CA1204871A - Averaging method for periodic strays elimination and the counting circuit for evoked responses measuring set-up for applying the method - Google Patents
Averaging method for periodic strays elimination and the counting circuit for evoked responses measuring set-up for applying the methodInfo
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- CA1204871A CA1204871A CA000446004A CA446004A CA1204871A CA 1204871 A CA1204871 A CA 1204871A CA 000446004 A CA000446004 A CA 000446004A CA 446004 A CA446004 A CA 446004A CA 1204871 A CA1204871 A CA 1204871A
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/316—Modalities, i.e. specific diagnostic methods
- A61B5/369—Electroencephalography [EEG]
- A61B5/377—Electroencephalography [EEG] using evoked responses
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B15/00—Suppression or limitation of noise or interference
- H04B15/005—Reducing noise, e.g. humm, from the supply
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Abstract
ABSTRACT OF THE DISCLOSURE:
An averaging method which eliminates periodic strays and which is usable in analog-digital computers performing an averaging procedure. Such a procedure which processes a set of signals picked up from an examined object elicits an averaged evoked response due to its capability of reducing internal noise and periodic strays originated in an environment comprising a mains supply network pro-portionally to the square root of N sweeps of the procedure, and in the case where the periodic strays and external stimuli are synchronous, the averaged periodic strays are not sufficiently reduced and distort the averaged evoked response making its right interpretation difficult. In order to overcome the latter problem, the averaging method eliminates the periodic strays from the set of signals during the averaging procedure in greater extend i.e. pro-portionally to the number of N sweeps of the averaging procedure resulting in their at least N-fold reduction thanks to introducing permanent desynchronization between the frequency ? of the external stimuli and the frequency ? of the periodic strays and thanks to introducing an odd number K of half-periods of the frequency ?, which number K determines the value of the period T according to the formula: T = ? t K, where K is a natural and odd integer.
An averaging method which eliminates periodic strays and which is usable in analog-digital computers performing an averaging procedure. Such a procedure which processes a set of signals picked up from an examined object elicits an averaged evoked response due to its capability of reducing internal noise and periodic strays originated in an environment comprising a mains supply network pro-portionally to the square root of N sweeps of the procedure, and in the case where the periodic strays and external stimuli are synchronous, the averaged periodic strays are not sufficiently reduced and distort the averaged evoked response making its right interpretation difficult. In order to overcome the latter problem, the averaging method eliminates the periodic strays from the set of signals during the averaging procedure in greater extend i.e. pro-portionally to the number of N sweeps of the averaging procedure resulting in their at least N-fold reduction thanks to introducing permanent desynchronization between the frequency ? of the external stimuli and the frequency ? of the periodic strays and thanks to introducing an odd number K of half-periods of the frequency ?, which number K determines the value of the period T according to the formula: T = ? t K, where K is a natural and odd integer.
Description
Averaging method for periodic strays elimination and a counting circuit for evoked re~ponses measurin~
, set-up :Eor appi~Jing the method.
~he subject o~: the presen-t invention is an averaging me~thod l`or ellmination of periGdic strays, especially s-tra~s of rnains ori~r,in, and a co~m-ting circuit in an evoked responses measurinFr set-up Eor applying the method~
The averagirlg rnethod Eor elimination or periodic strays, el~ o-~ mains origin, is appropriated for application in analog-digital computers employing the averaging procedure~
~l~he averaging procèdure elicits evoked responses ~rom a set of si~nals recorded ~rom an examined object. 'l'he set ot signals Uzs comprises: internal noise uszw and individual evoked responses Uo~y frorn the exanlined object and periodic strays u%p induced in this object ~rom an environmen-t comprising a source oE the mentioned strays, whereas the specified components o:E -the set o~ signals are independel1tO
`l`he above statemen-ts on -the set o~ signals Uys can be p-resented by the ~ollowing ~ormulas Uzs = Us~r-~ UOw ~ Uzpt The set of si~nals Uzs does not cornprise the component o~
apparatus nolse Usza resulting ~rom the con~-truction ol` the apparatus, which picks up and amplifies the set o~ signals uys, because t'ne apparatus internal noise should be so srnall as to be neglected within the se-t o~ siFrnals uz5 duri,ng i-ts eontinuous monitoring e,g~ when observing this set on a screen o~ a monitor o~ an averaging computer. 'l'he character of this
, set-up :Eor appi~Jing the method.
~he subject o~: the presen-t invention is an averaging me~thod l`or ellmination of periGdic strays, especially s-tra~s of rnains ori~r,in, and a co~m-ting circuit in an evoked responses measurinFr set-up Eor applying the method~
The averagirlg rnethod Eor elimination or periodic strays, el~ o-~ mains origin, is appropriated for application in analog-digital computers employing the averaging procedure~
~l~he averaging procèdure elicits evoked responses ~rom a set of si~nals recorded ~rom an examined object. 'l'he set ot signals Uzs comprises: internal noise uszw and individual evoked responses Uo~y frorn the exanlined object and periodic strays u%p induced in this object ~rom an environmen-t comprising a source oE the mentioned strays, whereas the specified components o:E -the set o~ signals are independel1tO
`l`he above statemen-ts on -the set o~ signals Uys can be p-resented by the ~ollowing ~ormulas Uzs = Us~r-~ UOw ~ Uzpt The set of si~nals Uzs does not cornprise the component o~
apparatus nolse Usza resulting ~rom the con~-truction ol` the apparatus, which picks up and amplifies the set o~ signals uys, because t'ne apparatus internal noise should be so srnall as to be neglected within the se-t o~ siFrnals uz5 duri,ng i-ts eontinuous monitoring e,g~ when observing this set on a screen o~ a monitor o~ an averaging computer. 'l'he character of this
- 2 -noise indicates i-ts identity ~^rith -the charae-ter o~' the ~r~ te noise , which due to its properties i~ non-c;ynchronou~ ~ritl the af'orernentioned signclls U~.
'~he mathematical :J`orrn O:r the averaging proce~'dure has been cl~3crib~d in the publ:ication by J.S. Bendat: ''MatherncJtical analysis of average responses values fox nonstationaYy c1.a~a"~
IEFE '~:ransaetions on I3io-Mcdieal l'~ngineerln~P~ B~ 72~
196~-, ancl i-ts technieal-clinieal realiza-tion has been deseribed by J. Kopec: "Polish eompu-ter ANOPS Eor medieal research cmcl i-ts elinieal appliea-tion ", Ae-ta Physi.ologiea Poloniea, 21:
113-123, 1970.
I-lither-to thc-~ internal noise USZ~r o:E the examirlecl objeet and -the periodlc s-trays Uzp were eonsidered to be 'non-synehronous signals in relation to the individual evoked responses UOw ancl the averaging procedure eould be cieseribed b~J -the followin6 formula:
N M
Uzs N n=1 ow ~ l~r p ¦
- Uo~r '~` 9~1~1 ~ ~- Uo,l ~rhere n=1,2,3,..0,N; I~J at leas-t several'hundred.
In the ex~-n1gle oE the above men-tioned situation, i:E the square root o~ N=256 sweeps of the averaging proeedure equals si~teen, and max.lrnura arnPlitudes o~ the internal noise Usz~r and of -the periodie strays U~p are equal to 64 ~V -t'ne~:their reclue-tion as a result o~ the averaging procedure is six-teen-Eold, thus their ma~i.rnurn averaged amplitucles Uszw and Uyp a-ce not greater than 4.~IV.
According to ihe above thc said averaging procedure, f'ro~ -the practic~l vie~r point, efficien-tl~ reduccs ~he noise and -the strays lrhen a ratio of rna}irnum arnpli.tude~ of -the said noise and strays to the least significan-t amplitudes of -the said individual evol~ed responses is les~ than 20:1 and the reductiorl is proportiorlal -to the .square root o~' N sweeps o:E
the averaging procedure providing that the no.ise and strays are non-synchronous in rela-tion to l;he indiv.idual evoked responses.
ln unfavourable.measuring conditions, even if -the require~
men-ts on the said ratio is fulfilled, amplitudes of the perloclic strays Uzp may become comparable with amplitudes of -the îndividual evoked resp~nses UO~J and the said strays may becolne synchronous ~n''relation to the individual evoked responses U0~, what makes -the averaged but considerable in qua-ntit~J perioclic s-tra~Js Uzp possible to supperirnpose on the averaged evokcd response UOw ~he supperimposed signal may! distort the averaged response to such an extend that its wave~orm ma~ be difficult ~'or inter.pretation.
