The use of feature tracking to assess ventricular strain during exercise stress CMR

Abstract

Background Exercise stress testing is the most physiological method of inducing myocardial stress, but its application to clinical and scientific CMR has been limited because of problems arising from cardiac and respiratory motion during stress. Under pharmacological stress, left ventricular strain measurement abnormalities by CMR have been demonstrated to be earlier and more sensitive markers of contractile dysfunction than global left ventricular ejection fraction or development of regional wall motion abnormalities alone. There are several validated methods of measuring myocardial strain. A recently proposed method is feature tracking (FT), which has advantages over other methods in having shorter acquisition and analysis times and not requiring additional scanning as the features are tracked from the clinically standard cine steady-state free precession (SSFP) sequences. This offers a potential method to assess myocardial strain during exercise stress. Methods Seven healthy volunteers without known cardiovascular disease gave informed consent and enrolled for supine cycle ergometry on the CMR scanner table (Lode, Groningen Netherlands). Subjects underwent a standardised incremental exercise protocol. Imaging included a standard short-axis stack of cine SSFP images from the cardiac base to apex, on a 3T Philips Achieva TX ® system using a 32-channel multi-transmit coil. Scan parameters included slice thickness of 10mm, repetition/echo time of 2.4/1.21ms, flip angle 40°, 9-11 slices, with 20 phases per slice. For this study, only the mid LV-slice was analysed. Diogenes CMR FT software (TomTec Imaging Systems, Munich, Germany) was used for strain analysis. This was based on contours manually drawn along the LV endocardial border of one frame, with the software automatically propagating the contour and following its features throughout the remainder of the imaged phases. Software-derived parameters include circumferential epicardial and endocardial, longitudinal, and radial tissue velocity, strain, strain rate and time to peak strain.