A.Li ni u in no l dng c th nghim y hc ghi li nhng xung in t cc neuron trong no c th nhn c t da u.Nh vo s pht trin ca khoa hc - k thut v c bit l nhng tin b nhanh chng ca k thut in t y-sinh trong thi gian gn y, nhiu nh khoa hc trn th gii xy dng v pht trin nhiu k thut x l tn hiu hin i ng dng trong phn tch v chn on chnh xc tn hiu in no (EEG) nghin cu kh nng iu khin in thoi thng qua vic gii m tn hiu EEG t EEG headset.B no lin tc sn sinh ra cc tn hiu in rt nh n t cc t bo no v t bo thn kinh dn truyn thng tin cho nhau. Trong sut qu trnh kim tra EEG,cc in cc (cc a kim loi phng ) c gn trn u ca ngi dng. Cc in cc ny thu nhn cc tn hiu in t no v gi chng ti mt my EEG. My EEG s ghi li cc tn hiu in t no a ti mt my tnh. Tn hiu ny ging nh nhng ng ln sng, v s i din cho cc mu sng no ca bn. o in no khng gy au v v hi. (Cc my o in no ghi li cc tn hiu in t no ca bn - n khng mang dng in no vo no hoc c th ca bn).Da vo tn hiu sng no ta c th tch lc cc tn hiu nhiu, gii m c u l tn hiu pht ra t t bo thn kinh c th ng dng iu khin Vi mong mun nghin cu ,hc hi v p dng cng ngh mi x l tn hiu EEG trn in thoi di ng,di s hng dn tn tnh ca thy Phm Vn Tin ging vin Vin in T-Vin Thng,nhm chng em chn ti Tch lc tn hiu in no (EEG) trn in thoi di ng lm ti Project 3. Do cng lm vic trong thi gian c hn cng vi nhng hiu bit cn hn ch,bi tp ln kh trnh khi nhng sai st ,nhm em mong nhn c kin ng gp ca thy v cc bn!.Nhm sinh vin lp KSTN-TVT-K54Trn Ngc Tn (TL)Nguyn c NamHong Vn Php

B.Ni dung1.C s vt l-y sinh ca tn hiu in no 1.1.c im ca tn hiu in no (EEG).in no (EEG Electroencephalogram ) o v biu din s thay i in th theo thi gian ca cc in cc c t cc v tr khc nhau trn da u tng ng vi cc vng ca v no trn th my tnh. Thng qua cc c trng bin , tn s, phn b khng gian, hnh thi, s phn cc ca in th, EEG cho ta cc thng tin v cc hot ng ca no.Trong qu trnh hot ng, no s pht ra cc xung in lan truyn theo cc dy thn kinh. Cc xung in ny phn nh trng thi hot ng v kch thch ca b no. Cc xung in no s lan truyn n lp v no c dy khong 23mm. B mt ca v no c dng cc lp, khe nh vi nhiu kch thc khc nhau lm lm tng din dch h thn kinh, vi tng din tch hn 2,5m2 bao gm hn 10 t nron thn kinh.Cc tn hiu c ghi trn da u c bin bin thin t vi V n xp x 200V v tn s nm trong phm vi t 0.5 n 70Hz. N u trng thi ca i tng o n nh trong mt khong thi gian, cc nhp ny c dng tun hon.Cc nhp c bn c chia thnh 5 di :+ Nhp delta: tn s 0.5 - 4Hz.+ Nhp theta: tn s 4 -7.5 Hz.+ Nhp alpha :tn s 8 13.5 Hz.+ Nhp beta : tn s t 14 -30 Hz.+ Nhp gamma : c tn s ln hn 30 Hz.

