Brain Injury:

Diagnostic Tests

MRI and CAT Scans:
The MRI and CAT scan slice the brain radiographically into slabs and can help in providing a brain injury diagnosis. The MRI does this with magnetic fields and the CAT scan uses x-rays. The MRI provides more detail than the CAT scan. This means that brain damage seen on an MRI - as small as 1 to 2mm in size - may not be detected by a CAT scan. The MRI is also better at detecting the remnants of old hemorrhaged blood. The CAT scan, however, is better than the MRI in detecting fresh blood in and around the brain. CAT scans are often repeated to insure that a traumatic brain injury is not becoming more extensive, usually in the early stages of ER treatment for TBIs.

MRA (Magnetic Resonance Angiography):
A common brain injury diagnostic tool, an MRA is a way of visualizing the carotid and vertebral arterial systems in the neck and brain without having to inject contrast into the bloodstream. The resolution is not as good as with conventional arteriography, but the patient is spared the risks of catheterization and allergic reactions to the dye. In conventional arteriography, a catheter is threaded from the femoral artery in the groin backward up the aorta into a carotid or vertebral artery in the neck, and then dye is injected up the catheter. As the dye flows into the brain, x-rays are taken of the cerebral vasculature.

EEG (Electroencephalogram):
An EEG monitors the brain's electrical activity by way of wires attached to the patient's scalp and can help in the diagnosis of a brain injury. These wires act like an antenna to record the brain's electrical activity. Normally, the resting brain emits signals at a frequency of 8 to 13 cycles per second (cps), called alpha activity, which is best seen in the occipital regions. Anything faster than 8-13cps is called beta activity. Slower rhythms include theta activity (6-7 cps) and delta activity (3-5 cps).

Theta and delta activity occur in the normal brain as the patient descends into sleep. If the patient is awake, any slowing of electrical activity in a focal area of the brain may indicate a lesion there. Similarly, widespread slowing indicates a widespread disturbance of brain function, often due to a bloodborne insult like low blood sugar, drug intoxication, liver failure, etc. Spiking discharges indicate an irritable area of cerebral cortex. If allowed to spread, the spikes may produce a seizure.

Quantitative EEG (QEEG, BEAM, Brain Mapping):
This test is performed in a way similar to EEG and is commonly used when diagnosing a brain injury. Brain wave activity varies throughout the day depending on the state of alertness. Each area of the brain normally spends a characteristic amount of time in alpha, beta, theta, and delta activity. Brain mapping computers are now capable of creating a map of the brain's electrical activity depicting how long each area of the brain spends in each of the basic rhythms. By comparing the patient's map with that of a control population, it is possible to localize areas of focal slowing of electrical activity. Alone, a QEEG is insufficient to diagnose brain damage but in combination with other neurologic tests, QEEG can help confirm brain inujury.

PET Scan (Positron Emission Tomography):
PET scanning is based on the fact that the brain uses glucose for energy. By labeling a glucose molecule with a radioactive "tag," and then inhaling radioactive glucose and placing the patient's head under a large geiger counter, one can identify abnormal areas of the brain that are underutilizing glucose. However, because cyclotrons are needed to generate the radioactive gas, this brain injury diagnostic procedure is not widely available.

SPECT Scan (Single Photon Emission Computed Tomography):
SPECT scanning is similar to PET scanning in that a radioactive chemical is administered intravenously to the patient, but the radioactive chemical remains in the bloodstream and does not enter the brain. As a result, the SPECT scan maps the brain's vascular supply and can help provide a brain injury diagnosis. Because damaged brain tissue normally shuts down its own blood supply, focal vascular defects on a SPECT scan are circumstantial evidence of brain damage. The advantage of a SPECT scan over a PET scan is its availability and generally cheap cost. Recent studies have demonstrated abnormal SPECT scans after head trauma when the CAT and MRI were normal, suggesting that the SPECT scan is more sensitive to brain injury then either CT or MRI scans. Because the radioactive chemicals used in SPECT and PET scans are carried to all parts of the body by vascular tree, SPECT scans and PET scans are used judiciously in patients of reproductive age.

Evoked Potentials:
Evoked studies take advantage of the fact that each time a sensory system of the body - vision, hearing, touch - is stimulated, an electrical signal is generated in the brain. These electrical signals can be detected with electrical wires on the scalp. This means that visual evoked recordings (VER) are recorded over the occipital lobes, brainstem auditory evoked recordings (BAER) over the temporal lobes, and somatosensory potentials (SSEP) over the parietal lobes.

Lumbar Puncture:
A lumbar puncture (spinal tap - not the band) is used to analyze cerebrospinal fluid. An analysis of the fluid can help tell doctors whether a traumatic brain injury has caused any bleeding in the brain and spinal cord areas, for example.

Magnetic Resonance Spectroscopy (MRS):
This brain injury diagnostic tool is used in conjunction with MRI, that detects the intra-cellular relationship of brain metabolites. Studies show that in an injured brain, the relationship between the amount of certain compounds in the brain changes in predictable ways, which can be picked up, non-invasively, by MRS. While MRS is in its early stages, it holds great promise in the objectivication of brain injury.

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