- Yes, vagal nerve stimulators (VNS) are MRI compatible if specific safety guidelines are followed.
- VNS devices can be safely scanned in 1.5T or 3T MRI machines when using a modified MRI protocol.
- MRI scans of the brain with VNS implants are considered safe with proper precautions.
- Device settings must be checked by a doctor before and after MRI scanning.
- Allowable scan regions depend on the VNS model and implant location.
What is a vagal nerve stimulator and how does it work?
A vagal nerve stimulator (VNS) is a small, implanted device that sends mild electrical impulses to the brain via the vagus nerve in the neck. It is a form of neuromodulation therapy most often used to treat epilepsy and depression that does not respond to conventional treatment.
The vagus nerve connects the brain to many important organs including the heart, lungs, and digestive system. It plays a role in regulating vital functions like heart rate and digestion. Stimulating this nerve can improve conditions like epilepsy by helping regulate excitability in the brain.
The VNS device consists of a pulse generator and wire with electrodes that are surgically implanted. The pulse generator is usually placed under the skin on the left chest below the collar bone. The electrodes attach to the left vagus nerve in the neck. When activated, the device sends signals along the vagus nerve up to the brain.
This stimulation of the vagus nerve influences certain brain networks involved in seizures or mood regulation. Although the exact mechanisms are not fully understood, VNS is thought to help prevent or shorten seizures and improve mood in treatment-resistant cases.
Are VNS devices MRI compatible?
Yes, vagal nerve stimulators are considered MRI compatible, meaning they can function safely during MRI scanning when certain guidelines are followed. However, standard MRI protocols must be modified to accommodate the presence of the VNS device.
VNS devices contain metal parts that can interact with and heat up during MRI scanning. So modifications like limiting scanner power or avoiding scanning near the device help prevent issues. Following device-specific protocols from the manufacturer helps ensure patient safety.
According to Cyberonics, a leading VNS manufacturer, their VNS Therapy System devices can be safely scanned under the right conditions at 1.5T or 3T field strength. This includes MRI scans of the head/brain region. However, scans of some body areas are restricted depending on the device model and implant location.
What safety guidelines should be followed for scanning VNS patients?
There are some key guidelines both doctors and MRI technicians should follow when scanning a patient with a VNS device:
- Use the device’s MRI mode – The VNS device must be put into an MRI mode or setting that suspends normal stimulation during the scan. This requires interrogation of the device before and after MRI to check settings.
- Limit SAR levels – The scanner should operate at or under a maximum whole body averaged Specific Absorption Rate (SAR) of 2.0 W/kg. Higher SAR levels can cause device heating.
- Avoid direct exposure – The area of the VNS implant should not be directly exposed to scanner’s transmit RF coil or receive-only coils. RF shielding helps limit exposure.
- Check lead wires – Device lead wires should be kept away from any heating risk. Looping or twisting of leads should be avoided.
- Know allowable scan regions – The VNS generator model and implant location determines which body regions can be safely scanned by MRI. Only permitted areas should be imaged.
- Watch for issues during scanning – Patients should be monitored for problems like painful stimulation, induced currents, or unusual heating during the MRI. Scanning should be halted if problems occur.
Following all protocol guidelines specified by the VNS device manufacturer is crucial to avoiding safety issues. Doctors should confirm a patient’s VNS model and implantation details before MRI to determine appropriate parameters.
Can patients with VNS get MRI scans of the brain?
Yes, MRI scans of the brain are considered safe for patients with a vagal nerve stimulator when proper precautions are taken. However, some restrictions apply depending on the VNS device model.
For example, Cyberonics indicates MRI head scans are permissible with their VNS generators as long as SAR levels do not exceed recommended limits. The same general safety guidelines outlined above should also be followed.
Specifically, MRI technicians should select an appropriate head coil and headset that avoids direct contact with the VNS generator. The latest VNS programming information should be provided so technicians can calculate safe SAR levels.
