What Happens If You Wear Metal in a CT Scan?

Metal inside a CT scanner does not pose a physical danger to you. Unlike an MRI machine, which uses powerful magnets that can heat or move ferromagnetic objects, a CT scanner uses X-rays, so metal won’t be yanked off your body or burn your skin. The real problem is what metal does to the images: it scatters and absorbs X-ray beams in ways that create bright and dark streaks, obscure surrounding anatomy, and can make parts of a scan completely unreadable. Whether the metal is a hip replacement, a dental crown, a belly button ring, or a zipper on your jeans, the effect ranges from mild distortion to diagnostic disaster depending on the metal’s type, size, and location.

What Metal Artifacts Actually Look Like

When X-rays hit a dense metal object during a CT scan, the resulting image often shows dramatic streaks radiating outward from the metal, dark bands or voids where anatomy should be visible, and bright halos around the implant or object. Radiologists call these “artifacts,” and they are not just cosmetic blemishes on the image. They can obscure tumors, fractures, infections, and other findings that the scan was ordered to detect. In a study of head and neck CT scans, roughly two-thirds of image slices containing metal dental hardware were rated non-diagnostic when processed with a standard reconstruction method.¹ That means the radiologist looking at those slices could not confidently say what was normal and what was not.

The severity depends on how much metal is present and where it sits relative to the anatomy your doctor needs to see. A single small titanium screw in your ankle creates a modest haze that a radiologist can often read around. A bilateral hip replacement made of cobalt-chrome, on the other hand, can wash out the entire pelvis in a blizzard of streaks.

Why Metal Wrecks CT Images

Two physical effects do most of the damage. The first is called beam hardening. A CT scanner’s X-ray beam contains photons at many different energy levels. When the beam passes through metal, the lower-energy photons get absorbed preferentially, leaving behind a beam that is “harder” (higher average energy) on the other side. The CT reconstruction software assumes a uniform beam, so this mismatch shows up as dark streaks and bands between dense objects.²

The second is photon starvation. Some metals are so dense that they absorb nearly all the X-ray photons along certain paths. When the detector on the other side receives almost no signal, the data for those angles becomes extremely noisy. That noise gets amplified during image reconstruction, producing thick, high-contrast streaks that conventional filtering cannot remove.³ These two effects often occur together, and their combined impact is what makes metal one of the most disruptive elements in CT imaging.⁴

Not All Metals Are Equally Bad

The type of metal matters enormously. Titanium, the material used in many modern orthopedic implants, is relatively well behaved. It is dense enough to show up clearly on a scan but not so dense that it obliterates everything around it. Stainless steel and cobalt-chrome alloys are significantly worse offenders, producing much larger artifact zones. In direct comparisons, titanium screws produced artifacts measuring about 2 millimeters on CT, while stainless steel screws produced artifacts around 2.6 millimeters, and the gap widens considerably on MRI.⁵ That difference might sound small in absolute terms, but those extra fractions of a millimeter translate into large zones of unreadable tissue when you are trying to see what is happening right next to a screw or plate.

Research comparing titanium to cobalt-chrome found titanium produced significantly fewer artifacts.⁶ This is one reason surgeons often prefer titanium hardware when postoperative imaging is expected to be important, for example in cancer patients who will need regular follow-up scans. It is also worth noting that the shape of the metal plays a role. Thin screws and wires produce less artifact than bulky plates or rods, and objects oriented along the scan axis tend to cause fewer streaks than objects positioned perpendicular to it.

Common Culprits People Ask About

If you are headed in for a CT scan, the technologist will typically ask you to remove jewelry, belts, bra underwires, hairpins, and anything else metallic that sits in or near the area being scanned. These removable items are the easiest problem to solve: just take them off. A necklace or earring left in place during a head or neck CT will streak across the images just like a surgical implant would. Piercings you can unscrew should come out. If you have a piercing that cannot be removed, tell the technologist so they can note it and potentially adjust technique.

Dental work is one of the most common sources of trouble. Crowns, fillings, bridges, and implants containing metals like gold, amalgam, or cobalt-chrome alloys sit in the middle of the head, right where the X-ray beam needs clear passage to image the mouth, jaw, sinuses, and brain base. These produce bright and dark streaking artifacts that can spread across reconstructed images and seriously complicate diagnosis.⁷ You obviously cannot remove dental fillings for a scan, so this is a situation where the imaging team has to work around the metal using software or scanning technique adjustments.

