A spinal cord stimulator (SCS) is an implanted medical device used to manage chronic, intractable pain, often in the back, trunk, or limbs. The system typically consists of an implanted pulse generator (IPG) placed under the skin, which connects to thin wires, called leads, that deliver mild electrical pulses to the epidural space near the spinal cord. Historically, the presence of these metallic and electronic components made magnetic resonance imaging (MRI) a dangerous, absolute contraindication for patients. This was a significant clinical challenge, as many patients with chronic pain conditions require detailed imaging. Advances in device technology have fundamentally changed this landscape, making it possible for many patients with an SCS to safely undergo an MRI scan today.
Understanding Device Compatibility
The ability to safely have an MRI depends entirely on the specific model and manufacturer of the implanted SCS system. Older devices are generally considered “MR Unsafe,” meaning they were not engineered to withstand the powerful magnetic and radiofrequency fields of an MRI machine. Modern SCS systems, however, are often labeled as “MR Conditional,” which denotes they are safe for the MRI environment only under a specific set of conditions. These conditions are not standardized across all manufacturers and vary significantly between models.
Compatibility is not a simple yes-or-no answer; it often depends on factors like the strength of the MRI magnet, commonly 1.5 Tesla or 3.0 Tesla, and the specific region of the body being scanned. For instance, some devices may be conditional for a head scan but not a full-body scan. Therefore, patients must know the exact model and manufacturer of their implanted pulse generator and leads. This information is typically found on the patient’s medical ID card or in their surgical records.
The manufacturer’s Instructions for Use (IFU) or labeling is the final authority on a device’s compatibility and the specific safety parameters required. This document details the precise operating limits of the MRI scanner that must be adhered to for the procedure to remain safe. Ignoring these instructions, even for a device labeled as MR Conditional, renders the procedure unsafe and exposes the patient to serious risks.
Mandatory Steps Before an MRI
Before a patient with an SCS can undergo an MRI, a strict protocol must be followed to ensure safety. The process begins with a mandatory consultation involving both the prescribing pain specialist and the radiologist or MRI facility staff. These practitioners must confirm that the specific SCS model is indeed MR Conditional and that the facility’s equipment can accommodate the scan’s technical requirements.
A crucial step involves contacting the SCS manufacturer or a device representative to verify all specific scan parameters. These parameters include the maximum magnetic field strength allowed, the maximum Specific Absorption Rate (SAR) limit, and confirmation of which body regions can be scanned. SAR is a measure of the radiofrequency energy absorbed by the body, and MR Conditional devices have strict limits that must not be exceeded.
Immediately before the patient enters the MRI scanner room, the SCS must be programmed to an “Off” state or a specialized “MRI Mode” using the clinician programmer. This specialized mode is designed to protect the device’s circuitry and the patient from unintended stimulation or excessive heating during the scan. In some systems, this pre-scan evaluation also includes checking the impedance, or electrical resistance, of the leads to ensure they are intact. After the MRI is complete, the manufacturer’s representative or the pain specialist must interrogate the device to confirm its integrity and reprogram it back to the patient’s therapeutic settings.
Potential Dangers of Ignoring Safety Guidelines
Failing to follow the manufacturer’s safety guidelines for an MR Conditional device, or attempting an MRI with an incompatible device, presents severe physical hazards to the patient. One of the most serious risks is thermal injury, or burns, to the tissue surrounding the electrodes and leads. The radiofrequency energy from the MRI scanner can induce electrical currents in the metallic leads, a phenomenon known as the “antenna effect,” which causes excessive localized heating. This heating can lead to irreparable damage to the spinal cord or surrounding nerves.
Another significant danger relates to the powerful static and gradient magnetic fields of the MRI machine. These forces can physically tug on the metallic components of the SCS, potentially causing the leads to shift or migrate from their intended position in the epidural space. Lead migration can cause new pain or nerve damage and requires an additional surgical procedure to correct or replace the system.
Ignoring the protocol can also result in permanent damage to the SCS device itself, specifically the sensitive internal electronics of the IPG. The strong magnetic fields can demagnetize components or induce currents that permanently short-circuit the device, rendering it non-functional and requiring surgical replacement. Furthermore, the induced electrical currents can cause unintended stimulation of the nervous system during the scan, which the patient may experience as a painful or jolting sensation.