While brain scans are possible, certain Cyberonics VNS device models limit exposures to just one or two scans. So doctors should check details to confirm if a head MRI is allowed based on prior scans. Overall, coordination between doctors and MRI staff helps facilitate safe brain imaging.
A 2017 study also demonstrated the safety of brain MRI scans in 53 epilepsy patients with VNS implants. Using a transmit/receive head coil and following VNS-specific guidelines, no significant issues occurred during any of the scans. This further verifies brain MRIs can be done when protocols are properly followed.
What body regions should be avoided when scanning VNS patients?
Certain body regions should not be imaged with MRI in patients with vagal nerve stimulators due to potential risks. Restrictions depend on the location of the VNS generator and type of lead wires.
For generators implanted in the upper left chest area, MRI scans should avoid direct exposure of the generator and lead wires. RF energy from MRI can be picked up by the VNS system and cause excessive heating, especially near the generator.
According to Cyberonics, their VNS systems allow MRI scans of the head, neck, and extremities (arms and legs). But MRI of the chest area is not permitted due to risks associated with scanning near the generator site.
If a Cyberonics VNS generator is implanted in the abdomen or other location, permitted scan regions may differ. Doctors should refer to exact model specifications to determine allowable MRI scan areas and special precautions.
No matter the VNS system or generator location, the implanted components should never directly interact with MRI coils or be exposed to high levels of RF energy. Limiting scans to approved body regions is essential.
Can MRI technicians independently scan VNS patients?
No, MRI technicians cannot scan VNS patients independently without coordination from the prescribing physician. Doctors overseeing VNS therapy must provide current device settings and programming details beforehand.
Since the VNS device needs to be properly set to MRI mode before scanning, interrogation of settings must be done by a healthcare professional familiar with the particular VNS system. The doctor determines allowable MRI parameters and bodies regions specific to that patient’s device model and situation.
Direct communication between the referring physician and MRI staff ensures proper protocols are followed. The doctor should also check device settings again after scanning to restore normal stimulation settings.
According to BJC HealthCare, radiologists and technicians should never scan VNS patients without official orders from the ordering physician that include VNS details. Independent scanning risks improper MRI protocols and safety hazards. Close coordination remains critical.
How should patients prepare for an upcoming MRI scan?
Patients with VNS devices should take certain steps to prepare for an upcoming MRI scan prescribed by their doctor:
- Keep all VNS documentation like the patient identification card handy for reference.
- Note the VNS model, serial number, implantation date, stimulation settings, and prior MRI history.
- Ask your doctor exactly which body region will be scanned. Discuss any special precautions.
- Schedule an appointment with your doctor before the MRI to put the device into MRI mode.
- Arrive early at the MRI facility in case delays occur when technicians set up scanner adjustments.
- Ask the MRI staff if they are experienced with VNS MRI protocols and safety guidelines. Request to see documentation.
- Remind staff of any scanning restrictions related to your VNS device and approved scan region.
- Watch for any uncomfortable sensations around the implant area during the scan and report them immediately.
- Follow up with your doctor soon after the MRI so device settings can be restored.
Proper preparation and coordination helps patients with VNS implants undergo safe, effective MRI scanning when needed.
What precautions should doctors take when ordering MRIs for VNS patients?
Doctors ordering MRI scans for vagal nerve stimulator patients should follow a number of important precautions:
- Review the patient’s full VNS history – Note implantation date, generator model, stimulation parameters, and any prior MRI scans.
- Check and record current device settings – Interrogate the VNS and set it to appropriate MRI modes before scanning.
- Specify approved MRI parameters – Indicate field strength, SAR level limits, coil type, and other protocol restrictions.
- Limit approved anatomy – Be clear about permissible scan regions based on VNS device details. Avoid chest area.
- Educate patient on risks – Discuss any safety hazards and possibilities of pain, induced currents, disrupted stimulation, or changes in heart rate.
- Coordinate with MRI staff – Provide complete MRI instructions and protocols for VNS device. Ensure staff expertise with VNS procedures.
- Follow up promptly after scan – Evaluate the patient, device, and MRI results for any issues. Restore normal VNS settings.
