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

Abstract

Background: Carotid artery intraplaque hemorrhage (IPH), an unstable component of atherosclerosis, is associated with an increased risk of stroke. Purpose: To investigate quantitative susceptibility mapping (QSM) as a tool for the evaluation of IPH and calcification in vivo. Study Type: Prospective Population: Ten healthy volunteers and 15 patients Field Strength/Sequence: 3.0 T Susceptibility-weighted imaging (SWI), magnetization-prepared rapid acquisition with gradient echo (MP-RAGE), T1-weighted Sampling Perfection with Application of optimized Contrasts using different flip angle Evolution (T1-SPACE), T2-weighted turbo spin-echo (T2WI) and time-of-flight (TOF) sequences. Assessment: The vessel wall area of the carotid artery was measured on QSM and compared with T1-SPACE on healthy volunteers. The presence of IPH was determined on QSM and MP-RAGE by two reviewers separately and histology was used as a reference. The area of IPH was measured on QSM and MP-RAGE on matched slices. The area of calcification was measured on QSM and T1-SPACE on matched slices. Statistical Tests: Bland-Altman analysis, Pearson correlation coefficients, linear regression analyses were performed to evaluate the concordance of area measurements. Cohen's kappa (κ) was analyzed to determine the agreement between IPH detections. Paired t-test was used to compare the group difference. Results: In 423 matched slices, 20.1% (85/423) and 19.6% (83/423) were detected to have IPH on MP-RAGE and QSM, respectively. IPH detection by QSM and MP-RAGE showed goodagreement (κ = 0.822, P < 0.001) between the two methods. There was no significant difference 3 in IPH area measurements between QSM and MP-RAGE (7.28 mm 2 ± 6.41 vs. 7.16 mm 2 ± 5.99, P = 0.575). There was no significant difference in calcification area measurement between QSM and T1-SPACE (3.51 mm 2 ± 1.78 vs. 3.41 mm 2 ± 2.02, P = 0.783). Data Conclusion:QSM is a novel imaging tool for the identification of IPH in patients with carotid atherosclerosis and enables differentiation of IPH and calcification.

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

“…Despite the idealised ex vivo experimental set up, the work presented here highlights the promise for DTI metrics to yield valuable insight into arterial microstructure which could ultimately provide novel insight into diseased tissue morphologies. For example, recent in vivo studies have used quantitative susceptibility mapping to investigate gross morphological features [69][70][71] and inflammation 72 in atherosclerotic plaques, but this approach also has potential to provide markers of tissue microstructure and integrity 73 . Ideally, a combination of methods which allow for the full characterisation of the microstructure within the vessel wall would provide the insight needed to better inform the risk of atherosclerotic plaque rupture.…”

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

“…Despite the idealised ex vivo experimental set up, the work presented here highlights the promise for DTI metrics to yield valuable insight into arterial microstructure which could ultimately provide novel insight into diseased tissue morphologies. For example, recent in vivo studies have used quantitative susceptibility mapping to investigate gross morphological features [67][68][69] and inflammation 70 in atherosclerotic plaques, but this approach also has potential to provide markers of tissue microstructure and integrity 21 . Ideally, a combination of methods which allow for the full characterisation of the microstructure within the vessel wall would provide the insight needed to better inform the risk of atherosclerotic plaque rupture.…”

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

“…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][10][11][12][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. Results from this study highlight that QSM is sensitive to the microstructural composition of arterial tissue, and with further development it has the potential to offer unique insight into the onset and progression of carotid atherosclerosis.…”