When and why

This is carried out when doctors suspect or need to exclude a lesion or abnormality in the brain. It can, therefore, be one of a number of investigations into the cause of a persistent headache, confusion, fits, memory problems or focal weakness in the arms or legs.

This uses either computer tomography (CT) or magnetic resonance imaging (MRI), dependent on the facilities available in the hospital. For both it involves lying flat and motionless within the scanning machine for approximately half an hour to an hour while the procedure is carried out. Occasionally sedation needs to be given.

Having an MRI scan can for some people be a claustrophobic experience. If this might be a problem you should tell the radiologist.

How it will help

A brain scan is a very useful test and can help to diagnose problems such as cerebral toxoplasmosis and lymphoma. An MRI scan can provide more detailed and clearer pictures of the brain and may be more useful in making a diagnosis of either HIV-associated dementia or PML. Brain scans are also done to monitor the effect and response to treatment.