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Tests and scans

Many of these tests will be done soon after admission to hospital as doctors need to rapidly assess the danger of the brain injury worsening.

What the tests examine

Neurological tests fall into two groups; tests that examine the structure of the brain and those examining the function of the brain. The first group includes the CT scan and MRI, the second group includes the EEG, SPECT scan, PET scan, and evoked studies.

The long-term effects of a brain injury may not be evident for some time. Those with a mild brain injury may be able to return to work but still have some cognitive challenges. Others may require higher levels of care or specialist housing.


The MRI (Magnetic Resonance Imaging) and CT (Computed Tomography, also known as CAT – Computerized Axial Tomography) scan the brain in cross sections. MRI does this with magnetic fields; the CT scan uses x-rays. The MRI has a higher degree of resolution than the CT scan so trauma seen by MRI may go unseen by CT scan. The X-rays used in CT scans are better at detecting fresh blood while the MRI scan is better at detecting the remnants of old hemorrhaged blood, or damaged but intact nerve tissue.

CT scans may be done frequently after the injury to keep an eye on the amount of brain injury. The MRA (Magnetic Resonance Angiogram) is a specialised form of MRI which detects blood vessels instead of brain tissue and can be used to check for bleeding or for the health of blood vessels.


The Electroencephalogram (EEG) records the ever changing tiny electrical signals coming from the brain using electrodes placed on the scalp. Slowing of electrical activity in some areas of the brain while the person is awake may indicate a lesion. Widespread slowing may indicate a widespread disturbance of brain function. Waves of electrical discharges indicate an irritable area of the cerebral cortex.

If allowed to spread, these spikes can produce a seizure. A Quantitative EEG is capable of creating a map of the brain’s electrical activity throughout the day. Comparison with a typical EEG makes it possible to see areas of slowing of electrical activity.

PET scan

Positron emission tomography (PET scan) shows the size, shape, and function of the brain. A small amount of a radioactive material (called the tracer) is added to some glucose molecules, which is then injected into a vein or breathed in by the patient. The glucose tracer travels through the blood to the brain, giving off photons. The patient is placed in a photon detector, and by counting the photons being emitted, and calculating their positions, it is possible to tell how much blood is being supplied to, and used by, the various parts of the brain. This can help determine the location, extent, and type of damage, making it easier to make a diagnosis.

Combined MRI/PET scan

This allows for the simultaneous measurement of anatomy, functionality and biochemistry. Although the scans are conducted separately, combining them in one machine ensures that the images overlap perfectly. This gives doctors a better picture of the state of brain tissue following an injury, or the progression of a degenerative condition such as Alzheimer’s disease.

SPECT scan

Single-photon emission computed tomography (SPECT), like PET, acquires information about the concentration of radio-nucleides introduced to the patient’s body. The radioactive chemical does not enter the brain itself but stays in the bloodstream. It allows examination of the brain’s blood supply which is normally reduced to damaged areas. Its advantage over PET scans is availability and cost.

Evoked potentials

Every time we hear, see, touch or smell our brain generates an electrical signal. Evoked potentials are recorded by placing wires on different parts of the scalp for different senses.

Lumbar puncture

A lumbar puncture is a diagnostic test where cerebrospinal fluid is extracted for examination, and pressure of the spinal column is measured. It is used to test for brain and spinal cord cancers, cerebral haemorrhage, and infections including meningitis and encephalitis.


Magnetic resonance spectroscopy is an imaging method of detecting and measuring activity at the cellular level. It provides chemical information and is used in conjunction with MRI which gives three-dimensional information and has great potential in the area of acquired brain injury.

Magnetic resonance angiography produces extremely detailed pictures of body tissues and organs without the need for x-rays. The quality is not the same as normal arteriography, but the patient is spared the risks of catheterisation and allergic reactions to the dye. The MRA procedure is painless. The magnetic field is not known to cause any tissue damage.

Intracranial pressure monitor

Swelling of the brain is a potentially very serious issue immediately after a traumatic brain injury so doctors often insert an intracranial pressure monitor into the skull to make sure there is no increased pressure that could worsen the injury.