Amid continuing concerns about the risk of serious injury or death with magnetic resonance (MR) thermometry, federal regulators have issued new recommendations designed to help prevent surrounding tissue from overheating during treatment.
The FDA issued a letter to health care providers on November 8, focusing on patient safety resulting from tissue overheating during inaccurate magnetic resonance (MR) thermometry readings, which can occur during magnetic resonance-guided laser interstitial thermal therapy device (MRgLITT) procedures.
The new recommendations are an update to an April 2018 FDA warning, which was issued about the risk of MR thermometry overheating and damaging surrounding tissue.
The FDA indicates it is working with two manufacturers that market MRgLITT devices, including Medtronic, which manufactures the Visualase Thermal Therapy System, and Monteris Medical, which manufactures the NeuroBlate System. Both manufacturers provided updated information with suggested procedural techniques for MRgLITT devices to reduce unintended thermal damage.
MRgLITT devices are used during neurosurgical procedures for a minimally invasive approach to ablate brain tumors or radiation necrosis. Surgeons place the tip of a laser probe into the brain, targeting the tissue to be ablated.
MR thermometry monitors changes in temperature using an MRI scanner, while the devices are used during surgical procedures. However, the information displayed by MR thermometry may be inaccurate leading to health care professionals underestimating the amount of thermal damage inflicted on patients, the FDA warned.
The devices do not take into consideration the spread of heat to surrounding tissue during target ablation procedures, underestimating the thermal damage to the surrounding areas. This can cause side effects, including neurological impairments, focal motor problems, aphasia, cognitive changes, increased intra-cerebral swelling or pressure, intracranial bleeding, and changes to vision.
As a follow-up to the initial warning, Medtronic issued three advisory letters to providers with detailed mitigation strategies. The FDA cleared premarket submission for a redesigned NeuroBlate System that updates labeling regarding the use of MR thermometry to help predict thermal damage.
The agency calls on health care providers to follow the recommendations from April, as well as additional recommendations from the new update. The recommendations call for health care providers to:
- Heat target areas slowly to reduce inaccurate MR thermometry readings and lessen the thermal spread to surrounding areas.
- Set low temperature targets on critical structures to 43 degrees Celsius or less.
- Keep the temperature below 85/90 degrees Celsius right outside the laser fiber’s image artifact (depending on which system is used).
- Keep the cooling system running throughout thermal monitoring, including when the laser is on and after it is shut off, to bring the tissue next to the fiber back too baseline temperature within 120 seconds post laser delivery.
Problems or side effects relating to MR thermometry for MRgLITT treatment should be reported following FDA Medical Device Reporting guidelines.