Development of Molecular Magnetic Resonance Imaging Tools for Longitudinal Tracking of Carotid Atherosclerotic Disease Using Fast Imaging with Steady-State Precession

Figures

• 

  Fig. 1. A Schematic diagram of experimental design. ApoE−/− mice (DT-MPIO n = 5, IgG-MPIO n = 5) were used to develop the atherosclerosis model as published [10]. Briefly, mice commenced on a high fat diet (HFD) 2 weeks prior to surgical implantation of a shear-stress modifying cuff on RCCA, leaving LCCA untreated as internal control. HFD was maintained until end of study. Mice were imaged on MRI (11.7 T Bruker BioSpec) at the following timepoints post-cuff placement: 5 weeks (baseline), 15 weeks (early), 20 weeks (intermediate), 30 weeks (advanced) and 50 weeks (very advanced disease stage). At each MRI session, mice were first imaged with conventional TOF-MRA, followed by pre-contrast FISP, intravenous bolus of IgG/DT-MPIO and lastly post-contrast FISP. The region of interest (ROI) for FISP imaging was placed in the lower half of carotid arteries based on the high prevalence of high-risk plaques in that region as atherosclerosis progresses [10]. Histological analysis was performed at the end of last MRI session (50 weeks). B Longitudinal tracking of carotid plaques from early to advanced disease stages by in vivo MRI. (a–e) Conventional TOF-MRA shows minimal or no stenosis in lower…

• 

  Fig. 2. A Magnitude of DT-MPIO-induced hypointense signal increased as atherosclerosis progressed in cuff-implanted RCCA, while IgG-MPIO-induced signal remains low throughout. Percentage difference between pre- and post-contrast SNR in FISP images (DT-MPIO n = 5, IgG-MPIO n = 5) were calculated for statistical analysis using Student’s t-test. *p < 0.05, **p < 0.01. B Histology of matching regions in RCCA and LCCA in both DT-MPIO and control IgG-MPIO groups. Histological analysis was performed in matching regions of carotid arteries (demarcated by yellow dashed lines) after imaging at week 50 post-cuff placement as described [8]. Histology confirmed that ample amount of fluorescent-labelled DT-MPIO was identified within the intima of the plaques in matching region of RCCA. These plaques bear vulnerable inflamed plaque phenotype (i.e. high expression of inflammatory biomarkers: MOMA-2, CD62P (P-selectin), VCAM-1, MMP2, MMP9, high “destabilising” lipid content, thin layers of “stabilising” smooth muscle cells in the cap of plaque). Histology sections in the IgG-MPIO group showed similar vulnerable inflamed plaque phenotype but with minimal amount of fluorescent-labelled IgG-MPIO identified…