RESUMO
RATIONALE AND OBJECTIVES: Time-of-flight magnetic resonance angiography (TOF/MRA) is increasingly used to assess the nature and severity of stenotic blood vessels. Flow artifacts associated with high flows and/or narrow constrictions may confuse the interpretation of these studies. Accurate TOF/MRA evaluations demand an understanding of the nature of these flow effects. METHODS: A two-dimensional TOF pulse sequence was used to acquire images of five smoothly constricted phantoms at various flows. Analysis included assessment of phantom appearance and quantification of apparent constriction diameter and signal variations. RESULTS: Most notable flow phenomena were a cone-shaped region of high signal, a region of signal void, and signal preservation along the wall. When visible, constriction diameter was accurately measured. CONCLUSIONS: The behavior observed in TOF/MRA images can be understood by considering the contributing mechanisms of phase dispersion, turbulence, poststenotic flow eddies, flow reversal, and flow separation.