1.2.Ngun gc v cc c trng tn s, bin ca cc loi nhiu chnh trong in no Trong cc tn hiu in no chng ta o c thng xuyn xut hin cc loi tn hiu l khng phi l tn hiu in no xut pht t da u, chng c gi l nhiu (artifact). Cc nhiu ny c chia thnh hai nhm chnh. N hm th nht l nhiu do thit b v mang tnh h thng (do tip xc in cc v sai s thit b o), loi nhiu ny thng kh d dng nhn bit v loi b v n c tnh tng quan cao. Nhm th hai l cc nhiu c ngun gc t sinh l ca con ngi nh nhiu cho chuyn ng ca mt, do nhy mt, do hot ng ca cc c bp, hot ng ca c tim. Di y chng ti s trnh by cc c im nhn dng ca cc loi tn hiu nhiu ny.1.2.1. c im nhn dng nhiu mt (Electrooculogram EOG)Tn hiu EOG l s chnh lch in p gia gic mc v vng mc ca mt. Chnh lch in p ny thay i trong sut qu trnh chuyn ng ca mt, v in p o c gn nh t l vi gc nhn . Chng ta c th ghi nhn chnh lch in p ny tng ng vi mc chuyn ng v hng chuyn ng ca mt lm knh tham chiu. Khi gic mc hay vng mc ca mt chuyn ng s khng nhng lm thay i chnh lch in th to ra tn hiu EOG m cn nh hng lm thay i in th cc v tr khc trn da u v do lm thay i tn hiu EEG. Tn hiu EOG c nhiu tnh cht c trng ring, khc bit vi cc tn hiu in no thng thng. Vic nghin cu v phn tch cc tnh cht ca cc tn hiu EOG l nn tng quan trng p dng v kim tra cc thut ton loi b nhiu mt EOG khi tn hiu in no.1.2.2. c im nhiu c (Electromyogram EMG)Tn hiu EMG l tn hiu to ra bi iu khin hot ng ca c bp v cha thng tin v cu trc c ca tng b phn c th khc nhau. Khi ta o in no, bnh nhn thng khng trnh khi mt s hot ng bnh thng nh co ngn tay, co tay, ni chuyn, c ng chn, quay u, quay ngi, tt c cc hot ng iu to ra nhiu c ln tn hiu in no.

5.Thut ton phn tch thnh phn c lp ICA trong phn tch tn hiu in no (EEG).5.1.Gii thiu thut tonPhn tch thnh phn c lp ICA (Independent Component Analysis) l mt k thut tnh ton v thng k pht hin nhng tha s tm n tn ti di nhng tp hp bin, php o hay tn hiu ngu nhin. ICA ch r tnh cht mt m hnh tng qut cho d liu a bin quan st c, m dng a ra in hnh l mt b c s d liu mu rng ln. Trong mt m hnh, nhng bin d liu c cho rng l nhng hn hp tuyn tnh hay phi tuyn tnh ca mt vi bin tm n cha bit, v phng thc trn cng cha bit. Nhng bin tm n c cho rng phi gauss v c lp vi nhau, v chng c gi l nhng thnh phn c lp ca d liu quan st c. Nhng thnh phn c lp ny cng c gi l nhng ngun hay nhng tha s c th c tm thy bng ICA.ICA c th c xem l s m rng ca phn tch thnh phn chnh v phn tch tha s. ICA l mt k thut mnh hn rt nhiu v kh nng tm kim nhng tha s hay ngun tm n m nhng phng php c in tht bi hon ton. Mt trong nhng ng dng thc t v c th ca ICA l ng dng ICA trong phn tch tn hiu no b. Tn hiu no b c o bng mt in no EEG (Electroencephalogram) vi cc tn s khc nhau. in cc c t v tr thch hp trn da u ghi cc xung ng xut pht t no. Tn hiu thu c t cc in cc l tng hp t nhiu tn hiu no ring bit v bao gm c nhiu. C hai loi nhiu chnh: nhiu do bnh nhn gy ra vi cc qu trnh sinh l ca c th, nhiu do yu t bn ngoi nh dng c, dng in, Mt s loi nhiu thng gp nh: nhy mt lin tc, mt vn ng sang bn, vn ng ca li, nhiu do co c, nhiu do mch, khch mi, nhiu m hi, do in cc tip xc km, nhiu kim loi, nhiu do chm in cc kim loi, nhiu do dng tnh in. Bi ton t ra l phi tm ra cc tn hiu no b ring bit ban u t cc tn hiu thu c cc in cc. Phn tch thnh phn c lp gii c bi ton trn bng cch loi tr cc tn hiu nhiu v tch ra cc tn hiu no cn tm.Mt trong nhng cng c mnh m c s dng thc hin cho nhim v trn l phn mm EEGlab, EEGlab l mt hp cng c v c giao din hnh nh, chy trn mi trng MATLAB cho nhng thu thp x l th nghim ring v/hay d liu EEG chun ca bt k s knh truyn. Nhng chc nng c th dng c bao gm d liu EEG, nhp knh truyn v thng tin s kin, s hnh dung d liu, x l (bao gm loi tr nhiu, lc, chn min, v chun ha), phn tch thnh phn c lp (ICA) v nhng phn tch thi gian/tn s bao gm knh truyn v thnh phn tp giao vi nhau h tr bi nhng phng php thng k bc cao t vic ly mu d liu.5.1. ng lc s thc y pht trin ca ICA

