Denoising ECG signal (Khử nhiễu tín hiệu điện tim)

I HC QUC GIA TP.H CH MINH TRNG I HC KHOA HC T NHIN

KHOA VT L-VT L K THUT CHUYN NGNH VT L TIN HC

--------------------------------

BO CO CHUYN

ti:

LC NHIU TRONG TN HIU IN TIM

GVHD: Th.S Ha Th Hong Yn

SVTH: Nguyn Quc Khnh

Nguyn Anh Hun

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TP H CH MINH 2015

LI CM N

LI CM N

hon thnh ti Lc nhiu trong tn hiu in tim chng em

nhn c s hng dn v gip nhit tnh ca nhiu tp th v c nhn.

Vi t cch l sinh vin, chng em xin chn thnh cm n c Ha Th Hong Yn nhit tnh truyn t, chia s ti liu v hng dn tn tnh khng ch nhng li khuyn qu bu xoay quanh vn thc hin ti m cn phng php hc tp nghin cu v cho chng em nhng bi ging hay, hp dn, lm ngun kin thc vng vng l nn tng chng em hc tp, lm vic v thc hin tt ti ny.

Xin gi li cm n ti cc thy c trong b mn v bn b trong lp gip nhm em hon thnh ti ny

Tp.H Ch Mnh, ngy 18/01/2015

Nhm sinh vin

Nguyn Quc Khnh Nguyn Anh Hun

MC LC

MC LC

CHNG 1: NHIU V NGUYN NHN GY NHIU ......................... 1

1.1. Khi qut v tn hiu in tim ............................................................... 1

1.2. Cc nguyn nhn gy nhiu. .................................................................. 1

1.2.1. Can nhiu nh hng n cht lng ghi tn hiu in tim. .......... 1

1.2.2. Nhiu tn s 50Hz hoc 60Hz t mng cung cp in. .................. 2

1.2.3. Nhiu do run c .............................................................................. 2

1.2.4. Nhiu do tip xc km gia in cc v bnh nhn ....................... 2

CHNG 2: PHNG PHP THCH NGHI DA TRN THUT TON LMS 3

2.1. t vn .............................................................................................. 3

2.2. Phng php thch nghi lc nhiu in p cho cc tn hiu y sinh ....... 4

2.2.1. Cu trc ca mch lc thch nghi ................................................... 4

CHNG 3: PHNG PHP THCH NGHI DA TRN THUT TON LMS VI KCH THC BC THCH NGHI THAY I .......................... 8

3.1. Mc ch ................................................................................................ 8

3.2. Thut ton LMS vi kch thc bc thay i ..................................... 8

CHNG 4: NG DNG CA PHNG PHP ................................... 12

4.1. Mc ch .............................................................................................. 12

4.2. Thit k ................................................................................................ 12

4.3. M phng Matlab ................................................................................ 12

4.3.1. To ra tn hiu ECG 50Hz ............................................................ 12

4.3.2. Tn hiu nhiu 50Hz t ngun in v nhiu b bin i trong qu trnh lan truyn trong cc tn s ln cn .................................................... 13

4.3.3. Hm kh nhiu vi kch thc bc c nh ............................... 14

4.3.4. Hm kh nhiu vi kch thc bc thay i .............................. 14

4.3.5. p dng hai phng php LMS ................................................... 15

KT LUN ....................................................................................................... 18

TI LIU THAM KHO................................................................................. 20

MC LC HNH NH

MC LC HNH NH Hnh 2.1. Gin khi ca mch lc. ............................................................ 3

Hnh 2.2. Cu trc mch lc FIR thch nghi ................................................... 4

Hnh 2.3. Mch lc FIR thch nghi dng thut ton LMS .............................. 5

Hnh 3.1. S hi t ca thut ton s dng (3.1) cho iu chnh (n), vi iu kin ta (w1(0),w2(0)) c chn ph hp. ........................................... 9

Hnh 3.2. S hi t ca thut ton s dng (3.1) cho iu chnh (n), vi iu kin ta (w1(0),w2(0)) c chn khng ph hp. .............................. 10

Hnh 3.3. Gradient ca trn mt phng (w1, w2) ...................................... 11

Hnh 4.1. Tn hiu ECG sch ........................................................................ 13

Hnh 4.2. Tn hiu nhiu ............................................................................... 13

Hnh 4.3. Tn hiu trn t ECG 50Hz v nhiu ............................................ 14

Hnh 4.4. Tn hiu lc vi kch thc bc c nh mu = 0.05 ................... 16

Hnh 4.5. Tn hiu lc vi kch thc bc c nh mu=0.5 ....................... 16

Hnh 4.6. Tn hiu lc vi kch thc bc thay i ................................... 16

Hnh 4.7. So snh tn hiu lc vi mu=0.05, mu=0.5 v mu thay i .......... 17

LI M U

LI M U

X l thch nghi l mt lnh vc c ngha hc thut gn lin vi nhng ng dng thc t sinh ng trong x l tn hiu. Ban u ng dng ca x l tn hiu thch nghi gii hn trong cc m hnh nhn dng, sa sng, lc nhiu, v s dng cc thut ton Newton, Steepest Descent, LMS, RLS, S thay i ca tp d liu u vo v cc iu kin rng buc ngy cng phc tp ko theo i hi ci thin thut ton c c hiu nng x l cao hn. Ngoi ra vic gii quyt vn nng cao hiu nng thut ton cn i hi vic xy dng cc iu kin m bo thut ton c th s dng c.

i vi ti ny, nhm sinh vin xin trnh by v phng php thch nghi trong lc nhiu v mt vi ng dng phng php.

