When is MRI unlikely to be helpful?

An MRI scan will not always be the most appropriate imaging option; other types of imaging such as X-ray, CT or ultrasound may be the first choice. Your health professional will usually only request an MRI scan if other types of imaging are not suitable or have not provided all the information required for a thorough assessment.

If your doctor believes imaging is required after a physical examination of a bone or joint-related injury, X-ray is usually the first choice. More sophisticated imaging — such as CT or MRI scans — are usually only ordered if the X-ray and doctor’s examination suggest further investigations are necessary.

MRI scans do not generally provide good images of hard bone, and are often less accurate than X-ray and CT scans at diagnosing many bone fractures. Similarly, if the signs of osteoarthritis are clearly visible on an X-ray, an MRI scan is unlikely to provide any more useful information.

Some lung conditions, such as pneumonia, are usually adequately diagnosed by physical examination and a simple chest X-ray. An MRI would rarely be required in the diagnosis of pneumonia.

Headache

People who experience severe headaches may think they need an MRI or CT scan to rule out a serious problem, such as brain tumour, but the majority of headaches are not due to any serious underlying health problem. In this situation, an MRI scan rarely provides any useful information.

Because MRI scans are so sensitive, they may even pick up 'incidental' changes in the brain. These changes may have no actual relationship to the headache, or to any other physical problem — but knowing about them could potentially cause you unnecessary worry and stress. MRI scans are only recommended if there is reason to think a headache may be due to a serious cause.

Acute low back pain

MRI scans are not recommended for most cases of acute low back pain. Most people with low back pain feel better after about a month whether they get a scan or not. Generally, it is only when pain is accompanied by other signs (e.g. weight loss, fever, signs of nerve compression such as weakness in the legs) that imaging is recommended.

MRI scans often show changes in the spine that have no relationship to the back pain. These incidental findings may lead to anxiety and stress and even unnecessary treatment.

A study of adults without symptoms of back pain found that about two-thirds had bulging discs or other spinal abnormalities on their MRI scans.

Another study found that back pain sufferers who had an MRI in the first month after symptoms occurred consumed higher doses of pain-relief medicines and were off work, on average, almost 6 times longer than those who did not have an MRI.

People with more severe symptoms were 8 times more likely to have surgery if they had had an MRI. Among those with milder symptoms, the difference was even greater — those who had an MRI were 33 times more likely to have surgery than those who did not have an MRI scan, even though they had similar symptoms.

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