'l'he above described si-tua-tion can be described by the folIowing formula: ' Z9 I~ UOw '1- Uzp) `~ ~ U ~ =
- ( U ~ 'U ) ~ 1 IJ ~ U ~ U
ow ~p ~ szw ow zp where n=1,2~3,0,.~Na N a-t least several hundred.
~2 In the example of the above described situatlon if -the square root of 1;~-256 sweeps oE the averaglng procedure equc113 six-teen and rnc~ximum amplitudes of -the :in-ternal noi~e U~z~/ and of periodic s-trays Uzp are equal to 64JU~ then the si~teen-:L'ol(1 reducti.on in the averaging procedure is ef'fec-tive only -to t~Le averaged internal noise us~w resultin~ in i-ts arnplitude no-t greater tha-n ~/uV, while the averagecl periodic s-trays Uæp behave like the averaged e~oked response UO~ ancl are no-t reduced and stay equal to 6~ ~V. In such a case kno~rn means for nolse and various strays reduc-tion are commonly used, i~e. means of analog and/or dlgital ~'iltering. l~he known fi.lter circui-ts may be divided into: low-pass ~ilters - eliminating s-tray~ and higher frequency signals, high-pass f`ilters -eliminatlng strays and lower frequency signals and band-reject Eil-ters - eliminating stra~s and signals oE Erequency equal to strays Erequency, ~ach kind of the above mentionéd fil-ters ïnter:Eeres and distorts the original wave~`orm o~ t'ne signals Uzs. In-ter:~erence and distor-tions introduced by the said fil-ters cause -that ap~rt f`rom ~trays they also eliminate signals o:C
component frequencies comprised in the evoked responses, as the said responses usually comprise signals o~ frequencies being cornparable to the fundamental ~'requency of -the str~ys.
'.L'he evoked re.sponses measurin~ se-t-ups, kno~m to us, described and manufactured by suc'n companies as: NICO~ET
BIOIirEDICA~ CO, ~ USA~ MED~,3~EC ~ ITED - Great Britain, DIS.
E'~EK'l'ROl`III~ A/S - Denmark, T~CHNICA~ UNI~F.RSI'l'Y OF ~ARS~
Poland are only able to eliminate periodic str2ys 'by means o r '30 the sa1d a~eraging procedure, which in case ~Jhe-n -the peri.odic ~æ~7~
s-trays Uzp and the indiv:idual evolced.responses U0~; are synchronous, can be supported b~, the said, lcnown :~ilte~ing circuits.
Construc-tion o~; a counting circuit :Eor the e~olced respon~"~s mea,suring set-up i3 a subjec-t of' the inv~nti.on. r~le ci^rcuit employing the averaging rnethod for elimination of the periodic strays rnakes the said measuring set~up no-t interfere and not dls-tor-t origin~l analog waveI'orm oE the individual evoked responses UOw f'rom the examined object, and makes periodic strays Uzp be unambi.gously.elimina-ted :Erora the averaged evoked response Uo~r proportionally to a number of N-sweeps and thu~
recluction ïs at least N-:~old what means t'hat the above mentiorled formula describing the averaged set of signals Uzs dur'ing the averaging procedure is as EO110~JS: ` _ , ~ n=1 ow N n~ Uzp + ~ ~ Usz~¦=
U ~ 1 U ~ 1 U ~ U
where n=1,2~3 " ..,N; N at least several hundred,.
In the example of the above sltuation, if the square root of N=256 sweeps o~ the averaging procedure equals sixteen and.
max~imum amplitudes of -the internal noise Uszw and the periodic strays U~p are equal to 64- ~V -then the sixteen fold reduction in -the averaging~procedure is effective only to the averaged internal noise ~sz~r resulting in their maximum averaged ampli-tudes not greater thc~n 4- ~V7 while the averaged periodic strays uzp are reduced a-t least 256-fold leaving cornponen-ts with amplitudes not grea-ter than 0.25 /uV in -the set of the averaged signals and in an ideal case when the periodic strays Uzp and the individual evoked responses UOW are non-synchronous and number of N sweeps approaches infinity, the reduction value also approaches infinity and thus components of the averaged periodic strays Uzp approach zero.
Tne aim of the subject invention is achieved by an averaging method for periodic strays elimination appropriated for application in analog-digital computers employing the averaging procedure, which procedure processing a set of signals U S picked up by electrodes from an examined object elicits an averaged evoked response UOW due to its capability of reducing internal noise Uszw and periodic strays Uzp originated in an environment comprising a mains supply network proportionally to the square root of N sweeps of the said procedure and in case the periodic strays and external stimuli are synchronous, the averaged periodic strays Uzp are not sufficiently reduced and distort the averaged evoked response making its right interpretation difficult and in order to avoid it means of analog and/or digital filtering supporting the averaging procedure are used or instead the averaging method distinct in this, that the periodic strays U p are eliminated from the set of signals U 5 during the averaging procedure in greater extend i.e.
proportionally to the number of N sweeps of the averaging procedure resulting in their at least N-fold reduction thanks to introducing permanent desynchronization between the frequency 1 of the external stimuli and the frequency t f the periodic strays and thanks to introducing an odd number K of half-periods of the said frequency t' which number K
determines the value oE the period T according to the formula:
T = 1 t K, where K is a natural and odd integer.
Preferably, the permanent desynchronization between the frequency 1 of the external stimuli and the Erequency t of the periodic strays is realized by introducing a phase shift by angle ~ = 180, which phase shift simultaneously ... ~
_ 7 ~ 871 corresponds to a time shift by one half-period of the said frequency - of the periodic stravs, in particular of mains origin and initial phases of the periodic strays at the beginning of two successive periods of the external stimuli or alternately at the beginning of two successive sweeps of the averaging procedure differ by the value of the introduced phase shift.
The present invention also relates to a counting circuit in an evoked responses measuring set-up for applying the averaging method for periodic strays elimination comprising a triggering circuit being directly connected to triggering inputs of an averaging computer and a photostimulator and delivering common pulses of frequency T triggering successive sweeps of the averaging procedure in the averaging computer and simul-taneously triggering successive external stimuli in particularphotostimuli in the photostimulator distinct in this, that the period T of the triggering pulses is a result of summing of half-periods of the periodic strays, e.g. of mains origin of frequency 1 done by a counting circuit by sensing the said periodic strays from an environment, e.g. comprising a mains supply network, from which by means of a cord supplying the measuring set-up the sinewave signal of the example periodic strays is fed to a sensing circuit comprising a transformer stepping down the signal voltage and an analog filter, which counter-,~ acts coming sporadic transient strays superimposed on theperiodic strays through the sensing circuit to further circuits, and the said sensing circuit after stepping down the voltage ~z~
_ 7a -and filter.ing the periodic strays sends it down a direct connection to a hal.f~period detectinn circuit, which provides a counting circuit with pulses determining successive half-periods of the sinewave signal, which is equivalent to the periodic strays induced in an examined object from an environment comprising the said source of the periodic strays in form of the mains supply network.
Preferably, the counting circuit is through a direct connection programmed by a circuit programming periods T with a given value of periods Tz, and the value of the period T is approximately equal to the value of the period Tz as the said programming circuit finds an odd number R, which best approximates the result of K-Tz. t ~ which number K delivered to the counting circuit and stored there results in this, that the circuit after counting every K half-periods provides the triggering circuit with pulses of frequency 1 = 2t .
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description thereof, given for the purpose of exemplification only and made in conjunc-tion with the accompanying drawings in which:
Figure 1 illustrates relations between angle and time parameters of sinuso;dal periodic strays;
Figure 2 shows a block diagxam of the evoked responses measuring set-up employing the averaging method;
Figure 3 shows electric signals related to the bloack diagram of Figure 2;
~2~
- 7 b -Figure 4 illustrates successive signals of the periodic strays taken to the averaging procedure; and Figure 5 illustrates successive sweeps of the averaging procedure.
The above described way of achieving the aim of the invention has the following advantages and disadvantages.
