Purpose: To investigate the appearance of reduced signal intensity in the center of blood vessels on magnetic resonance (MR) angiograms that can mimic intraluminal thrombus.
Materials and methods: Simulations and phantom studies were performed to analyze MR angiogram appearance distal to a pronounced curve.
Results: Saturation effects substantially lower the signal strength in the center of the vessel relative to that at the vessel periphery. These effects appeared even though the flow was well ordered and laminar. In curved geometries, secondary flow patterns produced counter-rotating vortices, which moved the fastest-moving particles to the outside of the curve and folded the slow-moving particles to the center of the vessel.
Conclusion: Imaging parameter choices that reduce saturation, such as acquisition of a two-dimensional section transverse to the vessel and through the questionable region, effectively eliminate the central hypointensity effect in vivo.