Magnetic Resonance Imaging: Basic Principles

Findings and Diagnosis: Segmental signal drops are seen in the upper sections of the vertebral arteries bilaterally, seen on both contrast-enhanced and TOF MR angiography images. T2 weighted image demonstrates signal voids in the vertebral artery areas bilaterally. Segmental signal drop in this fashion is quite unusual, particularly considering the fact that TOF-MRA image shows vascular signal in more superior section of the vascular territory (in the same direction).  Careful review of the clinical history in this case revealed a history of previous percutaneous stent placement into the vertebral arteries due to severe stenoses. Therefore, the diagnosis in this case is an artifactual signal drop in the vertebral arteries secondary to metal stents.  

Discussion:

Metal stents cause significant segmental signal loss on magnetic resonans angiography. In this case, demonstration of a flow related signal in the same direction within the more peripheral section of the artery using the TOF technique is quite helpful to rule out complete vascular occlusion. Using flow measuring angiography techniques (phase-contrast MRA) would be helpful to confirm the flow; however, assessing the vessels with other imaging techniques (CTA or conventional angiography) is generally preferred in daily clinical practice.  

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