CHNG 1: NHIU V NGUYN NHN GY NHIU

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1.1. Khi qut v tn hiu in tim

Tim l mt t chc c rng, ti s co bp mt cch th t cc c s to ra p lc y mu i qua cc b phn trn c th. Mi nhp tim c kch thch bi xung in t cc t bo nt xoang ti tm nh. Cc xung in truyn n cc b phn khc ca tim v lm tim co bp.

Vic ghi tn hiu in tm l vic ghi li cc tn hiu in ny. Tn hiu in tm m t hot ng in ca tim, v c th c phn tch thnh cc thnh phn c tnh c tn l song: P, Q, R, S,T. Mi thnh phn ny c c trng ring, p ng ring, du hiu ca nhp tim ring nhng c chung ngun gc l cc hin tng in sinh vt.

Tng hp tt c cc thnh phn sut in ng t mi t bo trong tim to ra mt tn hiu phn nh hot ng ca c tim, ngi ta gi l tn hiu in tim.

Tn hiu in tim c ln thay i theo thi gian v khc nhau ti cc im trn c th ngi. Bng cch o mt s im trn c th ngi. Bng cch o mt s im trn c th ngi v theo di hnh dng song thay i theo thi gian, ngi ta c th gip nhn bit c mt s tnh trng bnh l hoc chn thng.

1.2. Cc nguyn nhn gy nhiu.

1.2.1. Can nhiu nh hng n cht lng ghi tn hiu in tim.

Nh ni trn, sng in tim c bin nh , cho nn rt d b nh hng bi nhiu. Cc can nhiu chnh nh hng n cht lng ghi tn hiu in tim l:

Nhiu t mng cung cp in c tn s thay i ngu nhin.

Nhiu sng c do bnh nhn mt bnh tnh khi o gy ra.

Nhiu do tip xc khng tt gia in cc v bnh nhn gy ra.

Nhiu do tn s thp gy tri ng nn.

Nhiu do tn ti 2 ngun to tn hiu in tim trong cng mt c th nh ghp tim hoc do mang thai.

Tuy nhin qua kho st cc loi nhiu nh hng n cht lng ghi tn hiu in tim, lc nhiu t mng cung cp in l cp bch nht v tnh cht ph bin v kh kim sot ca loi nhiu ny. Cc loi can nhiu cn li do c di tn n nh nn c th gii quyt trit bng cc b lc c nh.


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1.2.2. Nhiu tn s 50Hz hoc 60Hz t mng cung cp in.

Nh ni trn, thng tin hu ch nm trong di tn thp, 0.05 100Hz, trong khi mng cung cp in c tn s 50Hz hoc 60Hz c mt khp ni trong bnh vin, phng khm, do li in c th tc ng ln thit b ghi sng in tim.

Nu tin hnh o in tim nhng ni c t trng mnh ca mng cung cp in th nhiu 50Hz hoc 60Hz s gy nh hng.

1.2.3. Nhiu do run c

Khi bnh nhn cng thng, lo s hoc mt bnh tnh s gy run c, to nhiu sng c. Di tn ca loi nhiu ny lun nm trong di 20-30Hz nn c th c lc bng b chn di c nh.

1.2.4. Nhiu do tip xc km gia in cc v bnh nhn

Nguyn nhn to ra can nhiu loi ny l do tip xc km gia in cc v da. Qu trnh c m t nh sau: B ngoi da rt g g. Lp biu b c c nhng t bo gi, cht, bi Ngoi ra cn c nhng si lng mc t di da. M hi lun c bi tit ra ngoi qua l chn lng. Thnh phn ca m hi cng rt phc tp vi nhng ion chnh l K+, NA+, Cl-. Da vo cng thc c th d dng thy rng lp tip xc ny to ra in th tip xc. Ngoi ra dn in ca cc t chc di da cng gy ra hin tng qu th khi c dng in chy qua.

Lp tip xc ny cng c phn cc v xut hin 2 lp in tch tri du 2 bn tip xc. Khi in cc chuyn ng tng i vi da dn n cc in tch b xo trn c lp tip xc in cc dung dch v c bit l c lp tip xc dung dch da. T in tch s c s phn b li v qu trnh ny ch dng li khi c cn bng. Thm vo phi tnh n s thay i in th nu nh ang c dng in chy qua. in th chnh lch khi c s chuyn dch c hc tng i gia da v in cc gi l artifact. Cc in cc c lm bng vt liu c in th bn pin cng cao th in th artifact cng mnh v in th ny thng rt ln so vi tn hiu in tim.

