Neuroimaging Flashcards
Nissl stain
Nissl stain: A dye that stains the cell body of the neuron; this method is particularly useful for detecting the distribution of cell bodies in specific regions of the brain
Golgi stain
Golgi stain: A method of staining brain tissue that marks a few selected individual cells, differentiating the cell body, as well as its extensions
Myelin stain
Myelin stain: Shows the myelin coating of axons, rendering it useful for mapping pathways in brain tissue
Horseradish peroxidase
Horseradish peroxidase: Allows mapping of neuronal pathways using axonal transport mechanisms; this technique works in both directions, that is, from the axon back to the cell body, and vice versa
Skull X-ray
Skull X-ray: Two-dimensional representation of the head. Disadvantages include low resolution of brain anatomy; advantages include low cost, availability, and its use in the diagnosis of skull fractures, which are easily seen using this technique.
Air encephalography (pneumoencephalography)
Air encephalography (pneumoencephalography): The radiographic visualization of the fluid-containing structures of the brain, which have been filled with
gas. An improvement over the skull X-ray, but because of its invasive nature and side effects, it is not used in contemporary medicine.
Computed transaxial tomography (CT scan)
Computed transaxial tomography (CT scan): CT renders an anatomic image of brain density based on multiple X-ray images of the brain. CT, which is readily available and can be used with almost anyone, provides a three dimensional perspective of the brain with acceptable differentiation of brain structures. Its disadvantages include the use of penetrating radiation and that CT does not provide as much spatial resolution as does magnetic resonance imaging.
Enhanced CT
Enhanced CT: A CT scan that involves injecting a contrast agent to provide better visualization of brain structures, particularly bleeds. Disadvantages are it is invasive and some patients may not tolerate the contrast agent well.
Angiography
Angiography: The roentgenographic visualization of blood vessels in the brain after introducing contrast material into the arterial or venous bloodstream.
Angiography is the most useful technique for examining the blood supply to and from the brain. One disadvantage is that a catheter must be inserted into the patient’s bloodstream, which requires an invasive medical procedure.
Sodium amytal injections (Wada technique)
Sodium amytal injections (Wada technique): The injection of sodium amytal temporarily anesthetizes one hemisphere. This is primarily a research
technique. It is used clinically to determine the lateralization of language before temporal lobectomy is performed. It is a complicated medical procedure
that requires placing an arterial catheter.
Gamma Waves
Gamma activity (35+ Hz) is a low-amplitude, fast-activity wave. Gamma rhythms are the fastest and are often associated with peak performance states and hyperarousal.
Beta Waves
Beta is a low-amplitude, fast-activity wave with a frequency of more than 12 Hz. Beta is often divided into high beta (18–35 Hz), typically associated
with a narrow focus, overarousal, and anxiety; mid-beta (15–18 Hz), often correlated with being active, alert, excited, or focused; and low beta (12–15 Hz),
which has been associated with relaxed, external attention.
Alpha Waves
Alpha activity (8–12 Hz) is the predominant background activity in wakeful persons. Alpha is most often associated with quiet, passive, resting, but
wakeful states.
Theta Waves
Theta activity ranges from 4 to 7 Hz and is most indicative of drowsiness, deeply relaxed states, and inwardly focused states.
Delta Waves
Delta activity is the slowest frequency (<0.5–4 Hz). High-voltage, slow frequency delta waves are never present in a wakeful, healthy person, but mostly occur during non–rapid eye movement (nondream) deep stage 4 sleep.
Electroencephalography (EEG)
Electroencephalography (EEG): EEG is one of the oldest brain-monitoring techniques. It measures the general electrical activity of the cortex. It is most
useful in assessing, in real time, the overall arousal state in a person. Increased electrode placements and computer integration capabilities have resulted in high-resolution EEG and BEAM (brain electrical activity mapping), a promising assessment and research tool of the electrical activity of neurons.
Evoked potential (EP)
Evoked potential (EP): EP, or event-related potential (ERP), is similar to EEG in that it assesses an electrical signal, but is related to a specific auditory (brainstem auditory-evoked response), visual (visual-evoked response), or sensory event (somatosensory-evoked response). Evoked potential assessment
provides not an evaluation of general brain activity, but a millisecondby-millisecond record of a specific sensory process.
Electrical stimulation
Electrical stimulation: Researchers have used electrical stimulation of nerve tissue to empirically map pathways of the cortex. More recently, clinicians
have introduced electrical stimulation in the treatment of Parkinson’s disease. Direct electrical stimulation of the brain, an invasive medical procedure, is used only in those cases for whom other interventions or diagnostic procedures have not succeeded.
Electromyography (EMG)
Electromyography (EMG): EMG is the electrical analysis of muscles, a diagnostic procedure useful in diagnosing peripheral nerve damage. The
procedure, however, is uncomfortable because it requires insertion of a needle into the muscle.
Electrocorticography (ECoG)
Often is performed during temporal lobectomy surgery to isolate a precise location of brain pathology. In addition, a surgeon can place depth electrodes in the brain close to the projected area of interest while the patient is awake and being monitored via 24-hour closed-circuit television. Depth electrodes and ECoG are invasive techniques
and entail risks, including infection. These methods
are used only when the medical benefits greatly outweigh the risks to the patient.
Magnetic resonance imaging (MRI)
Magnetic resonance imaging (MRI): MRI can provide the most detailed images of brain structures. The obtained images are of excellent clarity, but
individuals who have metal in their bodies are contraindicated for the procedure. Recent research focuses on the functional mapping of blood flow or oxygenation using MRI. The advantage of functional MRI over other functional procedures such as positron emission tomography is that it provides good spatial resolution and images in short time periods or “real time.”
Magnetoencephalography (MEG)
Magnetoencephalography (MEG): MEG is the magnetic equivalent of electroencephalography, in which a computer can calculate a three-dimensional
magnetic field of the brain. Superconducting quantum interference devices detect the small magnetic fields in the brain that are a marker of neural activity. A disadvantage of MEG is that it is expensive and not
readily available for clinical applications.
