Metals that exhibit magnetic attraction in the MRI setting may be subject to movement (deflection) during the procedure.  Both magnetic and non-magnetic metallic devices of certain geometries may also be subjected to heating caused by interactions with the magnetic field.  Of secondary concern, is the possibility of image artifacts that can compromise the procedure and image quality.

Implant Materials

Orthopaedic devices are manufactured from metals and polymeric materials.  BIOTEK metallic implants are produced from titanium in either the alloy or pure form and stainless steel.  With the exception of stainless steel, these materials have no magnetic attraction in the MRI environment and implant movement / deflection is not expected.  Stainless steels used in some BIOTEK devices may exhibit small magnetic interaction in the MRI environment.

Implant Movement

There are currently several researchers as well as an ASTM committee exploring methods for accurately assessing the MRI compatibility of implant devices.  The primary focus of the research has been the measurement of implant movement in response to a magnetic field.  Several studies have been conducted in which the movement/deflection of various orthopaedic implants are measured in the high magnetic field (0.3-1.5 Tesla) region of MRI units.  The results of these studies show no measurable movement of implants fabricated from titanium alloys.

In an effort to improve imaging capabilities, MRI units employing larger magnetic fields (3.0 Tesla) are also being used.  It is possible that implants exhibiting weak interactions in a 1.5 Tesla magnetic field may show a stronger interaction with the 3.0 Tesla field.  It has also been examined and found that the movement/deflection of selected orthopaedic implants fabricated from titanium and stainless steel in a 3.0 Tesla MRI unit exhibited little or no movement/deflection.

Implant Heating

Whereas several studies examining the movement/deflection of metallic implants have been performed, comparatively little information has been developed for the potential heating of implants caused by MRI induced electrical currents. MRI induced heating of an implant is important in that it has the potential to damage both the implant and the tissues surrounding the implant.
MRI induced heating of implanted devices is caused by the absorption of magnetic energy during the procedure. The rate of energy absorption is referred to as the specific absorption rate (SAR).  In general, only minor heating of passive (non electrified) metallic implants has been found in the MRI setting. However, significant heating is possible for implants that have an elongated shape (e.g. pacemaker lead) or those that provide a conductive loop (large all metallic external fixators). Polymers and composites do not conduct electric current and this minimizes the chance of significant heating of these devices.

Recommendations

Although studies indicate that the MRI procedure has minimal effects on most BIOTEK orthopaedic implant devices, there are certain devices, like external fixation devices that may have magnetic components and should not be used in an MRI environment. Patients should note that there are several different manufacturers and generations of MRI equipment available, and BIOTEK cannot make claims regarding the compatibility of BIOTEK implants with any specific MRI unit.  It is recommended that the patient contact the surgeon or the manufacturer of the MRI equipment to discuss the compatibility of BIOTEK implants with the MRI equipment before undergoing any test.