When is MRI used?

MRI (magnetic resonance imaging) scans are used to diagnose and monitor medical conditions, and can image almost every part of the body.

Like any imaging, an MRI scan should only be performed if it is likely to improve the management of your health condition.

The first and most important step to getting an accurate diagnosis of your condition or injury is your doctor taking your medical history and performing a thorough physical examination. An MRI scan — or in fact any imaging — should supplement, not replace, this step.

An MRI scan will not always be the most appropriate imaging option, and often other types of imaging, such as X-ray, CT or ultrasound, may be the first choice. Your doctor 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 imaging is required during pregnancy, MRI and ultrasound are preferred to X-ray and CT scans, as they do not involve radiation.

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.

While X-rays are generally better for diagnosing most broken bones (fractures), MRI scans are effective for identifying injuries to the soft tissue found around bones and joints, such as cartilage, tendons, muscles and ligaments.

Know your imaging options

It’s important to understand your options and know what each type of imaging involves. The following questions may help you to discuss the options with your doctor and the radiology practice, and help you find out more before your imaging.

Questions to ask your health professional about an imaging test

  1. How will the imaging help my condition or injury?
  2. What does the imaging test involve?
  3. Are there any risks associated with the test?
  4. Are there other options?
  5. How much will it cost?

The brain and spinal cord

An MRI scan can produce a detailed image of the brain and the nerves in the spinal cord. MRI can help diagnose or further assess medical conditions affecting the brain and nervous system, including:

  • brain tumours
  • stroke
  • epilepsy
  • meningitis (swelling of the tissue that covers the brain and spinal cord)
  • some cases of head or spinal cord injury (e.g. after a car accident)
  • chronic neurological conditions such as multiple sclerosis
  • aneurysms (a bubble-like weakening of a blood vessel in the brain)
  • Alzheimer’s disease and other dementias.

MRI scans are usually not necessary to investigate common forms of headache.

Bones and joints

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.

While X-rays are generally better for diagnosing most broken bones (fractures), MRI scans are effective for identifying injuries to the soft tissue found around bones and joints, such as cartilage, tendons, muscles and ligaments. An MRI scan can be used to help diagnose or further assess conditions such as bone infections (osteomyelitis), as well as more complex injuries involving ligaments and tendons. MRI is often used in the imaging of the spine and major joints, such as the knee or shoulder, in conjunction with X-rays.

Read Jack's story to learn more about the effective use of MRI in knee injuries.

A special form of MRI, called a magnetic resonance arthrogram (MRA), involves the injection of a contrast dye (gadolinium) into the joint. The contrast medium helps to show damage to the internal structure of the joint.

Breasts

MRI scans are now often used when breast cancer has been diagnosed, to determine how much of the breast and surrounding tissue is affected. In this case, an MRI is used after the cancer has been diagnosed by other methods, for example, mammography and biopsy (tissue sample).

MRI scans can also be used to screen for breast cancer in women without symptoms who are under 50 years of age and have a high risk of breast cancer because of their family history or a genetic mutation. In this younger age group only, MRI scans appear better than mammograms at detecting cancer. MRI breast cancer screening is now covered by Medicare if you meet the criteria, but you must be referred by a specialist.

Heart and blood vessels

MRI scans can be used to produce detailed images of the heart. They can examine the size of the heart chambers and the thickness of the heart wall, and can help diagnose problems such as congenital heart defects in children, or leaking heart valves.

MRI using contrast dye can help detect areas of limited blood flow to the heart muscle as a result of coronary artery disease or scarring of the heart muscle after a heart attack. The information obtained can help the doctors decide whether surgery or other treatments will be helpful in restoring heart function.

A special type of MRI, called magnetic resonance angiography (MRA), can be used to study the blood vessels throughout the body, including the neck, chest, heart, kidney, liver and limbs. Doctors can use this procedure to help diagnose and treat a range of conditions including:

  • aneurysms
  • narrowing of the arteries due to atherosclerosis in the blood vessels that supply blood to, for example, the kidneys, a leg, or the head via the carotid artery in the neck.

Internal organs

MRI is widely used to study the spread of cancers that affect specific organs (e.g. prostate cancer, cervical cancer or rectal cancer). MRI scans can also be used to diagnose diseases of the liver, the bile ducts and gallbladder, or the reproductive system, such as endometriosis or fibroids.