Neurology Imaging / Testing
Computed tomography (CT scan) uses X-rays to produce two-dimensional images of organs, bones, and tissues. A CT scan can aid in proper diagnosis by showing the area of the brain that is affected. CT scans can be used to quickly detect hemorrhage in the brain and to determine if someone who has had a stroke can safely receive intravenous treatment to dissolve clots. CT scans also may be used to detect bone and vascular irregularities, brain tumors and cysts, brain damage from head injury, hydrocephalus, brain damage causing epilepsy, and encephalitis, among other disorders. A contrast dye may be injected into the bloodstream to highlight the different tissues in the brain
CT scanning takes about 20 minutes and is usually done at an outpatient imaging center or in a hospital. The person lies on a special table that slides into a narrow, doughnut-shaped chamber. A sound system built into the chamber allows the person to communicate with the physician or technician. X-rays (ionizing radiation) are passed through the body at various angles and are detected by a computerized scanner. The data is processed and displayed as cross-sectional images, or “slices,” of the internal structure of the body or organ. Occasionally a light sedative may be given if the person is unable to lie still and pillows may be used to support and stabilize the head and body.
Magnetic resonance imaging (MRI) uses computer-generated radio waves and a powerful magnetic field to produce detailed images of body tissues. Using different sequences of magnetic pulses, MRI can show anatomical images of the brain or spinal cord, measure blood flow, or reveal deposits of minerals such as iron. MRI is used to diagnose stroke, traumatic brain injury, brain and spinal cord tumors, inflammation, infection, vascular irregularities, brain damage associated with epilepsy, abnormally developed brain regions, and some neurodegenerative disorders. MRI is also used to diagnose and monitor disorders such as multiple sclerosis. A contrast dye may be injected into the vein to enhance visibility of certain areas or tissues.
An MRI scanner consists of a tube surrounded by a very large cylindrical magnet. These scanners create a magnetic field around the body that’s strong enough to temporarily realign water molecules in the tissues. Radio waves are then passed through the body to detect the shifting of molecules back to a random alignment. A computer then reconstructs a three-dimensional picture or a two-dimensional “slice” of the tissue being scanned. MRI can distinguish between bone, soft tissues, and fluid-filled spaces because of differences in water content and tissue properties. The individual lies on a special table that slides into the tube and will be asked to remove jewelry, eyeglasses, removable dental work, clothing with metal and other items that might interfere with the magnetic imaging. The person may hear grating or knocking noises when the magnetic field direction is flipped. Earphones or earplugs can help block out the sounds. For brain MRI scans, a detector is placed over the head
Angiography is a test that involves injecting dye into the arteries or veins to detect blockage or narrowing. A cerebral angiogram can show narrowing or obstruction of an artery or blood vessel in the brain, head, or neck. It can determine the location and size of an aneurysm or vascular malformation. Angiograms are used in certain strokes where there is a possibility of unblocking the artery using a clot retriever. Angiograms can also show the blood supply of a tumor prior to surgery or embolectomy (surgical removal of a blood clot or other material that is blocking a blood vessel).
Angiograms are usually performed in a hospital outpatient or inpatient setting and may take up to 3 hours, followed by a 6- to 8-hour resting period. The person, wearing a hospital or imaging gown, lies on a table that is wheeled into the imaging area. A physician anesthetizes a small area of the leg near the groin and then inserts a catheter into a major artery located there. The catheter is threaded through the body and into an artery in the neck. Dye is injected and travels through the bloodstream into the head and neck. A series of x-rays is taken. The person may feel a warm to hot sensation or slight discomfort as the dye is released. In many situations, cerebral angiograms have been replaced by specialized MRI scans, called MR angiograms (MRA), or CT angiograms. A spinal angiogram is used to detect blockage of arteries or blood vessels malformations in the vessels to the spinal cord.
Electroencephalography, or EEG, monitors the brain’s electrical activity through the skull. EEG is used to help diagnose seizure disorders and metabolic, infectious, or inflammatory disorders that affect the brain’s activity. EEGs are also used to evaluate sleep disorders, monitor brain activity when a person has been fully anesthetized or loses consciousness, and may be used to confirm brain death.
This painless, risk-free test can be performed in a doctor’s office or at a hospital or testing facility. A person being tested usually reclines in a chair or on a bed during the test. A series of cup-like electrodes are attached to the scalp with a special conducting paste. The electrodes are attached to wires (also called leads) that carry the electrical signals of the brain to a machine. During an EEG recording session, a variety of external stimuli, including bright or flashing lights, noise or certain drugs may be given.
Individuals may be asked to open and close their eyes, or to change their breathing patterns. Changes in brain wave patterns are transmitted to an EEG machine or computer. An EEG test usually takes about an hour. Testing for certain disorders requires performing an EEG during sleep, which takes at least 3 hours.
In people undergoing evaluation for epilepsy surgery, electrodes may be inserted through a surgical opening in the skull to reduce signal interference. This is called an intracranial EEG. People typically remain in a hospital epilepsy monitoring unit while implanted electrodes are in place. During this time, the brain is monitored for seizures in order to determine where the seizures originate. People may also be asked to perform certain types of tasks (e.g., reading, speaking, or certain limited motor activities) so that the EEG can be used to identify brain regions that are important for normal function.
Electromyography, or EMG, is used to diagnose nerve and muscle disorders, spinal nerve root compression, and motor neuron disorders such as amyotrophic lateral sclerosis. EMG records the electrical activity in the muscles. Muscles develop abnormal electrical signals when there is nerve or muscle damage. During an EMG, very fine needles or wires are inserted into a muscle to assess changes in electrical signals at rest and during movement. The needles are attached through wires to an EMG machine. Testing may take place in a doctor’s office or clinic and lasts an hour or longer, depending on the number of muscles and nerves to be tested. Because of a slight risk of bruising or bleeding, people will be asked if they are on aspirin or blood thinners. Most people find this test to be somewhat uncomfortable.
An EMG is usually done in conjunction with a nerve conduction study (NCS). An NCS measures the nerve’s ability to send a signal, as well as the speed (nerve conduction velocity) and size of the nerve signal. A set of recording electrodes is taped to the skin over the muscles or skin. Wires connect the electrodes to an EMG machine. A small electrical pulse (similar to the sensation of static electricity) is given on the skin a short distance away to stimulate the nerve to the muscle or skin. The electrical signal is viewed on the EMG machine. The physician then reviews the response to verify any nerve damage or muscle disease. There is minimal discomfort and no risk associated with this test.