Taking these steps helps doctors oversee the process to minimize risks and maximize the safety of patients requiring MRI with an implanted vagal nerve stimulator.
What kinds of problems or risks can occur when scanning VNS patients?
MRI scanning of VNS patients does carry some risks if safety guidelines are not properly followed. Some potential problems include:
- Pain or burning at implant site – Due to induced currents or heating of the device during MRI exposure.
- Damage to device – From strong static/gradient/RF fields beyond recommended limits. May impact device function.
- Medical device interactions – VNS could negatively interact with cardiac pacemakers, insulin pumps, or other implants.
- Lead wire issues – Heating or current induction along leads can cause damage or patient discomfort.
- Changes in heart rate – VNS stimulation of the vagus nerve can influence heart rate variability.
- Disruption of normal stimulation – MRI modes alter standard VNS output. Effects may persist if settings aren’t restored.
- Neurological effects – Altered VNS signals to the brain could influence mood, seizures, or result in unintended nerve activation.
- Device movement or dislodgement – Forces during MRI may detach generator or lead wires from implantation site.
While risks are low with proper protocols, both patients and MRI staff must remain alert to any problems during the scan. Following all safety guidelines is key to avoiding complications.
Can children with VNS implants safely undergo MRI scanning?
Yes, MRI scanning is generally safe in pediatric patients with vagal nerve stimulator implants when appropriate guidelines are followed. However, there are some additional considerations in children:
- Brain and head region scans are most often needed in children due to conditions like epilepsy. Limiting SAR levels is important.
- Younger children may have difficulty remaining still during longer scan times. Sedation may be required.
- Smaller body size results in whole-body SAR exposure levels higher than adults for the same MRI power. Parameters may need adjusting.
- Language and developmental barriers may prevent clear communication about discomfort or odd sensations. Extra monitoring is beneficial.
- Special pediatric head coils that avoid direct VNS generator contact should be used.
- Any risks to children’s developing neurological systems require careful evaluation by the prescribing doctor.
With proper precautions, MRI scanning is generally considered safe in VNS patients as young as 2-3 years old when medically necessary. But doctors may restrict MRI in very young infants until further studies demonstrate safety. Close monitoring of children during scans helps identify any issues immediately.
What new MRI protocols or techniques enable safer VNS scanning?
Researchers continue developing new techniques to enable safer MRI procedures in patients with implanted vagal nerve stimulators:
- Ultra-low SAR fast spin echo techniques acquire images at a fraction of standard SAR levels to avoid device heating.
- Localized gradients and transmit coils around specific anatomy minimize overall MRI exposure to the VNS.
- Inline PET-MRI systems allow simultaneous PET and MRI scanning while limiting MRI energy near the VNS implant.
- MRI-conditional VNS systems with modified generator casings and lead wires better tolerate MRI fields.
- Remote control VNS devices can wirelessly adjust stimulation independent of MRI scanners to avoid interference.
- MRI safety notifications in electronic medical records automatically alert staff to VNS precautions when scheduling scans.
- Advanced image processing and metal artifact reduction methods improve image quality near VNS devices.
With ongoing innovations in both VNS therapies and MRI technologies, doctors continue gaining more options to safely scan patients with these implanted neuromodulation systems.
Summary: Key Points About VNS MRI Compatibility
- Vagal nerve stimulators are considered MRI compatible under certain guidelines:
- Use the device’s MRI mode and restrict SAR levels during scanning
- Approved scan areas depend on the VNS model and implantation site
- MRI of the brain is possible but other areas near the generator may be prohibited
- Doctors must check device settings before/after and coordinate closely with MRI staff
- Safety risks are low if protocols are followed; problems require immediate intervention
- Advancements are improving the safety and imaging capabilities for patients requiring both VNS and MRI
So in summary, yes vagal nerve stimulators can safely undergo MRI scanning when important safety practices are followed under the oversight of physicians experienced with both VNS therapy systems and MRI protocols. Close coordination between medical teams and patients enables the benefits of both VNS treatment and MRI imaging