Neurodiagnostics include the study and recording of electrical activity in the brain and nervous system. Tests are performed by technologists who record information on paper or computer, and the results are then interpreted by a specially trained physician.
An electroencephalogram, or EEG, records the electrical activity of the brain through highly sensitive electrodes placed at measured intervals on a patient's scalp. An EEG helps physicians in the diagnosis of a variety of neurological problems, including:
- Seizure disorders
- Degenerative brain disease
The EEG is also used to look for organic causes of psychiatric symptoms and disabilities in children.
What to Expect
The test usually takes about 90 minutes and is not painful. The principal role of the patient is simply to remain still, relaxed and comfortable.
The head is measured and electrodes are placed on the scalp with a paste-like substance. During the test, the patient may be asked to take repeated deep breaths (hyperventilate) and be shown a strobe light that flashes at different speeds. Both activities can help reveal brain patterns that are useful for diagnosis.
At times, physicians may order a sleep EEG to observe brain patterns that occur during sleep. For this test, the patient may be asked to stay awake most of the night before the EEG appointment or may be given a mild sedative.
24-Hour EEG Monitoring with Video
A 24-Hour EEG Monitoring with Video is a simultaneous recording of an EEG and videotaped behavior over extended periods. It is useful in diagnosing patients with intermittent or infrequent disturbances of electrical activity of the brain. This test is done on the nursing unit due to the long duration and complexity of the recording.
Evoked Potential (EP)
An Evoked Potential, or EP, is a recording of electrical activity from the brain, spinal nerves or sensory receptors to specific external stimulation.
EPs are helpful in evaluating a wide range of neurological problems, including:
- Spinal cord injuries
- Acoustic neuroma (tumor of the hearing nerve)
- Optic neuritis (swelling of the eye nerve)
- Demyelinating disease (multiple sclerosis)
What to Expect
Electrodes are applied to the scalp and other areas of the body, commonly the legs and arms. A series of stimuli is introduced, and a computer records the neurological responses. Hundreds of responses are received, amplified and averaged by a computer. The final response is plotted and graphed by computer and interpreted by physicians who analyze the waveforms and their speed of transmission.
There are different types of EP which evaluate different parts of the brain or spinal cord. Common examples include brainstem auditory evoked potential (BAER), visual evoked potential (VEP) and somatosensory evoked potential (SSEP).
- Auditory: The BAER helps in evaluating the auditory nerve pathways from the ears through the lower portion of the brain. Electrodes are attached to the scalp and earlobes, and earphones are placed over the ears. The earphones deliver a series of clicks or tones to each ear separately.
- Visual: VEPs evaluate the visual pathways of the nervous system from the eyes to the occipital (visual) cortex of the brain. Electrodes are applied to the scalp, and the patient is asked to focus on a pattern on a video screen while remaining fully alert. Each eye is tested separately.
- Somatosensory: SSEPs assess pathways from nerves in the arms or legs, through the spinal cord, to the brainstem or cerebral cortex. Electrodes are placed on the scalp, along the spinal cord, and along the arms or legs. A small electrical current is then applied to the skin overlying nerves on the arms or legs. The current creates a tingling sensation but is usually not painful. Each arm or leg is tested separately.
Transcranial Doppler (TCD)
Transcranial Doppler ultrasound assesses the blood flow velocity (speed at which blood flows) in the major arteries of the brain. The assessment of blood flow velocity helps to decide whether there is a narrowing or blockage in some of the arteries in the brain.
TCD technology is an important noninvasive diagnostic tool used in the Neuroscience Intensive Care Unit for the evaluation of subarachnoid hemorrhage-induced cerebral vasospasm.
What to Expect
The TCD ultrasound is a painless, noninvasive procedure and takes approximately one hour to complete.
The test is done by using a small probe over the temples. The skull is thin in this area and provides a "window" for the ultrasound beam. The probe is also placed over the eyelids, at the back of the neck and the sides of the neck.
To learn more about Neurodiagnostic Testing, or to schedule an appointment, please call Queen’s Neuroscience Institute Outpatient Center at 808-691-8866.