IVC filters can pose a threat to MRI safety, as some of the implantable filters are made of metal that can be attracted to the magnets used in MRIs. If precautions are not taken, people who have had an IVC filter implanted can suffer serious injuries if they have an MRI. The failure to warn doctors and patients about these risks have led to numerous IVC filter lawsuits against the manufacturers of the device.
- 1. MRI safety
- 1.1 Dangers posed by magnetic fields in MRI machines
- 1.2 FDA regulates medical implants for MRI safety
- 2. Some IVC filters are not MR Safe
- 3. Lawsuits over IVC filters causing MRI injuries
1. MRI safety
Because of the way magnetic resonance imaging, or MRI, machines work, objects made of certain metals pose a threat both to the machine and to people near it. Even metal objects that have been implanted can create problems. To avoid these problems, the U.S. Food and Drug Administration (FDA) has regulates medical implants to make sure people who have them do not mistakenly get hurt by an MRI machine.
1.1. Dangers posed by magnetic fields in MRI machines
MRI machines use magnets and radio waves to generate detailed pictures of internal tissues.
The magnet in an average MRI machine is extremely powerful – creating a magnetic field of 1.5-teslas, or around 1,000 times the strength of a typical household magnet.
The extreme strengths of the magnets used in MRI machines can create problems if there are other magnetic objects in the room when the MRI machine is turned on. If there is another magnetic object in the area, it can fly into the MRI machine's magnets. This can damage the machine and severely hurt anyone who is standing in the way.
1.2. FDA regulates medical implants for MRI safety
Among the metallic devices that can be a risk near an MRI machine are those that have been implanted. People who have had a metallic device implanted and who then get an MRI can get catastrophically hurt if the MRI's magnetic field is strong enough to pull the implant out of place or even out of their body.
To reduce this risk, the FDA has required medical device manufacturers to disclose how a particular implant will react when near an MRI machine. The categories include1:
- MR Safe, for medical implants that pose no risks when in the presence of MRI equipment,
- MR Conditional, for implants that can be made safe in the presence of MRI equipment, but only if the conditions for safe use are strictly followed, and
- MR Unsafe, for implants that pose a risk in the presence of MRI equipment that cannot be reduced.
However, the FDA's regulations only took effect in 1997, well after many IVC filter devices had been on the market for years. To add to the confusion, the FDA changed the regulations to their current form in 2005.2
2. Some IVC filters are not MR Safe
In recent years, IVC filter manufacturers have become more aware of the problems that their devices can create in an MRI room. However, some IVC filters still pose a risk.
While it is rare to find an IVC filter that has been labeled as MR Unsafe under the FDA's regulations, there are still some permanent IVC filters that were manufactured and implanted before 1997 and that are still in use. If you have had a permanent IVC filter that was implanted long ago and need an MRI, you should consult your doctor to determine whether your IVC filter could pose a problem.
Current IVC filters are far more likely to be deemed MR Conditional, instead. Some of the most common IVC filters that are MR Conditional are:
- Cook Medical's Bird's Nest IVC Filter,
- Cook Medical's Günther Tulip IVC Filter,
- Boston Scientific's Greenfield IVC Filter, and
- C.R. Bard's Denali Filter.
Patients with these IVC filters can still receive an MRI, so long as appropriate safety precautions are taken.
For example, patients who have had Bard's Denali IVC Filter implanted can have an MRI taken immediately after the device has been implanted if3:
- The MRI machine uses a static magnetic field of 3-tesla or 1.5-tesla,
- The spatial gradient magnetic field is 720-Gauss/cm or lower, and
- The MRI machine's whole-body-averaged specific absorption rate, or SAR, is kept at or below 2-W/kg.
Many other IVC filters require several weeks to pass between the implant procedure and the MRI. This time allows the IVC filter's struts to grip the insides of the inferior vena cava vein firmly enough that the magnetic field will not pull the device out of position.
3. Lawsuits over IVC filters causing MRI injuries
IVC filter manufacturers have often failed to fully disclose the risks of having an MRI while one of their devices is implanted. The injuries that have resulted from this failure to warn about the risks have led to hundreds of lawsuits against the maker of the device, seeking compensation for the injuries the victim has suffered.
See U.S. Food and Drug Administration, “Understanding MRI Safety Labeling.”
See Shellock FG, Woods TO, Crues JV, “MR Labeling Information for Implants and Devices: Explanation of Terminology,” Radiology 253(1):26-30 (October 2009).
C.R. Bard, “Denali Vena Cava Filter – MRI Safety.”