GE CARESCAPE - EEG practicalities; EEG measurement description; EEG frequency bands

EEGandauditoryevokedpotentials
EEGpracticalities
EEGmeasurementdescription
TheEEGsignaliscontinuouslymeasuredfromuptofourchannels.Thissupports
theinternational10-20system.
Measurementcanbereferentialorbipolar.Onthesignal,aspectralanalysisis
performedusingFastFourierTransform(FFT).Theresultisaspectrum,whichindicates
whatfrequenciesarepresentintheEEGsignal.EEGistraditionallydividedintofour
frequencybands:delta,theta,alphaandbeta.
InadditiontothecontinuousEEGmeasurement,itisalsopossibletomeasurethe
responseofthebraintoexternalauditorystimulationbymeasuringevokedpotentials,
EP.Whenmeasuringauditoryevokedpotentials,AEP,auditorystimuliaredeliveredto
thepatient’searsbyearphonesorheadphones,andtheresultingsignalismeasured
fromabovethecortex.Duringauditoryevokedpotentialmeasurement,EEGisalso
simultaneouslymeasuredfromthesameelectrodes.Frontalmuscularactivityisalso
assessedbyelectromyography,EMG,fromoneoftheEEGchannels.
EEGfrequencybands
Tocharacterizethespectralcontentofthesignal,thefollowingparametersare
calculated:
1.Delta
2.Theta
3.Alpha
4.Beta
5.Peakfrequency
6.50%ofpower
7.Medianfrequency
8.95%ofpower
9.Spectraledgefrequency,SEF
Powerindeltarange
Delta%=
Totalpower
x100%
Parameters:
●Spectraledgefrequency,SEF:Thefrequencybelowwhichnearlyallofthepoweris
present.
●Medianfrequency,MF:Dividesthespectruminhalf:50%ofthepowerisbelow
and50%abovethisfrequency.
●Frequencybandratios(Delta%,Theta%,Alpha%,Beta%)denewhatportionof
thepowerisinacertainfrequencyband.Forexample,Delta%=powerindelta
band/Totalpower.Thespectrumisdisplayedgraphicallyasasingle,continuously
updatingcurve,orcompressedspectralarray(CSA),wherespectraarestackedone
ontopoftheothertoformatrenddisplay.
382CARESCAPEModularMonitors2062971-001