A magnetic resonance imaging (MRI) scan is a valuable diagnostic tool that helps doctors see what’s going on inside your body. But early-stage research suggests that a contrast agent used in some MRIs may trigger a chain reaction that leaves metal nanoparticles embedded in body tissue.
While the research is still in its early phases, it raises some valid questions. Here’s what the study found—and what toxicologists, radiologists and biomedical experts say about the safety of MRIs with contrast.
What did the study find?
The study, published in the journal Magnetic Resonance Imaging, was based on test tube experiments designed to assess how oxalic acid—a compound found naturally in many plant-based foods—interacts with metal ions.
Researchers focused on oxalic acid’s effect on gadolinium, a metal used as an MRI contrast agent. (If you’re unfamiliar, contrast agents are substances injected into the body to alter how water molecules behave, resulting in sharper MRI images.)
The experiments revealed that oxalic acid caused small amounts of gadolinium to leach from the contrast agent, forming nanoparticles that were later found to enter cells from various organs.
Importantly, this research was done in vitro—outside the body—so it does not confirm that MRI contrast causes this effect in real patients. However, the findings do open the door to further investigation.
What is gadolinium, and when is it used?
Gadolinium is a rare earth metal commonly used in MRI contrast agents, explains radiologist Dr Richard Reitherm. It naturally occurs in the earth’s crust, typically bound in minerals such as bastnasite.
In contrast agents, gadolinium is tightly bound to other molecules to help it move safely through the body. It is usually excreted through urine after the scan and doesn’t typically cause health concerns in most people. However, some studies have found traces of gadolinium remaining in the kidneys and brain after an MRI with contrast. It can also be detected in blood and urine years later in some cases.
Gadolinium isn’t used in every MRI. “In general, it is not used for musculoskeletal MRIs,” says Dr Reitherman. “However, it is used for brain, breast, pelvic and abdominal MRIs.” For example, a suspected herniated disc may not require contrast, while imaging for appendicitis or tumours usually does.
“Contrast is used for a lot of things, and millions of people have had millions of doses with no issue,” Dr Reitherman adds.
How could gadolinium be bad for you?
It’s a bit complex. Gadolinium on its own is toxic, explains research assistant professor of biomedical imaging physics Dr Jeffrey Luci. However, in contrast agents used for MRIs, gadolinium is tightly bound within a larger organic molecule that prevents it from becoming free and potentially harmful.
“The purpose of that is so it can be excreted out of the body before it degrades into something dangerous,” adds Dr Reitherman. “The substance that’s injected is not toxic in its bound form.”
That said, some people do report mild side effects after receiving a gadolinium-based contrast agent, such as a burning or cool sensation near the injection site, headache or nausea. More serious complications—like kidney issues, neurological symptoms or skin reactions—are rare. One older study estimates that serious adverse reactions occur in just 0.03% of gadolinium injections.
Still, certain groups may be at higher risk. “While gadolinium contrast is generally considered safe when used as directed, it can lead to adverse outcomes in some patients,” says toxicologist Dr Kelly Johnson-Arbor. “People with chronic kidney disease are more susceptible, and exposure in these cases has been linked to a condition called nephrogenic systemic fibrosis (NSF), which causes skin thickening, swelling and pain.”
As for concerns about whether gadolinium particles accumulate in the body and lead to long-term health issues, experts say the evidence is still limited. “No one has shown that gadolinium build-up causes harm,” says Dr Luci. “But that doesn’t mean we shouldn’t continue to research it.”
It’s also important to distinguish this from heavy metal toxicity, which involves known harmful metals like lead, arsenic or mercury. “This is not the same,” explains associate professor of pharmacology and toxicology Dr Jamie Alan. “This was a preliminary study done outside the body, so it may not translate to human health. We need much more research before drawing conclusions about long-term effects.”
Why should you get an MRI with contrast if your doctor recommends it?
If your doctor has advised an MRI with contrast, experts agree it’s important to follow through. “This might be very important for diagnosis of your condition,” says Dr Alan. “MRIs are generally not ordered unless they’re absolutely necessary, due to cost and limited access.”
Dr Reitherman echoes this, noting that contrast is only used when it’s essential. “We don’t give contrast unnecessarily,” he says. In cases where a serious condition is suspected—such as a tumour—gadolinium contrast may be vital for detecting it clearly on the scan.
Still, Dr Reitherman adds that more research is needed to fully understand whether the nanoparticles seen in laboratory settings also form in humans, and if they have any health impact. “This is basic science—it’s where we begin,” he says. “But we still need human studies to determine whether there’s any real-world effect. Right now, it’s theoretical.”
If you have concerns, Alan encourages raising them with your doctor. “Generally, this imaging is safe. Serious reactions are very rare,” she says.
Dr Luci also emphasises that people should not avoid medically indicated scans. “We don’t want anyone to worry unnecessarily,” he says. “There’s currently no evidence suggesting these scans pose a meaningful risk to patients.”
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