Anterior Cervical Discectomy and Fusion (ACDF) is a common surgical procedure performed to alleviate chronic neck pain and nerve compression caused by disc degeneration or herniation. This operation involves removing the damaged disc and fusing the vertebrae using a graft and specialized hardware. For patients who have undergone this procedure, the safety of undergoing a Magnetic Resonance Imaging (MRI) scan is a frequent concern. MRI scans are generally safe after ACDF, but the presence of implants requires specific considerations and precautions.
Understanding ACDF Hardware Materials
The concern about MRI compatibility stems from the metallic implants used to stabilize the spine during fusion. Older spinal hardware sometimes contained ferromagnetic materials, which were strongly attracted to the MRI magnet, posing a risk of movement or heating. Modern ACDF hardware primarily uses materials with different magnetic properties.
The most common material for interbody cages and plates is Titanium (Ti) or its alloys, which are non-ferromagnetic or weakly paramagnetic. Another material is Polyether ether ketone (PEEK), a biocompatible polymer plastic that is entirely non-metallic and non-magnetic. PEEK cages cause almost no magnetic interference, though they may sometimes be coated with titanium to promote bone growth.
MRI Safety Concerns and Modern Implants
The safety of having an MRI with an implant revolves around three main theoretical risks: heating, movement, and induced current. The risk of implant movement is negligible with modern ACDF hardware because the plates and screws are securely integrated into the bone. The materials used, like titanium, are not ferromagnetic, meaning the static magnetic field of the MRI will not pull the hardware out of place.
The primary safety focus is on heating, which occurs when the radiofrequency (RF) energy from the MRI scanner induces currents in the conductive metal. Titanium and PEEK implants have low magnetic susceptibility, which minimizes the heat transfer compared to other metals.
Manufacturers rigorously test these devices, and the vast majority of ACDF hardware used since the early 2000s is classified as “MRI Conditional.” This classification confirms the implant is safe under specific conditions, such as a maximum magnetic field strength, often up to 1.5 Tesla (T) or 3.0T.
The third concern, induced current, is also related to the RF field creating currents within the implant. For modern spine hardware, the size and shape of the implants are typically too small and non-linear to pose a significant risk of severe heating or induced current. The safety of the procedure depends entirely on the specific hardware’s testing and labeling, which is why documentation is so important.
Impact of Hardware on Image Quality
While modern ACDF hardware is generally safe, its presence can significantly compromise the diagnostic quality of the images. This phenomenon is known as “artifact,” which appears as large dark spots, signal voids, or bright streaks on the MRI image. Artifacts occur because the metal disrupts the local magnetic field uniformity, which the MRI scanner relies on to create a clear picture.
The degree of artifact depends heavily on the material, with non-metallic PEEK causing the least distortion and titanium causing relatively mild distortion compared to stainless steel. This image degradation is a practical consequence, not a safety risk. It can make it challenging to visualize the delicate soft tissues immediately surrounding the implant, such as the spinal cord, nerve roots, and the interface between the bone and the cage.
Necessary Pre-Scan Precautions
Before scheduling an MRI, the patient and the medical team must take several critical steps to ensure both safety and image utility. The patient should first obtain the specific details of the implanted hardware, including the manufacturer, model name, and the material composition. This information is usually documented in the patient’s operative report or discharge paperwork and should be available from the surgeon’s office.
The surgeon’s office must then provide documentation confirming the hardware’s “MRI Conditional” status, which specifies the safe limits for the scan, such as the Tesla strength of the magnet. Once this critical information is confirmed, the radiologist can adjust the scanning protocol to minimize the artifact.
This may involve using specialized sequences, which are designed to improve visualization near metal, such as:
- Metal Artifact Reduction Sequence (MARS)
- MAVRIC (Multi-Acquisition with Variable Resonance Image Combination)
- WARP (Water-selective, Adiabatic, Respiration-compensated, Parallel)