title: Disappearing iliac vessels: an MR phase cancellation phenomenon.
abstract: Magnetic resonance images often fail to distinguish the iliac vessels on one side. Phantom studies and theoretical analysis demonstrated that this phenomenon arises from a loss of the flow void effect. At a certain angle, the additional phase accumulation that results from motion in the section-selection direction exactly cancels the additional phase accumulation from motion in the frequency-encoding direction. Thus, vessels that cut through the imaging plane near this critical angle have substantial signal intensity. This artifact can be eliminated by alternating the direction of the section-selection gradient on sequential phase encodings.
mesh_terms: D006801:Humans; D007083:Iliac Artery / Q000033:anatomy & histology* / Q000502:physiology; D007084:Iliac Vein / Q000033:anatomy & histology* / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy; D008961:Models, Structural; D012039:Regional Blood Flow