Magnetic resonance angiography has long been proposed
as a non-invasive alternative to x-ray angiography. The
‘time-of-flight’ of blood through an imaging plane or
motion-induced phase shifts in the MR signal allow
contrast between moving blood and surrounding tissue.
Furthermore, subtraction of velocity-compensated and
velocity-encoded images can produce physiologically
relevant data such as flow rate and wall shear rate.
However, the wide range of fluid dynamics phenomena in
the human body threaten the accuracy of MR angiograms
and result in a variety of artifacts in anatomical imaging.
Pulsatile flow can cause ghosting in images1. Flow oblique
to the imaging axis can cause displacement artifacts2. High
shear rates can cause signal loss3. More importantly, many
MR techniques in use today fail in the critical area of
arterial disease detection: signal loss occurs in stenosed
arteries, resulting in images which overestimate the degree
of stenosis or misrepresent a total occlusion of the artery.