Validation of Left Ventricular High Frame Rate Echo-Particle Image Velocimetry against 4D Flow MRI in Patients

Aims Accurately measuring intracardiac flow patterns could provide insights into cardiac disease pathophysiology, potentially enhancing diagnostic and prognostic capabilities. This study aims to validate Echo-Particle Image Velocimetry (echoPIV) for in-vivo left ventricular intracardiac flow imaging against 4D flow MRI. Methods and Results We acquired HFR contrast-enhanced ultrasound images from three standard apical views of 26 patients who required cardiac MRI. 4D flow MRI was obtained for each patient. Only echo image planes with sufficient quality and alignment with MRI were included for validation. Regional velocity, kinetic energy and viscous energy loss were compared between modalities using normalized mean absolute error, cosine similarity and Bland-Altman analysis. Among 24 included apical view acquisitions, we observed good correspondence between echoPIV and MRI regarding spatial flow patterns and vortex traces. The velocity profile at base-level (mitral valve) cross-section had cosine similarity of 0.92 ± 0.06 and normalized mean absolute error of 14 ± 5%. Peak spatial mean velocity differed by 3 ± 6 cm/s in systole and 6 ± 10 cm/s in diastole. The kinetic energy and rate of energy loss also revealed a high level of cosine similarity (0.89 ± 0.09 and 0.91 ± 0.06) with normalized mean absolute error of 23 ± 7% and 52 ± 16%. Conclusions Given good B-mode image quality, echoPIV provides a reliable estimation of left ventricular flow, exhibiting spatial-temporal velocity distributions comparable to 4D flow MRI. Both modalities present respective strengths and limitations: echoPIV captured inter-beat variability and had higher temporal resolution, while MRI was more robust to patient BMI and anatomy.