IN-VITRO ASSESSMENT OF THE BEHAVIOR OF MAGNETIC-RESONANCE ANGIOGRAPHYIN THE PRESENCE OF CONSTRICTIONS

RATIONALE AND OBJECTIVES. Time-of-flight magnetic resonance angiograph y (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 studie s. Accurate TOF/MRA evaluations demand an understanding of the nature of these flow effects. METHODS. A two-dimensional TOF pulse sequence w as used to acquire images of five smoothly constricted phantoms at var ious flows. Analysis included assessment of phantom appearance and qua ntification of apparent constriction diameter and signal variations. R ESULTS. Most notable flow phenomena were a cone-shaped region of high signal, a region of signal void, and signal preservation along the wal l. When visible, constriction diameter was accurately measured. CONCLU SIONS. The behavior observed in TOF/MRA images can be understood by co nsidering the contributing mechanisms of phase dispersion, turbulence, poststenotic flow eddies, flow reversal, and flow separation.