• MRI Guidelines Overview (Appendix B)
• Warnings
• Limitations
• Risks
• Precautions
• Supervision
• MRI exposure requirements
• Preparation for the MRI examination
• During the MRI examination
• Post-MRI examination review

MRI and Spinal Cord Stimulation for Chronic Pain (Appendix B) (Back to top)

Medtronic recommends that you do not conduct an MRI examination of any part of the body on a patient using a radio-frequency (RF) transmit body coil. If all of the instructions stated in this Appendix B are followed, MRI examinations of the head only using an RF transmit/receive head coil may be safely performed.

It is important to read this information in its entirety before conducting an MRI examination on a patient with any implanted component of a Medtronic neurostimulation system for chronic pain. These instructions do not apply to other implantable products or other devices, products, or items. Contact Medtronic at the appropriate address or phone number listed at the back of this document if you have any questions.

Due to the number and variability of parameters that affect MRI compatibility, the safety of patients or continued functioning of neurostimulation systems exposed to MRI cannot be absolutely ensured. MRI systems generate powerful electromagnetic fields that can produce a number of interactions with implanted components of the neurostimulation system. Some of these interactions, especially heating, are potentially hazardous and can lead to serious injury or death. However, when all instructions stated in this Appendix B are followed, MRI examinations of the head only may be safely performed. In addition, neurostimulation system components can affect the MRI image, potentially impacting the diagnostic use of this modality. The following information describes the potential interactions and control measures that should be taken to minimize the risks from these interactions.

The instructions in this Appendix B describe how to conduct a head-only MRI examination of a patient with a neurostimulation system implanted for chronic pain, using a transmit/receive head coil of a 1.5-Tesla horizontal bore MRI. MRI examinations of any other part of the body are not recommended, as these require the use of the MRI RF transmit body coil, which may produce hazardous temperatures at the location of the implanted lead electrodes.

Warnings (Back to top)

MRI RF transmit body coil – Medtronic recommends that you do not conduct an MRI examination using an RF transmit body coil on a patient with any implanted neurostimulation system component because the interaction of the MRI with the neurostimulation system may lead to serious injury or death. See the section “Risks associated with MRI examination” listed below.

MRI transmit/receive head coil – An MRI examination of the head only (no other part of the body) can be conducted safely using an RF transmit/receive head coil when all instructions in this Appendix B: MRI and spinal cord stimulation for chronic pain are followed.

Limitations (Back to top)

• MRI should not be considered for patients with neurostimulation systems if other potentially safer diagnostic methods such as CT, xray, ultrasound, or others will provide adequate diagnostic information.
• These instructions apply only to Medtronic neurostimulation interventions for chronic pain for approved indications.
• The instructions in this Appendix B apply to all Medtronic fully implantable neurostimulators, leads, and extensions used for chronic pain therapy.

Note: The instructions contained in this Appendix B are not applicable to MRI examinations of patients with radiofrequency (RF) neurostimulators.

Medtronic recommends physicians not prescribe MRI for a patient who has an implanted Itrel 3 Model 7425 Neurostimulator. The Itrel 3 Neurostimulator is highly susceptible to reset or damage when subjected to an MRI examination. If reset, the neurostimulator must be reprogrammed. If damaged, the neurostimulator must be replaced. The Itrel 3 Neurostimulator has an increased risk of induced electrical current, which may stimulate or shock the patient.

Contact Medtronic for information about newer models or any updates.

• The RF transmit/receive head coil must not cover any implanted system component.
• If the patient has any other implants or products that prohibit or contraindicate an MRI examination, follow the instructions from the manufacturer. The instructions in this Appendix B apply only to the Medtronic products listed above.
• Do not conduct an MRI examination if the patient's neurostimulation system has a broken lead wire, because higher than normal heating may occur at the break or lead electrodes. Excessive heating can cause tissue damage and result in severe injury or death.
• Physicians should not prescribe MRI for patients undergoing trial neurostimulation and having systems that are not fully implanted.
• If the MRI targeted image area is near the neurostimulator, it may be necessary to move the neurostimulator to obtain an image, or use alternate imaging techniques. MRI images may be severely distorted or image target areas can be completely blocked from view near the implanted neurostimulation system components, especially near the neurostimulator.
• Do not remove the neurostimulator and leave the lead system implanted as this can result in higher than expected lead heating. Excessive heating can cause tissue damage and result in severe injury or death.

Risks (Back to top)

Risks associated with MRI examination – Exposing a patient with an implanted neurostimulation system or component to MRI may potentially injure the patient or damage the neurostimulator. The known potential risks are as follows:

• Induced electrical currents from the MRI to the neurostimulation system or component may cause heating, especially at the lead electrode site, resulting in tissue damage. Induced electrical currents may also stimulate or shock the patient.

Note: This warning applies even if only a lead or extension is implanted.

Factors that increase the risks of heating and patient injury include, but are not limited to, the following:

• High MRI specific absorption rate (SAR) RF power levels
• Information for prescribers 2005-06
• Low impedance leads or extensions (Medtronic product names or model numbers designated by a “Z,” an “LZ,” or “low impedance”)
• MRI RF transmit/receive coil that is near or extends over the implanted lead system
• Implanted lead systems with small surface area electrodes
• Short distances between lead electrodes and heat-sensitive tissue

• Exposure to gradients exceeding a dB/dt limit of 20 Tesla per second may result in overstimulation or shocking, particularly for unipolar-capable devices.
• MRI may permanently damage the neurostimulator, requiring explant or replacement.
• MRI may affect the operation of the neurostimulator. The MRI may also reset the parameters to power-on-reset settings, requiring reprogramming with the clinician programmer.
  