Every consecutive external stimulus appearing after time T
causes 8~
-that every sweep of the averaging procèdure is.delayed b~the tirne shif-t o:f one half-pe.riod o:f the periodic strays ~Jha-t means -tl-at -the aforemen-tioned stIays U~p comprised in the set o~ s:lgn~is Uz~ are also shifted in.-time by one,hal:f of its period t ln respect -to every indiviclual evoked respons~ 'U0~, which response 5s also comprised ln the said set o:L' ,sjgna:L3 ' 'Uzs, the con~idered respon3e is talcen froln thc precedin~ pe~lod ~` in respect -to -the following one what is sho~m in ~irr,s.3 an~.! 4 rhe aforementionecl time shif-t of one hal:f o:E the period rl' secures permanent'desynchroni~a-tioll be-tween the periodic s-trays and the e~ternal stimuli, and consequently between the pe-riodic s-trays and -tlle individual evoked responses U0~ and theref'oIo 15 ' -the said strays are e:f~`ectively elimina-ted in -the avera&ring proceclure propor-tionally to the number of` N sweeps of: -the aver.aging procedure wha-t is illustrated in ~igs.3 and 5.
'l~he averaging method for perioctic strays eli~nination and a coun-ting circuït in an evoked responses measuring sçt-up for applyin~ the me-thod is free from firm assumptions concerning the frequency T o:f the e~rternal stimull -thanks to employ:ing the counting circui-t in the evokecl rcsponses measuring set-up. 'l'he sald set-up has.wide capabili-ties, especial.ly in tlle few seconcl range of the period 'l` o:E the 25 e..~ternal s-tirnuli because -the rne-thod is not dependent on a tolerance of the frequenc~y t o:f -the periodlc strays) and ln ~articular of the strays'of mains origin and more eff'ec-tively reduces the said strays in case an even number of N s~reeps o:t' the ave:ra~ing procedure is applied.
'~0 Application of.the a-~eraging method :for peri.odic s-trays 9 _ elimination and of the counting circuit for evoked responses measuring set-up for applying the method is of particular importance for electrophysiological examinations determining the degree of conduction loss of nervous paths between a sense organ and a corresponding reeeption region of the cortex. Under unfavourable measuring conditions during a reception of the e.g. visual evoked responses (individual evoked responses UOW) the averaging procedure elicits from an electroencephalogram (internal noise Uszw) the afore-mentioned evoked responses recorded from the scalp (examinedobject) activated by photo stimuli (external stimuli), there is the very often met situation, when the averaging procedure may also elicit remaining components of the strays of mains origin eliciting them together with the individual evoked responses belonging to the set of signals Uzs when the strays are in synchrony with sweeps of the averaging procedure.
The counting circuit according to the invention prevents in every case from appearing of the said synchrony.
In Figures 4 and 5 the strays signal is shown alone which represents the desynchronized periodic strays in respect -to successive pulses, whlch are -triggering successive s~teeps of the averaging procedure and are trigrgering t~le e~.te~nal stimuli which are corre~pondin~ to the s~teeps and are correlclte(l through the e~aminéd object with the individua1 evoked responses, ~hich responses ~nd -the in-ternal noise are omittod :Cor the simplicity of the diagrarn. 'l'he internal noic;e 'nas been also omitted ïn l~ig ~ ~or clearance o~ signals 7A, 7 and 7~ representation.
'l'he method oE the periodic strays elimination accordinrr to the invention is based on -the perma~ent desynchroni~ation of the f`requency ~ o~ the said strays in respect to the frequenc~
T oE pulses which are triggering successive s~reeps of the averaging procedure after'every external stlmulus. A triggering pulse pulse originates both an external stimulus and a sweep oE the averaging procedureO 'I'he desynchroni~ation bet~^reen the frequency t of the said strays and successive sweeps oE
the averagi~g procedure is based on this, tha-t e~ery time period '~ bet~reen consecutive external stimuli is determined by a number ~ of halI-periods of'the periodic strays o~ the period t, i.e. 'l' = -t ~ The elirnination o~ the said s-tray-.
is condi-tioned by ~ulfilling the a'bove formula for the sequence of nwrlbe~s ~ = 1,3,5,... ~hat means, that if the ~
periodic strays o:~ frequency 1t are supperim;posed on an indivicl~lal evoked response and are shifted by angle C~ = 180 i.n rela-tion to the preceding individual evoked response, the to-tal elimination o~ the periodic strays will occur. Accur'acy of determinirlg of the periodic s-trays hal~perlods has no prac-tical '~ 30 meaning, as discrepancy of -the parameters can be so srnall, tlla~
the phase shi~t b~r angle 'betwecn successive sweeps ma~J di~`,i'er by sing].e degrees, and the recluction o~ the said ~tra~s ~/i.ll be much more e~fective than is the case o:~ -the h:itherto used averaging procedurej when the elimi.na-tion is proportional to the number of r~ sweeps.
o exempli~ -the ave-caging method for periodi.c strays eli.l.lina-tion in l?igs, 3,~ and 5 the iaeal phase shi:~t of.angle C~= 180 is intro~uced and for better illust~a-tion oI' the periodic strays elimination in Elgro5 the two-i~old magni~ica-tion o~ the amplitude scale in relation to li`ig,4 is introdu'ced.
~esicles, thc des~Jnchronized sinusoidal stra~s picked up -together ~rith the internal noise U5ZW and the individuai evoked re~ponses U0~ during each sweep of the averagin~ procedure are sho~m in ,' Fi~s. 3 and 4 7 alld they all are repeated in success:ive time interva].s between eve~y t~10 successive external stimuli o~' , ~requency r~, which time intervals corresnoncl to sweeps of -the~
averagin~, procedure. '~he saicl sweeps ol the av,eraging procedure 20' are sho~l in ~ .5~ where wave~orm "~ represents the ~irst sweep~ wave~orm "3" represents -the second sweep of the averaging procedure and during the second ~weep -the f:irs-t total elirnina-tion o~` the periodic strays tal~es place c~nd :~urther ~raveforms ~C't, "D" and ~E" are results of the successive sweeps of the averaging proceclure, and during the :Eourth s~yeep the second total elirnination o~ the period:ic srtrays takes place. In c~n eY~c~nple case o~ the phase shift b~r~- 180 total elimina-tion o:E the per.iodic strays takes place af-ter every secon~
successive sweep of the avera~ing procedure, ~AJhich sweeps are counted starting :~rorn -the wave~orm ~A'! béing the firs-t sweep.
-:
~ 12 ~
De,scription of the avcrag,in~; me-thod for '-tlle periodi.c 3tra~
elilnirlation~ i.n practical case requires a dctai.].ed discussioJl, which borrows sorne e~ample da-ta, since the said -periodic strallu may be in particular o~ mains ori~in ~li-th variou.~l v.~].ue5 Or -the nomina]. frequency 1t depending on -the place and examina,tion condi-tions ~md rna~t be e,g. 50 c/s, 60 c/s, 4.0~ c/s, etc, I~or example a mains network ma~J be a source of the perioc1ic s-tra~Js in :Eorm of the s.inusoid~-~,l signal of the nominal -frequency 1t = 50 cjs ~rith the ac~nissible -toJ.erance ~At =1 c/,;
what means that the period t o:E the said s-tra~ts at a given moment o~ the e`x~mina-tion course may be of any value comprised within the -toler.~nce interval -tmin= 19.6 ms ~ t ~ 20.4 ms =trn~x, 'Lo deterrrlL:ne an odd number o-f I~ o-ne rnus-t asswae an experi,men-t..l ~`requellc,~t ,~ or c~l ~perimental p~:ciocl'.'~z,~ e.g. '1'z - 3 s and then correct -tlle value in respect -to an odd mul-tipl~ of the number of l~ of the haiE-periods of -the nominal -frequency 1t 2 ~ 2 '3 s n of the peri.odic strays: Xz - -t - = 20 ms ~ ' the resulting Kz is an even number and according -to the assu~lption -the number l,~lUSt be odd, one malces -t'he ~z odcl in an arbitrary way so, that -the Kz may be here 301, ~hat'causes, that in this case talcing into account -the said tolerance o-~' the ,eriodic stra,-,rs frequency -the 'l' m~t be comprised ~-thin the interval 2,9~9~ s ~ 3.0702 s açcordingr -to -the :~ollowing l'ormula 'L'min= ~ tmin ~ = ~ 19~6 ms 301 = 2,9~.9~ s max 2 tmax K = 2~ 2004 ms 301 = 3.0702 s, '.L'he above in~erval within which the period 'l' may be co!nprised is so narro~l -that i-t ha.3 ~o practica] rneani.n~ ^`or t~le assuined va.lue o:E
-the period ~l~z, .
