Improvement in the visibility and accurate representation of intracranial vessels may be achieved on cranial time-of-flight (TOF) MR angiography (MRA) when the signal intensity of orbital and superficial fat is suppressed. This may be accomplished by placement of spatial radiofrequency presaturation bands along the periphery of the head. The objective of this study was to evaluate the potential for this peripheral presaturation technique to result in a spurious appearance of vascular occlusion.Materials and Methods
Three-dimensional TOF MRA of the head was performed in three patients. Flow-compensated spoiled gradient echo images were acquired in the transaxial plane, using the peripheral presaturation technique. The MRA acquisitions were then subsequently repeated in each patient following retraction of the peripheral presaturation bands. A phantom study was also performed to assess the slice profile of the presaturation bands.Results
There was absence of flow-related enhancement, indicating apparent vascular occlusion, involving one carotid siphon in each patient on initial MRA images. Following lateral retraction and/or removal of presaturation bands, the carotid siphons were documented to be patent, with normal caliber and flow-related enhancement demonstrated. Image analysis and phantom experiments indicate this vascular pseudoocclusion is due to proximity of the lateral presaturation band to the lateral aspect of the petrous segment of the internal carotid artery. In this location, there is inadvertent saturation of flowing spins due to imperfections in the presaturation band slice profile.Conclusion
The use of peripheral presaturation bands for cranial TOF MRA is useful for improving vascular depiction. However, patent vessels may occasionally demonstrate an absent signal intensity, suggesting occlusion when this technique is used. Awareness of this diagnostic pitfall is important so that serious misdiagnosis does not occur.