CHNG 2: PHNG PHP THCH NGHI DA TRN THUT TON LMS

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2.1. t vn

Trong cc b lc s quy c (FIR v IIR), mi thng s ca qu trnh dng xc nh cc c trng ca h thng coi nh bit. Cc thng s ny lun thay i, gy ra s bt n v tn hiu. V th ngi ta a ra b lc FIR c cu trc mi, m trong , cc h s ca b lc c th thay i c c th thch ng vi s thay i bt ng ca cc yu t li vo. Mch lc FIR c cc h s thay i nh vy c gi l mch lc FIR thch nghi. Gin khi ca mch lc nh vy c trnh by trong hnh sau:

Hnh 2.1. Gin khi ca mch lc.

Trong s ny, tn hiu li vo l mt dy thi gian ri rc x[n], mch lc c c trng bi p ng xung h[n], cn tn hiu li ra thi im n l mt dy y[n].

Li ra ny c s dng xc nh mt p ng mong mun d[n]. Cc h s ca mch lc phi c chn la sao cho dy tn hiu mong mun c dng ph hp nht vi tn hiu li vo. iu ny c th c thc hin nu dy tn hiu sai s e[n] hi t v khng nhanh nht. lm c iu ny, ta phi ti u ha mt hm sai s c xc nh theo phng php thng k hoc phng php quyt nh. i vi phng php thng k, th hm sai s c s dng l gi tr ton phng trung bnh ca tn hiu sai s e[n]. Nu tn hiu vo v tn hiu mong mun l nhng tn hiu dng, th vic cc tiu ha sai s ton phng trung bnh a n mt mch lc rt ni ting l mch lc Wiener, c gi l ti u theo ngha ton phng trung bnh. Hu ht cc thut ton thch nghi l p dng cho cc loi mch lc Wiener. Trong phng php quyt nh, cch chn hm sai s l mt tng trng s ca tn hiu sai s ton phng. Vic cc tiu ha hm ny dn n mt mch lc ti u i vi dy d liu cho.

h[n]=h0,h1, +

Tn hiu vo x[n]

y[n] Tn hiu sai s e[n]

Tn hiu mong mun d(n)


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Nh vy, mch lc c thit k hoc bng cc cng thc thng k hoc bng cc cng thc xc nh. Trong cc thit k xc nh, cn phi tnh ton mt s i lng trung bnh khi s dng dy d liu cho m mch lc cn x l. Ni cch khc, thit k c mch lc Wiener cn phi bit trc cc tnh cht thng k ca cc tn hiu c s. Trong trng hp ny, cc tn hiu c s thng c cho l tn hiu dng v trung bnh theo thi gian bng trung bnh thng k.

Mc d php o trc tip cc gi tr trung bnh ca tn hiu c th c thc hin thu c nhng thng tin cn thit cho vic thit k mch lc Wiener hoc cc mch lc ti u, nhng trong nhiu ng dng thc t, cc gi tr trung bnh ca tn hiu li c s dng theo cch gin tip, trong sai s li ra ca mch lc tng quan vi cc mu ca tn hiu vo ca mch lc theo mt s cch v s dng kt qu ca phng trnh quy iu chnh cc h s ca mch lc theo kiu lp.

S dng phng php lp c th a n cc li gii thch nghi c kh nng t hiu chnh. C ngha l nu cc tnh cht thng k ca tn hiu thay i i vi thi gian, th nh nghim lp, cc h s ca mch lc c th t iu chnh thch nghi vi cc tnh cht thng k mi. Nghim lp, ni chung rt c a chung v n d m ha trong phn mm v d thc thi trong phn cng hn cc nghim khng lp.

2.2. Phng php thch nghi lc nhiu in p cho cc tn hiu y sinh

2.2.1. Cu trc ca mch lc thch nghi

Cu trc thng c s dng trong mch lc thch nghi c m t nh hnh:

Hnh 2.2. Cu trc mch lc FIR thch nghi

Trong :

x[n]: Vector tn hiu u vo ca mch lc.


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x[n] = [x(n) x(n-1) x(n-2) x(n-N+1)]T

w: L vector trng s ca b lc thch nghi

w = [w(0) w(1) w(N-1)]T

y[n]: L li ra ca mch lc

y[n] = [][ ]1=0 [] (2.1)

d[n]: Li ra mong mun

e[n]: L sai s gia tn hiu mong mun d[n] v tn hiu u ra y[n]

e[n] = d[n] y[n] (2.2)

Bi ton thch nghi s t iu chnh ma trn cc trng s w sao cho sai s e[n] l nh nht.

2.2.2. Thut ton ton phng trung bnh ti thiu LMS

Thut ton ton phng trung bnh ti thiu LMS (Least Mean Square) l thut ton c p dng rng ri trong x l s tn hiu thch nghi. N thuc h cc thut ton gradient thng k ln u tin c Windrow-Hoff p dng nm 1960 v sau pht trin thnh nhiu thut ton mi nh tnh cht n gin v bn vng ca thut ton ny. N l thut ton lc thch nghi tuyn tnh bao gm hai qu trnh: qu trnh lc v qu trnh thch nghi. Trong qu trnh lc, thut ton ny s dng mch lc ngang tuyn tnh c li vo x(n) v li ra y(n). Qu trnh thch nghi c thc hin nh s iu khin t ng cc tp trng s ca cc h s ca mch lc sao cho n tng ng vi tn hiu sai s l hiu ca tn hiu li ra v tn hiu mong mun d(n). S thut ton nh trong hnh.

