12104008_ecg acquisition and filtration

8/18/2019 12104008_ecg Acquisition and Filtration

1/41

ECG ACQUISITIONAND FILTERATION

Sunil Kumar (12104008)PEC University of Technoloy! "n#ia

$ct 1%! 201&

1%'10'201& Sunil (PEC) 1


2/41

1%'10'201& Sunil (PEC) 2

Electrocardiography

Each livin cell acts as a small attery that #eolari*es an#reolari*es +hen there is a #isturance,

• Electrocar#iorahy (EC-) is the ac.uisition of electrical activity ofthe heart cature# over time y an e/ternal electro#e attache# to

the sin,• Each of the cell memranes that form the outer coverin of the

heart cell have an associate# chare +hich is #eolari*e# #urinevery heart eat,

• These aear as tiny electrical sinals on the sin +hich can e#etecte# an# amlie# y the EC-,


3/41

1%'10'201& Sunil (PEC)

ECG Basics

• The term 3lea# in conte/t to an EC- refers to the voltae#i5erence et+een t+o of the electro#es! an# it is this#i5erence +hich is recor#e# y the e.uiment,

• 6or e/amle 37ea#" is the voltae et+een the left arman# riht arm electro#es, 7ea#" an# 7ea#"" are referre# to

as 7im lea#s,• 91:9% are referre# to as chest lea#s, The EC- tracin 91 is

the #i5erence et+een the voltae at 9c1(the voltae at the

electro#e on the chest) an# the averae of 7ea#"! 7ea#""!an# 7ea#""",

• ; stan#ar# 12:7ea# EC- system consists of eiht actualvalues an# four #erive# values,


4/41

1%'10'201& Sunil (PEC) 4

Suerosition of all the action otentials ro#uces theEC- sinal


5/41

1%'10'201& Sunil (PEC) &

Tale ! ives a snashot of various lea# voltaes! actualan# #erive#,


6/41

1%'10'201& Sunil (PEC) %

T"#ES OF ARTIFACT IN ECG SIGNAL

"t ecomes #i=cult for the secialist to #ianose the #iseases if theartifacts are resent in the EC- sinal

>a?or sources of noise are1, Po+er line interference2, >uscle contractions, Electro#e contact noise4, >otion ;rtifacts

&, @aseline +an#erin%, Aoise enerate# y electronic #evices use# in sinal rocessin

circuitsB, Electrical interference e/ternal to the su?ect an# recor#in system8, ih:fre.uency noises in the EC-D, @reath! lun! or o+el soun#s contaminatin the heart soun#s

(PC-),


7/411%'10'201& Sunil (PEC) B

Electrical Sig$als

The rimary electrical comonents cature# are themyocar#ium! muscle! sin:electro#e interface! an# e/ternal

interference,


8/411%'10'201& Sunil (PEC) 8

Co%%o$ Fre&'e$cies O( The I%porta$tCo%po$e$ts O$ The ECG

•

eart rate 0,%B F & * (i,e, 40 F 00 m)•P:+ave 0,%B F & *•GHS 10 F &0 *• T:+ave 1 F B *•3ih fre.uency otentials 100:&00 *


9/411%'10'201& Sunil (PEC) D

Co%%o$ Fre&'e$cies O( The Arti(act A$d Noise O$ The ECG)

•>uscle & F &0 *•Hesiratory 0,12 F 0,& * (e,, 8 F 0 m)•E/ternal electrical &0 or %0 * (;'C 3mains or3line fre.uency)

•$ther electrical tyically I10 * (musclestimulators! stron manetic el#s! acemaers+ith ime#ance monitorin)


10/411%'10'201& Sunil (PEC) 10

Circ'it Desig$

;n EC-Js ?o is to amlify the small sinal

measure# from the heart as +ell as to lteroutsi#e an# internal noise,


11/411%'10'201& Sunil (PEC) 11

A%pli*er

1, EC- sinals vary from the microvolt to the

millivolt rane,2, The sinals measure# nee# to e amlie# in

or#er to e etter interrete#, ue to the small si*e of the sinal! the ain

shoul# e lare,

4, Tyically a ain of over 1000 is imlemente# iniootential amlier circuits,

&, The amliers shoul# have a hih commonmo#e re?ection ratio to eliminate lare o5setsinals,