Hnh 5.1 :Bi ton cocktail party

Hy tng tng rng bn trong mt cn phng c ba ngi ang ni cng mt lc. Cn phng ny c ba microphone c t ba v tr khc nhau. Cc microphone cho ra ba tn hiu theo thi gian c thu li x1(t), x2(t) v x3(t). Mi tn hiu thu c ny l tng ca cc tn hiu ting ni t ba ngi ang ni, k hiu s1(t), s2(t) v s3(t), v c biu din di dng:

Trong , aij = 1,2,3 l cc thng s ph thuc vo cc khong cch t microphone n ngi ni. Bi ton c t ra l chng ta phi xp x cc tn hiu ting ni ban u si(t) m ch s dng cc tn hiu c thu li xi(t). y chnh l bi ton ba tic (cocktail party problem). n gin m hnh bi ton, ta s b qua cc tr v thi gian cng nh cc yu t khc (nhiu, ).Tht ra, nu bit c cc thng s trn ln aij, ta c th gii cc phng trnh tuyn tnh (5.1), (5.2) v (5.3) trn. Tuy nhin, cn phi nhn mnh rng chng ta hon ton khng bit aij cng nh l si(t), do bi ton s phc tp hn.Mt cch tip cn gii bi ton ny l s dng cc tnh cht thng k ca cc tn hiu si(t) xp x c aij ln si(t). Tht ra, ta hon ton c th gi s rng s1(t), s2(t) v s3(t) l c lp thng k mi thi im t.ICA ban u c pht trin gii quyt cc bi ton tng t nh bi ton ba tic, tch ring cc tn hiu t on hnh qun (xe, ngi, chuyn ng ) trong qun s. Do s quan tm n l thuyt ICA ngy cng tng, ICA ngy cng c nhng ng dng trong nhiu lnh vc khc nhau.V d, cc tn hiu in no c cho bi mt in tm EEG (Electroencephalogram EEG). D liu EEG bao gm bn ghi cc tn hiu in th nhiu vng khc nhau trn da u. C tn hiu in ny l trn ln ca cc tn hiu thnh phn ca no b v hot ng ca cc c. Trng hp ny cng tng t nh bi ton ba tic: chng ta mun tm cc thnh phn ban u ca cc hot ng ca no b nhng chng ta ch quan st c cc trn ln ca cc thnh phn . ICA c th tm ra thng tin hu ch v hot ng no b bng cch truy xut vo cc thnh phn c lp ca n. 5.2.nh ngha ICA5.2.1.ICA di dng xp x ca m hnh sn sinh nh ngha ICA, chng ta c th s dng m hnh cc bin n (latent variables) thng k. Chng ta quan st c n bin ngu nhin x1, , x2, l t hp tuyn tnh ca n bin ngu nhin s1, , s2 di dng:

vi i = 1,,n (5.4)Trong aij (i, j = 1, , n) l cc h s thc. Theo nh ngha, cc si l c lp thng k vi nhau.y chnh l m hnh ICA c bn. M hnh ny mang tnh sinh sn (generative model), ngha l n m t cch thc m d liu quan st c to ra bi mt qu trnh trn ln cc thnh phn si. Cc thnh phn c lp si l cc bin n, ngha l chng khng c quan st mt cch trc tip. Cc h s trn ln cng c gi s l cha bit. Tt c nhng g ta c c l xi, v chng ta phi xp x c cc h s trn ln aij ln cc thnh phn c lp bng cch s dng xi. thun tin, ta k hiu ma trn A l ma trn c cc thnh phn aij, ma trn s c cc thnh phn si, v ma trn x c cc thnh phn xi. Do , m hnh trn ln c th c biu din di dng ma trn:x=A.s(5.5)hay