Hnh 2.3. Mch lc FIR thch nghi dng thut ton LMS

Gi s mch lc ngang c N-tap trng s v l dy s thc, khi tn hiu li ra c vit:


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y[n] = [][ ]1=0 (2.3)

Trong tap trng s w0[n]... , wN-1[n] c chn la nh th no sai s

e[n] = d[n] y[n] (2.4)

c gi tr cc tiu. Ni chung trong mch lc thch nghi, tp trong s l hm ca ch s thi gian n, v chng c thch nghi lin tc vi s thay i thng k ca tn hiu. Thut ton LMS iu chnh tap trng s ca mch lc sao cho sai s e[n] c cc tiu ha theo ngha ton phng trung bnh, v th mi c tn l thut ton ton phng trung bnh ti thiu. Khi cc qu trnh x[n] v d[n] l cc qu trnh ngu nhin dng, th thut ton ny hi t n nghim ca phng trnh Wiener-Hopf. Ni cch khc, thut ton LMS l mt s thc t thc hin cc mch lc Wiener-Hopf, nhng khng gii mt cch tng minh phng trnh Wiener-Hopf. N l mt thut ton tun t c s dng thch nghi tap trng s ca mch lc nh s quan st lin tc tn hiu li vo x[n] v tn hiu li ra mong mun d[n].

Nh vy, thut ton LMS chnh l s thc thi thng k ca thut ton gim bc nhanh nht, trong hm ph tn J=E[e2[n]] c thay bng gi tr xc nh tc thi j[n] = e2[n]. Khi phng trnh truy hi tnh tp trng s ca mch lc c xc nh bng phng trnh:

w[n+1] = w[n] - e2[n] (2.5)

trong w[n] = [w0[n], w1[n],,WN-1[n]]T, l thng s bc ca thut ton cn l ton t vi phn c xc nh bng vector ct nh sau:

=

[

[0]

[1]

[1]]

(2.6)

Nh vy thnh phn th k ca vector e2[n] l:

e2[n] = 2e[n]

[]

(2.7)

Thay e[n] = d[n]-y[n] vo phng trnh trn v do d[n] c lp vi wi, ta c:

e2[n] = -2e[n]

[]

(2.8)

By gi, thay y[n] t (2.3) vo (2.8) ta c:


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e2[n] = -2e[n]x[n-i] (2.9)

Hoc di dng tng qut l:

e2[n] = -2e[n]x[n] (2.10)

Trong : x[n] = [x[n], x[n-1] x[n-N+1]]T

Thay kt qu t (2.10) vo (2.5)

w[n+1] = w[n] + 2 e[n]x[n] (2.11)

y l phng trnh truy hi xc nh tap trng s ca mch lc i vi cc dy li vo v dy sai s. N c gi l thut ton LMS quy, thch nghi mt cch quy cc h s ca mch lc c sau mi mu mi ca tn hiu li vo x[n] v mu tn hiu mong mun d[n]. Cc phng trnh (2.3), (2.4) v (3.1) theo th t l ba bc hon chnh mi mt php lp ca thut ton LMS. Phng trnh (2.3) l qu trnh lc, n c thnh thu c tn hiu li ra ca mch lc. Phng trnh (2.4) c s dng tnh sai s. Cn phng trnh (3.1) dng thch nghi mt cch quy tap trng s ca mch lc sao cho sai s xc nh t gi tr cc tiu. Trong phng trnh ny, l thng s bc, n iu khin tc hi t ca thut ton ti nghim ti u.

Nu chn ln th tc hi t nhanh; nu chn gi tr b th tc hi t s chm hn. Tuy nhin nu qu ln th thut ton s khng n nh v do vy m bo tnh cht n nh ca thut ton LMS, phi c chn sao cho:

0 < < 2

2 (2.12)

Vi : C: Bin nhiu ca u vo tham chiu.

CHNG 3: PHNG PHP THCH NGHI DA TRN THUT TON LMS VI KCH THC BC THAY I

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CHNG 3: PHNG PHP THCH NGHI DA TRN THUT TON LMS VI KCH THC BC THCH NGHI THAY I

3.1. Mc ch

Thut ton lc c thc hin thng qua cc hm, do vy c th d dng thay i gi tr ca kch thc bc cho ph hp vi yu cu ca ngi s dng v tc hi t, n nh. Hin nay chng ti gi chn gi tr kch thc bc = 0.05 trong trng hp mi trng nhiu thay i chm v yu cu cao v cht lng tn hiu sau lc cng nh n nh. Khi mi trng nhiu lun thay i kch thc bc = 0.5 t ra ph hp nht, thut ton c kh nng hi t rt nhanh. Nhng n nh v cht lng tn hiu sau lc khng tt bng trng hp = 0.05. Trng hp kch thc bc thay i dnh cho nhiu pht sinh t ngun in ca my pht vi tn s ca nhiu c di thay i rng v tc thay i ln. Vi u im thut ton n gin, phn mm nhng lc nhiu cho tn hiu y sinh c th c s dng cho c mc ch o to.