Orthopedic hardware is the other big category. Hip replacements, knee replacements, spinal fusion rods, plates, and screws are all permanent fixtures. When stainless steel is involved, the artifacts tend to be much worse than with titanium.⁸ Patients with bilateral metal hip replacements face a particular challenge because the two dense objects sit on opposite sides of the pelvis and the artifacts from each side overlap in the middle, right where the bladder, prostate, uterus, and rectum need to be visualized.

The One Genuine Safety Risk With Electronic Implants

While passive metal objects like screws and jewelry pose no physical risk in a CT scanner, active electronic implants are a different story. Implantable cardioverter-defibrillators (ICDs) and pacemakers contain sensitive circuitry that can malfunction when exposed to the high X-ray doses a CT scanner delivers. A documented case reported ventricular oversensing during a chest CT in a patient with an ICD, meaning the device incorrectly detected heart rhythms that were not there.⁹ Oversensing can lead to inappropriate shocks or, in some configurations, failure to deliver a needed shock.

If you have an ICD or pacemaker, the CT scan is not automatically off the table, but the imaging team needs to know about it beforehand. They may adjust the scan protocol to minimize direct irradiation of the device, monitor you during the scan, or have the device checked by a cardiologist afterward. This is one area where the concern is not about image quality but about genuine patient safety.

Metal Can Also Increase Your Radiation Dose

Modern CT scanners use automatic exposure control, a system that adjusts the X-ray beam intensity in real time to keep image quality consistent as the beam passes through different thicknesses of tissue. When the scanner encounters a dense metal implant, it ramps up the X-ray output to try to push enough photons through the metal and get usable data on the other side. This means patients with metal implants can receive higher radiation doses in the area around the implant than they otherwise would. Research measuring this effect found that a single metal hip prosthesis increased the local radiation dose indicator by about 14%, while bilateral hip prostheses increased it by roughly 30%.¹⁰

For a single scan, this extra dose is unlikely to matter clinically. But for patients who need repeated CT monitoring over years, such as people being followed for cancer recurrence near a metal implant, the cumulative difference adds up. Some researchers have proposed adjusting automatic exposure control settings when metal is present, or placing the metal information into the planning software to avoid unnecessary dose escalation.

How Radiologists Reduce Metal Artifacts

Nobody expects patients to have their hip replacements removed for a scan, so radiologists and imaging physicists have developed a range of strategies to work around metal. These fall into three broad categories.

Software-Based Correction

Metal artifact reduction (MAR) software has become standard on modern scanners. These algorithms identify the corrupted data in the raw scan measurements and replace it with estimated values, then reconstruct the image. One well-studied method called Normalized Metal Artifact Reduction (NMAR) was shown to reduce metal artifacts significantly, particularly for implants surrounded by bone, and even performed well with dental fillings, which cause some of the most severe distortions.¹¹ Commercial implementations of similar algorithms, such as GE’s Smart Metal Artifact Reduction (SMAR), have been shown to produce images rated substantially higher in quality by radiologists compared to standard reconstruction.¹²

These algorithms are not perfect. A phantom study of hip prostheses showed that while MAR software successfully revealed lesions that had been hidden by metal artifacts on standard images, it also introduced new artifacts in other parts of the image.¹³ Radiologists typically review both the corrected and uncorrected images side by side to make sure the software is not creating phantom findings or erasing real ones.

Dual-Energy CT

Dual-energy CT scanners fire X-rays at two different energy levels simultaneously or in rapid alternation. This lets the software generate “virtual monochromatic” images that simulate what the scan would look like if the X-ray beam contained only photons at a single, chosen energy level. Because beam hardening is fundamentally a problem of multi-energy beams, these single-energy reconstructions sharply reduce the worst artifacts. Research has shown this approach reduces artifacts across all common implant alloys, though the improvement is most dramatic with titanium and more modest with stainless steel and cobalt-chrome.¹⁴ Combining dual-energy imaging with MAR software often produces the best results, particularly for denser alloys.¹⁵