(5.6)Vy nh ngha ICA nh sau:

Cho s l cc ngun vo ban u, x l cc hn hp, A l ma trn trn ln vi cc h s aij (i = 1, , n; j = 1, , m). M hnh trn ln ca ICA c dng x = As hoc Cc thnh phn s c th c ti to li hon ton khi chng l c lp thng k v c phn b phi gauss.5.2.2.Tin x l cho ICATm gi tr trung tm C bn v cn thit nht cho qu trnh tin x l l tm trung tm x, tr i vect tr trung bnh ca n m = E{x} sao cho x l mt bin c tr trung bnh zero. Hm ny cho s c tr trung bnh zero. Lm n gin l thuyt v cc thut gii.Ta s dng php quy tm i vi cc bin trn ln xi, bng cch tr i tr trung bnh.xi = xi E{x}(5.7) Sau khi thc hin ICA, cc thnh phn c lp cng c tr trung bnh bng 0 vE{s} = A-1E{x}(5.8)Tr trung bnh b tr i c th c ti to bng cch cng A-1E{x} vo cc thnh phn c lp c tr trung bnh bng 0.Trng haVi cc bin ngu nhin cho trc, ta c th thc hin bin i tuyn tnh chng thnh cc bin phi tng quan. iu ny gi l trng ha (whitening).Phi tng quan l 1 tnh yu hn tnh c lp. 2 bin ngu nhin c gi l phi tng quan khi hip phng sai ca chng bng 0:Cov(y1,y2) = E{y1y2} E{y1}E{y2} = 0Nu cc bin ngu nhin c lp th chng phi tng quan, nhng ngc li cha ng.Mt tnh mnh hn phi tng quan l tnh trng ha (whitness).Tnh trng ha ca vector ngu nhin y c tr trung bnh =0 l cc thnh phn ca n l phi tng quan v phng sai ca chng bng n v:E{yyT} = I.Lm trng ha c ngha l chng ta bin i tuyn tnh vector d liu c quan st x bng cch nhn tuyn tnh n vi mt m trn V no :z = Vxsao cho vector z trng ha.S dng trng ha s bin i ma trn trn ln thnh mt ma trn mi A:z = V.A.s = AsLi ch ca trng ha l ma trn A l trc chun:E{zzT} = AE{ssT} AT = AAT = Iiu ny c ngha l ta c th hn ch cng vic tm kim ma trn trn ln trong khng gian cc ma trn trc chun. Thay v phi gii quyt n2 thng s, ta ch phi xp x ma trn A c n(n-1)/2 thng s. Do trng ha gip ta gii quyt phn na bi ton ICA.Do lm trng ha n gin hn nhiu nn ta cn phi gim s phc tp ca bi ton theo cch ny.c lng ICAC nhiu cch gii quyt bi ton ICA:+ Cc i ha tnh phi Gauss (nongaussianity)+ c lng kh nng cc i (maximum likelihood)+ Cc tiu ha thng tin h tng (mutual information)Trong cc phng php trn, trc tin nh ra mt hm i tng (objective function), cn gi l hm tr gi (cost function), ri dng mt thut ton cc i ha tr tuyt i hm i tng ny c lng cc thnh phn c lp.Theo nh l gii hn trung tm (central limit theorem), tng ca nhiu bin ngu nhin c phn b gn Gauss hn bt c bin ngu nhin gc no. m hnh ICA vector ngu nhin x l trn tuyn tnh ca cc thnh phn s c lp vi nhau, v vy cc thnh phn trn x s c phn b gn Gauss hn. Do c lng ICA nhm n cc i ha tnh phi Gauss bi v iu ny s cho ta cc thnh phn c lp.Ta c th o tnh phi Gauss bng Negentropy. Negentropy da vo l thuyt thng tin lng entropy5.3.Thut ton Fast ICAChng ta xt 1 vector d liu x c phn b theo m hnh d liu ICA, n l s pha trn ca cc thnh phn c lp. Gi s ta c lng c 1 thnh phn c lp c dang:y = wTx = wixitrong w l 1 hng ca ma trn nghch o ca A, vi A l ma trn trn (x = As).Nh vy, xp x c cc thnh phn c lp, ta phi xc nh w cc i tnh phi Gauss ca wTx.Xc nh wFastICA s dng thut ton sau xc nh cc i tnh phi Gauss ca wTx. Tnh phi Gauss y c o c theo xp x negentropy J(wTx). B1: Chn vector ngu nhin w.B2: Tnh ton tnh xp x negentropy vi J(wTx)w = E{zg(wTz)} - E{g(wTz)}wB3: Chun ha, chia vector w cho chun ha di ca n to ra vector n v w = ||wnew - wold||