3.2. Thut ton LMS vi kch thc bc thay i

tng tc hi t ca thut ton LMS, Daniel Olgun Olgun xut vic thay i kch thc bc thch nghi theo cng thc:

(n+1) = (n) + 2(n), (3.1) Vi:

: Yu t qun, c gi tr nm trong di: 0


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BW =2C2, Vi:

BW: rng khe trit (BandWidth). : Kch thc bc thch nghi. C: Bin ca tn hiu tham chiu.

Do vy, khi thut ton hi t c th nhn gi tr nh rng khe trit hp. Trong tn hiu in tm , nh R ti mi chu k hot ng c c

tnh bin i t ngt . Do vy php tnh 2(n) trong (3.1) c th dn n vic khng tha mn iu kin n nh ca thut ton v lm mt cc thng tin hu ch khi rng khe trit qu ln. Hn na khi gn gi tr ln khi khi to v s dng cng thc (3.1) lm gim dn n gi tr tt nht. iu ny c th lm cho thut ton khng hi t hoc hi t chm nu ngu nhin ta chn im khi to ca ma trn trng s gn cc tiu.

Theo cc ti liu th chng ta cng c bit, nhiu cng b bin i trong qu trnh lan truyn t ngun nhiu n u thu tham chiu . S sai lch ny c m hnh ha bng mt i lng ngu nhin c phn phi Gaussian. V c m t trong cng thc sau: N(n) = x1(n) + normrnd(mean, sigma). lch chun sigma phn nh khong cch t im cc tiu n thi im khi to ca ma trn trng s . Mi quan h gia lch chun vi s vng lp c m t trong hnh

Hnh 3.1. S hi t ca thut ton s dng (3.1) cho iu chnh (n), vi iu kin ta (w1(0),w2(0)) c chn ph hp.


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Hnh 3.2. S hi t ca thut ton s dng (3.1) cho iu chnh (n), vi iu kin ta (w1(0),w2(0)) c chn khng ph hp.

Qua d dng thy rng nu khng tha mn gi thit ngt ngho v chn gi tr trng s khi to, thut ton s hi t chm. xut c a ra da trn s khai thc thng tin v s thay i ln ca vector gradient trong thut ton LMS.

i vi hm bc II xc nh dng Gradient c gi tr ln khi xa im cc tiu v c gi tr nh khi gn im cc tiu (Hnh Gradient trn mt phng (W1 W2)). tng c th m t trn mt phng ny. Ti thi im k , kch thc bc thch nghi nn nhn gi tr ln khi ta (w1(n), w2(n)) cch xa ta (w1*, w2*) ca im cc tiu ca b mt hiu nng bc II. Ngc li, kch thc bc thch nghi nn nhn gi tr nh khi ta (w1(n), w2(n)) gn ta ca im cc tiu. S la chn kch thc bc thch nghi nh vy s gip thut ton lc tha mn cc iu kin v tc hi t v n nh ca thut ton. Nhn ra rng phn b ln ca Gradient () trn mt phng (w1, w2) c tnh cht gn nh p ng c tng trn v cng thc cp nht bc thch nghi c ngh nh sau:

(n+1) = |1()()| +

({1()||=1,,})2

vi: N: l s mu trong mt chu k ca tn hiu tham chiu.

: rng l tng cho di trit .

({1( )|| = 1, , })2: tr li gi tr C2 ti thi im n.

(n): Kch thc bc cho vic iu chnh trng s ti thi im n.

|1()()| = = 1

2|()| phn nh vic phn b ln ca Gradient

() trn mt phng (w1, w2),

x1(n): Nhiu thu c u vo tham chiu ti thi im n,


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(n): u ra ca b lc nhiu ti thi im n.

Hnh 3.3. Gradient ca trn mt phng (w1, w2)

iu kin hi t ca b lc trit tn s dng cng thc (n+1) c xc

nh v chng minh trong [1] khi < 12.

u im ca thut ton LMS vi kch thc bc thay i

Trong bi ton lc nhiu ra khi tn hiu in tim, ngun gy nhiu l ng ti in, nhiu c c im l ch tn ti trn 1 tn s, do vy gii php ph hp l s dng b lc trit tn c tn s trit trng vi tn s ca nhiu. Tuy nhin, khi tn s ca nhiu thay i ngu nhin xung quanh tn s ca cc tn hiu cn bo tn th bi ton lc nhiu c th coi nh bi ton iu chnh tn s trit ca b lc trit tn vi di trit hp sao cho ch loi b nhiu 1 tn s m khng lm suy gim n cc tn hiu c tn s ln cn. B lc trit tn thch nghi c xem l mt trong s gii php tt nht cho vn ny. c bit, vic s dng thut ton LMS vi kch thc bc thay i p ng c 2 yu cu trn, ng thi ci thin ng k hiu nng ca b lc c v tc hi t ln n nh trong qu trnh tm kim ma trn trng s ti u W*.

