Vessel wall and adventitial DCE-MRI parameters demonstrate similar correlations with carotid plaque microvasculature on histology.

Purpose: To assess parameter agreement of volume transfer coefficient (K-trans) between two vascular regions and to study the correlation with microvessel density on histology. The dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) parameter K-trans is frequently used to study atherosclerotic plaque microvasculature. K-trans has been reported using different descriptive statistics (mean, median, 75th percentile) either for the whole vessel wall or the adventitia in previous studies. Materials and Methods: DCE-MRI parameter agreement was analyzed in 110 symptomatic patients with 2mm carotid plaque that underwent a 3T carotid DCE-MRI examination. K-trans was estimated in the entire vessel wall and adventitia. Twenty-three patients underwent carotid endarterectomy and were used for comparison with histological quantification of microvessel density of the plaque using CD31 immunohistochemistry. DCE-MRI parameters in the vessel wall regions were compared using Pearson's correlation coefficient, Bland-Altman analysis, and a two-sided paired samples t-test. Correlation of the DCE-MRI parameters with histology was studied using the Pearson's correlation coefficient. Results: Median adventitial K-trans was 5% higher (P=0.003) than entire vessel wall K-trans, with no differences for other descriptive statistics. Vessel wall and adventitial K-trans showed similar moderately strong correlations with plaque microvessel density on histology (Pearson's : 0.59-0.65 [P < 0.003] and 0.52-0.64 [P < 0.011], respectively). Conclusion: The similar moderately strong correlations for vessel wall and adventitial K-trans with microvessel density on histology suggested that both regions reflected plaque microvessel density. Care should to be taken when comparing absolute values between studies. Future studies incorporating thresholds for risk stratification need to agree upon standardization of DCE-MRI parameters.