There is no universally set number of MRI scans that a person can have in a year or in their lifetime. MRI uses a strong magnetic field and radiofrequency energy, not X-rays or other ionizing radiation. Therefore, there is no radiation dose that accumulates with each scan, as there is with radiography and computed tomography.
“The American College of Radiology does not believe there is enough evidence to recommend full-body screening in people without symptoms, risk factors, or a family history,“ the organization states. However, this does not mean that repeated MRI scans are dangerous. When monitoring tumor disease, multiple sclerosis, joint and spinal injuries or the effect of treatment, a new examination may be ordered according to medical necessity.
Contrast is a separate issue
Some examinations use gadolinium contrast agents, which make certain tissues and blood vessels more visible. They are excreted mainly through the kidneys. The US Food and Drug Administration states that in people with normal kidney function, the retention of small amounts of gadolinium is not directly associated with harmful effects, but recommends that the contrast be used when it brings diagnostic benefit.
This is the reason why doctors ask about kidney disease and in some patients order a kidney function test before the injection. In severe kidney damage, the risk of the rare complication nephrogenic systemic fibrosis is higher, and the decision to use contrast is made only after assessing the benefits and risks.
The European Society of Urogenital Radiology specifies specific intervals between two injections of gadolinium contrast: about 4 hours in normal or moderately reduced kidney function and 7 days in severely reduced function or dialysis. These periods refer to the repeated administration of contrast, not to the MRI itself. In an emergency, the doctor may consider a different approach.
When the examination is not without risk
The absence of ionizing radiation does not mean that MRI is suitable for everyone without prior screening. The strong magnetic field can affect some pacemakers, neurostimulators, insulin pumps, vascular clips and other devices. Some implants are only permissible under specific conditions, so the patient must report any metal or electronic object in the body.
Other possible problems are related to loud noise, heat, claustrophobia, the need for immobilization and possible sedation. In contrast studies, allergic reactions are also possible, which are usually rare.
Routine whole-body scanning in people without complaints is also not recommended as a general preventive test. According to the American College of Radiology, there is not enough evidence that such an approach prolongs life, and incidentally detected changes may lead to additional tests and procedures. The practical conclusion is that there is no “safe frequency“ of MRI as a fixed number: it is important that each study has a clear medical reason and that the appropriate protocol is chosen, with or without contrast.