Evaluation of an active vena cava filter for MR imaging in a swine model.

Purpose: To evaluate the feasibility of magnetic resonance (MR) imaging-guided placement of an active vena cava filter (AVCF) in a swine model, the effectiveness of the system in filtering thrombi, and the detection of thrombi with MR imaging.

Materials And Methods: This study was approved by the government committee on animal investigations. An AVCF tuned to the Larmor frequency of a 1.5-T MR unit was placed in the inferior vena cava (IVC) of seven pigs under real-time MR imaging guidance. Steady-state free precession sequences with four different flip angles (90°, 40°, 25°, and 15°), T1-weighted turbo spin-echo sequences with two flip angles (90° and 15°), and black-blood proton-density-weighted sequences with a flip angle of 90° were performed before and after filter placement. In six cases, extracorporeally produced thrombi were injected through the femoral access to test filter function. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed before and after filter deployment and compared by using the signed-rank test.

Results: All AVCFs were successfully deployed. Significant differences (P < .05) in the SNR and CNR of the IVC were found before and after AVCF placement and between sequences with different flip angles. Intravenous thrombi were caught in all cases and clearly depicted with MR imaging. On black-blood proton-density-weighted images, high-signal-intensity thrombi inside the filter were clearly detectable without any overlaying artifacts.

Conclusion: MR imaging-guided deployment and monitoring of an AVCF is feasible. The AVCF enhances the SNR and CNR, resulting in clear depiction of thrombi inside the filter without the need for contrast material. Design modifications for improved intracaval fixation and retrieval of the prototype AVCF will be required.