CHNG 4: NG DNG CA PHNG PHP

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4.1. Mc ch

Thc hin phn thch cc k thut loi b nhiu khc nhau trong tn hiu in tm (ECG) , m c th l loi b cc tn s 50/60Hz (powerline interference) can thip vo tn hiu in tm bng cch p dng thut ton thch ng LMS loi b nhiu.

4.2. Thit k Trong x l tn hiu s th ch yu l tn hiu ri rc, cc tn hiu ny c

i din bi cc hm ton hc nh sin, cos hay l cc hm tuyn tn.

Trong ti ny chng em cp n hai tn hiu, tn hiu u vo l tn hiu ECG (50Hz) v tn hiu nhiu 50Hz t ngun in. Trong ti ny em dng hai thut ton so snh l thut ton LMS vi kch thc bc c nh v thut ton LMS vi kch thc bc thay i tm ra thut ton no ti u hn c.

Tn hiu in tm ECG (50Hz) c trn vi tn hiu nhiu 50Hz, c hai u c to gi lp bng cc thut ton trn Matlab. Sau dng hai thut ton LMS lc v tm ra kt qu ph hp vi thc t nht.

Nhng thng tin quan trng ca tn hiu in tm ECG nm trong di tn t 47-53 Hz v nhng tn hiu nhiu s lm nh hng n cht lng ca tn hiu ny.

Mc tiu quan trng nht chn b lc thch nghi l kh nng iu chnh.

H s ca b lc v cc yu t c ch nh l lm th no xc nh cc quy tc hay thut ton nng cp h s. Cc b lc thch nghi nh gi hiu sut t tn hiu v phi trin cc gii php v xc nh cc lc, h s cn c nng cp.

4.3. M phng Matlab

4.3.1. To ra tn hiu ECG 50Hz Fs=1000; Length=1000*10; %i=1:Length; ECG_signal=ecg(50); ECG=ECG_signal; for i=1:Length/50-1 ECG_signal= [ ECG_signal ECG]; clc end


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Hnh 4.1. Tn hiu ECG sch

4.3.2. Tn hiu nhiu 50Hz t ngun in v nhiu b bin i trong qu trnh lan truyn trong cc tn s ln cn

%Noise_sin frequency1=50; for i=1:length(ECG_signal); Noise_sin(i)=sin(2*pi*frequency1*i/Fs); end

%Noise_cos frequency2=50; for i=1:length(ECG_signal); Noise_cos(i)=cos(2*pi*frequency2*i/Fs); end

Hnh 4.2. Tn hiu nhiu


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Hnh 4.3. Tn hiu trn t ECG 50Hz v nhiu

4.3.3. Hm kh nhiu vi kch thc bc c nh function [denoised_ecg, dieukien] = LMS_fixed_stepsize(NOISY_ECG,

Noise_sin, Noise_cos, mu)

w1=0; w2=0;

l=length(NOISY_ECG);

y(1)=0.15; for k=2:l y(k)=(Noise_sin(k)*w1+Noise_cos(k)*w2); denoised_ecg(k)=NOISY_ECG(k)-y(k); w1=w1+2*mu*Noise_sin(k)*denoised_ecg(k); w2=w2+2*mu*Noise_cos(k)*denoised_ecg(k); dieukien(k)=((NOISY_ECG(k)*(Noise_sin(k)-y(k)))+(NOISY_ECG(k-

1)*(Noise_sin(k-1)-y(k-1))))/2; end;

4.3.4. Hm kh nhiu vi kch thc bc thay i function [denoised_ecg, mu_dem] = LMS_variable_stepsize(NOISY_ECG,

Noise_sin, Noise_cos, ecg)

w1=0; w2=0; mu=2.9; l=length(NOISY_ECG); mu_dem=zeros(1,l); %alpha=25.5; alpha=2; for k=1:l denoised_ecg(k)=NOISY_ECG(k)-(Noise_sin(k)*w1+Noise_cos(k)*w2); mu=alpha*abs(denoised_ecg(k)*Noise_sin(k)); w1=w1+mu*Noise_sin(k)*denoised_ecg(k); w2=w2+mu*Noise_cos(k)*denoised_ecg(k); mu_dem(k)=mu; end;


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4.3.5. p dng hai phng php LMS

clear all;

close all;

%Tao tin hieu ECG 50Hz

Fs=1000;

Length=1000*10;

ECG_signal=ecg(50);

ECG=ECG_signal;

for i=1:Length/50-1

ECG_signal= [ ECG_signal ECG];

clc

end

%Noise_sin

frequency1=50;

for i=1:length(ECG_signal);

Noise_sin(i)=sin(2*pi*frequency1*i/Fs);

end

%Noise_cos

frequency2=50;

for i=1:length(ECG_signal);

Noise_cos(i)=cos(2*pi*frequency2*i/Fs);

end

%Main

[ecg]=ECG_signal;

L=length(ecg);

sigma=0.15;

ms=2;

mu_002=0.05;

mu_05=0.5;

N=Noise_sin+normrnd(0,0.01,1,L);

NOISY_ECG=ecg+N;

