Magnetic Resonance Thermometry May Carry Risk Of Tissue Overheating, FDA Warns

Federal regulators warn that using magnetic resonance thermometry during MR guided laser interstitial thermal therapy may result in serious side effects, injury or even death. 

In a safety alert issued April 25, the FDA indicates that using magnetic resonance thermometry during magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) can cause the surrounding tissue to overheat during treatment and result in serious side effects, which may lead to death.

MRgLITT devices are commonly used in neurosurgical procedures for a minimally invasive approach to ablate brain tumors, epileptic foci, or radiation necrosis. Surgeons place the tip of a laser probe into the brain, targeting the tissue to be ablated. Then controlled thermal energy is delivered to the tissue.

MR thermometry is used to monitor the changes in temperature at the treatment area using a magnetic resonance imaging scanner.

The FDA warns that preliminary data on MR thermometry reliability with MRgLITT devices indicate the information displayed by MR thermometry may be inaccurate.

The devices may not take into consideration the spread of heat to surrounding tissue because the target area to be ablated returns to normal temperature quickly. Thus, MR thermometry underestimates thermal damage to surrounding areas.

The agency indicates that MR parameters, such as voxel size, or the measurement of the image resolution or detail, may contribute to inaccurate MR thermometry and cause potential errors in the ablation assessment. More so, MR image acquisition time may also interfere and cause errors in assessment.

The FDA reviewed Medical Device Reports and current literature describing adverse events occurring when devices were used to treat intra-cranial lesions. A wide range of side effects were indicated, including neurological impairments, focal motor problems, aphasia, cognitive changes, increased intra-cerebral swelling or pressure, intracranial bleeding, and changes to vision.

Investigators said that some events required urgent medical or surgical intervention and were also associated with subsequent patient deaths. It is unclear whether the inaccuracy of the MR thermometry directly caused or contributed to the deaths; however, the risk was increased.

• The FDA offered several recommendations to surgeons conducting the procedures:
• Discuss with patients the benefits and risks of using the devices.
• Discuss the availability of alternative treatments.

The FDA recommends that if MRgLITT treatment is the best available option, focus on heating the target slowly to reduce potentially inaccurate MR thermometry readings and lessen the thermal spread to surrounding areas.

Researchers also warn doctors should consider certain settings to reduce the risk, including setting low temperature targets on critical structures to 43 degree Celsius or less and following the outer perimeter or isothermal contour line at the cumulative equivalent minutes of 43 degree Celsius=2 minutes or less, so that no critical structures are within the contours line.

Problems or side effects relating to MR thermometry for MRgLITT treatment should be reported following FDA Medical Device Reporting guidelines.