Characterization of Carotid Plaque Components by Quantitative Susceptibility Mapping

Abstract

BACKGROUND AND PURPOSE: Intraplaque hemorrhage in the carotid artery is related to an increased risk of cerebrovascular ischemic events. We aimed to investigate whether quantitative susceptibility mapping can characterize carotid artery plaque components and quantify the severity of intraplaque hemorrhage. MATERIALS AND METHODS: For this ex vivo quantitative susceptibility mapping study, 9 carotid endarterectomy specimens were imaged on a 3T MR imaging scanner using a 3D multi-echo gradient-echo sequence and a microscopy coil. The samples were examined histologically using immunostains, including glycophorin A and Prussian blue. The areas of erythrocytes, iron deposits, calcification, and fibrous matrices observed on stained sections were compared with quantitative susceptibility mapping findings and their mean susceptibility values. RESULTS: Intraplaque hemorrhage and iron deposits were observed only in areas hyperintense on quantitative susceptibility mapping; calcifications and fibrous matrices were prevalent in hypointense areas. The mean susceptibility values for necrotic cores with intraplaque hemorrhage but no iron deposits, cores with iron deposits but no intraplaque hemorrhage, cores without either intraplaque hemorrhage or iron deposits, and cores with calcification were 188 6 51, 129 6 49, À11 6 17, and À158 6 78 parts per billion, respectively. There was a significant difference in the mean susceptibility values among the 4 histologic components (P , .01). The mean susceptibility values of the whole plaque positively correlated with the percentage area positive for glycophorin A (r 4 0.65, P , .001) and Prussian blue (r 4 0.47, P , .001). CONCLUSIONS: Our findings suggest that quantitative susceptibility mapping can characterize the composition of carotid plaques and quantify the degree of intraplaque hemorrhage and iron deposits. ABBREVIATIONS: CR 4 contrast ratio; GYPA 4 glycophorin A; ICH 4 intracranial hemorrhage; IPH 4 intraplaque hemorrhage; QSM 4 quantitative susceptibility mapping; SV 4 susceptibility value

Quantitative susceptibility mapping of carotid arterial tissue ex vivo: Assessing sensitivity to vessel microstructural composition

“…In diseased arterial tissue, key components of the tissue microstructure, such as collagen fibers, smooth muscle cells, and elastic lamina, become disrupted, impairing vessel function 60 . A number of recent studies have demonstrated the application of QSM for imaging carotid plaque in vivo, highlighting that many technical challenges associated with imaging carotid arteries using QSM in a clinical setting can be overcome 9‐13 . These studies have demonstrated marked improvement in the depiction of intraplaque hemorrhage and calcification in vivo but have largely ignored differences in regional plaque susceptibility that may be driven by compositional variations in the microstructure of fibrotic plaque tissue.…”

“…Quantitative susceptibility mapping (QSM) is an MRI method capable of spatially mapping the magnetic susceptibility of biological tissue. [6][7][8] Recently, a number of studies have applied QSM to carotid plaques and demonstrated marked improvement in intraplaque hemorrhage and calcification depiction compared to conventional multi-contrast MRI [9][10][11][12][13] based on the inherent differences between the magnetic susceptibilities of these structures: calcifications are diamagnetic, whereas hemorrhages are paramagnetic. 14 1.…”

Quantitative Susceptibility Mapping for Characterization of Intraplaque Hemorrhage and Calcification in Carotid Atherosclerotic Disease

“…The signal intensity of IPH on MP-RAGE or other T1-weighted images depends on the acuity of blood products. It is known that IPH experiences a dynamic degradation process, successively in the form of deoxyhemoglobin, methemoglobin, and hemosiderin [23] . Among these blood products, methemoglobin is considered to be a source of high signal intensity because of its reduced T1.…”

“…Therefore, MR signal may be complex due to the distribution and concentration of methemoglobin. A chronic inflammatory cascade incited by atherosclerosis can lead to a smaller apparent volume of IPH that over time leads to hemosiderin deposition or sequestration within foamy macrophages [23] . This is supported by histologic findings of erythrocyte membranes and iron present within the necrotic cores of atherosclerotic coronary plaques even in the absence of recent hemorrhage [24] .…”

Quantitative susceptibility mapping of carotid arterial tissueex vivo: assessing sensitivity to vessel microstructural composition

“…. A number of recent studies have demonstrated the application of QSM for imaging carotid plaque in vivo, highlighting that many technical challenges associated with imaging carotid arteries using QSM in a clinical setting can be overcome[9][10][11][12][13] . These studies have demonstrated marked improvement in depiction of IPH and calcification in vivo but have largely ignored differences in regional plaque susceptibility that may be driven by compositional variations in the microstructure of fibrotic plaque tissue.…”