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Session: Imaging - Cardiac System
Session starts: Thursday 24 January, 13:30
Presentation starts: 14:00
Room: Lecture room 559

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Harm Nieuwstadt (Erasmus MC)
Tom Geraedts (Philips Healthcare)
Eline Kooi (MUMC)
Ton van der Steen (Erasmus MC)
Jolanda Wentzel (Erasmus MC)
Frank Gijsen (Erasmus MC)

Abstract:
Carotid atherosclerosis is a disease characterized by plaque formation in the carotid bifurcation. Vulnerable plaques, consisting of a large lipid-rich necrotic core (LRNC) separated by a thin fibrous cap (FC) from the lumen, are most prone to rupture and can be visualized in vivo by carotid MRI [1]. How accurate MRI can quantify plaque components such as thin FC’s and LRNC’s in vivo, remains unknown because of the lack of an accurate ground truth on the sub millimeter scale. To circumvent this problem, we chose a novel approach by simulating carotid MRI using the open-source package JEMRIS [2]. We simulated an in vivo T1W gadolinium contrast enhanced MRI protocol, specifically designed to image FC’s. We simulated identical timings, turbo-spin echo factor, acquired in-plane voxel dimensions and k-space filling. A set of 33 ground truth vulnerable plaque geometries derived from cross-sectional histological data from 12 patients were used as 2D sample models for the MRI simulations. Segmentation on simulated images was performed by 3 expert MR readers and measurements were compared to the ground truth by correlation coefficient (R) and within readers by the intraclass correlation coefficient (ICC). MR readers segmented the lumen with high correlation and excellent agreement (R = 0.996, ICC = 0.99). Measured vessel wall area correlated well (R = 0.96, ICC = 0.94), but was found to be overestimated by 15%. MR readers were found to systematically under predict LRNC area by -31%, but their measurements correlated well (R = 0.95, ICC = 0.94). Measured FC thickness showed a weak correlation (R = 0.71, ICC = 0.69). FC’s smaller than 0.6 mm were severly overestimated in thickness by 201 ± 217%, where FC’s between 0.6 and 0.9 mm were measured more accurate and slightly underestimated: -6 ± 15%. We conclude that in vivo MRI can accurately quantify plaques with regard to vessel wall area and LRNC, but shows limitations for thin FC measurements. This might influence the reliability of in vivo MRI when assessing vulnerable plaque risk by quantifying FC thickness. This research was supported by the Center for Translational Molecular Medicine and the Netherlands Heart Foundation (PARISk). REFERENCES [1] H.R. Underhill et al., Nature Reviews in Cardiology, 7, pp. 165–173, (2010). [2] T. Stocker et al., Magnetic Resonance in Medicine, 64, pp. 186–193, (2010).