12/411%'10'201& Sunil (PEC) 12

A%pli*er

Thus cominations of #i5erential amliers are use# toconstruct +hat is calle# an instrumentation amlier,

@asic "nstrumentation ;mlier


13/411%'10'201& Sunil (PEC) 1

A%pli*er

The rst stae is the inut stae of the amlier follo+e# ythe ain stae,

"nut an# ain staes of instrumentationamlier

• The inut stae i#eally sulies no common mo#e ain thuseliminatin common mo#e noise,

• The ain stae has lo+ ime#ance an# sulies a #i5erentialain,

• The amlier amlies only the #i5erential comonent +ith aain an# rovi#es a hih common mo#e re?ection ratio,


14/411%'10'201& Sunil (PEC) 14

Filteri$g

EC-s are su?ect to many #i5erent in#s of noise internally an#e/ternally,

EC- artifacts


15/411%'10'201& Sunil (PEC) 1&

Filteratio$ Usi$g A$alog De+icesUse# to mo#ulate %0 * noise from o+er lines ase# on +hatresistor! caacitor! an# in#uctor values are chosen,

Secon# or#er an# sto lter


16/411%'10'201& Sunil (PEC) 1%

Right Leg Dri+e

• To re#uce interference from the amlier,• The riht le #rive inverts an# amlies the averae common mo#e

sinal ac into the atientJs riht le,• This action cancels %0 * noise from ;C o+er an# creates a cleanerEC- outut sinal,

Hiht le #rive connection


17/411%'10'201& Sunil (PEC) 1B

ECG Circ'it


18/411%'10'201& Sunil (PEC) 18

• 6ilterin on an EC- is #one four fol# hih:ass! lo+:ass!notch! an# common mo#e lterin,

• ih:ass lters remove lo+ fre.uency sinals (i,e, onlyhiher fre.uencies may ass),

• 7o+:ass lters remove hih fre.uency sinals,• The hih:ass an# lo+:ass lters toether are no+n as

a an#ass lter! literally allo+in only a certainfre.uency an# to ass throuh,• The notch lter is use# to eliminate the line fre.uency

an# is usually rinte# on the EC- (e,, L%0 *),• Common mo#e re?ection is often #one via riht:le #rive!

+here an inverse sinal of the three lim electro#es aresent ac throuh the riht le electro#e,


19/41

1%'10'201& Sunil (PEC) 1D

Sig$al #rocessi$g Basics

• ; fre.uency of 1 * means a sinal reeats itselfevery one secon#,

• $ur hearts ro#uce electrical activity recor#e# yelectro#es as a sig$al,

• The sinoatrial no#e res at rouhly &0 to D0eats er minute! an# +e +ill say ,- eats per%i$'te is the hay me#ian,

• This means the heart has a fun#amentalfre.uency of ! /0 at this heart rate, Therefore!all of the EC- comonents (P! GHS! an# T) +illoccur at or aove this fre.uency,

•

EC- sinal reeats itself! each time the heartcycles throuh systole an# #iastole,• Me can rea it #o+n into in#ivi#ual +aves

or har%o$ics, This rocess of reain #o+n asinal into a series of sine waves is no+n

as Fo'rier A$alysis.


20/41

1%'10'201& Sunil (PEC) 20

Each of the harmonics (sine +aves) have acertain a%plit'de! (re&'e$cy! an# phase,


21/41

1%'10'201& Sunil (PEC) 21

1hat Electrical Sig$als Are Recorded By The ECG2

The recor#in is ma#e throuh electro#es on the sin! +hich caturemore than ?ust the electrical activity of the heart,

The rimary electrical comonents cature# are the myocar#ium!muscle! sin:electro#e interface! an# e/ternal interference


22/41

1%'10'201& Sunil (PEC) 22

• The sin:electro#e interface re.uires secial note!as it is the larest source of interference!ro#ucin a C comonent of 200:00 m9,

