Intracranial TOF-MRA for estimation of extracranial proximal artery stenosis

Essential for the prognosis of patients with acute ischemic stroke is a fast admission to therapeutic approaches like intravenous or intraarterial fibrinolysis. In the latter beside the precise localization and size of an ischemia especially possible obstacles in the access to an occluded vessel are important to know for optimal treatment. Moreover even in intravenous fibrinolysis the effectiveness of thrombolysis seems to decrease with the existence of an additional extracranial artery stenosis. MRI-protocols including DWI-PWI-imaging may allow tailor-made treatment within minutes. One part of most stroke routine MRI-protocols is the so called intracranial „Time of flight“ Magnetic Resonance Angiography (TOF-MRA). With this technique, the intracranial as well as the distal parts of the extracranial vessels are displayed non-invasively utilizing flow-sensitive sequences. Typically, the more proximal parts of the arteries are investigated by ultrasound after the hyperacute stage of the disease to avoid further time-loss. However intracranial TOF-sequences may reliable demonstrate extracranial proximal artery-stenosis by illustrating intensity-attenuation in the displayed distal part of a proximal stenotic artery. In this study we compare TOF-MRA data from patients diagnosed with mid- to high-grade ICA-stenosis. The signal intensity upon TOF-MRA was correlated with data from CT-Angio, Doppler and DSA. The decrease of the TOF-signal intensities of the distal parts of the extracranial arteries mapped by the typical intracranial TOF thereby correlates with the grade of the DSA- or CTA-measured extracranial stenosis. Therefore intracranial TOF allows an approximate determination of the grade of a possible extracranial stenosis right within the first MR-imaging without direct investigation of the extracranial arteries. This could be relevant for the therapeutic approach taken, i.e. when decisions are taken about intraarterial interventions.