On the cause of increased aliasing in the slice-select direction in 3D contrast-enhanced magnetic resonance angiography

The combination of short repetition times and large flip angles typically used in 3D contrast-enhanced magnetic resonance angiography (3D CE MRA) can significantly alter the expected shape of the slab profile for unenhanced tissues, which can cause increased aliasing in the slice select direction. In this work, this increased slice select aliasing is demonstrated and explained from both theoretical and experimental points of view. The effect is due to the Ernst angle of unenhanced background tissue occurring on the falling edges of the flip angle profile that has been set for the significantly reduced T₁ of contrast-enhanced blood. The deleterious aliasing effects are magnified substantially when the chosen volume is placed close to surface coil reception with the slice select direction perpendicular to the coil axis. (C) 2000 Wiley-Liss, Inc.