A Spinal Cord Stimulator (SCS) is a device implanted under the skin to manage chronic pain by sending low-level electrical pulses to the spinal cord. The system consists of an implanted pulse generator, typically placed in the flank or lower abdomen, and leads with electrodes threaded into the epidural space of the spine. Because up to 74% of patients with chronic back and leg pain require a non-spine MRI within a decade of implantation, the need for scanning is common. Whether a patient with an SCS can safely undergo an MRI depends entirely on the specific model of the implanted device and a set of strict conditions.
The Physical Conflict Between SCS Devices and MRI Technology
The central challenge in scanning a patient with an SCS is the intense physical environment created by the MRI machine. An MRI uses a powerful static magnetic field, pulsed magnetic field gradients, and radiofrequency (RF) fields to generate detailed images. The metallic components of the SCS, including the battery, insulated leads, and electrodes, interact dynamically with these forces.
The static magnetic field can exert force and torque on ferromagnetic material within the pulse generator, risking device movement or migration from its implant pocket. The RF energy transmitted by the scanner can induce electrical currents in the SCS leads, which act like antennae. This induced current can lead to excessive heating at the electrode tips, potentially causing thermal injury to the surrounding spinal cord tissue.
Furthermore, the powerful magnetic fields can damage the internal electronics of the implanted pulse generator, resulting in malfunction or a resetting of the device’s programming. The pulsed gradient magnetic fields can also induce voltages and currents in the leads, causing unintended stimulation that the patient might experience as an uncomfortable, jolting sensation. To mitigate these hazards, newer SCS systems are designed with technical advancements such as internal spiral conductors and electromagnetic interference protection, paving the way for conditional scanning.
Navigating SCS Device Compatibility Standards
Modern SCS technology has moved away from being “MRI Unsafe.” However, no neurostimulation device is classified as “MRI Safe,” a label reserved for non-metallic objects. Nearly all contemporary systems fall under the “MRI Conditional” designation, meaning they pose no known hazard only when used under specific conditions defined by the manufacturer. Determining eligibility for a scan involves checking several variables related to the device and the imaging procedure.
The conditions depend heavily on the implanted system’s model and manufacturer, often specifying the maximum allowable magnetic field strength. For instance, some SCS systems are approved for full-body scans at 1.5 Tesla (T) but not at the stronger 3.0T field strength. Other models may permit scanning at both 1.5T and 3.0T, but only with restrictions on location, such as head-only scans, or with a lower specific absorption rate (SAR). The SAR is a measure of the RF power deposited in the patient’s body, and manufacturers specify strict limits to prevent thermal tissue damage.
Patients must know the exact make, model, and date of implantation of their device to confirm compatibility and the required conditions. The configuration of the implanted leads, such as whether they are percutaneous or surgically placed paddle leads, also impacts the conditionality. The physician ordering the MRI must consult the specific, detailed guidelines for the patient’s device, as performing a scan outside of these parameters can result in serious injury or device damage.
Essential Pre- and Post-Scan Safety Protocols
If an SCS system is confirmed to be MRI Conditional, a strict protocol must be followed to ensure patient safety and device integrity. The process requires coordination between the patient’s pain specialist, who manages the SCS, and the MRI technician or radiologist performing the scan.
Pre-Scan Requirements
The pain specialist and imaging staff must confirm that the prescribed scan parameters, including magnetic field strength and SAR limits, align precisely with the device’s manufacturer guidelines. Before the patient enters the MRI room, the SCS device must be placed into a specific “MRI mode” or fully turned off. This step, usually performed by the pain specialist using a programmer, deactivates the stimulation and engages internal safeguards. Stimulation must be disabled because leaving it on can increase the potential for uncomfortable, unintended stimulation or device damage.
During and Post-Scan Monitoring
During the imaging procedure, the patient must be continuously monitored. Patients should be aware of potential sensations, such as warming, tugging, or vibrating, near the implanted pulse generator. If any sensation becomes uncomfortable or intolerable, the patient must immediately notify the MRI personnel so the scan can be paused. Following the scan, the patient’s pain specialist or a trained technician must check the SCS system’s functionality and restore it to its normal therapeutic settings. Failure to follow this protocol can compromise patient safety or lead to permanent device malfunction.