%Khu nhieu voi kich thuoc buoc nhay mu=0.05

[denoised_ecg_FS_002,dieukien_002]=LMS_fixed_stepsize(NOISY_ECG,Noise_sin,No

ise_cos, mu_002);

for k=0:(L/4-1)

mse_mu_002(k+1)=((ecg(4*k+1)-denoised_ecg_FS_002(4*k+1))^2 + (ecg(4*k+2)-

denoised_ecg_FS_002(4*k+2))^2 +(ecg(4*k+3)- denoised_ecg_FS_002(4*k+3))^2

+(ecg(4*k+4)- denoised_ecg_FS_002(4*k+4))^2)/4;

end;

[denoised_ecg_FS_05,dieukien_05]=LMS_fixed_stepsize(NOISY_ECG,Noise_sin,Nois

e_cos,mu_05);

for k=0:(L/4-1)

mse_mu_05(k+1)=((ecg(4*k+1)-denoised_ecg_FS_05(4*k+1))^2 + (ecg(4*k+2)-

denoised_ecg_FS_05(4*k+2))^2 +(ecg(4*k+3)- denoised_ecg_FS_05(4*k+3))^2

+(ecg(4*k+4)- denoised_ecg_FS_05(4*k+4))^2)/4;

end;

[denoised_ecg_VS,mu_dem]=LMS_variable_stepsize(NOISY_ECG,Noise_sin,Noise_cos

,ecg);

for k=0:(L/4-1)

mse_mu_vs(k+1)=((ecg(4*k+1)-denoised_ecg_VS(4*k+1))^2 + (ecg(4*k+2)-

denoised_ecg_VS(4*k+2))^2 +(ecg(4*k+3)-denoised_ecg_VS(4*k+3))^2

+(ecg(4*k+4)-denoised_ecg_VS(4*k+4))^2)/4;

end;


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Hnh 4.4. Tn hiu lc vi kch thc bc c nh mu = 0.05

Hnh 4.5. Tn hiu lc vi kch thc bc c nh mu=0.5

Hnh 4.6. Tn hiu lc vi kch thc bc thay i


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Hnh 4.7. So snh tn hiu lc vi mu=0.05, mu=0.5 v mu thay i

Kt lun: Nh ta thy trn hnh 4.7, trong trng hp kch thc bc

c nh =0.05 sai s trung bnh bnh phng MSE phn nh tc hi t chm ca thut ton nhng c n nh tt. Trong trng hp kch

thc bc c nh =0.5 sai s trung bnh bnh phng MSE phn nh tc hi t cao nhng c n nh thp. Trong trng hp kch thc bc thay i, sai s trung bnh bnh phng MSE phn nh tc

hi t nhanh v 0 hn trng hp =0.05 nhng c n nh cn cao hn c trng hp =0.05.

KT LUN

18

KT LUN

Trong bo co ny nhm trnh by mt cch tng quan phng php thch nghi trong lc nhiu tn hiu in tim v ng dng ca phng php.

Bo co ny dnh cho cc vn v cc gii php v loi b nhiu t ngun in thng xuyn n khc t tn hiu. Kt qu t c ph hp mc tiu ra.

Ni chung cc b lc FIR c s dng v cc loi ca cc b lc c kin trc n gin v hp l l n nh, do , b lc FIR c la chn cho s pht trin ca h thng. Nghin cu c thc hin cho vic la chn cc b lc v thut ton, hai loi ca cc b lc thch nghi l FIR (Finite impulse response) v IIR (Infinite impulse response) v hai loi thut ton, LMS (Least Mean Square) v RLS (Recursive least squares). Cc thut ton LMS l thut ton thch ng lc c s dng rng ri nht trong cc thit b gim st y sinh hc, v vy n c quyt nh c s dng cho cc ti c c nhng gii php cn thit cho mc ch chnh. Cc ng dng ca thut ton LMS c th c thc hin do s n gin ca n.

Mt b lc thch nghi c s dng trong cc ng dng i hi phi c c im khc nhau trong b lc p ng cc iu kin tn hiu bin. Tc thch ng v chnh xc ca vic loi b nhiu sau khi thch ng l cc bin php quan trng ca hiu sut cho nhiu thut ton hy b. Mc tiu ca cc b lc thch nghi l ph hp vi h s b lc nhiu cc b lc thch nghi c th tr i nhiu t tn hiu ra.

Cc th nghim cho cc m phng ca tn hiu in tm c thc hin. Tn hiu b hng do s nhiu n ngun ca 50Hz. Quan st, thy rng tn s ca nhiu dng in l 50Hz m sau trn vi tn hiu ECG gc. Sau khi i qua cc thut ton LMS sn lng lc gn nh tng t nh tn hiu ECG sch vi mt s phm vi bin dng chp nhn c.

Gi tr ca kch thc bc ng mt vai tr quan trng trong vic xc nh tc hi t, n nh v li cn st li sau khi hi t. T l hi t c iu

khin bi LMS kch thc bc . Cc th tn hiu in tm c m t trong cc kt qu m phng xc minh thch ng ca thut ton thch nghi LMS bng

cch thay i cc thng s nh kch thc bc, gi tr hi t () v lc c tc dng khc nhau trn th u ra. Kt qu cho thy LMS l mt thut ton hiu qu s dng cho cc b lc thch nghi trong vic thc hin hy b nhiu.

