Abstract 2093: Quantitative Assessment Of Venous Thrombus Resolution And Macrophage Content In Mice Using Ferumoxytol-enhanced Magnetic Resonance Imaging

Abstract

Objective: The objective of this study is to explore the feasibility of ferumoxytol-enhanced magnetic resonance imaging (Fe-MRI) for noninvasive assessment of deep venous thrombus (DVT) resolution and macrophage content in resolving thrombi in a surgical murine model of inferior vena cava (IVC) ligation. Background: Imaging evaluation of acute DVT or post-thrombotic syndrome (PTS) in animal or clinical models is limited to assessment of anatomy. We hypothesize that Fe-MRI, used to evaluate macrophage content in other inflammatory diseases, can be useful to evaluate thromboinflammatory features after DVT. Methods: Nineteen wild-type CD-1 mice underwent surgical IVC ligation to induce DVT. Mice received either saline or administered 5 mg/kg of 14E11, a Factor XI inhibitor, before the procedure. Fe-MRI was performed from days 6-7 after ligation to evaluate thrombus volume, perfusion and macrophage content via T2, and T2 *-weighted images. Mice were euthanized at days 3-15 after surgery. The thrombi and adjacent vein walls were excised, weighed, formalin fixed, and paraffin embedded for histological analysis. Specimens were stained with specific antibodies to evaluate macrophage activity, collagen deposition, neovascularization, and recanalization. Significance was determined using the Mann-Whitney U or Student’s t-test. Results: After IVC-ligation in control mice, thrombus weights decreased by 59% from day 3 to day 15. FXI inhibition led to reduced macrophage content in both thrombus (p = .008) and vein wall (p = .01), decreased thrombus volume (p = .03), decreased thrombus mass (p = .01) and impaired thrombus perfusion (p = .01) compared to control mice. Iba1 staining supported these findings, showing significantly reduced macrophage presence in thrombi (p = .02). Conclusions: Fe-MRI T2 and T2 * relaxation times can be used to characterize and quantify post-thrombotic changes of perfusion, macrophage activity, and volume over time in a surgical mouse model of venous thrombosis. This approach could lead to better quantification of in vivo inflammation correlating monocyte and macrophage activity within resolving thrombi and veins and may serve as a useful tool in research and clinically in the evaluation of DVT or PTS.