Can You Have an MRI With a BB in Your Body?

Whether you can safely have an MRI with a BB lodged in your body depends almost entirely on what that BB is made of. A standard steel BB is ferromagnetic, meaning it responds strongly to the powerful magnet inside an MRI scanner, and that response can include movement, heating, and severe distortion of the images. A lead pellet, on the other hand, is not ferromagnetic and poses far less risk. The trouble is that many people who have carried a BB or pellet for years have no idea what material it is, and the answer is not always straightforward even with imaging.

Steel Versus Lead Makes All the Difference

The classic BB fired from an air rifle or BB gun is a small steel sphere, usually copper-plated. Steel is ferromagnetic, and ferromagnetic materials interact aggressively with the static magnetic field of an MRI scanner. By contrast, many air gun pellets are made of lead, which is not ferromagnetic at all. A study testing the most widely available air gun pellets found that while many were made of lead and posed no magnetic risk, some contained steel and were “deflected strongly in a magnetic field.”¹ This distinction is the starting point for every safety decision about scanning someone with a retained BB or pellet.

The problem is that the word “BB” gets used loosely. Some people use it to mean any small projectile from an air gun, including lead pellets, while others mean the standard 4.5 mm steel ball bearing. If you’re the patient, and you were shot with an air gun years ago, you may not remember (or may never have known) what type of ammunition was involved. That uncertainty is what makes these cases tricky for radiologists.

What the Magnet Can Do to a Steel BB

An MRI machine generates a magnetic field tens of thousands of times stronger than the earth’s. When a ferromagnetic object enters that field, two forces act on it. The first is translational force, which pulls the object toward the center of the magnet. The second is torque, which tries to rotate the object so that it aligns with the magnetic field lines. For a BB embedded in soft tissue, either force can cause it to shift position.

Research using retained metallic shrapnel in an ex-vivo model found that ferromagnetic fragments translated along the bore axis by roughly 1 to 3 millimeters and experienced torque angles averaging about 16 degrees, with some fragments twisting as much as 54 degrees.² Those numbers sound small, but context matters enormously. A millimeter of movement in the thigh muscle is probably harmless. A millimeter of movement next to the spinal cord, a major blood vessel, or inside the eye could be catastrophic. The presence of a ferromagnetic projectile near vital structures is considered a contraindication for MRI precisely because of this risk.³

One thing that slightly mitigates the danger for BBs that have been in the body for a long time is tissue encapsulation. Over months and years, the body forms a fibrous capsule of scar tissue around any foreign object. That capsule can act as a physical restraint, limiting how far the BB can move even under strong magnetic pull. However, no one knows exactly how strong a given patient’s scar capsule is, so this is not something doctors count on as a guarantee of safety.

Heating From Radiofrequency Energy

Movement is not the only hazard. MRI scanners use radiofrequency (RF) pulses to generate the signals that create images, and those pulses deposit energy in the body as heat. Metal objects can concentrate that energy, leading to localized heating around the implant. RF-induced heating during MRI occasionally causes burn injuries to patients.⁴ The amount of heating depends on the size, shape, orientation, and electrical properties of the metal fragment, as well as the specific MRI sequence being used.⁵

In practice, the heating concern with small projectiles like BBs seems to be less dramatic than the movement concern. Testing of various bullet types at 1.5 Tesla (the most common clinical MRI field strength) found that none exceeded the FDA’s limit of a 2°C temperature rise.⁶ Still, a broader survey of MRI safety incidents found that burns were the most common type of injury reported by imaging departments, accounting for nine of 14 serious injuries in one survey.⁷ Burns from metallic implants are a recognized risk even if the retained object is small.

Why the Eye Is the Highest-Risk Location

Of all the places a BB can lodge, the eye raises the most alarm. The globe of the eye is a small, delicate, fluid-filled structure, and even tiny ferromagnetic fragments inside it can cause serious damage when subjected to magnetic force. One reported case involved a 65-year-old metalworker who had no known history of eye injury but experienced intense pain during a brain MRI due to a hidden metallic foreign body inside his eye.⁸ The fragment was not detected by standard screening, which underscores how difficult it can be to catch small metallic pieces embedded in tissue around the eyes.

