Inferior Vena Cava Filters:
https://emedicine.medscape.com/article/419796-overview


In patients w/ conditions like congestive heart failure where anticoagulation may be contraindicated (or, in Krasnov's case -- inconvenient), a Greenfield filter (a type of inferior vena cava (IVC) filter) designed to trap thrombi + prevent pulmonary embolism (PE) may be indicated. The filter is conical, made of stainless steel or titanium + consists of six zigzag-shaped legs w/ hooks that anchor it to the IVC wall, allowing it to trap emboli larger than 5 mm, as well as a significant portion of smaller ones.




Folks w/ Greenfield vena cava filters can generally undergo MRI after placement, but safety considerations depend on the filter type. The original stainless steel Greenfield filter is considered MR conditional, +, while early guidelines recommended waiting six weeks post-implantation to allow for proper anchoring, recent evidence suggests an MRI can be performed immediately after placement without increased risk of migration.

Newer versions of the Greenfield filter (like the titanium Greenfield filter), are made from nonferromagnetic materials and are also considered MR conditional, allowing MRI at 1.5 T or 3.0 T under specified conditions. Despite this, some studies have reported higher rates of filter tilt, migration, + perforation w/ the titanium variant. Overall, most IVC filters, including modern Greenfield designs, are labeled as MR conditional, meaning MRI is safe under specific conditions, + patients w/ nonferromagnetic filters can undergo MRI at any time after implantation.