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Basics of EEG - A brief review of the EEG.ppt
- 1. Basic EEG
- 2. What is the EEG good for? • Diagnosis • Epilepsy • Coma (LTM studies) • Drug effects • Metabolic diseases, ie hepatic failure • Infections • Psychiatric conditions • Brain death • Focal lesions • Specific diseases with unique EEG signatures (CJD, SSPE) • Dementing illnesses (with serial EEGs over the years) • Prognosis • Epilepsy • After an injury • Severity of lesion • Outcome following a perinatal injury (ie burst suppression, regression)
- 3. What is the EEG NOT good for? • Measuring IQ • When normal in the presence of neurologic symptoms (think what it may mean?) • Focal lesions that are semi-acute or very chronic • Multifocal conditions ( MS, strokes) • Can be affected by systemic illnesses (ie heart or lung disease, fever etc)
- 4. Approach • How is the EEG recorded and seen? – What is the montage? – Sensitivity and speed – What do the up and down deflections mean? • Is the activity real or an artifact? • Is it normal for age and state? • Is there an abnormality? • What is the message to the referring person?
- 6. Approach • How is the EEG recorded and seen? – What do the up and down deflections mean? • Is the activity real or an artifact? • Is it normal for age and state? • Is there an abnormality? • What is the message to the referring person?
- 7. Rules governing pen deflections Direction of Pen Deflection Up Down Voltage Input G1 Relative to G2 Negative Positive Voltage Input G2 Relative to G1 Positive Negative Positive Channel “G1 - G2” G1 G2
- 8. The rules of polarity: if there are two electrodes, there are more than 1 solutions Up Amplifier G1 G2 - G1 G2 + Down G1 G2 + G1 G2 - G1 G2 - - + + G1 G2 Isoelectric: G1, G2 see the same (or no) activity G1 G2
- 9. The rules of polarity: Bipolar montage G1 G2 - G2 G3 G1 G2 + G2 G3 Negative phase reversal Positive phase reversal
- 10. G1 Ref G2 Ref -10 G3 Ref -5 G4 Ref The rules of polarity: Referential montage G2 Look at amplitudes pen
- 12. Approach • How is the EEG recorded? • Is the activity an artifact? – Artifacts do not have a field – Artifacts have double phase reversals • Is it normal for age and state? • Is there an abnormality? • What is the message to the referring person?
- 13. Electrode artifact: T4 (no field)
- 14. Double phase reversal BIPOLAR REFERENTIAL
- 15. Approach • How is the EEG recorded? – What is the montage? • Is the activity real or an artifact? • Is it normal for age and state? • Is there an abnormality? • What is the message to the referring person?
- 16. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 L R Bipolar Montage (Double Banana)
- 18. Transverse Montage 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 L R
- 20. Bipolar Montage: Look for phase reversals • The maximum of activity occurs at the site of the phase reversal* • A phase reversal may occur across two adjacent electrodes, which are on an isopotential line. In this case, the relative maximum involves the equipotential electrode • In the absence of a phase reversal, the maximum of activity occurs at the end of the chain of electrodes involved in that activity * Phase reversals associated with epileptic spikes are often surface-negative. Structural lesions that provide polymorphic slowing can be identified by surface-positive or surface-negative potentials.
- 21. Construction of fields from bipolar recordings A-B B-C C-D D-E A B C D E
- 22. Construction of fields from bipolar recordings A-B B-C C-D D-E A B C D E
- 23. Where is this activity coming from? Fp1-F3 F3-C3 C3-P3 P3-O1
- 26. Referential Montage: • The focus is where the amplitude is maximal • Usually there is no phase reversal
- 27. C-R B-R A-R D-R E-R Construction of fields from referential recordings A B C D E
- 28. Referential Montage: • If there is a phase reversal there are two options • The reference electrode is part of the field; change it and the phase reversal will disappear or • There is a horizontal dipole
- 30. Construction of fields from either referential or bipolar recordings C-R B-R A-R D-R E-R REFERENTIAL BIPOLAR A B C D E A-B B-C C-D D-E A B C D E
- 31. Approach • Develop a systematic approach • Determine baseline features • Determine reactivity • Assess intermittent changes • Identify features that are diagnostic of epilepsy Seizure patterns Epileptiform discharges (spikes/sharp waves)
- 32. Waveforms Frequency (Hz) Delta <4 Theta 4-7 Alpha 8-13 Beta 13-24 Gamma >24 Ripples Fast ripples
- 33. Definition of Rhythms • In EEG terminology, a rhythm consists of waveforms of the same frequency with a characteristic topography and specific reactivity
- 37. K complex, sleep spindles
- 38. EEG Classification • Normal • Abnormal • Type and Localization/ special notes • Technically unsatisfactory • Technically difficult General Classification
