Microvascular imaging of asymptomatic MCA steno-occlusive patients using ultra-high-field 7T MRI

It is common that physicians are faced with patients who have severe steno-occlusion of intracranial arteries in the absence of clinical symptoms. This study is to determine whether a 7T magnetic resonance angiogram (MRA) could provide the improved depiction of microvessels of asymptomatic patients with steno-occlusive middle cerebral artery (MCA) and possible clues for diagnosis of their clinical symptoms. All the patients who were identified as severe MCA steno-occlusions underwent a 7T MRA study. Three of these also underwent conventional angiography (TFCA). The vascular densities around the steno-occlusive MCA and posterior cerebral artery (PCA) branches as control vessels were measured and the difference between the median values of 7T and 3T MRA data was also analyzed. The results of 7T MRA revealed numerous microvessels not visible by conventional MRA. These 7T MRA images were also comparable to those obtained by an invasive conventional angiography (TFCA). The median values of vascular densities observed by 7T MRA were significantly higher than those by 3T MRA (5.28 at 7T vs. 1.45 at 3T for steno-occlusive MCA, p = 0.012, while 3.39 at 7T vs. 3.32 at 3T for normal PCA, p = 0.093). Ultra-high-field 7T MRA is a totally noninvasive angiographic technique that is capable of visualizing microvascular circulation that is usually difficult with conventional MRA. This visualization technique, therefore, could provide an important avenue on the diagnosis of steno-occlusion as well as the search of the roles of the microvessel, especially collaterals, in the preservation of normal blood circulation in patients with asymptomatic MCA steno-occlusion.