• Comare this to the electrical activity of yourheart! +hich is in the rane of 0,1 to 2 m9N Theinterference seen from this comonent is

manie# y motion! either atient movement! orresiratory variation,


23/41

1%'10'201& Sunil (PEC) 2

FILTERING TEC/NIQUES FOR ECG SIGNAL #ROCESSING

• The EC- sinal is very sensitive in nature• The sinal voltae level is as lo+ as 0,& to &m9 an# is

suscetile to artifacts that are larer than it,• The fre.uency comonents of a humanOs EC- sinal fall into

the rane of 0,0& to 100*• lterin remains an imortant issue


24/41

1%'10'201& Sunil (PEC) 24

6ilterin on an EC- is #one four fol# hih:ass! lo+:

ass! notch! an# common mo#e lterin,

• /igh3pass *lters remove lo+ fre.uency sinals (i,e,only hiher fre.uencies may ass),

• Lo43pass *lters on the EC- are use# to remove hih

fre.uency• The hih:ass an# lo+:ass lters toether are no+n

as a a$dpass *lter! literally allo+in only a certainfre.uency an# to ass throuh,

• The $otch *lter is use# to eliminate the line

fre.uency an# is usually rinte# on the EC- (e,, L%0*),

• Co%%o$ %ode re5ectio$ is often #one via riht:le#rive! +here an inverse sinal of the three limelectro#es are sent ac throuh the riht le

electro#e,

/i h *l


25/41

1%'10'201& Sunil (PEC) 2&

/igh3pass *lters

• /igh3pass *lters remove lo+ fre.uency

sinals (i,e, only hiher fre.uencies mayass),

• /igh3pass *lters remove lo+:fre.uencycomonents such as motion artifact!

resiratory variation! an# aseline +an#er,Unlie lo+:ass lters! analo hih:asslters #o not attenuate much of the sinal,

• o+ever! analo high-pass flters suerrom phase shit a5ectin the rst & to 10

harmonics of the sinal, This means that a0,& * hih ass lter! +hich is a lo+erfre.uency than the myocar#ium ro#uces!still can a5ect fre.uencies u to & *N

L *l


26/41

1%'10'201& Sunil (PEC) 2%

Lo43pass *lters

• Lo43pass *lters on the EC- are use# toremove hih fre.uency muscle artifact an#

e/ternal interference,• They tyically attenuate only the amlitu#e

of hiher fre.uency EC- comonents,• ;nalo lo+:ass lterin has a noticeale

a5ect on the GHS comle/ an# :+aves ut#o not alter reolari*ation sinals,

R l O( C 6 d N i


27/41

1%'10'201& Sunil (PEC) 2B

Re%o+al O( Co%%o$ 6ode Noise

"nterference usually manifests as common mo#e noiseacross oth terminals of the #i5erential amlier, This

noise can e remove# y the follo+in metho#s• "solate the front:en# roun# electronics from the #iital

system as much as ossile,• Use instrumentation amliers +ith very hih common

mo#e re?ection ratios on the or#er of 100#@

• rive the atient o#y +ith an inverte# common mo#esinal, The riht le of the atient is #riven +ith a sinal+hich is the inverte# averae of 7ea#"! 7ea#""! an#7ea#""",

• Shiel# the #evice usin metallic shiel#s to revent hih

fre.uency H6 from ein coule# into the system,• Use shiel#e# cales to ac.uire the EC- +hich are #riven

+ith a common voltae to re#uce noise from eincoule#,

• ;art from the aove metho#s! a numer of soft+arealorithms are resent for the removal of noise after thesinal has een ac.uire#,

B li 1 d i


28/41

1%'10'201& Sunil (PEC) 28

Baseli$e 1a$deri$g

• The main source of aseline +an#erin isresiration,

• @aseline +an#er (@M) that may e #ue toresiration or the motion of the atients or theinstruments

