Experimental Multi-Parametric MRI Characterization of Iliocaval Venous Thrombosis Pathological Changes

Objective Iliocaval thrombotic obstruction is a challenging condition, especially since thrombus age and corresponding pathological remodeling at presentation are unknown, which directly impacts management. Our aim was to assess the ability of Magnetic Resonance Imaging (MRI) in determining age thresholds of experimentally created inferior vena cava (IVC) thrombosis in pigs. Methods We used a previously described swine model of IVC thrombosis. Animals underwent MRI at baseline, immediately after thrombosis creation and after a follow-up period extending from 2 to 28 days. Thirteen animals were divided into 3 groups according to disease’s chronicity: acute (AG, N1 = 5), subacute (SAG, N2 = 4) and chronic group (CG, N3 = 4) with a mean thrombosis age of respectively 6.4 ± 2.5, 15.7 ± 2.8 and 28 ± 5.7 days.A T1 weighted volumetric interpolated breath-hold examination sequence was used to anatomically delineate IVC thrombus as a region of interest. Three other MRI sequences were used to assess thrombus signal. Results Kruskal-Wallis showed a statistically significant difference in T1 relaxation times after contrast injection (P = .026) between the 3 groups of chronicity: AG (360.2 ± 102.5) was significantly different from CG (336.7 ± 55.2 ms; P = .003) and SAG (354.1 ± 89.7 ms) was significantly different from AG (P = .027). There was a statistically significant difference in native T2 relaxation times (P = .038) between the 3 groups: AG (160 ± 86.7 ms) was significantly different from SAG (142.3 ± 55.4 ms; P = .027) and SAG was significantly different from CG (178.4 ± 11.7 ms; P = .004). Conclusions This study highlighted MRI characteristics in a swine model that may have the potential to significantly differentiate a subacute and a chronic stage from an acute stage of deep venous thrombosis in humans. Further clinical studies in humans are warranted.