  The Itrel 3 Model 7425 Neurostimulator is highly susceptible to reset or damage when subjected to an MRI examination. If reset, the neurostimulator must be reprogrammed. If damaged, the neurostimulator must be replaced. An Itrel 3 neurostimulator also might exhibit unpredictable behavior if subjected to an MRI examination.
• The neurostimulator may move within the implant pocket and align itself with the MRI field, which may cause patient discomfort or a recent neurostimulator implant incision to open.

Precautions (Back to top)

Patient interaction during MRI – If possible, do not sedate the patient so that the patient can provide feedback of any problems during the examination.

Monitor the patient during the MRI examination. Verify that the patient is feeling normal and is responsive between each individual scan sequence of the MRI examination. Discontinue the MRI immediately if the patient becomes unresponsive to questions or experiences any heating, pain, shocking sensations/uncomfortable stimulation, or unusual sensations.

Supervision (Back to top)

MRI procedure using an RF transmit/receive head coil - If all of the instructions stated in this Appendix B are followed, MRI examinations of the head using an RF transmit/receive head coil may be safely performed.

Prior to the MRI examination, an individual with the proper knowledge of MRI equipment such as an MRI radiologist or MRI physicist must ensure the MRI examination will be conducted according to the information outlined in this Appendix B.

Note: Due to the additional requirements in these instructions, MRI examination time may be significantly extended

MRI Exposure Requirements (Back to top)

Prior to an MRI examination, determine whether the patient has multiple active medical device implants (such as deep-brain stimulation systems, implantable cardiac defibrillators, and others). The most restrictive MRI exposure requirements must be used if the patient has multiple active medical device implants. Contact the appropriate manufacturers of the devices if you have questions.

If the following requirements cannot be met, do not proceed with the MRI examination.

• Use only an RF transmit/receive head coil.*
• Use only a 1.5-Tesla horizontal bore MRI (do not use open-sided or other field strength MRI systems).
• Enter the correct patient weight into the MRI console to ensure the head SAR is estimated correctly.

The MRI scan sequences must meet the following requirements. If they do not, the pulse parameters must be adjusted so that they comply with these requirements.

• Use MRI examination parameters that limit the head SAR to 1.5 W/kg or less for all RF pulse sequences.
• Limit the gradient dB/dt field to 20 Tesla per second or less.

*Important: If you are unsure if your MRI has RF transmit/receive head coil capability or if it displays “head SAR”, check with your MRI manufacturer.

Note: The requirements provided are based on in-vitro testing and should result in a safe MRI examination of a patient with an implanted Medtronic neurostimulation system when all instructions in this Appendix B are followed. However, due to the many variables that affect safety, the safety of patients or continued functionality of neurostimulator systems exposed to MRI cannot be absolutely ensured. The user of this information assumes full responsibility for the consequences of conducting an MRI examination on a patient with an implanted neurostimulation system.

Preparation for the MRI examination (Back to top)

Do the following prior to performing an MRI examination on a patient with an implanted neurostimulation component:

1. Inform the patient of all of the risks of undergoing an MRI examination as stated in this Appendix B.
2. If possible, do not use sedation so the patient can inform the MRI operator of any heating, discomfort, or other problems.
3. Instruct the patient to immediately inform the MRI operator if any discomfort, stimulation, shocking, or heating occurs during the examination.
4. Determine if the patient has any other implants or conditions that would prohibit or contraindicate an MRI examination. If you are unclear what implants may be present, perform an X-ray to determine implant type and location. Do not conduct an MRI examination if any conditions or implants that would prohibit or contraindicate an MRI are present.
5. Verify that all proposed MRI examination parameters comply with the “MRI exposure requirements” listed above. If not, the parameters must be modified to meet these requirements. If parameters cannot be modified, do not perform an MRI.
6. If the patient has implanted leads but does not have an implanted neurostimulator, perform the following steps:

• Wrap the external portion of the leads/percutaneous extensions with insulating material, such as dry gauze.
• Keep the external portion of the leads/percutaneous extensions out of contact with the patient.
• Keep the external leads/percutaneous extensions straight, with no loops, and running down the center of the head coil. Information for prescribers 2005-06

7. If the patient has an implanted neurostimulator, perform the following steps:

• Review the neurostimulator with a clinician programmer and print out a copy of the programmed parameters for reference.
• Test for possible open circuits by measuring impedance on all electrodes. An impedance measurement greater than 4000Ω for Itrel 3, Synergy, Synergy Versitrel, SynergyPlus+, or SynergyCompact+ indicates a possible open circuit. An impedance measurement greater than 3600Ω for Restore indicates a possible open circuit.
• If an open circuit is suspected, obtain an X-ray to identify whether the open circuit is caused by a broken lead wire. If a broken lead wire is found, do not perform an MRI examination.

Warning: Do not conduct an MRI examination if the patient's neurostimulation system has a broken lead wire, because higher than normal heating may occur at the break or lead electrodes. Excessive heating can cause thermal lesions and result in severe injury or death.

8. If the system is functioning properly and no broken lead wires are found, program the neurostimulator to the settings provided in Table 3.

Recommended neurostimulator settings for MRI examinations

During the MRI examination (Back to top)

• Monitor the patient both visually and audibly. Check the patient between each imaging sequence. Discontinue the MRI examination  immediately if the patient is unable to respond to questions or reports any problems.
• Conduct the examination using only the MRI pulse sequence that the MRI radiologist or physicist has confirmed meets the “MRI exposure requirements” outlined in this Appendix B.

Post-MRI examination review (Back to top)

• Verify that the patient feels normal.
• Verify that the neurostimulator is functional.
• Reprogram the neurostimulator to pre-MRI settings.