Because of this risk, anyone with a history of metalworking, grinding, or welding is routinely asked about it before an MRI. These occupations produce tiny metal shavings that can embed in the eye without the person realizing it happened. The screening is not just about BBs from air gun injuries; it extends to any possible ferromagnetic fragment near the orbit.

The spine and areas near major blood vessels are also high-concern zones. An MRI of the spine with retained metallic fragments in the spinal canal requires careful evaluation of the risk versus the diagnostic benefit.⁹ A fragment that shifts even slightly near the spinal cord could cause nerve damage or paralysis. The same logic applies to fragments near the carotid arteries, the heart, or the brain.

Image Quality Takes a Hit Either Way

Even when a BB is deemed safe enough to scan, there is another problem: image distortion. Any metal in the body creates artifacts on MRI, dark voids, bright halos, and geometric warping that can obscure the surrounding anatomy. The severity depends on the metal’s composition. Nonferromagnetic bullets and pellets produce only mild to moderate artifact on standard MRI sequences, while ferromagnetic bullets cause severe artifact and image distortion.¹⁰ The interaction between a ferromagnetic projectile and the MRI’s magnetic field creates marked susceptibility artifacts that degrade diagnostic quality.¹¹

This matters in practical terms. If you have a BB in your knee and need an MRI of your brain, the artifact is irrelevant because the BB is far from the area being imaged. But if the BB is in your shoulder and you need a shoulder MRI, the artifact may wipe out the very anatomy the scan is supposed to reveal. In that scenario, even a non-ferromagnetic pellet that is perfectly safe to scan may make the study diagnostically useless, pushing you toward an alternative like CT instead.

The Hidden Problem of Impurities

One complication that catches people off guard is that a projectile described as “copper” or “lead” can still be ferromagnetic. Testing of ballistic fragments has revealed that some bullets labeled as copper-jacketed lead turned out to be ferromagnetic, likely due to steel impurities in the jacket or core material.¹² In one study, two of four ferromagnetic bullets were reportedly copper or copper-nickel-jacketed lead; the ferromagnetism was attributed to impurities. Bullets manufactured outside the United States were overrepresented among the ferromagnetic specimens.

This means you cannot rely on a general assumption like “lead pellets are safe” without actually verifying whether the specific pellet in your body is truly non-ferromagnetic. The country of manufacture, the brand, and even the batch can matter. For standard steel BBs there is no ambiguity (steel is ferromagnetic, full stop), but for pellets and bullets of supposedly non-ferromagnetic materials, impurities introduce genuine uncertainty.

How Doctors Screen Before Letting You Into the Scanner

Every MRI facility uses a screening questionnaire that asks about metallic implants, prior surgeries, and history of injury involving metal fragments. If you disclose a retained BB or pellet, the next step is typically an X-ray or CT scan to locate the fragment and evaluate what it might be.

Plain X-rays are the simplest and cheapest screening tool, but they have limitations. They can miss very small fragments, especially in the orbit. CT scanning is more sensitive. One study found that CT could detect metallic particles as small as 0.07 cubic millimeters, compared to 0.12 cubic millimeters for plain film X-rays.¹³ A more recent comparison found that CT significantly outperformed both digital radiography and digital tomosynthesis for detecting intraorbital metallic foreign bodies, particularly steel fragments. Steel fragments weighing 0.8 milligrams or less went undetected on standard X-ray and tomosynthesis, but CT caught steel fragments as small as 0.4 milligrams.¹⁴

Still, there is an ongoing debate about when orbital screening with imaging is warranted. Plain film X-rays can miss foreign bodies that show up on MRI itself, creating a paradox where the screening test is less sensitive than the scan it is supposed to clear you for.¹⁵ CT is more reliable but involves ionizing radiation and is not always available on short notice. For a known BB in a limb, this is less of an issue; the fragment is obvious and its location is easy to characterize. But for someone who might have tiny fragments they don’t know about, the screening question gets complicated.

Can Imaging Tell You Whether Your BB Is Ferromagnetic?