• The aseline +an#er (@M) mainly cause# y

resiration• "t is havin the fre.uency rane et+een 0,1& to

*,• Use# the +avelet transform to eliminate the

@aseline +an#erin•

@aseline +an#er is a lo+:fre.uency comonentresent in the EC- system, This is #ue to o5setvoltaes in the electro#es! resiration! an# o#ymovement,

• The o5set also limits the ma/imum value of ain

+hich can e otaine# from the instrumentation

R l O( B li 1 d


29/41

1%'10'201& Sunil (PEC) 2D

Re%o+al O( Baseli$e 1a$der This noise can e remove# y• "mlementin a high3pass *lter usin har#+are,• The cut:o5 fre.uency shoul# e such that the EC- is un#istorte#

+hile the aseline +an#er must e remove#,• ; tyical value of the cut:o5 fre.uency is 0,0&*,• Since this cut:o5 fre.uency is very lo+! this metho# re.uires

uly caacitors , "n this metho#! t+o staes of ain areimlemente# since the o5set can saturate at the outut of theinstrumentation amlier,

• The t+o:stae lter also maes the system more comle/,• This system re.uires a lo+ resolution ;C! tyically 8 to 1% its

of resolution,

6iure sho+s the sinal chain Qo+ for imlementin thehih ass lter in har#+are,

# Li I t (


30/41

1%'10'201& Sunil (PEC) 0

#o4er Li$e I$ter(ere$ce

• ue to imroer roun#in of EC- e.uiment an#interference from near y e.uiment,

• "t is remove# y usin notch lter,• >a?or source of such noise is electrical activity of the

muscles• 6iR the noise resent #ue to o+er line interface

(&0)• The suression of @aseline Man#er an# Po+er

"nterference can e #one usin #iital ""H lter

( I$*$ite I%p'lse Respo$se)

R l ( li i


31/41

1%'10'201& Sunil (PEC) 1

Re%o+al o( po4er3li$e $oise

The amlitu#e of o+er:line noise is verylare an# enerally ets coule# into the

system! #esite care to revent common:mo#e noise in the #iital #omain, Po+er:linenoise is remove# y imlementin a notchlter at &0'%0* in the #iital #omain,

Fir%4are ased $oise correctio$


32/41

1%'10'201& Sunil (PEC) 2

Fir%4are3ased $oise correctio$

• >any soft+are alorithms are availale +hich hel in lterin of

EC- after #iiti*ation,• These alorithms are often use# in hih:en# e.uiment an# are

usually rorietary to the manufacturer,• The microcontroller nee#s to have su=cient caacity to

imlement these comle/ alorithms,• The transfer function of the lter can e imlemente# in the

#iital #omain,• Care has to e taen in choosin the or#er of the lter, "t shoul#

e hih enouh to enale a stee roll:o5! ut not so hih as torevent the e5ect of rinin,

• Use# a Qe/ile #iital:lter loc! the microcontroller can

imlement the #esire# fre.uency resonse nee#e# for EC-system,• ih:see# analo multile/ers allo+ the ac.uisition of various

channel #ata! an# a hih inut ime#ance instrumentationamlier shoul# e use# e/ternal to the microcontroller toamlify the sinal,

• The availaility of a hih resolution ;C on the or#er of 20 its: :


33/41

• EC- sinal is measure# on static con#ition since the aearance

of hearteats varies consi#eraly! ut also movements!resiration an# mo#ications in the electrical activity of the o#y,

• Electrical an# mechanical noise comonents are a##e# to sinalan# it ma#e #i=cult to e/tract ey features,

• "n eneral! measure# EC- sinal #ata contains muscle artifactnoise! aseline +an#er noise! electro#e movin artifact noise!

an# %0* o+er line noise,• The o+er line noise can e easily remove# y notch lter since

its fre.uency centere# on %0*,

• Mavelet interolation lter (M"6) is e5ective to remove musclenoise,

• 6or aseline +an#er noise removal! nite imulse resonse (6"H)lter an# innite imulse resonse (""H) lter! an# a#atale lterare +i#ely use#,

1%'10'201& Sunil (PEC)

@ # lt i h S t l (2010)


34/41

1%'10'201& Sunil (PEC) 4

@an# ass lterimanshu! S, et al (2010)

