Wide-angle Tissue Doppler Imaging at High Frame Rate Using Multi-line Transmit Beamforming: An Experimental Validation In-Vivo

Color tissue Doppler (TDI) is a well-established methodology to assess local myocardial motion/deformation. Typically, a frame rate of ~200 Hz can be achieved by imaging a narrow sector (~ 30°, which can only cover one cardiac wall) at moderate line density, using a dedicated pulse sequence and multi-line acquisition (MLA). However, a wide angle sector (i.e., wide field-of-view) is required in some clinical applications in order to image the whole left ventricle, which implies a drop in the temporal resolution. Hereto, the aim of this study was to propose a novel imaging sequence using a multi-line transmit (MLT) beamforming approach to achieve high frame rate color tissue Doppler imaging while preserving a wide field-of-view (i.e., 90° sector). To this end, a color MLT-TDI sequence achieving a frame rate of 208 Hz with a 90°-sector was implemented on an ultrasound experimental scanner interleaved with a conventional color TDI sequence achieving the same frame rate but only with a 22.5 °-sector. Using this setup, the septal wall of 9 healthy volunteers was imaged and the corresponding velocity was extracted by means of a standard autocorrelation estimator. The curved M-mode velocity images as well as the velocity profiles obtained from selected sample volumes of MLT-TDI images presented physiologic patterns, very similar to those from conventional TDI. For several typical clinical relevant velocity properties, such as the peak systolic/diastolic velocities, good agreement and strong correlation between color MLT-TDI and conventional color TDI were found by means of Bland-Altman analysis and correlation coefficients. The results thus demonstrate the feasibility of the novel MLT based TDI methodology to achieve high frame rate color TDI without compromising the field-of-view. This may open the opportunity to simultaneously assess regional myocardial function of the whole left ventricle at high temporal resolution.