Abstract 20143: Direct in vivo Quantification of Intraplaque Hemorrhage and Fat in Atherosclerosis by Magnetic Resonance Imaging

Introduction: Intraplaque hemorrhage (IPH) and lipid core (LC) are hallmarks of rupture-prone atherosclerotic plaque. HYPOTHESIS: We hypothesized that IPH and LC can be quantified using R2* and fat measurements derived from four-point Dixon magnetic resonance imaging (MRI). Methods: Four patients scheduled for carotid endarterectomy underwent MRI in a 3T scanner applying: (a) T1weighted: TE=9ms, TR=1053ms (b) 4-point Dixon 3D gradient echo: TE=3.6ms, R=18ms, flip angle=10°, 2 REST slabs (c) 4-D flow MRI: TE=3.1ms, TR=5.4ms, flip angle=10°. IPH and fat were quantified from Dixon using custom software (Figure: visualization of IPH, red and LC, yellow as measured from Dixon MRI). After surgery, plaques were paraffin embedded and enface images were taken every 50μm. Every 200μm sections were taken for histology. A 3D histology volume was generated from this data and registered to MRI with the vessel lumen as a landmark. Area of IPH and LC upon histology was correlated to MRI values within these areas and MRI signal within IPH and LC was compared to MRI signal outside these areas. Results: Registration of 3D histology was through combining features from T1weighted MRI, first echo from Dixon and 4D flow MRI. Throughout all plaques the correlation between R2* and area of IPH as well as fat from Dixon and area of LC upon histology was high (IPH: Pearson r 0.451, 95% CI: 0.364 t- 0.530, P<0.0001; LC: Pearson r 0.148, 95% CI: 0.0635 - 0.231, P<0.001). Throughout each plaque R2* within IPH was significantly higher than outside (mean difference±SEM/patient: (i) 11.96 ± 2.091 (ii) 7.616 ± 2.154 (iii) 12.66 ± 1.412 (iv) 14.13 ± 2.144; P<0.001). Fat from Dixon was significantly higher inside LC than outside (mean difference±SEM/patient: (i) 1.796 ± 0.386 (ii) 3.078 ± 0.328 (iii) 6.610 ± 0.651 (iv) 0.481 ± 0.242 N=167; P<0.0001). Conclusions: R2* and fat measured from Dixon MRI reliably quantifies the extent of IPH and LC in atherosclerotic plaques as validated by 3D histology.