Unit
- Origins of EEG: Hans Berger recorded the first human electroencephalogram in 1924, demonstrating that electrical activity from the brain could be measured through the scalp. This groundbreaking discovery laid the foundation for clinical neurophysiology and noninvasive brain monitoring.
- Basic principle: EEG measures the summed postsynaptic potentials of cortical pyramidal neurons. These potentials are generated by synchronous activity of thousands of neurons and are recorded through electrodes placed on the scalp.
- Frequency bands: Brain rhythms are categorized into delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz), and gamma (above 30 Hz) bands. Each band is associated with different states of consciousness and pathological conditions.
- Clinical significance: EEG is essential for diagnosing epilepsy, sleep disorders, encephalopathies, and brain death. It also aids in monitoring during surgeries and intensive care.
- Advantages: EEG offers high temporal resolution (millisecond range), portability, and relatively low cost compared to other neuroimaging modalities like MRI and PET.
- Limitations: Spatial resolution is poor because signals pass through the skull and scalp. EEG cannot directly measure deep brain structures and is prone to artifacts from muscle activity, eye movements, and environmental interference.
- Digital EEG evolution: Modern EEG systems convert analog signals to digital format, enabling advanced signal processing, quantitative analysis, and long-term storage. Digital filters and montage reformatting improve diagnostic capability.
- Standardization efforts: Organizations like the American Clinical Neurophysiology Society (ACNS) have established guidelines for EEG recording, interpretation, and reporting to ensure consistency across laboratories.
- Role in epilepsy: Interictal epileptiform discharges (spikes and sharp waves) are hallmark EEG findings in epilepsy. Prolonged monitoring can capture ictal patterns to localize seizure foci.
- Emerging applications: EEG is increasingly used in brain-computer interfaces, cognitive neuroscience research, and monitoring of anesthesia depth. These applications require standardized operations to ensure data reliability.
- Montage selection: EEG displays can be reformatted into different montages, including bipolar longitudinal, transverse, referential, and average reference. Each montage highlights specific aspects of brain activity, such as phase reversals for focal lesions or diffuse slowing. Proper montage selection is essential for accurate interpretation.
- Common artifacts: Physiological artifacts from eye movements, blinks, muscle tension, and sweat can mimic pathological waveforms. Environmental artifacts include electrode popping, 60 Hz line interference, and faulty connections. Recognizing and minimizing these artifacts is critical for clean recordings.
- Infection control: Electrodes, caps, and leads must be cleaned and disinfected between patients according to facility protocols. Single-use items should be discarded, and reusable components require high-level disinfection to prevent cross-contamination. Proper hygiene protects both patients and technologists.
Scope of Practice
Role: EEG Technologist in a Hospital Neurodiagnostics Lab
Within scope:
- Setting up and calibrating EEG equipment according to manufacturer specifications.
- Applying electrodes using the 10-20 system and verifying impedance levels.
- Conducting standard and prolonged EEG recordings following established protocols.
- Monitor the patient during recording and document observations and events.
- Perform basic artifact identification and troubleshooting under supervision.
Outside scope:
- Interpreting EEG results or providing a clinical diagnosis independently.
- Modifying recording protocols without physician or supervisor approval.
- Administering medications or altering patient medications for activation procedures.
- Performing invasive EEG techniques like depth electrode placement.
- Releasing EEG reports without review by a qualified neurologist.
Quick Revision
- EEG measures cortical electrical activity with high temporal resolution but limited spatial resolution.
- Frequency bands (delta, theta, alpha, beta, gamma) reflect different brain states and pathologies.
- EEG is critical for epilepsy diagnosis, sleep studies, and monitoring in critical care.
- Digital EEG and standardization improve diagnostic accuracy and workflow consistency.
- Technologists operate within a defined scope, ensuring quality recordings without independent interpretation.