Thc~ aEorementioned avel aging me-thod Cor -the pe:riod:ie S t~ ys e L:~.rllination ~?n~lbl~ cle~ ni.nr~ O r I;~.L(? ~bO~J~? ~le3cri b~f~d ~f~vo~c?cl 5 re3pon3es m( asuring se~-t-up, whieh eompri.se,s a eireui.t :ror coun-l;ing ha:L:L'-pe~.liods o:C ttle sai.d stra;~Is l,rhieh elreult (IeterIn:i.nes the ~ eriocl 'l' o:E the external 3-timuli., whieh arc-~ in e~re:~y case non-3~ne~ronou,s ~rith -thc peliodie stray,s e.g. 0~' rnains ori~in, ~l~he ~e-t-u~ or mea~;uri.ng evoked responses, in particula:r 10 for r~easurin~; visual evoked responses f`or app:L;~i.ng t~le ~bove deseribed rne thod is :Eurnished with cireui.t 1 ,se-nsing the periodie s-tra~s U~p coming from an environmen t 2 eomprising a souree o:f the perioàie strays of :Erequeney t~rhieh strays sensed b~
thC! cireuit 1 come directl-,~ Erom tne mains ,supl~ly net~ o:rk;
1~ a ei:reui-t ~ detec-ting half-perio(l,s o:~ t;he peLiodic s-tra~3, a eireui-t ~; programming the period T of the e;~ternal stimuli ~
whieh circui-t s,~ts a circui-t 5 -to eoun-t a proper nwnber O:r K
half-period,s, a circuit 6 tri.ggerincfr s.irQultaneously suceessive sweeps OI thfe averag:ing proeedure in an a~reraging eompu-ter ~
20 ancl per-tinent sueeessive ex-te~ al stimuli whieh are nrodueed b~ an elee-t:rolurnineseen-t matri}~ of a pho tos timula-tor 3, the -pllo-tos tirnulater ~ equlpped wi-th lhe elee tro].urQineseent matrix is a sou:rce o:E -the e~te:rnal stil~Iuli, a circuit 9 ~ an inst.rumentation ampli:Eie:r for ampli1`~Jing the set of signals Ur~3,, 25 whieh si~nals are piekecl up :Erom an ercunilled objeet 10 b~r means o:f electrodes 11 o~ Ag l~gCl t~-~pe~ the a~Te~ aging eompute r~mning the averagi.ng proceclure of ~the sai d se-t o~ signals and c~ block 12 - memory and displ'ay .~or storing and di~play:i.rLg results of the averaging procedure~
0-oera-tiorI o:~' -the evoke~d responses measuri.ng set-u~ 'o~
- 1'1. -ap]?lyinp; the averaL~ -Lg l~rle-thod :Eor, perioc~:i.c stro.~,rs cJ,inlinatior, is decri~ed below, , 5 '~he sai(1 s-tra-ys coming :Erom the envi:Lonmt,n-t 2 comprir-,ing a source of the str~.ys, in an e~alnpl.e o:~ ma:ins origin, are sensed directly in the source by rneans of a line supplying the ~rholt? se~t-up and -the si~lnal picked up in th:i.3 ~ay is ~e(l di.rectl,~J ^to the sensinl~ circui-t 1~, q'he circuit 1 sensing the pe,io(lic stl-~a~rs comprise3 a s-tepping-do~m trans:CoIDIer, :Erom ~rhlch the periodic strays in Eorm o~' a sinusoidal sigrnal wit~
voltagt or'.' several vol-ts is Ee-l to a lolr-}?ass ~ilter coun-ter-ac-ting coming o:f' sporadic -transi.ent strays'super:Lmposed on the periodic strays through the sensing circuit to f'urther circui-ts.
~15 'L'hen the~ 50 :Eil-tert-~d str~ys are sent to -the circuit ) detect:in,~r`
halE-perlods o:E the said sinusoida.~l periodic strays, ~rhich circuit prodv.ces pulses correspo-nding to every positive and negati~e peaks oE the sinewa~eform o:E -the pe~:iodic strays.
~ounting circuit ~ is provi~ed wi.th khe said pulses and CQU~tS
them tlll the number programme(l by the ci,rcuit ~ ~ progrcaMmin~
-the period o~'-the ef-teInal sti.rlluli., 'l'he sclid pro,,ralnmin~ circui-t de-t,er.m~.nes a }?er-tinent number li corresponding approximatel~
to :the ra-te of -t'he periocl'l' O:r the external sti-lnuli to l-,he halfi-perioc~ 2 t of the perio(lic str~,ys, and the ~ is al~rays an odd number. 'l'he a:Eorementioned counting circui-t ~ produces every li halE-periods a pulse, which is sen-t directly to the circuit,,6, ~rhich -triggers direc-tly -the pho-tostimulator 8 and th3 a~erc~glng computer ~ ~'he photos-timulator 8, trit,gered b~
a pulse :.froln the said circuit 6 gener~ltes -the e~ternal s-timuli in :f'orrn ol'-the photostimuli which through an eye and visual . 15 . .
nervous path produce an elec-troph~siolog:ical rcsponse :in pertinen-t.re~ions o:f a cor.te~. lhe elec-trophyc3iolo~lcal :resr)onxe cor.r.esponds to an individual evoked response U0~r~rhich is piclsed up b~ the e~ectrode-- 11 place~ on the scalp of the e~amined object ~. 'Ihe said in~ividual evoked res~onse U0~
is picke~ up together ~ith the internal noise usæ~ in this ca~e being calle~ an electro(rlce-phalo~ram, and ~rith -tlle perio(l:ic s-tr~ys Uz~ originatecl from the environment 2 comprising a main ~uppl~J net~rork The saicl set of signals is fecl to clifIeréntial :inputs o r the ci.rcuit '~ - -two channel ins-trwnenta-tion ampli:f.i.er.
The ;aid circui-t 2 in each of i-ts channels ampli:ries the said se-t oI` signals U~s to match its output voltage ~ri.t;h an voltar-;e ranFrc of analo~ inpu-ts o:L` the averaginr computer 7. ~ach trig~rerinp; pulse starts successive sweeps o:f` the averaging procedure for the se-t o.~ si~nals Uæs 'I'he averaged. set of signals Uzs equals -the avera~ed evol~ed response U0w. l`he product of avera~?ring of -the set o:f.
sigrnals U~s ln -the averaging compu-ter ~ is sent :~rom the col~puter to the bloclc 12 - memory an(l cli.spl~y to ~rovide a ~ossibili.t~ for fu-ture displaying and selecting~ a resul-t and -to pr.ovi.de data for furtner statis-tical anal~sis ~lïth the use of a big digital compllter Procura-tor: ~s~Jchoneurological Instit1l-te
'~he mathematical :J`orrn O:r the averaging proce~'dure has been cl~3crib~d in the publ:ication by J.S. Bendat: ''MatherncJtical analysis of average responses values fox nonstationaYy c1.a~a"~
IEFE '~:ransaetions on I3io-Mcdieal l'~ngineerln~P~ B~ 72~
196~-, ancl i-ts technieal-clinieal realiza-tion has been deseribed by J. Kopec: "Polish eompu-ter ANOPS Eor medieal research cmcl i-ts elinieal appliea-tion ", Ae-ta Physi.ologiea Poloniea, 21:
113-123, 1970.
I-lither-to thc-~ internal noise USZ~r o:E the examirlecl objeet and -the periodlc s-trays Uzp were eonsidered to be 'non-synehronous signals in relation to the individual evoked responses UOw ancl the averaging procedure eould be cieseribed b~J -the followin6 formula:
N M
Uzs N n=1 ow ~ l~r p ¦
- Uo~r '~` 9~1~1 ~ ~- Uo,l ~rhere n=1,2,3,..0,N; I~J at leas-t several'hundred.
