Electroencephalography (EEG)

Introduction to EEG
Notes about EEG and Working
Notes about EEG Electrodes

ppt By,
AJU REMESH (Ajumon R)
[email protected]

1. Electro Encephalo Graph (EEG) Ajumon . R

2. 2 Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity of the brain. EEG describes general functions of brain activity. It sense the neuron signals operating in a non synchronized manner in physical sense.

3. 3 Monitoring the EEG has proven to be an effective method of diagnosing many neurological illness and diseases. such as epilepsy , tumour , cerebrovascular lesions , ischemia and problems associated with trauma. It is also used to diagnose sleep disorders, coma, encephalopathies , and brain death.

4. 4 An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain. Special sensors are attached to your head and hooked by wires to a computer. The computer records your brain's electrical activity on the screen or on paper as wavy lines. Certain conditions, such as seizures, can be seen by the changes in the normal pattern of the brain's electrical activity. E E G Several types of Electrodes may be used to record EEG. Peel and Stick Electrodes. Silver Plated Electrodes. Needle Electrodes (rare case).

5. 5 EEG Electrodes are smaller than ECG electrode. They may be applied separately to the scap or may be mounted in special bands. In either case, electrode jelly or paste is used to improve the electrical contact. If the electrodes are intended to be used under the skin or scalp,needle electrodes are used (rare case). EEG Electrodes give high skin contact impedence as compared to ECG electrodes. Good electrodes impedence should be generally below 5 kilohms . Impedence between pair of electrode must also balanced or the difference between this should less than 2 kilohm .

6. 6 Figure shows, most commonly used electrode for EEG. “ Chlorided silver discs” Diameter approximately 6 – 8 mm . Contact with the scalp is made via an electrolytic paste. They have AC resistance varying from 3–20 kilohm . Fig (A) is a “Pad Electrode”. Which made from silver rod bulled out at the end and padded with sponge. It screwed into an insulated mount and held in place on the head with a rubber cap. To hold 3 such electrode, an adjustable tripod mout is employed. Another type of electrode consist of multiple fine chloride silver wires(fig. B) fixed in a rigid plastic cup. The plastic cup is fixed with an adhesive. It is filled with jelly through a hole in top

7. 7 Monopolar and Bipolar recording. Monopolar : EEG may recorded by picking up the voltage difference between an active electrode on the scalp with respect to a reference electrode on the ear lobe or any other part of body. Bipolar : In bipolar, voltage difference between the scalp electrode is recorded. Bipolar recording is more popular than Monopolar . Fig A: Bipolar Fig B: Monopolar

8. 8 Block diagram of Electroencephalograph The basic block diagram of EEG machine with both analog and digital componets is shown in fig 5.11

9. 9 Placement of Electrodes Electrodes are identified according to their postiton on the head: Fp - Frontal-Polar P - Parietal F - Frontal T - Temporal C - Central O - Occipial

10. 10 EEG electrodes are arranged on the scalp according to a standard known as the “10/20 system”. Adopted by the American EEG Society. There are 21 electrode locations in the 10/20 system. Placement of electrode at distance of 10% and 20% of measured coronal,sagittal and circumferential arcs between the landmarks on the cranium (fig 5.12) A new montage convention has recently ben introduced in whch electrodes are spaced at 5% distance along the cranium. These are called “Closely spaced electrodes” (shown in fig 5.13)

11. 11 Electrode montage selector: The montage selector panel containing switches that allow the user to select which electrode pair will have signals subtracted from each other to create an array of channels of output called montage. Preamplifier: Every channel has an individual, multistage, ac coupled, very sensitive amplifier with different input and adjustable gain in a wide range. I ts frequency response can be selected by single stage passive filters. Another parts of EEG machines are: A nolog to digital coverter . Oscilloscope and computer. Writer unit with Chart drive and Ink-writing Oscilloscope.

12. 12 Example of EEG Wave Form:

13. 13 EEG activity is dependent on the level of consciousness :

14. 14 Thank you… Contact me: Aju Remesh AMR Media (P)Ltd Nechipuzhoor P.O Palai - 686574 Mob : [phone] Email : [email protected] Web : www.amrmedia.ml FB : www.facebook.com/AjuRemesh007