Tilting the Gantry and Repositioning the Patient

Sometimes the simplest tricks help. The CT gantry, the big donut the patient slides through, can be tilted slightly on many scanners. Tilting it by just a few degrees changes the angle at which X-rays pass through the metal, redistributing the artifacts away from the anatomy of interest. One technique demonstrated that a gantry tilt of only six degrees could reduce metal artifacts by more than 90%.¹⁶ Similarly, positioning the patient slightly differently, for example having someone with dental fillings turn their head to the side, can redirect streaks away from structures the radiologist needs to see.¹⁷

When Artifacts Hide Real Disease

The practical cost of metal artifacts is not abstract. When a scan is ordered to check for cancer recurrence near a spinal fusion or to evaluate tissue around a hip replacement, the artifacts from the hardware can land directly on top of the area of concern. In the head and neck study mentioned earlier, applying an advanced artifact reduction algorithm actually unmasked two malignant lesions that had been completely hidden on standard reconstructions.¹ Without the improved reconstruction, those tumors would have gone undetected on that scan.

This is why it matters whether your imaging center has modern artifact reduction tools. Not every scanner or every facility has dual-energy capability or up-to-date MAR software. If you know you have significant metal hardware and your scan is being ordered to evaluate something near it, asking your referring doctor whether the imaging center is equipped to handle metal artifacts is a reasonable and potentially important question.

Carbon Fiber Implants and the Move Away From Metal

One increasingly popular approach to the artifact problem is to avoid metal in the first place. Carbon fiber-reinforced polyetheretherketone (CFR-PEEK) implants are now available for spinal and some other orthopedic applications. These composite materials are strong enough to support the spine but nearly transparent to X-rays, meaning they produce almost no artifact on CT or MRI. In direct comparisons, CFR-PEEK implants produced dramatically fewer artifacts than standard titanium implants, and the difference was larger than any software-based or hardware-based correction technique could achieve.¹⁸

These implants are particularly attractive for patients with spinal tumors who need both surgical stabilization and ongoing radiation therapy or imaging surveillance. Titanium rods and screws in the spine make it difficult to plan radiation fields accurately and hard to tell whether a tumor is growing or shrinking on follow-up scans. Carbon fiber-reinforced screws largely eliminate both problems.¹⁹ The trade-off is cost and availability: these implants are more expensive than titanium and are not yet universally stocked.

Tattoo Ink and Swallowed Objects

Two situations come up less often but are worth knowing about. Tattoo inks frequently contain metallic pigments such as iron, mercury, cobalt, copper, and zinc. On CT, these pigments can occasionally show up as faint radio-opaque deposits. This is mostly a curiosity rather than a diagnostic problem on CT, though it has caused confusion on mammograms when pigment migrates to lymph nodes in the armpit.²⁰ The burning risk with tattoo ink that people sometimes hear about relates to MRI, not CT, and even in MRI it is uncommon.

Swallowed metallic foreign objects, particularly in children, are sometimes evaluated with CT after an initial X-ray. CT is useful because it can show the precise location, shape, and relationship of the object to the bowel wall. The metallic object will produce some local artifact, but since the clinical question is usually “where is this thing and is it stuck,” the artifact is less of an issue than it would be for detecting subtle soft-tissue pathology. Plain X-rays remain the usual first step because they involve less radiation.²¹

What to Tell the Technologist

Before any CT scan, you will be asked about metal in and on your body. Be thorough. Mention implants, surgical clips and staples, dental work, body piercings you cannot remove, and any electronic devices like pacemakers, insulin pumps, or neurostimulators. For removable items, take them off if they are anywhere near the scan area. A wedding ring during a head CT does not matter; during a hand CT, it does.

If you have significant hardware and your scan is for something near it, ask ahead of time whether the facility has metal artifact reduction software or dual-energy CT. This is especially relevant if you are being scanned to monitor a condition like cancer recurrence, where a missed finding has serious consequences. Not every facility advertises these capabilities, but a quick phone call to the radiology department can save you from getting a scan that turns out to be unreadable and having to repeat it somewhere better equipped.

For people choosing implant materials before surgery, especially if they know they will need regular follow-up imaging, it is worth discussing with the surgeon whether titanium or carbon fiber-reinforced options are available and appropriate. The difference in imaging quality can be substantial over years of surveillance scans.