Definition & Overview
Brain imaging, also called neuroimaging, is the process of examining the brain and the nervous system using various imaging techniques. There are many different brain imaging scans that provide either a direct or an indirect image of the brain. The scans are used for diagnostic and cognitive research purposes. Brain scans generally fall into two categories - structural and functional imaging.
Structural imaging refers to brain scans that examine the structure of the nervous system. It is frequently used to diagnose intracranial disease and injury to any of the brain’s structures. Functional imaging, on the other hand, is used to diagnose metabolic diseases such as Alzheimer’s disease.
Who Should Undergo and Expected Results
Brain imaging is beneficial for patients suspected of having problems or medical conditions affecting their brain. However, the diagnosis and treatment of neurological diseases is not the only purpose of brain imaging. The procedure also helps doctors to understand the function of the different parts of the brain and conduct research and develop new technologies for the treatment of brain disorders. The two main types of brain disorders are:
- Structural diseases
- Bleeding (which can be due to an injury)
- Blood clots
- Birth defects
- Functional diseases
- Alzheimer’s disease
- Memory disorders
Brain disorders can cause various symptoms or complications, including:
- Vision loss
- Compromised brain function – For example, if a tumour presses on an intracranial nerve, the person will likely suffer from reduced brain function.
How is the Procedure Performed?
Brain imaging can be performed either invasively or non-invasively using several different techniques, including:
- CT scan – CT scans use a series of x-ray beams to produce cross-sectional images of the brain. This is purely a structural scan and does not provide information on the brain’s function.
MRI scan – An MRI brain scan provides an anatomical image of the brain by detecting radiofrequency signals produced by radio waves in a magnetic field. This offers detailed images of the brain in various dimensions. Although expensive, an MRI scan is a safe, painless, and non-invasive brain imaging technique.
Angiography – This test provides a series of x-rays that are produced after a special dye or contrast material is injected into the patient’s veins. The method provides images of the brain’s blood vessels.
PET scan – Positron emission tomography (PET) scan involves the use of radioactive materials that are injected into or inhaled by the patient. The radioactive material helps the scanner create an image of the parts of the brain that are metabolically active by releasing a neutron and a positron. When the neutron and positron hit each other, they are destroyed and release gamma rays as a result. The gamma rays are then detected to provide an image of the brain. A PET brain scan is more expensive than a CT scan but it provides an image of brain activity. It is thus considered as a functional scan.
Electroencephalography – Also known as an EEG, this test amplifies the patterns of neuronal electrical activity in the brain, which it measures over a continuous period. Through this method, brain waves are categorised under different frequency profiles, such as:
- Delta – The patient is in a deep sleep or coma.
- Theta – There is limbic activity, which means the patient is capable of memory and emotions.
- Alpha – The person is alert but cannot actively process information.
- Beta – The person is alert and can actively process information.
- Gamma – The brain is able to form coherent concepts due to the active communication among its various parts.
Functional MRI – This is a modified form of an MRI scan that produces images of brain activity in its various regions instead of simply visualising the brain’s structures.
Transcranial magnetic stimulation (TMS) – This is a noninvasive procedure that stimulates nerve cells in the brain using magnetic fields.
- Magnetoencephalography – This scan measures the magnetic fields created by the nerve cells and the electrical activity in the brain.
Different brain imaging scans can also be combined to obtain supporting data to address the limitations of each type of scan.
Possible Risks and Complications
The different types of brain imaging scans come with their own set of risks and disadvantages. This is why most neuroimaging scans are used with caution.
Most neuroimaging scans, including PET and MRI scans, are quite expensive. A PET scan also exposes the patient to radiation and the risk of developing an allergic reaction to the radioactive material used. On the other hand, an MRI scan is not safe for use on patients who have metallic devices implanted in their bodies, such as a pacemaker.
MRI scans also require patients to lie still. Thus, they are not advisable for uncooperative patients. The way the procedure is performed also carries some risks for patients who are claustrophobic.
“Types of Brain Scans.” American Brain Tumor Association. http://www.abta.org/brain-tumor-information/diagnosis/types-of-brain-scans.html
Kapur N, Kopelman MD. “Advanced brain imaging procedures and human memory disorder.” Oxford Journals. 65(1): 61-81. http://bmb.oxfordjournals.org/content/65/1/61.full