Mobile High- SQUID System for MCG Measurement

Abstract

We developed a mobile high critical temperature (high- T _c) superconducting quantum interference device (SQUID) system for a magnetocardiogram (MCG) measurement. The device is composed of a small cryostat, a high- T _c SQUID magnetometer, and digital flux-locked loop (FLL) electronics. A small commercially obtained vacuum bottle enables the device to be hand-held. Large dynamic range was achieved through the digital FLL processing. We also proved the feasibility of this mobile high- T _c SQUID system using simple construction. MCG measurements while holding a cryostat and also in unshielded conditions were successfully demonstrated.

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IE且 ヒ ItRAN S^C TlO N SO NAP PuEDSU PERCO N DU C T]VrTY.〉 O L J9.N O .3J U N E2009
MobileHigh-Tc SQUID Systemfor
MCG Measurement
Daisuke Oyama.M e m b e r :/ C E E ,K o i chiro Kobayashi. MelT lber; /EEC, Masahito Yoshizawa, and
Y o s hinori Uchikawa, Membel; JEEE
8 7 I
AbsL rocI- We deyeloped a m ob i一 eh ig h critieal temperdL ure
syst em ror 琉magnelocardiogram (MCG) meL L SurCment. The
deyicc is composedof asmall cryostAt, ahigh･ TT c SQUID magne･
tomeler, E nd digital nux-locked loop (FLL) e)tlcfronics. A slmH
commercial一 y oblaincd vacuum boL ue enables the device lo be
ha)td･hcld･Largedynamicrangewasadlieved一 IlrO ughthedigilB I
FLL processlng. We a一 so proved the feasibility or this nlO bile
highlTT CSQUIDsystemusi一 一 gsimpleconslruction.MCC meL q ure -
IllentSIVhijehoJdinE 掛 CryO Slal i川 d alsoinunshiclded colldilion s
IVCreSuC eC SSrully demonstrated.
IIIdex Ter"L S- Flux-locked loop (下 1 ･L), mugnclocardi鴨ram,
m obile, SQUIJ) magnclomctcrs.
(high･ Tc) supt!rconducting quanluJn in le r rerencedevice(SQUID)
L
used T or biomagneL ic measuremenlS. 1日heir applicaL ions are
1 0 beexpanded. thedevices must be madee. lSy tOhandle.The
most eagerly desired features include opcraL ionby hand like a
stethoscop e , wilhoul liquid heHum. unゝ hielded operatjon, aJld
一 owcost.A mobi一 ehigh-TeSQUIDsy. Stemisoneway inwhich
L hcse opel-ational rcalureSCanbe reE lliZCd･
)n recent years. Some groups have demonsL mted magne1 0-
cardiogmm (MCG) measuremenlS using speciaH y designed
high-Tc SQUID gradiomeler Chips Lり - 【 3] or elecL n 'c gra-
diomeler System l4ト【 81. They accomplished MCG mea-
suremen【 s with 800d signaL -1 0-noise ratio without magnetic
shielding. 1 1 1COnL raSL . O ur aimis to achieve anMCG measL lre一
m enl WithlhecryoslaLheld by lhe hand･
The mobi)C SQUID system Which is 1 0 be hand-he一 d must
haveasmallcryogenic sensorpan.Wecomposedi10rahigh-Tt
SQUID magne1 0meler and a smaHvacuumboIL Ie･And more-
over. they arecommercially obtainedoncs inordertomakethe
Systemsimple and low-cost.
The mobile SQUID system needs a hrgc dynamic range,
whichcanaHowsmovemenl inthegeomagnelic 触ld.Dmngde-
velopedextreme一 y hi島 hpe仙)rmancereadoutekctTO nics which
can achieve a la ∫ge dynamic range lhrough the workjn且Or a
nux-Jocked loop (ド L L) elecL TO nics with flux-quantt l CO unling
1 . Im oDUCT1 0N
OW CRm CAL temperature (low-TC) supcl'conducL ing
quantum interference devices (SQUIDs) are general一 y
Mn n us crlPLre ceivedAu且 IJS t26.2008.Firstp u blish e dJulle05.2009:G u n- col
versionpub JlS h edJu lyJO .2009ThIswol.kW a ssupp orte dbyth eMln lゝ L ryO rEd-
tlC at1 0n.ScICn t:C.Sp orts.andCultu T t.Gm n d-Ill-AJdF orJSPSF亡 nO W も 1 8-J784
a JldGran d･ in･ AldlorYoungSclen lIIL S(a) 1 87∝ 川 05･
D Oy…iI.K Kob ay恥h=ln dM YoshltaW aar t W IL hlW u teUnL V亡 ri lty. IWalC.
Japiln(C -m n ll 1 530600順 州ate･ U .JCjpJ･
Y UchlkaW 山 swithl'oLyoDcnkiUniycrゝ il).Sn llar na.Jn p n n.
DlSJI;llOb jcc‖d cnli触( 10.1IO 9rrASC.2009･ 2O 1 9200
Fig. L . A blockdlagm mO rlh em obltCSQUlr ) sysIC m . ll 1 SC O l叩O S C do r il
hJAh -TcSQUll) m agn ctom cler.aS m aHvacu umb oIL le.di旦 ilallycon trolkdド LL
cJccL TOIH e ゝ .andah oゝ lC O r nPuter.
1 91. Their devices were reilli之 ed with stale-Or-1 he-art or elec-
tronics.Ontheotherhand. the Rux･quanlaCO unL Ing alsocanbc
exccuL edby anordinary elecL ric circuituSlng adouble-counter
meL J1 0d l1 01 .
We tried to develop a very simple. low-cost mobile SQUIJ)
system using a high-TT e SQUID magnc1 0meL er and ド LL elec-
tronics. A dynamic rar唱 e Whichis wideenoughforT nO biteop-
eration wa. s achieved, and we have demonslraled ～ tCG mea-
surement. qwi山L he mobile SQU】 D sysICm.
lI. CoMPOSmONOF MoBJLF . SQUIDSYsTEM
Fig. I isab一 ockdiagramO l our)atesLmobi一 eSQUJD syslem･
Thesystemiscomposedorahigh-Tc SQUID, acryoslaL , adig-
itally controHed ド LL circuit. andahostcomputer･
A general-purpose high-TL SQUID mag一 一 etomelCr (Sum-
i1 0mO Elecuう c Industries LL d., CL35081).2) was used. rts
crrccL ive ma旦 netOmeL er area is O･ 8 nln-2､and the scns山vlly
L 3/4' is 2･ 7 nT /Oo･where B is the magnetic nu又dens.毛 ly in
its Sensitive area and Oo iH he nut･quantum. The maJtlmum
modulaL jon voltage is t'? _.0 /LV . lts inlTinsic noise Jevel is 0.2
pT /肋 l/2
A commerciaH y obtained vacuumbolt)e(Sumh0mOElecL ric
lndusL ries Ltd.. K H _4) was usedas acryoslal. Jt is made F rom
ゝ m i nlesssL eel andcanbeheldinthehandanditsH quidnitrogen
capacJly isabou10.5 日t was notCustom-designed.
Thedigita) ド LL cireuil ismadeororr-the-shcJFelecL lic pan :
an 8-bit O ne-Chip microconL rOller. a 1 21bil A/D convcrler, a
16-bit D/A converter. and some amplifiers. The electronics is
conL rO lled by ahostCO rnPuL erthroughthemicroconlroller.
A F Iux-quanta eountlng method was used to achieve a large
dyn amjc range 1 9】 . This iゝbased on lhe periodicily Or lhe
SQUIDIs vohage-Ru又 characL erislic･The jntegralO r Oranド LL
is r eset al every lime the F eedback Ru入eXCeeds J ¢ o and
thecorresponding E l)o steps are L hcn counted. Though this
L O B I-8223/‡') _50OO20091 El:E