5.5.M phng v thc hin thut ton Fast ICA.5.5.1.M phng vi EEGlab toolbox.EEGLAB l mt cng c ca Matlab x l tn hiu EEG ,MEG v cc tn hiu in sinh khc bng ICA,time/frequency analysis hoc articfact rejection.Download ti http://sccn.ucsd.edu/eeglab/.

Hnh 5.2 : GUI EEGLAB Toolbox.

Ta s chy th vi tn hiu eeg_data gm 32 knh tn hiu,30504 mu v vi tn s 128Hz.

Hnh 5.3 : D liu EEG data mu.Biu din tn hiu EEG 32 knh : Plot -> Channel data (Scroll)

Hnh 5.4 : Gin 32 knh tn hiu m phng trn EEGLABy l tn hiu tng thu c t cc tn hiu thnh phn,nhim v by gi l s dng thut ton ICA tm ra cc tn hiu thnh phn. y ta s thit lp s thnh phn c lp cng l 32, v s dng cng c Tool -> Runica ca Matlab.Khi ,Matlab s c lng vecto wchange < mt gi tr ngng xc nh th dng li

Hnh 5.5 :Matlab x l d liu bng thut ton Fast ICA.Sau cng,Matlab c th xut ra cho ta 32 d liu thnh phn Plot -> component activation (scroll)

Hnh 5.6 :Gin 32 tn hiu thnh phn5.5.2.Thc hin thut ton Fast ICA trn C.Sau khi chuyn tn hiu t nh dng *.edf sang nh dng *.txt ,ta thu c file Eyeblink2.edf_All_Sample.txt cha d liu ca 19 knh EEG.Trong ubuntu,g dng lnh ./buildmain khi ng chng trnh:

S mu tn hiu tng ng vi s hng;s knh tng ng vi s ct cn nhp,v s thnh phn c lp cn phn tch l s comp. y ,ta chn s mu l 1024,c 19 knh v cn phn tch thnh 19 thnh phn c lpChng trnh trn C s gm 2 chc nng chnh :+Bin i ICA thun :t mu tn hiu trn phn tch thnh cc tn hiu thnh phn.+ Bin i ICA ngc : t mu tn hiu trn phn tch thnh cch tn hiu thnh phn,sau loi b 1 thnh phn c lp ( y minh ha cho nhiu mt ) v khi phc li tn hiu ban u sau khi loi b tn hiu nhiu .

ICA TranformVi vic chn bin i ICA thun,ta s in ng dn ca mu tn hiu trn vo

Sau tn hiu trn a vo s c phn tch thnh cch thnh phn c lp da trn s lng thnh phn m mnh yu cu ( y l 19 thnh phn ) v xut d liu cc thnh phn ny dng ma trn ra file *.txt.

Ta c th chn 1 thnh phn bt k xut ring d liu ra file *.txt v kim tra dng tn hiu ca n bng th. y chn thnh phn mang th t s 7.

a vo Excel kim tra dng tn hiu

ICA Transform InverseVi vic chn bin i ICA ngc,cng s in ng dn file d liu EEG cn loi b nhiu v khi phc li

Chng trnh s t ng bin i ICA tn hiu trn nh trong ICA TransformTip theo chn thnh phn tn hiu c lp cn loi b ( Remove Component) . y minh ha thnh phn th 18.

V cui cng ta s chn knh tn hiu cn khi phc li sau khi loi b 1 tn hiu thnh phn ( coi l tn hiu nhiu ).V d l channel 1.