Experimental venous thrombi: MRI characteristics with histopathological correlation

Objectives: The purpose of this study was to evaluate the MRI characteristics of venous thrombus over set time thresholds with histopathological correlation in a porcine model. Methods: Inferior vena cava thrombi were induced in 12 pigs. MRI was performed in three pigs 2 h, 1 day, 3 days and 2 weeks after thrombus induction. Results: The MRI characteristics were analysed in correlation with histopathological findings. The thrombi after 2 hours, which consisted of red blood cells (RBCs), showed isointensity on T(1 )weighted images (T(1)WIs) and hyperintensity on both T(2 )weighted images (T(2)WIs) and diffusion-weighted images (DWIs). The mean apparent diffusion coefficient (ADC) value was 1.93 × 10(-3) mm(2) s(-1). The thrombi after Day 1, which consisted of RBCs and migrating neutrophils at the periphery, showed isointensity on T(1)WIs, slight hyperintensity on T(2)WIs and hypointensity on DWIs. The mean ADC value was 1.62 × 10(-3) mm(2) s(-1) [corrected]. The thrombi after Day 3, which consisted of RBCs and peripheral inflammatory cells including macrophages, showed isointensity with peripheral hyperintense regions on T(1)WIs and hypointensity on both T(2)WIs and DWIs. The mean ADC value was 1.67 × 10(-3) mm(2) s(-1). After 2 weeks, the thrombi, which revealed RBC lysis surrounded by granulation tissues, showed isointensity on T(1)WIs and hyperintensity on T(2)WIs and DWIs. The mean ADC value was 2.48 × 10(-3) mm(2) s(-1). Conclusion: The temporal MRI characteristics seemed to be related to chemical and physical changes in RBC and organisation of granulation tissues. Free radicals generated by macrophages might also be related to some extent.