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a Oram obilehigh-T, SQUIDsyskm" ilhaP 托A InpSO f84
d B Ez )C hsystemcanm e asu rem agn eu亡 Signa JslnS hade d
a n dlO J
process is usuaHy cxecuL ed by a high-perF ormaJICe digital
s鳩 nal processor, in our system th e microcontTO uer COVerS il
wiul a doub)e counter meulO d l101. TTle integraljon and the
reset aredone by the rnicrocontIO ller･Thecounter isseparated
into L he m i CrocontlO ller and 也 e host computer. TTlCTefore
the flux-quanta counung pr∝esslng Can be accomplished by
low･cost microcontro]lcr.
nl. E xpERJMENTAL PERFOR州 ANCES
The design)ng oh he preiamP in 山e digital fu
is a key racl T or the performance or the sysL em･The dynam i c
range and noise perforT nanCe O f the SQUD systemdepend on
thepreamp･Tnthispaper. L hepreampwasdeterm i nedby exper-
imenlaHy companng of ampliRcationsor84, 94 and l04 dB.
Fig･2 sho､ vs the active area for eachcase. Tlle Systems Can
measuremagnetic signa一 son一 y intheseshadedareas.Theywere
propoT tiond to L hc ampliBcaL ion.
Fig. 3 sho､ vs noise specb'a measured inside anMSR. W仙e
noise levc)s were 0.32 pT /1 1 号 1/2 wiL h 84 dB, 0.33 pT /IL笈 ]/2
with94 dB. and 0.88 pT /f]･ 'Jl /2 wiul 104 dB. The )arse peaks
appea-jngaround l00HZWereSuggestedtobecausedby power
一 inenoise(50Hz) anditshamlO nics_They 'W ereincrcascdby 山 e
prcamp oH O 4 dB.
FromtheseresulL S,W eChosethepreanlPOr94dB as themost
suitab一 eortheL hTee amPliRcalions. Dung has theoTedcally dis-
cussedthedesignoTanFLL tll1.However.experjmenL a l com-
pahsonsarc alsoeffectivefor rabricalionof alow-costsystern･
electronics
lV. MCG M EASUREMEN 'TS
Wedemonstratedtwoeズ amPIesorMCG measurernenlsmade
wkh the devclopcd mobile high-TL ･SQUID sysICm. FirsL an
MCG signal was measured uslng this sysL enl With the small
cryostaLheld by the halld near一 hesubjectlschesl.Fig.4 sho､ vs
lhe measured waverorm, The measurement was carried out in-
side an MSR･rl is ゝ uggesL ed that Rucluatjonor ule Signa一 was
caused by vibration or the hand･Afthough the magT)Clic nu又
density Was morethan JOnT, L hc sysL cmcouldmaintainsteady
operationby vinuc oritslargedynamic range.Fi且 .5shows the
MCG waverormana一 ysed by adigital baJld-pass 仙 er (5 1 0 40
0.11 1 01 00 1 000
Frequency(Hz)
F tg. 3･ Magn eticn oisesp ectraoram obilchigh･ Tt SQUIDsystemm cASuT td
ln S 】 deaMSR.lbeyw c托 n 托 AS u Jd wIL hprcam psor84dB.94d B.a Jld1 04dB
8
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Fi且 .4. Magn eticslgT lalm casurcdusin 島 am O bik SQU IDsystemW iththeh a n d ･
h e)acr yostbt.
0
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TL rne(S)
040.5 0.607
Flg.5. Anan alysedMCGwaverorm ThisWasO btain edb) ap plyln gad鳩 IL a )
b an d-pa ss帥cr(5to401 12) an d 1 5-1 im cs averaging.77 1 cm 的 Su T C m C n tW a s
caT ricdoutinsidea llMSR.
Hェ ) and 15-times averagin g (15 seconds). The R wave " h ich
chaTaCleristicaHy showsheaJl aCUVlty is observed.
Second. Fig.6ShowsawaverormrneasuTedoulSidc anMSR.
T he cryosLat Was Put 0n a L abJe at this case. The position and
hcight ol the tablewereadjuslable,L OCO rreSPO ndasubject一 ying

