Real-time phase-contrast MRI of cardiovascular blood flow using undersampled radial fast low-angle shot and nonlinear inverse reconstruction

Velocity‐encoded phase‐contrast MRI of cardiovascular blood flow commonly relies on electrocardiogram‐synchronized cine acquisitions of multiple heartbeats to quantitatively determine the flow of an averaged cardiac cycle. Here, we present a new method for real‐time phase‐contrast MRI that combines flow‐encoding gradients with highly undersampled radial fast low‐angle shot acquisitions and phase‐sensitive image reconstructions by regularized nonlinear inversion. Apart from calibration studies using steady and pulsatile flow, preliminary in vivo applications focused on through‐plane flow in the ascending aorta of healthy subjects. With bipolar velocity‐encoding gradients of alternating polarity that overlap the slice‐refocusing gradient, the method yields flow‐encoded images with an in‐plane resolution of 1.8 mm, section thickness of 6 mm and measuring time at 3 T of 24 ms (TR/TE = 3.44/2.76 ms; flip angle, 10º; seven radial spokes per image). Accordingly, phase‐contrast maps and corresponding velocity profiles achieve a temporal resolution of 48 ms. The evaluated peak velocities, stroke volumes, flow rates and respective variances over at least 20 consecutive heartbeats are in general agreement with literature data. Copyright © 2011 John Wiley & Sons, Ltd. We describe a new method for quantitative flow measurements using phase‐contrast MRI in real time. The approach combines bipolar velocity‐encoding gradients of alternating polarity with strongly undersampled radial fast low‐angle shot (FLASH) acquisitions and phase‐sensitive image reconstructions by regularized nonlinear inversion. Preliminary applications focused on through‐plane flow in the ascending aorta of healthy subjects at a temporal resolution of 48 ms.