Neurostimulation Systems: Deep Brain Stimulation
MRI Guidelines for Medtronic Deep Brain Stimulation Systems Medtronic Inc.
Models:
Kinetra: 7428
Soletra: 7426
Itrel II: 7424
Activa PC Deep Brain Neurostimulator (Model 37601)
Activa RC Deep Brain Neurostimulator (Model 37612)
Activa SC Deep Brain Neurostimulator (Model 37602)
Activa SC Deep Brain Neurostimulator (Model 37603)
Various models of the Activa products (Medtronics, Inc.) used for deep brain stimulation are MR Conditional. Comprehensive labeling information must be reviewed to ensure patient safety.
Carefully review the latest MRI labeling conditions and guidelines at: www.medtronic.com/mrimanuals
MR healthcare professionals are advised to contact the respective manufacturer in order to obtain the latest safety information to ensure patient safety relative to the use of an MR procedure.
REFERENCES
www.medtronic.com
www.medtronic.com/mrimanuals
Urgent Device Correction Change of Safe Limits for MRI Procedures Used With the Medtronic Activa Deep Brain Stimulation Systems
This letter is intended to inform you of a safety concern regarding the Medtronic Activa Deep Brain Stimulation (DBS) system instructions for performing MRI (magnetic resonance imaging). Medtronic's instructions have until now recommended a use of a displayed MRI head specific absorption rate (SAR) of not more than 0.4 W/kg. Medtronic recently determined that an SAR of 0.4 W/kg can cause excessive heating of implanted DBS electrodes during MRI. Medtronic is, however, not aware of any adverse events that resulted from this problem when MRI was conducted on DBS patients following Medtronic's MRI instructions.
Medtronic changed the instructions for use of the Activa DBS system. The recommended maximum displayed head SAR is now 0.1 W/kg. This is the only change to the instructions for use of the Activa DBS system. The revised instructions apply to the following Activa DBS system components:
Model 7424 Itrel II Neurostimulator (DBS applications only)
Model 7426 Soletra Neurostimulator
Model 7428 Kinetra Neurostimulator
Models 3387, 3389 DBS Leads
Models 7482, 7495 DBS Extensions
Explanation of the issue:
Medtronic's original testing relied on the MRI system's displayed head SAR value. We have now determined that the displayed value used in the original testing was inaccurate. This inaccuracy resulted in MRI instructions for our DBS systems that did not provide an adequate safety margin for MRI machines that have an accurate displayed SAR.
Medtronic recently retested the heating of Activa DBS electrodes by MRI scans at specific SAR values, using standardized methods and phantoms. At an actual applied SAR of 0.4 W/kg, the temperature of a DBS electrode embedded in a phantom increased by 5 degrees C. This temperature increase is near or at the level that can cause tissue injury. By contrast, the maximum temperature rise of the DBS electrode was less than 2 degrees C for an applied head SAR of 0.1 W/kg over a 15 minute scan. Therefore we have determined that an actual applied head SAR of 0.1 W/kg provides a reasonable thermal safety margin.
In the same series of tests, we evaluated the accuracy of the SAR display of three different 1.5 Tesla MRI machines using a transmit-receive (T/R) head coil. The actual SAR was measured in a calorimetric phantom. The two new machines had measured SARs corresponding to the displayed SARs. The older model MRI machine produced SARs as low as 1/4 of the displayed SAR.
If your MRI machine and specific software version develop actual SARs that are appreciably lower than the displayed SARs, then a displayed SAR of 0.1 W/ kg may not produce adequate images. Imaging problems resulting from a difference between actual SARs and displayed SARs would need to be addressed by the manufacturer of your specific MRI machine.
We appreciate your assistance with this matter and regret any inconvenience this may cause you and your patients. The Medical Community can further our understanding of Activa Deep Brain Stimulation Systems by reporting adverse events to Medtronic at 800-328-0810 or FDA at 800-332-1088. If you have any questions or comments, please contact your Medtronic representative or Medtronic Neurological Technical Services at 800-707-0933.
*The information for the Activa System was reprinted with permission by Medtronic, Minneapolis, MN, www.medtronic.com.
MR healthcare professionals are advised to contact the respective manufacturer in order to obtain the latest safety information to ensure patient safety relative to the use of an MR procedure.
REFERENCES
www.medtronic.com/mri
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