Real-time MR-guided retrieval of inferior vena cava filters: an in vitro and animal model study.

Objective: To develop interventional magnetic resonance (MR) guidance techniques for inferior vena cava (IVC) filter retrieval in vitro and demonstrate feasibility in vivo.

Methods: Three optional IVC filters and their retrieval systems were investigated. Experiments were performed on a 1.5-T MR system. Real-time MR imaging was optimized by using a custom-built IVC phantom. A three-dimensional (3D) contrast-enhanced MR venography sequence was optimized in vitro for improved detection of thrombus trapped within the filters. Filters were then retrieved in vitro and in vivo in a swine model under MR guidance. In-vivo retrieval procedure time was measured.

Results: The combination of one of the nitinol filters and a loop snare was suitable for real-time MR procedures. With a 90° flip angle, 3D MR venography allowed detection of simulated thrombus within the filter. A radial true fast imaging sequence with steady-state precession allowed visualization of the loop snare and IVC filter hook and successful retrieval of the filter in vivo and in vitro. In-vivo MR fluoroscopy time for retrieval was 97 seconds ± 51 (mean ± SD).

Conclusions: MR-guided retrieval of a nitinol-based IVC filter by using a loop snare is feasible with the use of optimized sequences and passive device tracking.