Circle or semi-circle hyper-intensity on T1 high-resolution isovolumetric examination (THRIVE) indicates the young age of experimentally induced caval thrombus.

To evaluate the age of caval thrombus that experimentally induced in swine by use of magnetic resonance imaging (MRI). Caval thrombus was experimentally created in 15 swine by autologous clot injection assisted with caval net knitting. Serial high-resolution MR images were obtained using magnetic resonance venography (MRV) and T1 high-resolution isotropic volume examination (THRIVE) sequences in a 3.0-T MR system at 1, 7, 14, 21, and 28 days post model creation. At each time point, three pigs were sacrificed and the thrombotic vena cava was processed for histopathological examinations respectively. Caval thrombus was successfully induced in 15 pigs in group A. The signal intensity (SI) change of caval thrombus on THRIVE was age-dependent, with a typical sign of circle or semi-circle hyper-intensity at 7-day-old model while SI of thrombus was lower than that of muscle from day 14 throughout day 28. The histo-pathological findings revealed that RBCs-rich thrombus at day 1 without blue-stained particles, RBCs layers with infiltration of inflammatory cells and sporadically distributed blue-stained particles at 7-day-old thrombus. At day 14, 21 and 28, blue-stained particles became richer, coupled with formation of granulation tissue and fibrous tissue. The swine model in the study is good for age evaluation of venous thrombosis. The peripheral circle or semi-circle hyperintensity on THRIVE indicates the young age of caval thrombus in swine.