In the ex~-n1gle oE the above men-tioned situation, i:E the square root o~ N=256 sweeps of the averaging proeedure equals si~teen, and max.lrnura arnPlitudes o~ the internal noise Usz~r and of -the periodie strays U~p are equal to 64 ~V -t'ne~:their reclue-tion as a result o~ the averaging procedure is six-teen-Eold, thus their ma~i.rnurn averaged amplitucles Uszw and Uyp a-ce not greater than 4.~IV.
According to ihe above thc said averaging procedure, f'ro~ -the practic~l vie~r point, efficien-tl~ reduccs ~he noise and -the strays lrhen a ratio of rna}irnum arnpli.tude~ of -the said noise and strays to the least significan-t amplitudes of -the said individual evol~ed responses is les~ than 20:1 and the reductiorl is proportiorlal -to the .square root o~' N sweeps o:E
the averaging procedure providing that the no.ise and strays are non-synchronous in rela-tion to l;he indiv.idual evoked responses.
ln unfavourable.measuring conditions, even if -the require~
men-ts on the said ratio is fulfilled, amplitudes of the perloclic strays Uzp may become comparable with amplitudes of -the îndividual evoked resp~nses UO~J and the said strays may becolne synchronous ~n''relation to the individual evoked responses U0~, what makes -the averaged but considerable in qua-ntit~J perioclic s-tra~Js Uzp possible to supperirnpose on the averaged evokcd response UOw ~he supperimposed signal may! distort the averaged response to such an extend that its wave~orm ma~ be difficult ~'or inter.pretation.
'l'he above described si-tua-tion can be described by the folIowing formula: ' Z9 I~ UOw '1- Uzp) `~ ~ U ~ =
- ( U ~ 'U ) ~ 1 IJ ~ U ~ U
ow ~p ~ szw ow zp where n=1,2~3,0,.~Na N a-t least several hundred.
~2 In the example of the above described situatlon if -the square root of 1;~-256 sweeps oE the averaglng procedure equc113 six-teen and rnc~ximum amplitudes of -the :in-ternal noi~e U~z~/ and of periodic s-trays Uzp are equal to 64JU~ then the si~teen-:L'ol(1 reducti.on in the averaging procedure is ef'fec-tive only -to t~Le averaged internal noise us~w resultin~ in i-ts arnplitude no-t greater tha-n ~/uV, while the averagecl periodic s-trays Uæp behave like the averaged e~oked response UO~ ancl are no-t reduced and stay equal to 6~ ~V. In such a case kno~rn means for nolse and various strays reduc-tion are commonly used, i~e. means of analog and/or dlgital ~'iltering. l~he known fi.lter circui-ts may be divided into: low-pass ~ilters - eliminating s-tray~ and higher frequency signals, high-pass f`ilters -eliminatlng strays and lower frequency signals and band-reject Eil-ters - eliminating stra~s and signals oE Erequency equal to strays Erequency, ~ach kind of the above mentionéd fil-ters ïnter:Eeres and distorts the original wave~`orm o~ t'ne signals Uzs. In-ter:~erence and distor-tions introduced by the said fil-ters cause -that ap~rt f`rom ~trays they also eliminate signals o:C
component frequencies comprised in the evoked responses, as the said responses usually comprise signals o~ frequencies being cornparable to the fundamental ~'requency of -the str~ys.
'.L'he evoked re.sponses measurin~ se-t-ups, kno~m to us, described and manufactured by suc'n companies as: NICO~ET
BIOIirEDICA~ CO, ~ USA~ MED~,3~EC ~ ITED - Great Britain, DIS.
E'~EK'l'ROl`III~ A/S - Denmark, T~CHNICA~ UNI~F.RSI'l'Y OF ~ARS~
Poland are only able to eliminate periodic str2ys 'by means o r '30 the sa1d a~eraging procedure, which in case ~Jhe-n -the peri.odic ~æ~7~
s-trays Uzp and the indiv:idual evolced.responses U0~; are synchronous, can be supported b~, the said, lcnown :~ilte~ing circuits.
Construc-tion o~; a counting circuit :Eor the e~olced respon~"~s mea,suring set-up i3 a subjec-t of' the inv~nti.on. r~le ci^rcuit employing the averaging rnethod for elimination of the periodic strays rnakes the said measuring set~up no-t interfere and not dls-tor-t origin~l analog waveI'orm oE the individual evoked responses UOw f'rom the examined object, and makes periodic strays Uzp be unambi.gously.elimina-ted :Erora the averaged evoked response Uo~r proportionally to a number of N-sweeps and thu~
recluction ïs at least N-:~old what means t'hat the above mentiorled formula describing the averaged set of signals Uzs dur'ing the averaging procedure is as EO110~JS: ` _ , ~ n=1 ow N n~ Uzp + ~ ~ Usz~¦=
U ~ 1 U ~ 1 U ~ U
where n=1,2~3 " ..,N; N at least several hundred,.
In the example of the above sltuation, if the square root of N=256 sweeps o~ the averaging procedure equals sixteen and.
max~imum amplitudes of -the internal noise Uszw and the periodic strays U~p are equal to 64- ~V -then the sixteen fold reduction in -the averaging~procedure is effective only to the averaged internal noise ~sz~r resulting in their maximum averaged ampli-tudes not greater thc~n 4- ~V7 while the averaged periodic strays uzp are reduced a-t least 256-fold leaving cornponen-ts with amplitudes not grea-ter than 0.25 /uV in -the set of the averaged signals and in an ideal case when the periodic strays Uzp and the individual evoked responses UOW are non-synchronous and number of N sweeps approaches infinity, the reduction value also approaches infinity and thus components of the averaged periodic strays Uzp approach zero.
Tne aim of the subject invention is achieved by an averaging method for periodic strays elimination appropriated for application in analog-digital computers employing the averaging procedure, which procedure processing a set of signals U S picked up by electrodes from an examined object elicits an averaged evoked response UOW due to its capability of reducing internal noise Uszw and periodic strays Uzp originated in an environment comprising a mains supply network proportionally to the square root of N sweeps of the said procedure and in case the periodic strays and external stimuli are synchronous, the averaged periodic strays Uzp are not sufficiently reduced and distort the averaged evoked response making its right interpretation difficult and in order to avoid it means of analog and/or digital filtering supporting the averaging procedure are used or instead the averaging method distinct in this, that the periodic strays U p are eliminated from the set of signals U 5 during the averaging procedure in greater extend i.e.
proportionally to the number of N sweeps of the averaging procedure resulting in their at least N-fold reduction thanks to introducing permanent desynchronization between the frequency 1 of the external stimuli and the frequency t f the periodic strays and thanks to introducing an odd number K of half-periods of the said frequency t' which number K
determines the value oE the period T according to the formula:
T = 1 t K, where K is a natural and odd integer.
Preferably, the permanent desynchronization between the frequency 1 of the external stimuli and the Erequency t of the periodic strays is realized by introducing a phase shift by angle ~ = 180, which phase shift simultaneously ... ~
_ 7 ~ 871 corresponds to a time shift by one half-period of the said frequency - of the periodic stravs, in particular of mains origin and initial phases of the periodic strays at the beginning of two successive periods of the external stimuli or alternately at the beginning of two successive sweeps of the averaging procedure differ by the value of the introduced phase shift.
The present invention also relates to a counting circuit in an evoked responses measuring set-up for applying the averaging method for periodic strays elimination comprising a triggering circuit being directly connected to triggering inputs of an averaging computer and a photostimulator and delivering common pulses of frequency T triggering successive sweeps of the averaging procedure in the averaging computer and simul-taneously triggering successive external stimuli in particularphotostimuli in the photostimulator distinct in this, that the period T of the triggering pulses is a result of summing of half-periods of the periodic strays, e.g. of mains origin of frequency 1 done by a counting circuit by sensing the said periodic strays from an environment, e.g. comprising a mains supply network, from which by means of a cord supplying the measuring set-up the sinewave signal of the example periodic strays is fed to a sensing circuit comprising a transformer stepping down the signal voltage and an analog filter, which counter-,~ acts coming sporadic transient strays superimposed on theperiodic strays through the sensing circuit to further circuits, and the said sensing circuit after stepping down the voltage ~z~
_ 7a -and filter.ing the periodic strays sends it down a direct connection to a hal.f~period detectinn circuit, which provides a counting circuit with pulses determining successive half-periods of the sinewave signal, which is equivalent to the periodic strays induced in an examined object from an environment comprising the said source of the periodic strays in form of the mains supply network.
