Volumetric diffusion and fat imaging of symptomatic carotid plaques on seven tesla magnetic resonance imaging

BACKGROUND: Stroke caused by carotid plaques is a major cause of morbidity and mortality. Magnetic resonance imaging (MRI) can assess the degree of stenosis and plaque composition. Inflammation and lipid content are challenging to image with conventional imaging and MRI sequences, although being a major pathogenetic factor. This study investigates novel approaches to quantify inflammation or hemorrhage and lipid volume in association with neurologic symptoms on ex-vivo 7 T MRI. METHODS: Plaques from 44 patients with low calcification content were selected for imaging. T1w magnetization transfer water sat (T1-MTWS), diffusion tensor imaging (DTI), T1w, T2w, and T2*w images were acquired. Signal intensities (SIs) were referenced to agarose gel and volumetrically quantified. Hypo-/hyperintense volumes as well as volumetric SI measurements were compared between plaques from symptomatic versus asymptomatic patients. Histological validation was performed for specimens with areas of diffusion restriction or lipid signal. RESULTS: SIs were indifferent on T1w and T2*w images. Plaques from symptomatic patients were more hypointense on T2w-images (90.3% vs. 73.4%, p = 0.02). Lower apparent diffusion coefficient (ADC) volume was associated with symptoms (%hypointense volume on ADC from DTI - area under the receiver operator curve: 0.76 (0.61-0.90)). Plaques displaying signals on T1-MTWS images were symptomatic in 9/10 cases, but the odds-ratio was insignificant (OR: 1.3 (0.95-1.8)). CONCLUSION: This study highlights the potential for 7 T MRI to assess radiological properties indicative of vulnerable plaque features, such as inflammation or hemorrhage and lipid content in association with neurologic symptoms. To date, 7 T MRI is not commonly available for clinical routine, but these findings support further research into more sophisticated imaging techniques to improve risk stratification before revascularization therapy.