Definition & Overview
An MRI for the brain is a diagnostic test most commonly used to detect brain tumours and diagnose brain cancer. It works by placing the patient within a magnetic field and using radio wave energy to take images of the brain inside the head. MRI is the more sophisticated diagnostic test when compared to normal X-ray, ultrasound, or CT (computed tomography) as it can provide extensive information that other imaging tests cannot.
Who Should Undergo & Expected Results
The most common reason or symptom that prompts doctors to request for an MRI scan is an unbearable headache. Persistent, recurrent, or chronic headaches that have no known underlying cause can be further investigated using an MRI scan. Aside from this, an MRI scan may also be necessary to determine the cause of several other symptoms including:
- Change in consciousness
- Uncontrolled, abnormal movements
- Problems with vision or hearing, or both
The following conditions can be diagnosed by an MRI:
- Arteriovenous malformation (a congenital condition characterized by twisted blood vessels)
- Blood clots
- Bleeding in and around the brain
- Head injury
- Huntington’s disease
- Parkinson’s disease
- Alzheimer’s disease
- Multiple sclerosis
- Pituitary gland problems
A patient can expect an MRI scan to provide results containing vital information that may point to the presence of:
- Tissue damage
- Infection in the brain
- Symptoms of stroke
In reading the results of an MRI of the brain, the normal results should show a normal head structure from the brain, blood vessels, spaces, nerves, down to the surrounding structures. There should also be no abnormal growths or tumours, bleeding, abnormal blood vessels or AV malformations, abnormal pockets of fluid, bulges and blockages in the blood vessels, or signs of infection.
How Does the Procedure Work?
An MRI scan can only be performed by an MRI technologist, but the resulting images are analyzed and interpreted by a radiologist or a neurologist. When undergoing an MRI of the brain, the patient will be asked to lie down inside a special scanning machine with a strong magnetic force. All metal objects such as jewellery, watches, hair accessories, and even hearing aids or dentures, need to be removed to avoid magnetic interference. In some patients, there is a possibility that magnets may be present in the body without them knowing it. Thus, if a patient works around a lot of metals or has had an accident involving metal, it is best to take an X-ray first to see if the patient is eligible for the exam.
During the test, the patient will be given a hospital gown to wear, but sometimes patients are allowed to wear their own clothes. The patient will then be asked to lie down inside the machine and keep still while the test is being done. If there is a need to do so, the technologist may hold down the patient using straps, while the head is wrapped with a coil. Once ready, the table where the patient is lying down is slid into the machine where the MRI magnet is also located. Once inside the machine, patients can expect to hear a fan and to feel some air being blown. As the pictures are being taken, some snapping sounds may also be heard. Patients are often given headphones or earplugs to reduce the sound, and it is also possible to request for a sedative, if necessary, so that it will be easier to keep still. The test, however, is not painful. The only discomfort may be due to lying down on the hard table for an extended period or due to the confined space inside the machine, which may cause some people to feel claustrophobic.
There may be cases where the doctor will inject a dye-based contrast material into the veins so that the brain’s structure will show up more clearly on the scan results. This dye is more commonly used when trying to detect problems pertaining to blood flow, blood clots, or tumours. The material will cause some coolness in the veins, warmth in the head, or a tingling sensation in the mouth if the patient has metal-based dental appliances. If a dye material is to be used, it will be administered intravenously through a vein in the hand or arm in just around 2 minutes. The whole test, on the other hand, takes anywhere between 30 minutes and 2 hours, depending on the patient’s condition and his or her ability to keep still.
The images that an MRI scan produces can be stored on a computer so it can be studied and reviewed by doctors. Different views or angles can also be printed out on films or photographs to make analysis easier. The results are released right after the test, although the printed copies may take 1 to 2 days.
Possible Complications and Risks
There are no known complications related to undergoing an MRI scan, although the magnet tends to be very powerful. To avoid risks, a detailed discussion with your doctor is a must, as the magnetic force can affect:
- Medical devices such as pacemakers, ICDs or implantable cardioverter-defibrillators, or even artificial limbs
- Metal pieces in the eyes where the retina can be easily damaged (If an X-ray shows that a patient has metal pieces in the eyes, an MRI scan cannot be performed.)
- Iron pigments found in tattoos
- Medicine patches
The risks involved in undergoing an MRI only increase when contrast material is used. A contrast material may cause allergic reactions, which, although mostly mild and treatable with medication, may also cause gadolinium that can bring nephrogenic systemic fibrosis, a serious problem for those who have kidney disease. Thus, MRI scan using dye-based contrast material is only performed when it is safe for the patients.
Wilkinson ID, Paley MNJ. Magnetic resonance imaging: basic principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 5.
Saunders D, Jäger HR, Murray AD, Stevens JM. Skull and brain: methods of examination and anatomy. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 55.