- 39. EEG Classification (cont’d) • EEG abnormalities • Slowing • Voltage attenuation/suppression • Changes in fast rhythms • Spikes/Sharp waves • Periodic and pseudoperiodic discharges • Seizure patterns
- 40. EEG Classification (cont’d) • Generalized • Focal • Generalized and focal/multifocal Localization
- 41. Slow-Wave Abnormalities Abnormality Posterior background rhythm slowing <8 Hz Generalized rhythmic* delta (theta) Generalized Slowing * Rhythmic activity is composed of waves with similar duration and morphology. Rhythmic and polymorphic activity may occur in combination. Etiologies Nonspecific Bilateral structural lesions (often anterior), or midline subcortical lesion Nonlesional diffuse disturbance such as metabolic disorder. Increased ICP Correlate Mild general disturbance Acute or subacute dysfunction of cortical and subcortical grey structures
- 42. Frontal Intermittent Rhythmic Delta Activity (FIRDA)
- 43. Slow-Wave Abnormalities (cont’d) Abnormality Continuous polymorphic delta (theta) Focal Slowing Correlate Disturbance of subcortical white matter Etiologies Lesions such as tumor, stroke, abscess, hematoma, contusion Nonlesional postictal phenomenon, migraine
- 44. Focal slowing- Bipolar Longitudinal
- 46. EEG abnormalities • Transient abnormalities associated with seizures and epilepsy – Spikes and slow waves – Sharp waves – Spike-wave complexes
- 47. Electroclinical seizure, focal (left temporal onset) 50 y/o M with episodes of spacing out, automatisms (picking, chewing)
- 48. 3 Hz Spike and Wave discharge
- 50. Slow and Spike Wave Discharge
- 51. EEG: Focal Seizures • Left parietal- posterior temporal seizure
- 53. PLEDS (or LPDs) Pseudoperiodic Lateralized Epileptiform Discharges or Lateralized Periodic Discharges
- 54. PLEDS and focal slowing / seizure
- 55. Hypsarrhythmia
- 57. (Pseudo) Periodic Discharges Waveform Biphasic or polyphasic (initially surface negative) Duration 100-200 msec Amplitude 100-200 V Repetition rate 1–2 sec Reactivity No Background Slow Seizures 80% Level of consciousness Depressed
- 59. Triphasic Waves * • Hepatic encephalopathy • Uremia • Severe electrolyte imbalance • Anoxia • Subdural hematoma *: New term proposed : Continuous 2/s GPDs (with triphasic morphology)
- 60. Triphasic waves
- 61. Generalized Periodic Discharges (GPDs) Creutzfeldt-Jacob S.S.P.E. Waveform Single wave, triphasic Two or more slow discharges repeating at 2 Hz Duration 100-600 msec 1-3 sec Repetition rate 1/sec 1/4 sec to 1/14 sec Afterdischarge 3-7 Hz rhythmical or May be flattening flattening (1 sec) Myoclonus Yes Yes Triggering by sensory stimuli Yes No
- 63. SSPE
- 64. Stand Up For Epilepsy The legendary Sumo Hakuhō Shō with aspiring Sumo wrestler Shun Hagiwara Country: Japan Photographer: Haruo Horikawa
- 66. 2 days after SE: seizure
- 68. PLEDS and focal slowing/ seizure?
- 69. Triphasic waves metabolic encephalopathy (hepatic encephalopathy uremia), anoxia, severe electrolyte disturbances, SDH 70 y/o M, alcohol abuse, change in MS
- 70. Generalized seizure: Absence (3 Hz Spike and Wave discharges),
- 72. Vetex wave, Vertex montage
- 73. K complex, Average montage
- 76. Driving response
- 77. Eye blinks
- 78. Driving response (10Hz), no response to EO
- 79. PDR (12Hz), responds to EO (same patient as prior)
- 80. EEG: first contact will need a new EEG that we will show in DB, transverse, refer
- 82. EEG: first contact will need a new EEG that we will show in DB, transverse, refer
- 84. EEG: first contact will need a new EEG that we will show in DB, transverse, refer
- 86. Amplifier G1 G2 - G2 G3 + G1 G2 + G2 G3 - G1 G2 - - G2 + + G1 G2 - G2 G3 G1 G2 + G2 G3 + The rules of polarity: Bipolar montage FIX
- 87. Voltage Input G1 Relative to G2 Negative Positive Voltage Input G2 Relative to G1 Positive Negative Direction of Pen Deflection Up Down Amplifier G1 G2 - G1 G2 + G1 G2 + G1 G2 - Up = Negative charge Down: Positive charge The rules of polarity (channel G1-G2) it also good to show just the deflection first and then the – or + signs
- 88. Need a 4 bipolar channel recording showing a spike • And another one with the same example in a referential montage
- 90. Need a 4 bipolar channel recording showing a spike • And another one with the same example in a referential montage
- 93. Bipolar montage
- 94. Horizontal and perpendicular dipoles
- 95. Draw a horizontal dipole in referential and bipolar montage
- 96. EEG: Rhythms
- 97. Mu rhythm
- 100. Sleep Spindles – stage 2 sleep
- 101. Sleep spindles
- 102. Sleep spindles
- 103. Sleep spindles
- 104. EEG Classification Normal Abnormal Technically unsatisfactory Technically difficult General Classification
- 105. EEG Classification (cont’d) Clinical seizures Invariant record Other Special Notes
- 106. Polymorphic Slowing
- 107. Frontal Intermittent Rhythmic Delta Activity (FIRDA)
- 108. Focal slowing and spikes
- 109. Focal slowing, right temporal
- 110. Focal slowing, right temporal
- 111. Spike-waves, central