Preferably, the counting circuit is through a direct connection programmed by a circuit programming periods T with a given value of periods Tz, and the value of the period T is approximately equal to the value of the period Tz as the said programming circuit finds an odd number R, which best approximates the result of K-Tz. t ~ which number K delivered to the counting circuit and stored there results in this, that the circuit after counting every K half-periods provides the triggering circuit with pulses of frequency 1 = 2t .
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description thereof, given for the purpose of exemplification only and made in conjunc-tion with the accompanying drawings in which:
Figure 1 illustrates relations between angle and time parameters of sinuso;dal periodic strays;
Figure 2 shows a block diagxam of the evoked responses measuring set-up employing the averaging method;
Figure 3 shows electric signals related to the bloack diagram of Figure 2;
~2~
- 7 b -Figure 4 illustrates successive signals of the periodic strays taken to the averaging procedure; and Figure 5 illustrates successive sweeps of the averaging procedure.
The above described way of achieving the aim of the invention has the following advantages and disadvantages.
Every consecutive external stimulus appearing after time T
causes 8~
-that every sweep of the averaging procèdure is.delayed b~the tirne shif-t o:f one half-pe.riod o:f the periodic strays ~Jha-t means -tl-at -the aforemen-tioned stIays U~p comprised in the set o~ s:lgn~is Uz~ are also shifted in.-time by one,hal:f of its period t ln respect -to every indiviclual evoked respons~ 'U0~, which response 5s also comprised ln the said set o:L' ,sjgna:L3 ' 'Uzs, the con~idered respon3e is talcen froln thc precedin~ pe~lod ~` in respect -to -the following one what is sho~m in ~irr,s.3 an~.! 4 rhe aforementionecl time shif-t of one hal:f o:E the period rl' secures permanent'desynchroni~a-tioll be-tween the periodic s-trays and the e~ternal stimuli, and consequently between the pe-riodic s-trays and -tlle individual evoked responses U0~ and theref'oIo 15 ' -the said strays are e:f~`ectively elimina-ted in -the avera&ring proceclure propor-tionally to the number of` N sweeps of: -the aver.aging procedure wha-t is illustrated in ~igs.3 and 5.
'l~he averaging method for perioctic strays eli~nination and a coun-ting circuït in an evoked responses measuring sçt-up for applyin~ the me-thod is free from firm assumptions concerning the frequency T o:f the e~rternal stimull -thanks to employ:ing the counting circui-t in the evokecl rcsponses measuring set-up. 'l'he sald set-up has.wide capabili-ties, especial.ly in tlle few seconcl range of the period 'l` o:E the 25 e..~ternal s-tirnuli because -the rne-thod is not dependent on a tolerance of the frequenc~y t o:f -the periodlc strays) and ln ~articular of the strays'of mains origin and more eff'ec-tively reduces the said strays in case an even number of N s~reeps o:t' the ave:ra~ing procedure is applied.
'~0 Application of.the a-~eraging method :for peri.odic s-trays 9 _ elimination and of the counting circuit for evoked responses measuring set-up for applying the method is of particular importance for electrophysiological examinations determining the degree of conduction loss of nervous paths between a sense organ and a corresponding reeeption region of the cortex. Under unfavourable measuring conditions during a reception of the e.g. visual evoked responses (individual evoked responses UOW) the averaging procedure elicits from an electroencephalogram (internal noise Uszw) the afore-mentioned evoked responses recorded from the scalp (examinedobject) activated by photo stimuli (external stimuli), there is the very often met situation, when the averaging procedure may also elicit remaining components of the strays of mains origin eliciting them together with the individual evoked responses belonging to the set of signals Uzs when the strays are in synchrony with sweeps of the averaging procedure.
The counting circuit according to the invention prevents in every case from appearing of the said synchrony.
In Figures 4 and 5 the strays signal is shown alone which represents the desynchronized periodic strays in respect -to successive pulses, whlch are -triggering successive s~teeps of the averaging procedure and are trigrgering t~le e~.te~nal stimuli which are corre~pondin~ to the s~teeps and are correlclte(l through the e~aminéd object with the individua1 evoked responses, ~hich responses ~nd -the in-ternal noise are omittod :Cor the simplicity of the diagrarn. 'l'he internal noic;e 'nas been also omitted ïn l~ig ~ ~or clearance o~ signals 7A, 7 and 7~ representation.
'l'he method oE the periodic strays elimination accordinrr to the invention is based on -the perma~ent desynchroni~ation of the f`requency ~ o~ the said strays in respect to the frequenc~
T oE pulses which are triggering successive s~reeps of the averaging procedure after'every external stlmulus. A triggering pulse pulse originates both an external stimulus and a sweep oE the averaging procedureO 'I'he desynchroni~ation bet~^reen the frequency t of the said strays and successive sweeps oE
the averagi~g procedure is based on this, tha-t e~ery time period '~ bet~reen consecutive external stimuli is determined by a number ~ of halI-periods of'the periodic strays o~ the period t, i.e. 'l' = -t ~ The elirnination o~ the said s-tray-.
is condi-tioned by ~ulfilling the a'bove formula for the sequence of nwrlbe~s ~ = 1,3,5,... ~hat means, that if the ~
periodic strays o:~ frequency 1t are supperim;posed on an indivicl~lal evoked response and are shifted by angle C~ = 180 i.n rela-tion to the preceding individual evoked response, the to-tal elimination o~ the periodic strays will occur. Accur'acy of determinirlg of the periodic s-trays hal~perlods has no prac-tical '~ 30 meaning, as discrepancy of -the parameters can be so srnall, tlla~
the phase shi~t b~r angle 'betwecn successive sweeps ma~J di~`,i'er by sing].e degrees, and the recluction o~ the said ~tra~s ~/i.ll be much more e~fective than is the case o:~ -the h:itherto used averaging procedurej when the elimi.na-tion is proportional to the number of r~ sweeps.
o exempli~ -the ave-caging method for periodi.c strays eli.l.lina-tion in l?igs, 3,~ and 5 the iaeal phase shi:~t of.angle C~= 180 is intro~uced and for better illust~a-tion oI' the periodic strays elimination in Elgro5 the two-i~old magni~ica-tion o~ the amplitude scale in relation to li`ig,4 is introdu'ced.
~esicles, thc des~Jnchronized sinusoidal stra~s picked up -together ~rith the internal noise U5ZW and the individuai evoked re~ponses U0~ during each sweep of the averagin~ procedure are sho~m in ,' Fi~s. 3 and 4 7 alld they all are repeated in success:ive time interva].s between eve~y t~10 successive external stimuli o~' , ~requency r~, which time intervals corresnoncl to sweeps of -the~
averagin~, procedure. '~he saicl sweeps ol the av,eraging procedure 20' are sho~l in ~ .5~ where wave~orm "~ represents the ~irst sweep~ wave~orm "3" represents -the second sweep of the averaging procedure and during the second ~weep -the f:irs-t total elirnina-tion o~` the periodic strays tal~es place c~nd :~urther ~raveforms ~C't, "D" and ~E" are results of the successive sweeps of the averaging proceclure, and during the :Eourth s~yeep the second total elirnination o~ the period:ic srtrays takes place. In c~n eY~c~nple case o~ the phase shift b~r~- 180 total elimina-tion o:E the per.iodic strays takes place af-ter every secon~
successive sweep of the avera~ing procedure, ~AJhich sweeps are counted starting :~rorn -the wave~orm ~A'! béing the firs-t sweep.
