelation with a 5 x 5 mm kernel and 95% overlap. Ciné-loop and M-mode displacement images and elastograms and temporal plots depicted the high repeatability of all estimates over 2-5 cardiac cycles. Axial and lateral displacements both ranged between 0.04 mm at peak systole and -0.04 mm at peak diastole. Axial and lateral strains also had similar magnitudes with averages within 6% and –8% and 5% and –5%, respectively. Axial displacements and strains were also estimated from the MR cardiac tagging data using a simple zero-crossing algorithm to track the motion of the horizontally-placed tags. The peak systole and displacement estimates obtained from the ultrasonic and MR tagging data correlated well (r=0.81; p<0.05) as were the strain estimates (r=0.65; p<0..05). The correlation between elastographic and MR tagging results indicates that myocardial elastography could offer comparable quality estimates to those obtained with MR cardiac tagging; with the added advantage of higher temporal and spatial resolution representing thus a viable alternative to the quantitative assessment of myocardial function.