Once a fragment is located, the next question is whether it is made of ferromagnetic material. Researchers have explored whether imaging characteristics, such as how the fragment looks on CT or X-ray, can predict its composition. The wound appearance on CT can sometimes suggest bullet composition, which has implications for MRI safety.⁶ For example, certain fragmentation patterns or densities on CT correlate with steel versus lead construction. But these methods are not foolproof, and the literature still lacks definitive guidelines for every scenario.

A recent review synthesized existing recommendations into simplified triage algorithms designed to help clinicians stratify risk and avoid unnecessarily excluding patients from MRI.¹¹ The general approach considers the type of ammunition (if known), the location of the fragment, and what imaging reveals about the fragment’s characteristics. If the BB is known to be steel and sits near a sensitive structure, MRI is typically ruled out. If it is known to be lead and sits far from critical anatomy, scanning may proceed with appropriate caution.

What Happens When You Need the MRI but Have a Risky BB

Sometimes the clinical need for an MRI is urgent, but the patient has a retained metallic fragment that raises safety concerns. In these cases, doctors weigh the diagnostic benefit of the MRI against the risk of the retained metal. If the BB is in a limb far from the area being scanned, the risk is generally low and the scan can often proceed. If the fragment is near the body part being imaged, the risk-benefit calculation changes.

Alternative imaging modalities are often the practical solution. CT scans provide excellent bone and soft-tissue detail without any magnetic field, so they are unaffected by metallic foreign bodies. Ultrasound can evaluate some soft-tissue structures without posing any risk from metal. For vascular imaging, CT angiography can substitute for MR angiography in many cases.

Surgical removal of the BB is sometimes considered, but it is rarely done solely to enable an MRI. Extraction carries its own risks, including damage to surrounding tissue, infection, and the possibility that the BB has migrated to a location that makes surgery more difficult than expected. Removal is more commonly recommended when the BB is already causing symptoms like pain, infection, or lead toxicity (in the case of lead pellets that are slowly degrading). If the BB is asymptomatic and has been stable for years, most surgeons prefer to leave it in place unless there is a compelling reason to remove it.

Common Misconceptions Worth Clearing Up

One widespread belief is that any metal in your body automatically disqualifies you from MRI. That is not true. Non-ferromagnetic metals like titanium, lead, and many surgical-grade stainless steels are MRI-compatible under most circumstances. The issue is specifically with ferromagnetic materials (mainly iron, nickel, cobalt, and alloys containing them), which include standard steel BBs.

Another misconception is that a BB that has been in your body for decades is somehow safer to scan because it has “settled in.” While tissue encapsulation does provide some restraining force, no one can guarantee that the scar tissue will hold against the pull of a powerful magnet. The scar capsule has never been tested against that force until the moment you enter the scanner, and by then it is too late to change course.

A third common error is assuming that the heating risk is the main danger. For small ferromagnetic objects like BBs, movement and torque are generally the bigger concerns. Heating is real but tends to be more of an issue with larger implants, wires, or objects with particular geometries that concentrate RF energy. Research consistently shows that for small projectiles tested at clinical field strengths, temperature rises stayed below dangerous thresholds, though this does not eliminate the risk entirely.

BBs Near the Skin Surface

If a BB is lodged just under the skin, especially in a hand, foot, or superficial muscle, the clinical picture changes somewhat. Superficial BBs are easier to locate, easier to characterize with imaging, and in some cases easier to remove if needed. They are also less likely to be near vital structures where even tiny movement could cause serious harm.

For a superficial steel BB far from the area being scanned, many radiologists will proceed with the MRI after documenting the fragment’s location and discussing the risks with the patient. The magnetic pull still exists, but the consequences of a small shift in a superficial location are usually manageable. The patient may feel a pulling or warming sensation during the scan, and the informed consent process should cover the possibility that the BB could move. If the BB is directly in the area being scanned, artifact will likely compromise the images regardless of safety, making the scan pointless for that region.

Ultimately, every case involving a retained BB and an MRI comes down to an individualized assessment. The material, location, proximity to vulnerable structures, and clinical necessity of the scan all factor in. If you have a BB in your body and need an MRI, the most important thing you can do is tell the MRI team about it before you get anywhere near the scanner room. That single piece of information triggers the safety evaluation that determines whether the scan can go forward, needs to be modified, or should be replaced with an alternative study.