-:
~ 12 ~
De,scription of the avcrag,in~; me-thod for '-tlle periodi.c 3tra~
elilnirlation~ i.n practical case requires a dctai.].ed discussioJl, which borrows sorne e~ample da-ta, since the said -periodic strallu may be in particular o~ mains ori~in ~li-th variou.~l v.~].ue5 Or -the nomina]. frequency 1t depending on -the place and examina,tion condi-tions ~md rna~t be e,g. 50 c/s, 60 c/s, 4.0~ c/s, etc, I~or example a mains network ma~J be a source of the perioc1ic s-tra~Js in :Eorm of the s.inusoid~-~,l signal of the nominal -frequency 1t = 50 cjs ~rith the ac~nissible -toJ.erance ~At =1 c/,;
what means that the period t o:E the said s-tra~ts at a given moment o~ the e`x~mina-tion course may be of any value comprised within the -toler.~nce interval -tmin= 19.6 ms ~ t ~ 20.4 ms =trn~x, 'Lo deterrrlL:ne an odd number o-f I~ o-ne rnus-t asswae an experi,men-t..l ~`requellc,~t ,~ or c~l ~perimental p~:ciocl'.'~z,~ e.g. '1'z - 3 s and then correct -tlle value in respect -to an odd mul-tipl~ of the number of l~ of the haiE-periods of -the nominal -frequency 1t 2 ~ 2 '3 s n of the peri.odic strays: Xz - -t - = 20 ms ~ ' the resulting Kz is an even number and according -to the assu~lption -the number l,~lUSt be odd, one malces -t'he ~z odcl in an arbitrary way so, that -the Kz may be here 301, ~hat'causes, that in this case talcing into account -the said tolerance o-~' the ,eriodic stra,-,rs frequency -the 'l' m~t be comprised ~-thin the interval 2,9~9~ s ~ 3.0702 s açcordingr -to -the :~ollowing l'ormula 'L'min= ~ tmin ~ = ~ 19~6 ms 301 = 2,9~.9~ s max 2 tmax K = 2~ 2004 ms 301 = 3.0702 s, '.L'he above in~erval within which the period 'l' may be co!nprised is so narro~l -that i-t ha.3 ~o practica] rneani.n~ ^`or t~le assuined va.lue o:E
-the period ~l~z, .
Thc~ aEorementioned avel aging me-thod Cor -the pe:riod:ie S t~ ys e L:~.rllination ~?n~lbl~ cle~ ni.nr~ O r I;~.L(? ~bO~J~? ~le3cri b~f~d ~f~vo~c?cl 5 re3pon3es m( asuring se~-t-up, whieh eompri.se,s a eireui.t :ror coun-l;ing ha:L:L'-pe~.liods o:C ttle sai.d stra;~Is l,rhieh elreult (IeterIn:i.nes the ~ eriocl 'l' o:E the external 3-timuli., whieh arc-~ in e~re:~y case non-3~ne~ronou,s ~rith -thc peliodie stray,s e.g. 0~' rnains ori~in, ~l~he ~e-t-u~ or mea~;uri.ng evoked responses, in particula:r 10 for r~easurin~; visual evoked responses f`or app:L;~i.ng t~le ~bove deseribed rne thod is :Eurnished with cireui.t 1 ,se-nsing the periodie s-tra~s U~p coming from an environmen t 2 eomprising a souree o:f the perioàie strays of :Erequeney t~rhieh strays sensed b~
thC! cireuit 1 come directl-,~ Erom tne mains ,supl~ly net~ o:rk;
1~ a ei:reui-t ~ detec-ting half-perio(l,s o:~ t;he peLiodic s-tra~3, a eireui-t ~; programming the period T of the e;~ternal stimuli ~
whieh circui-t s,~ts a circui-t 5 -to eoun-t a proper nwnber O:r K
half-period,s, a circuit 6 tri.ggerincfr s.irQultaneously suceessive sweeps OI thfe averag:ing proeedure in an a~reraging eompu-ter ~
20 ancl per-tinent sueeessive ex-te~ al stimuli whieh are nrodueed b~ an elee-t:rolurnineseen-t matri}~ of a pho tos timula-tor 3, the -pllo-tos tirnulater ~ equlpped wi-th lhe elee tro].urQineseent matrix is a sou:rce o:E -the e~te:rnal stil~Iuli, a circuit 9 ~ an inst.rumentation ampli:Eie:r for ampli1`~Jing the set of signals Ur~3,, 25 whieh si~nals are piekecl up :Erom an ercunilled objeet 10 b~r means o:f electrodes 11 o~ Ag l~gCl t~-~pe~ the a~Te~ aging eompute r~mning the averagi.ng proceclure of ~the sai d se-t o~ signals and c~ block 12 - memory and displ'ay .~or storing and di~play:i.rLg results of the averaging procedure~
0-oera-tiorI o:~' -the evoke~d responses measuri.ng set-u~ 'o~
- 1'1. -ap]?lyinp; the averaL~ -Lg l~rle-thod :Eor, perioc~:i.c stro.~,rs cJ,inlinatior, is decri~ed below, , 5 '~he sai(1 s-tra-ys coming :Erom the envi:Lonmt,n-t 2 comprir-,ing a source of the str~.ys, in an e~alnpl.e o:~ ma:ins origin, are sensed directly in the source by rneans of a line supplying the ~rholt? se~t-up and -the si~lnal picked up in th:i.3 ~ay is ~e(l di.rectl,~J ^to the sensinl~ circui-t 1~, q'he circuit 1 sensing the pe,io(lic stl-~a~rs comprise3 a s-tepping-do~m trans:CoIDIer, :Erom ~rhlch the periodic strays in Eorm o~' a sinusoidal sigrnal wit~
voltagt or'.' several vol-ts is Ee-l to a lolr-}?ass ~ilter coun-ter-ac-ting coming o:f' sporadic -transi.ent strays'super:Lmposed on the periodic strays through the sensing circuit to f'urther circui-ts.
~15 'L'hen the~ 50 :Eil-tert-~d str~ys are sent to -the circuit ) detect:in,~r`
halE-perlods o:E the said sinusoida.~l periodic strays, ~rhich circuit prodv.ces pulses correspo-nding to every positive and negati~e peaks oE the sinewa~eform o:E -the pe~:iodic strays.
~ounting circuit ~ is provi~ed wi.th khe said pulses and CQU~tS
them tlll the number programme(l by the ci,rcuit ~ ~ progrcaMmin~
-the period o~'-the ef-teInal sti.rlluli., 'l'he sclid pro,,ralnmin~ circui-t de-t,er.m~.nes a }?er-tinent number li corresponding approximatel~
to :the ra-te of -t'he periocl'l' O:r the external sti-lnuli to l-,he halfi-perioc~ 2 t of the perio(lic str~,ys, and the ~ is al~rays an odd number. 'l'he a:Eorementioned counting circui-t ~ produces every li halE-periods a pulse, which is sen-t directly to the circuit,,6, ~rhich -triggers direc-tly -the pho-tostimulator 8 and th3 a~erc~glng computer ~ ~'he photos-timulator 8, trit,gered b~
a pulse :.froln the said circuit 6 gener~ltes -the e~ternal s-timuli in :f'orrn ol'-the photostimuli which through an eye and visual . 15 . .
nervous path produce an elec-troph~siolog:ical rcsponse :in pertinen-t.re~ions o:f a cor.te~. lhe elec-trophyc3iolo~lcal :resr)onxe cor.r.esponds to an individual evoked response U0~r~rhich is piclsed up b~ the e~ectrode-- 11 place~ on the scalp of the e~amined object ~. 'Ihe said in~ividual evoked res~onse U0~
is picke~ up together ~ith the internal noise usæ~ in this ca~e being calle~ an electro(rlce-phalo~ram, and ~rith -tlle perio(l:ic s-tr~ys Uz~ originatecl from the environment 2 comprising a main ~uppl~J net~rork The saicl set of signals is fecl to clifIeréntial :inputs o r the ci.rcuit '~ - -two channel ins-trwnenta-tion ampli:f.i.er.
