Metal Implant, Painful Joint? How MARS MRI/CT Sees Past Titanium and Steel

Millions of people live with metal implants hip or knee replacements, spinal rods, plates, screws, or dental hardware. These devices restore mobility and relieve pain for many, yet a significant number of patients continue to experience joint pain, swelling, or limited movement months or years after surgery. When symptoms persist, doctors need clear images of the soft tissue, bone, and implant interface and this is exactly where conventional MRI and CT often fall short. Metal creates large dark voids, bright streaks, and geometric distortions that hide the very structures that need evaluation. This is where MARS MRI and metal-artifact-reduction CT change the diagnostic picture, allowing radiologists to see past titanium, cobalt-chromium, stainless steel, and other alloys.

Why Metal Creates Problems in Imaging

Metal implants distort the local magnetic field in MRI and cause photon starvation plus beam-hardening effects in CT.

In MRI:

The disrupted magnetic field produces signal voids and spatial distortion that can extend several centimetres beyond the implant, swallowing up muscle, tendons, bone marrow, and fluid right where a doctor needs to look.

In CT:

Dense metal absorbs far more X-rays than surrounding tissue, causing bright and dark streaks to radiate outward from the hardware, obscuring bone and soft tissue detail.

These artifacts historically limited the usefulness of advanced imaging in patients with orthopaedic hardware, sometimes forcing clinicians to rely on plain X-rays or clinical examination alone. Modern metal artifact reduction strategies have changed that.

What MARS MRI Actually Does

MARS stands for Metal Artifact Reduction Sequence (or, more broadly, Metal Artifact Reduction Strategies). It isn’t a single sequence, but a family of optimised pulse sequences and reconstruction methods designed to minimise susceptibility artifacts around metal. Key technical approaches include:

Higher receiver bandwidth:

Reduces the spatial extent of distortion around the implant.

View-angle tilting (VAT):

Corrects in-plane geometric errors caused by the disrupted magnetic field.

SEMAC (Slice Encoding for Metal Artifact Correction):

Addresses through-plane distortion by correcting slice-selection errors near the metal.

MAVRIC (Multi-Acquisition Variable-Resonance Image Combination):

Acquires data across a range of resonance frequencies and combines them into a single, artifact-reduced image.

High-resolution matrices, thinner slices, and spin-echo rather than gradient-echo sequences:

Spin-echo protocols use a refocusing pulse that counters signal dephasing near metal.

Together, these methods shrink the black signal voids and restore visibility of the bone-implant interface, synovium, tendons, muscles, and surrounding soft tissue. On a modern 3T system with dedicated MARS packages, images that were previously non-diagnostic often become clinically useful.

The Complementary Role of Metal-Artifact-Reduction CT

CT remains excellent for evaluating the implant itself and the adjacent cortical bone. Dual-energy CT (or specialised single-energy MAR algorithms) reduces beam-hardening and photon-starvation streaks, while virtual monoenergetic reconstructions at higher keV levels further suppress metal-related artifacts.

In many centres, MARS MRI and MAR CT are used together, each covering what the other can’t: CT for bone and implant integrity, MRI for soft-tissue detail, fluid collections, and early infection or inflammatory changes.

Clinical Situations Where MARS Imaging Matters

Doctors typically recommend a MARS-protocol scan for patients with:

• Persistent or new pain after total hip or knee arthroplasty
• Suspected periprosthetic joint infection
• Possible aseptic loosening or osteolysis
• Adverse local tissue reaction (ALTR) or metallosis around metal-on-metal or modular implants
• Spinal instrumentation with residual neurological symptoms
• Soft-tissue evaluation around plates, screws, or fracture fixation devices

MARS MRI can reveal synovitis, fluid collections, bone-marrow oedema, soft-tissue oedema, and pseudotumours that are invisible or poorly seen on standard sequences findings that have shown meaningful sensitivity and specificity for detecting infection and guiding surgical planning, including locating occult collections that may need debridement.

What the Patient Experiences

A MARS MRI examination looks and feels like a conventional MRI. You’ll lie on the scanning table for roughly 30 – 45 minutes depending on the joint or region being imaged. No special preparation is required beyond removing removable metal objects and informing the technologist of the exact type and location of your implant. Most orthopaedic implants used today are MRI-conditional meaning they can be scanned safely under specific conditions, and the radiology team confirms this before proceeding.

Advanced techniques like SEMAC or MAVRIC can add some time to the scan because of additional encoding steps, though experienced centres balance artifact reduction with reasonable scan times. For MAR CT, radiation exposure can be modestly higher than a routine CT in some protocols, since higher tube voltage or additional projections may be used a trade-off that’s usually well justified by the diagnostic gain.

Interpreting the Results

A normal MARS study doesn’t always exclude every complication, but it markedly improves diagnostic confidence. Positive findings extensive synovitis, extracapsular oedema, bone destruction, or fluid collections can support a diagnosis of infection or adverse tissue reaction and help the orthopaedic surgeon plan next steps. Negative or limited findings may allow a more conservative approach or point the workup elsewhere.

Because residual artifacts can still occur, particularly with stainless-steel or large cobalt-chromium components, the radiologist’s experience with metal imaging and correlation with clinical and lab data remain essential to a reliable diagnosis.

If you have orthopaedic hardware and unexplained joint pain, it’s worth discussing a MARS MRI or metal-artifact-reduction CT scan with your doctor to get a clearer diagnostic picture than conventional imaging can offer.

Conclusion

Persistent pain around a metal implant no longer has to mean diagnostic uncertainty. Specialised MARS MRI combined with metal-artifact-reduction CT allows clear visualisation of the tissue that conventional imaging often obscures, helping catch loosening, infection, or adverse tissue reactions early enough to guide timely treatment. For patients seeking expert imaging around orthopaedic hardware, advanced MARS capability is available at Picture This.