Use# an# ass lter +ithcuto5 fre.uency 0,&*:1&0*

esine# amlier usininstrumentation amlier

;%20 (;nalo evices)

The #ata samle# at a rate of 1 K*,

;fter ac.uirin the sinal it isrocesse# y @utter+orth (""H) r#or#er #iital lter

The rst #iital lter is an# sto lter et+een 4D,& to &1,4*to eliminate o+er line interference,

@utter+orth lter havin various or#ers! the lo+est or#er ein

the est in time #omain! an# hiher or#er ein etter infre.uency #omain

# ti i lt i P # T t l (200D)


35/41

1%'10'201& Sunil (PEC) &

a#ative noise lterin Pa#ma T, et al (200D)

• 6or removal of &0 * that is the o+er line interferenceecause! the EC- sinal also contains &0 * sinal an#

if normal an# re?ect lter is use#! then the &0 *sinal +hich is very imortant in the EC- sinal +ill elost,

• Therefore y otin a#ative noise lterin! the o+er

line fre.uency can e eliminate# at the same timeretainin the &0 * sinal in the oriinal +aveform


36/41

6i! a#atale noise re#uction alorithm

1%'10'201& Sunil (PEC) %


37/41

1%'10'201& Sunil (PEC) B

• The active hih:ass lter removes the aselineQuctuations,

•

6or removin +i#e an# noises! un#ecimate# +avelettransform (UMT) is alie#! +hich has a etter alanceet+een smoothness an# accuracy than the #iscrete+avelet transforms (MT),

• "t is #i=cult to #eal +ith electrical interference since itcanJt e ltere# +ithout comromisin the EC- comle/ecause of its similarity to the EC- sinal fre.uency! soit is est to monitor a+ay from other e.uiment!ensurin cale an# lea# +ires #o not cross the o+ercales of other e.uiment or vent tuin,


38/41

1%'10'201& Sunil (PEC) 8

• To re#uce muscle tremor an# atient movement!

attemt to +arm a shiverin atient or mae themmore comfortale in a recline# osition! if ossile!rather than a#?ust a lter settin an# then continuallychec lea# +ire:to:electro#e connection an# electro#e:to:atientJs sin a#hesion to ensure EC- .uality an#

revent false alarms,

• Mhen it comes to EC- .uality! the electro#e tye!electro#e alication! an# sin rearation are factorsthat lay an imortant role in sen#in a oo# EC-

sinal to the monitor for analysis,

S'%%ary


39/41

1%'10'201& Sunil (PEC) D

S'%%ary

• Technoloical a#vances in communication an#lo+ o+er circuit #esin have enale# the#eveloment of etter! safer EC- #evices +ith acaacity to incororate the latest #ianosticfeatures,

• @ut the issue of the sensitivity of EC- sinal

ettin #istorte# y even a small noise maes thestu#y of EC- lterin alon +ith the various tyesof lters very sinicant ,

• ence the ac.uisition an# analysis of EC- sinal

still remain a challenin tas! #esitetechnoloical a#vances,• @ut further stu#y an# research shoul# continue to

#evelo cost e5ective an# Qe/ile metho#s ofEC- lterin +ith imrove# erformance of

various lters alie# to EC- sinal rocessin,

Re(ere$ces


40/41

• imanshu S,! Kumar! , S, , ;sho! 9,! uliet! ;, 9, (2010);#vance# EC- Sinal Processin usin 9irtual "nstrument!

"nternational , of Hecent Tren#s in Enineerin an# Technoloy! 9ol, ! Ao, 2,

• ;#vances in Aeural Aet+ors : "SAA 200% Pt, """ Thir#"nternational

• ECE 44& @iootential amliers reare# y Professor

;n#re+ >ason "A; #ata sheet,

• htt''+++,ems12lea#,com'2014'0'10'un#erstan#in:ec:lterin'

• htt''+++,eetimes,com'#ocument,asV#oci#W12B8&B1

1%'10'201& Sunil (PEC) 40

Re(ere$ces


41/41

12104008_ecg acquisition and filtration

Documents