The ;aid circui-t 2 in each of i-ts channels ampli:ries the said se-t oI` signals U~s to match its output voltage ~ri.t;h an voltar-;e ranFrc of analo~ inpu-ts o:L` the averaginr computer 7. ~ach trig~rerinp; pulse starts successive sweeps o:f` the averaging procedure for the se-t o.~ si~nals Uæs 'I'he averaged. set of signals Uzs equals -the avera~ed evol~ed response U0w. l`he product of avera~?ring of -the set o:f.
sigrnals U~s ln -the averaging compu-ter ~ is sent :~rom the col~puter to the bloclc 12 - memory an(l cli.spl~y to ~rovide a ~ossibili.t~ for fu-ture displaying and selecting~ a resul-t and -to pr.ovi.de data for furtner statis-tical anal~sis ~lïth the use of a big digital compllter Procura-tor: ~s~Jchoneurological Instit1l-te
Claims (3)
1. An averaging method for periodic strays elimination appropriated for application in analog-digital computers employing the averaging procedure, which procedure processing a set of signals Uzs picked up by electrodes 11 from an examined object 8 elicits an averaged evoked response Uow due to its capability of reducing internal noise Uszw and periodic strays Uzp originated in an environment 9 comprising a mains supply network proportionally to the square root of N sweeps of the said procedure and in case the periodic strays and external stimuli are synchronous, the averaged periodic strays Uzp are not sufficiently reduced and distort the averaged evoked response making its right inter-pretation difficult and in order to avoid it means of analog and/or digital filtering supporting the averaging procedure are used or instead the averaging method distinct in this, that the periodic strays Uzp are eliminated from the set of signals Uzs during the averaging procedure in greater extend i.e. proportionally to the number of N sweeps of the averaging procedure resulting in their at least N-fold reduction thanks to introducing permanent desynchronization between the frequency ? of the external stimuli and the frequency ?
of the periodic strays and thanks to introducing an odd number K of half-periods of the said frequency ? , which number K determines the value of the period T according to the formula o T = ? t K, where K is a natural and odd integer.
of the periodic strays and thanks to introducing an odd number K of half-periods of the said frequency ? , which number K determines the value of the period T according to the formula o T = ? t K, where K is a natural and odd integer.
2. An averaging method for periodic strays elimi-nation as in Claim 1 distinct in this, that the permanent desynchronization between the frequency ? of the external stimuli and the frequency ? of the periodic strays is realized by introducing a phase shift by angle .alpha.= 180°, which phase shift simultaneously corresponds to a time shift by one half-period of the said frequency ? of the periodic strays, in particular of mains origin and initial phases of the periodic strays at the beginning of two successive periods of the external stimuli or alternately at the beginning of two successive sweeps of the averaging procedure differ by the value of the introduced phase shift.
3. A counting circuit in an evoked responses measuring set-up for applying the averaging method for periodic strays elimination comprising a triggering circuit 6 being directly connected to triggering inputs of an averaging computer 7 and a photostimulator 8 and delivering common pulses of frequency ? triggering successive sweeps of the averaging procedure in the averaging computer 7 and simultaneously triggering successive external stimuli in particular photostimuli in the photostimulator 8 distinct in this, that the period T of the triggering pulses is a result of summing of half-periods of the periodic strays, e.g. of mains origin of frequency ? done by a counting circuit 5 by sensing the said periodic strays from an environment 2, e.g. comprising a mains supply network, from which by means of a cord supplying the measuring set-up the sinewave signal of the example periodic strays is fed to a sensing circuit 1 comprising a transformer stepping down the signal voltage and an analog filter, which counteracts coming sporadic transient strays supperimposed on the periodic strays through the sensing circuit to further circuits, and the said sensing circuit after stepping down the voltage and filtering the periodic strays sends it down a direct connection to a half-period detecting circuit 3, which provides a counting circuit 5 with pulse determining successive half-periods of the sinewave signal, which is equivalent to the periodic strays induced in an examined object 10 from an environment 2 comprising the said source of the periodic strays in the form of the mains supply network.
A counting circuit in an evoked responses measuring set-up as in Claim 3 distinct in this, that a counting circuit 5 is through a direct connection programmed by a circuit 4 programming periods T with a given value of periods Tz and the value of the period T is approximately equal to the value of the period Tz, as the said programming circuit 4 finds an odd number K, which best approximates the result of , which number K delivered to the counting circuit 5 and stored there results in this, that the circuit after counting every K half-periods provides the triggering circuit 6 with pulses of frequency .
A counting circuit in an evoked responses measuring set-up as in Claim 3 distinct in this, that a counting circuit 5 is through a direct connection programmed by a circuit 4 programming periods T with a given value of periods Tz and the value of the period T is approximately equal to the value of the period Tz, as the said programming circuit 4 finds an odd number K, which best approximates the result of , which number K delivered to the counting circuit 5 and stored there results in this, that the circuit after counting every K half-periods provides the triggering circuit 6 with pulses of frequency .
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP84100957A EP0151656B1 (en) | 1984-01-31 | 1984-01-31 | Averaging method for elimination of periodic strays and a circuit arrangement for applying the method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1204871A true CA1204871A (en) | 1986-05-20 |
Family
ID=8191740
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000446004A Expired CA1204871A (en) | 1984-01-31 | 1984-01-25 | Averaging method for periodic strays elimination and the counting circuit for evoked responses measuring set-up for applying the method |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4665499A (en) |
| EP (1) | EP0151656B1 (en) |
| AT (1) | ATE42032T1 (en) |
| CA (1) | CA1204871A (en) |
| DE (1) | DE3477641D1 (en) |
| DK (1) | DK8400311A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1187446B (en) * | 1985-06-18 | 1987-12-23 | Consiglio Nazionale Ricerche | DEVICE TO SEPARATE THE SIGNAL FROM NOISE AND BACKGROUND CONTRIBUTION, PARTICULARLY FOR COMPUTERIZED ELECTROCHEMICAL INSTRUMENTS |
| US5331969A (en) * | 1985-07-30 | 1994-07-26 | Swinburne Limited | Equipment for testing or measuring brain activity |
| US5199439A (en) * | 1990-01-16 | 1993-04-06 | Stanley Zimmerman | Medical statistical analyzing method |
| US5119321A (en) * | 1990-05-14 | 1992-06-02 | Harris Corporation | Adaptive threshold suppression of impulse noise |
| GB9418872D0 (en) * | 1994-09-19 | 1994-11-09 | Special Trustees For The Unite | Electrophysiological data collection system |
| AUPP354898A0 (en) | 1998-05-15 | 1998-06-11 | Swinburne Limited | Mass communication assessment system |
| AUPP354798A0 (en) | 1998-05-15 | 1998-06-11 | Swinburne Limited | Decentralised patient management system |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL291827A (en) * | 1961-03-17 | |||
| FR1518881A (en) * | 1967-02-14 | 1968-03-29 | Thomson Medical | Improvements in devices and methods for the detection and summation of low amplitude signals, especially bioelectric signals |
| US3901215A (en) * | 1971-08-20 | 1975-08-26 | Erwin Roy John | Method of testing the senses and cognition of subjects |
| US4199817A (en) * | 1977-01-25 | 1980-04-22 | Conkling Laboratories | Digital averager |
| US4171696A (en) * | 1978-01-30 | 1979-10-23 | Roy John E | Prevention of distortion of brainwave data due to eye movement or other artifacts |
| US4326539A (en) * | 1978-11-28 | 1982-04-27 | Wladimir Obermajer | Process for measuring the cardiac volume |
| US4407959A (en) * | 1980-10-29 | 1983-10-04 | Fuji Electric Co., Ltd. | Blood sugar analyzing apparatus |
| US4462411A (en) * | 1981-01-07 | 1984-07-31 | The University Of Melbourne | Evoked response audiometer |
| FI63635C (en) * | 1981-06-22 | 1983-07-11 | Instrumentarium Oy | FILTRATIONSARRANGEMANG FOER ELIMINERING AV NAETSTOERNINGAR |
| US4561449A (en) * | 1982-11-30 | 1985-12-31 | Minnesota Mining And Manufacturing Company | Auditory-evoked-action-potential-measuring system |
| US4543957A (en) * | 1983-06-13 | 1985-10-01 | Ernest H. Friedman | Human response apparatus and method |
-
0
- DK DK8400311D patent/DK8400311A/da unknown
-
1984
- 1984-01-25 CA CA000446004A patent/CA1204871A/en not_active Expired
- 1984-01-31 AT AT84100957T patent/ATE42032T1/en not_active IP Right Cessation
- 1984-01-31 EP EP84100957A patent/EP0151656B1/en not_active Expired
- 1984-01-31 DE DE8484100957T patent/DE3477641D1/en not_active Expired
- 1984-02-07 US US06/577,677 patent/US4665499A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0151656B1 (en) | 1989-04-12 |
| DE3477641D1 (en) | 1989-05-18 |
| ATE42032T1 (en) | 1989-04-15 |
| DK8400311A (en) | 1985-07-25 |
| US4665499A (en) | 1987-05-12 |
| EP0151656A1 (en) | 1985-08-21 |
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