Echocardiographic Particle Image Velocimetry: A Novel Technique for Quantification of Left Ventricular Blood Vorticity Pattern

Background: In this study, the functionality of echocardiographic particle imaging velocimetry (E-PIV) was compared with that of digital particle imaging velocimetry (D-PIV) in an in vitro model. In addition, its capability was assessed in the clinical in vivo setting to obtain the ventricular flow pattern in normal subjects, in patients with dilated cardiomyopathy, and in patients with mechanical and bioprosthetic mitral valves. Methods: A silicon sac simulating the human left ventricle in combination with prosthetic heart valves, controlled by a pulsed-flow duplicator, was used as the in vitro model. Particle-seeded flow images were acquired (1) using a high-speed camera from the mid plane of the sac, illuminated by a laser sheet for D-PIV, and (2) using a Siemens Sequoia system at a frame rate of 60 Hz for E-PIV. Data analysis was performed with PIVview software for D-PIV and Omega Flow software for E-PIV. E-PIV processing was then applied to contrast echocardiographic image sets obtained during left ventricular cavity opacification with a lipid-shelled microbubble agent to assess spatial patterns of intracavitary flow in the clinical setting. Results: The velocity vectors obtained using both the E-PIV and the D-PIV methods compared well for the direction of flow. The streamlines were also found to be similar in the data obtained using both methods. However, because of the superior spatial resolution of D-PIV, some smaller scale details were not revealed by E-PIV. The application of E-PIV to the human heart resulted in reproducible flow patterns in echocardiographic images taken within different time frames or by independent examiners. Conclusions: The E-PIV technique appears to be capable of evaluating the major flow features in the ventricles. However, the bounded spatial resolution of ultrasound imaging limits the small-scale features of ventricular flow to be revealed.