Bng cch tng lc n cho thy mt tc hi t nhng lm cho nhiu kt qu chnh xc hn v bng cch gim gi tr kch thc bc n to ra s hi t chm hn nhng ci thin s n nh v chnh xc. Tn hiu hi phc gn ging vi tn hiu ECG sch. C th thy rng vic thc hin cc chc nng nh thut ton mt cch chn xc v hiu qu. Bng cch so snh th ca cc tn hiu u vo v tn hiu u ra, ta nhn thy rng cc chng trnh m phng thc hin tha ng v loi b nhiu t tn hiu ECG u vo v tn hiu ECG mong mun c ly li.

KT LUN

19

Hiu sut tng th ca thut ton LMS cho vic lc nhiu t ngun in c th t c.

Hn na, phng php lc t chi mc thng thng cng cho thy hot ng chnh xc trong khi cc b lc nhiu t tn hiu ECG ban u. K thut ny cho vic x l, thc hin v loi b cc tn hiu nhiu t tn hiu ECG u vo c thc hin tha ng. C th kt lun rng, nhiu tn s thp v nhiu tn s cao c th c loi b t tn hiu ECG gc bng cch thc thin phng php lc t chi mc thng thng.

Mc d n cn nhiu thiu st v mt kin thc, song qua n ny nhm tc gi cng cung cp mt s thng tin c bn v v lc nhiu v rt mong c phn hi tch cc t c v cc bn.

TI LIU THAM KHO

20

TI LIU THAM KHO

1. Lun n Cc phng php thch nghi trong lc nhiu tn hiu in tim ca TS. Hong Mnh H Vin Cng Ngh Thng Tin.

2. Electrocardiogram (ECG) Signal Processing ca Leif Srno (Lund University Sweden) v Pablo Laguna (Zaragoza University Spain).

3. Computer Aided ECG Analysis State of the Art and Upcoming Challenges ca Marko Velic, Ivan Padavic v Sinisa Car.

CHNG 1: NHIU V NGUYN NHN GY NHIU1.1. Khi qut v tn hiu in tim1.2. Cc nguyn nhn gy nhiu.CHNG 1:1.1.1.2.1.2.1. Can nhiu nh hng n cht lng ghi tn hiu in tim.CHNG 1:1.1.1.2.1.2.1.1.2.2. Nhiu tn s 50Hz hoc 60Hz t mng cung cp in.CHNG 1:1.1.1.2.1.2.1.1.2.2.1.2.3. Nhiu do run c1.2.4. Nhiu do tip xc km gia in cc v bnh nhn

CHNG 2: PHNG PHP THCH NGHI DA TRN THUT TON LMSCHNG 1:CHNG 2:2.1. t vn 1.2.

CHNG 1:CHNG 2:2.1.2.2. Phng php thch nghi lc nhiu in p cho cc tn hiu y sinh2.2.1. Cu trc ca mch lc thch nghiHnh 2.2. Cu trc mch lc FIR thch nghiHnh 2.3. Mch lc FIR thch nghi dng thut ton LMS

CHNG 3: PHNG PHP THCH NGHI DA TRN THUT TON LMS VI KCH THC BC THCH NGHI THAY ICHNG 3:3.1. Mc ch3.2. Thut ton LMS vi kch thc bc thay iHnh 3.1. S hi t ca thut ton s dng (3.1) cho iu chnh (n), vi iu kin ta (w1(0),w2(0)) c chn ph hp.Hnh 3.2. S hi t ca thut ton s dng (3.1) cho iu chnh (n), vi iu kin ta (w1(0),w2(0)) c chn khng ph hp.Hnh 3.3. Gradient ca trn mt phng (w1, w2)

CHNG 4: NG DNG CA PHNG PHPCHNG 3:CHNG 4:4.1. Mc ch4.2. Thit k4.3. M phng Matlab4.3.1. To ra tn hiu ECG 50HzHnh 4.1. Tn hiu ECG sch

CHNG 1:CHNG 2:CHNG 3:CHNG 4:4.1.4.2.4.3.4.3.1.4.3.2. Tn hiu nhiu 50Hz t ngun in v nhiu b bin i trong qu trnh lan truyn trong cc tn s ln cnHnh 4.2. Tn hiu nhiuHnh 4.3. Tn hiu trn t ECG 50Hz v nhiu

4.3.3. Hm kh nhiu vi kch thc bc c nh4.3.4. Hm kh nhiu vi kch thc bc thay i4.3.5. p dng hai phng php LMSHnh 4.4. Tn hiu lc vi kch thc bc c nh mu = 0.05Hnh 4.5. Tn hiu lc vi kch thc bc c nh mu=0.5Hnh 4.6. Tn hiu lc vi kch thc bc thay iHnh 4.7. So snh tn hiu lc vi mu=0.05, mu=0.5 v mu thay i

KT LUNTI LIU THAM KHO

Documents

Denoising ECG signal (Khử nhiễu tín hiệu điện tim)