Non‐contrast enhanced MR angiography: Physical principles

Noncontrast‐enhanced magnetic resonance angiography (NCE‐MRA) methods have been demonstrated in anatomies throughout the body. Previously established NCE‐MRA techniques suffered from long scan times or low sensitivity. Advances in hardware and software have made NCE‐MRA scan times clinically feasible. Recent concerns over the safety of gadolinium‐based contrast material combined with the expense of the material and its administration have generated a demand for NCE‐MRA. In response, several new NCE‐MRA methods have been developed. The physical mechanisms underlying five general classes of NCE‐MRA methods (inflow effect, flow‐dependency on cardiac phase, flow‐encoding, spin labeling, and relaxation) are explained. The original techniques of time‐of‐flight (TOF) and phase contrast MRA (PC‐MRA) are briefly introduced. New developments in NCE‐MRA, including hybrid of opposite‐contrast (HOP‐MRA), four dimensional PC‐MRA (4D Flow), cardiac‐gated 3D fast‐spin‐echo, flow‐sensitive dephasing (FSD), arterial spin labeling (ASL), and balanced steady‐state free‐precession (bSSFP) are highlighted. The primary applications, advantages, and limitations of established and emerging NCE‐MRA techniques are discussed. J. Magn. Reson. Imaging 2012;36:286–304. © 2012 Wiley Periodicals, Inc.