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electroencephalogram clinical and technical practices
tasneem hamedon 17 October 2012
Transcript of electroencephalogram clinical and technical practices
MSc. in Biomedical Engineering Electroencephalogram clinical and technical practices EEG EEG (Electroencephalogram) is the record of electrical activity of brain( superficial layer i.e. the dendrites of pyramidal cells) by placing the electrodes on the scalp. Alpha wave -- 8 – 13 Hz.
Beta wave -- >13 Hz. (14 – 30 Hz.)
Theta wave -- 4 – 7.5 Hz.
Delta waves – 1 – 3.5 Hz. EEG Waves Different types of brain waves in normal EEG EEG machine.
Silver cup electrodes/ metallic bridge electrodes.
Quiet dark comfortable room.
Skin pencil & measuring tape. EEG Requirements The first recordings were made by Hans Berger in 1929 D T A B Alpha wave rhythmic, 8-13 Hz
mostly on occipital lobe
20-200 μ V
relaxed awake rhythm with eyes closed Beta wave irregular, 14-30 Hz
mostly on temporal and frontal lobe
excitement Theta wave Delta wave slow, < 3.5 Hz
normal sleep rhythm rhythmic, 4-7 Hz
Drowsy, sleep Procedure of EEG recording Ask the subject to close his/her eyes.
Select a montage.
Press run switch. Press the calibration knob to check voltages & time constant.
Always observe subject for any abnormal muscle activity. Spark A standard EEG makes
use of 21 electrodes linked in various ways (Montage).
Ask the subject to lie down in bed. (cc) image by nuonsolarteam on Flickr Apply electrode according to 10/20% system.
Check the impedance of the electrodes. Each electrode site is labeled with a letter and a number.
The letter refers to the area of brain underlying the electrode
e.g. F - Frontal lobe and T - Temporal lobe.
Even numbers denote the right side of the head and
Odd numbers the left side of the head. EEG Electrodes Types of recording Bipolar – both the electrodes are at active site
Bipolar montage are parasagital montage.
Unipolar – one electrode is active and the other is indifferent kept at ear lobe.
Always watch for any abnormal muscle activity.
Ask the subject to open eyes for 10 sec. then ask them to close the eyes. Different sets of electrode arrangement on the scalp by 10 – 20 system is known as montage. EEG Montages HOW?!!!! EEG machines use a differential amplifier to produce each channel or trace of activity. Each amplifier has two inputs. An electrode is connected to each of the inputs. Differential amplifiers measure the voltage difference between the two signals at each of its inputs. The resulting signal is amplified and then displayed as a channel of EEG activity. The manner in which pairs of electrodes are connected to each amplifier of the EEG machine is called a montage. Each montage will use one of three standard recording derivations, common reference, average reference or bipolar.
Common reference derivation: Each amplifier records the difference between a scalp electrode and a reference electrode. The same reference electrode is used for all channels. Electrodes frequently used as the reference electrode are A1, A2, the ear electrodes, or A1 and A2 linked together. Average reference derivation: Activity from all the electrodes are measured, summed together and averaged before being passed through a high value resistor. The resulting signal is then used as a reference electrode and connected to input 2 of each amplifier and is essentially inactive. All EEG systems will allow the user to choose which electrodes are to be included in this calculation. Bipolar derivation: These sequentially link electrodes together usually in straight lines from the front to the back of the head or transversely across the head. For example the first amplifier may have electrodes FP1 and F3 connected to it and the second amplifier F3 and C3 connected to it. Age
Infancy – theta, delta wave
Child – alpha formation.
Adult – all four waves.
Level of consciousness (sleep)
Hypocapnia(hyperventilation) slow & high amplitude waves.
Low glucocorticoids Factors influencing EEG slow waves
Eye artifacts (including eyeball, ocular muscles and eyelid)
Glossokinetic artifacts (minor tongue movements)
Movement by the patient
settling of the electrodes
Poor grounding of the EEG electrodes
the presence of an IV drip External artifacts Biological artifacts What are the follOWing type of artifacts?!!! LET’S ANSWER Desynchronization or Alpha block
Eyes opening (after closure)
Thinking by the subject (mathematical calculation)
NORMAL EEG CHANGES 1 Alpha rhythm changes to beta on eye opening (desynchronization / - block)
Eye opening 2 Beta waves are observed
Thinking 3 Intermittent photic stimulation
Increase rate & decrease amplitude
Decrease rate & increase in amplitude
Provocation test 4 Represent fluctuating dendritic potentials from superficial cortical layers
Deep parts of the brain are not well sampled What is EEG and what is
montage?!! Answer: The electroencephalogram (EEG) is a recording of the electrical activity of the brain from the scalp.
Arrangements of electrodes by 10/20% system is known as montage.
What is the advantage of provocation
test while recording EEG?!! Answer: Provocation test e.g. hyperventilation, intermittent photic stimulation are done to trigger the epileptic focus.
2 1 Thank You ANY Q.s? Finished