Surgical clip artefact mimicking arterial stenosis: a problem with magnetic resonance angiography

In three patients undergoing three-dimensional phase contrast magnetic resonance angiography (MRA) for evaluation of renal transplant arteries, a convincing stenosis was demonstrated that was not present on conventional angiograms. In each patient there was a stainless steel surgical clip in the soft tissues adjacent to the renal artery. Although the clip artefact was easily recognized on the acquired tomographic magnetic resonance slices, it was completely indistinguishable from a true stenosis on the final projection images. This may limit the use of MRA in post-surgical vascular evaluation unless review is made of the phase contrast images.