AUDIENCE: Neurology, Risk Manager
ISSUE: FDA is providing preliminary information concerning magnetic resonance (MR) thermometry reliability with magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) devices.
FDA is currently evaluating data which suggests that potentially inaccurate MR thermometry information can be displayed during treatment. For example, MR parameters such as voxel size (measurement of the image resolution or detail) and MR image acquisition time (e.g., up to 8 seconds) may contribute to inaccurate MR thermometry readings and potential errors in the ablation assessment. In addition, MRgLITT devices may not account for the continued thermal spread of energy to the surrounding tissue (as the target ablation area returns to its baseline temperature), which may result in an underestimation of thermal damage.
The FDA has reviewed Medical Device Reports (MDRs) and literature reports which describe adverse events such as neurological deficits (e.g., focal motor deficits, aphasia, cognitive changes), increased intracerebral edema or pressure, intracranial bleeding, and/or visual changes (e.g., visual field deficits, blurry vision) when these devices were used to treat intra-cranial lesions. Several of these reports note events which required urgent medical and/or surgical intervention, and may have been associated with patient deaths. However, it is unclear at this time, whether an inaccuracy of MR thermometry directly caused or contributed to these events.
BACKGROUND: MRgLITT devices are commonly used in neurosurgical procedures for minimally invasive ablation of brain tumors, epileptic foci, or radiation necrosis. During these procedures, the tip of a laser probe is stereotaxically placed within the tissue to be ablated, and controlled thermal energy is delivered to the target tissue. MR thermometry is used to monitor the changes in temperature at the treatment site using a Magnetic Resonance Imaging (MRI) scanner, and proprietary software information is displayed on a workstation to aid the physician in assessing and controlling thermal damage.
The FDA recommends that health care providers
Consider and discuss with your patients the benefits and risks of these devices, as well as the availability of any alternative treatment modalities on an individual patient basis. Should an MRgLITT device be the best available treatment option:
Physicians should consider heating the target tissue slowly to reduce the potential for inaccurate MR thermometry readings. Additionally, heating the tissue slowly may lessen unanticipated thermal spread. For example:
Heating tissue at a rate of 4 degrees Celsius per second, and an MR acquisition time of 8 seconds, may result in uncertainties of up to 32 degrees Celsius during MR thermometry readings
Heating tissue at a rate of 1 degrees Celsius per second, and an MR acquisition time of 8 seconds, may result in uncertainties of up to 8 degrees Celsius during MR thermometry readings
While heating the target tissue slowly, physicians should also consider using one of the following settings to mitigate the risk of unintended damage to surrounding tissue or nearby critical structures:
Set the low temperature targets on nearby critical structures to 43 degrees Celsius or less
Follow the outer perimeter or isothermal contour line at the Cumulative Equivalent Minutes of 43 degree Celsius (CEM43)=2 minutes or less so that no critical structures are within the contour line
Contact the applicable manufacturer for further information regarding recommended heating parameters
Report problems to the FDA
Device manufacturers and user facilities must comply with the applicable Medical Device Reporting (MDR) regulations. Health care personnel employed by facilities that are subject to FDA's user facility reporting requirements should follow the reporting procedures established by their facilities. Prompt reporting of adverse events can help the FDA identify and better understand the risks associated with medical devices. Please include the following information in the report, if known:
Information on the manufacturer, brand of MRgLITT device used
Reason for treatment (e.g. tumor ablation, epileptic foci, etc.)
Anatomical location of treatment
Peak temperature, time needed to reach the peak temperature, and total laser-on time for each ablation
Information on the MRI (manufacturer, brand, field strength, transmit coil, receive coil, and MR imaging parameters)
Thermal damage dimensions estimated by the device; and actual thermal damage dimensions as measured by the health care provider
Patient outcome and whether additional treatment was needed
Read the MedWatch Safety Alert: https://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm605609