In a recent study, atherosclerotic plaques involving the basilar artery were more frequently identified on BBMRI than on time-of-flight MRA. Luminal narrowing can be identified with conventional angiographic studies, and the goal of VWI is the definite characterization of a focal stenotic lesion as athrosclerosis, the discrimination of active and stable plaques, and the demonstration of nonstenotic atherosclerotic burden.
T2 hyperintensities and heterogeneous signal are reportedly absent in vasculitis and RCVS. When compared with reversible cerebral vasoconstriction syndrome (RCVS) and vasculitic lesions, ICAD lesions are significantly more likely to have eccentric wall involvement, and can demonstrate lesional T2 hyperintensity presumably corresponding to the fibrous cap (80 % sensitivity), which presents as a T2 juxtaluminal hyperintense band occasionally overlying a T2 hypointense component, the lipid core. Ītherosclerotic plaques in the intracranial circulation tend to present as eccentric and usually irregular wall thickening with or without luminal stenosis and variable enhancement (Figs. Atherosclerotic changes identified on BBMRI in non-stenotic intracranial arteries appear to be the most significant risk factor for white matter hyperintensities.
Subtle atherosclerotic changes, including wall thickening and positive remodeling, have been observed in non-stenotic arteries in stroke patients when compared with controls. Furthermore, BBMRI can detect small atherosclerotic plaques in vessels that are not yet stenosed even in advanced atherosclerosis due to remodeling. Nevertheless, plaque features detected by BBMRI, such as enhancement and hemorrhage, have been shown to relate to downstream strokes (Figs. These components are better demonstrated in the extracranial circulation due to the larger vessel size, and current MRI techniques cannot characterize consistently individual intracranial atherosclerotic disease (ICAD) components. The hallmark of atherosclerosis on BBMRI is the heterogeneity of the thickened vessel wall due to various plaque components, which may include lipid core, fibrous cap, intraplaque hemorrhage, calcifications, and enhancement (Figs. In this text we review the major current applications of BBMRI in the intracranial circulation. A short axis view perpendicular to an intracranial vessel is best for evaluation of vessel wall thickening and pattern of enhancement (Fig. Specific vessel wall characteristics that are sought on VWI include vessel wall thickening (smooth, irregular, circumferential, concentric, eccentric), signal, and enhancement. Three-dimensional (3D) sequences have more recently become achievable and have the advantage of a large field of view, which allows substantial coverage in a single acquisition in a clinically acceptable scan time obviating the need for prospective slice placement, and isotropic resolution, which allows post hoc reconstruction along the short and long axis of vessels minimizing overestimation of wall thickness (Fig.
The 2D sequences are prone to partial volume artifacts, which are accentuated by the tortuosity and small size of intracranial vessels. Black blood MRI (BBMRI) sequences are designed to achieve blood flow suppression and have historically utilized 2-dimensional (2D) pre- and postcontrast T1- or proton-weighted sequences to characterize the vessel wall. Intracranial VWI is especially challenging due to the small caliber and tortuosity of the intracranial vessels necessitating submilimeter spatial resolution and high field strength magnets. Blood flow and CSF suppression are essential for optimal vessel wall visualization in the intracranial circulation.