In vivo transthoracic measurement of end-diastolic left ventricular stiffness with ultrasound shear wave elastography: A pilot study
End-diastolic left ventricular (EDLV) stiffness is a strong biomarker of diastolic heart failure (DHF). Ultrasound shear wave elastography (SWE) can provide a quantitative and noninvasive measure of myocardial stiffness, which makes SWE a promising tool for clinical diagnosis of DHF. In practice, however, in vivo transthoracic heart study with SWE is very challenging due to the difficult imaging situation of the heart. Recently, we proposed a pulse-inversion harmonic imaging (PIHI) approach for shear wave detection and showed substantial improvement of shear wave signal quality from the heart. In this study, we further developed a multi-zone PIHI shear wave detection method to enhance harmonic excitation and further improve shear wave signal quality. We also developed a cardiac shear wave speed (SWS) calculation method that allows manual tracing of the shear wave propagation path. This path length is used to estimate the SWS using an algorithm based on the Radon transform of the motion data. A pilot study was conducted to test the repeatability of measuring EDLV stiffness of healthy subjects with the multi-zone PIHI approach and the cardiac SWS calculation method. Five subjects were recruited and studied on three different days. Statistical analyses showed good repeatability of SWS measurements across 3 days for subjects 1 and 4, and between days 2 and 3 for subjects 1, 2, 3 and 4. The overall success rates of detecting robust shear waves from subjects 1 to 5 are 94%, 83%, 96%, 98%, and 27%, respectively. The overall SWS measurements for all subjects are in good agreement with literature values from animal studies. These results indicate that the proposed SWE methods with multi-zone PIHI detection and cardiac SWS calculation is reliable in measuring EDLV stiffness and has great potential for diagnosing DHF in future studies.