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OYA^lA LIL Il 'MOlIlLE 川GIt-rcSQUIt) SYS¶;州FORMCGMEASUREMENT
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FIE. 6. Mngnctic signal mcaゝ ured using a m obileSQUn) systemwhich､ 叫S
setoI川 (abJc inunshieJdcdconditions.
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F鳩 .7･ AnaJyscdMCG(blackIIn亡 )andECG(8myIIne)waveroT TT lゝ llleyW ert:
ob(alned by applying AdlgL L dHow･pass mter(JOHL) aT L d63-tim esavcr喝ing.
◆ nlClneiL SuremCnl W asCAm亡 doutoutsideAnMSR
付
言
0
01
0203
T lme (S)
04 0.50.607
under Lhc table･T he power line noise or50 Hz Can be majnly
seen iII Fig. 6.
T he dynamic range or our mobile high-T e SQUID system
aJso was e恥 clive Tor unshielded opcralion. F ig. 7 presents si 一
mulL aneOuSly taken MCG and ECG data. T hey arlalyscd by a
digiL aH ow-pass filter (40 Hz) and 63-limes ( I rm 'nuL e) aver-
aging. QRS complex is Shown.
Our experiments dcmonsrraled LhaL the mobi一 e high-7T c
SQUID system Can be used For MCG measul･ emenLS. However,
practical biomagJleLic measuremenLs requlre much higher -10isc
perrormance･ Sorne gradiomeL erS t)ト【 8J and digilal signal
processing methods I12日 131have been invesLigatcd to cance一
873
magnetic noises. lLis hoped that the app l ic atio ns o r them LO the
mobHe SQUID sysLem w i ll improve th e no ise pe rfo - anc e ･
V. CoNCLUSION
We developed a mobile high-r c SQU rD . qy sLem W hi c h js to
be hand-held Tor MCG measurcmcnls. lt has ve ry s impJc c ry 0 -
genic pall and digitally controHed ド LL electronics IOObtain a
large dynamic range. E xperimental comparisons orpreamps a r e
errecLive ror た Ibricalionof a low-costSystem. MCG sigT laJswe r e
stICCeSSf u lly nlCaSured ､ vhile holding a cTyOSl. ･ ll and also in u n-
shielded conditions.T hissyslem isefrecLivc inexpansionof bi o ･
magnetic measurement applicalion･
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