超高場(chǎng)強(qiáng)磁共振下DBS電極周?chē)M織的病理改變

MR-DBSInducedThermalInjuryontheBrainWhythistopic1,MR

compatibilitywithDBSonanimals.2,HarshrequirementsofclinicalMR-DBS.IndicationsofMR-DBSAccordingtoMRIguidelinesforDBS，whenMRcannotbesubstitutedbyotherexaminationslikeCTorultrasonic，thepatientwithDBScanundergoMR，IPGbeingturnedoff.11.5TMR，T-Rheadcoil2headSAR(specificabsorptionrate)≤0.1W/KG3dB/dt≤20T/sContraindicationsonspecification1，otherartificialimplants2，anesthetizedpatients3，othersubstituteexaminationavailable4，bodycoil,headTcoilorheadRcoil5，not1.5TMedtronic’svouchIntroductionDBS:aleadingtoolforFunctionalNeurosurgery，appliedforessentialtremor(1997),PD(2002),dystonia(2003)(FDA)。Future:epilepsy,obsession,majordepression

andchronicpain.IntroductionFrom2003,100,000patientsreceivedDBStreatmentglobally,morethan4000inChina,manyofwhichneedMRassistanceforguidenceoffurthertreatment.IntroductionWhatwillhappenwhenpatientswithDBSundergoMRexamination?

+

=?First,takealookatreportsonmedicaldevicesinducedthermalinjuryduringMRexamination.Cases1991,GBashein:acaseoffull-thicknessskinburninjuryinthevicinityofoxymeteraftercervicalMRscanning.acaseofsuperficialthighskinburninjurybeneaththeoxymeterwireafterheadMR.Cases1992,StevenG:acaseoflargeareaofsecond-degreeburninaxillaafterlumbosacralMR.Aspecificallydesignednon-MR-disruptivethermometerwassuspectedtobethecause.1996,Jones：FullthicknessburnattheECGcontactafterMR1997,Jackson:EyelidedemaandcongestionafterheadMR,probablyduetothepigmentationofeyelinerwhichcontainsmetalWillMR-DBSleadtoburn?Themechanismsoftheheating.HowtoensurethesafetyofpatientswithDBSinfaceofMR?ContentsIntroductionforMRheatingofconductsMechanismsofMR-DBSheatingBrainthermaldamageConfirmationofthermaldamageCasesIntroductionforMRheatingofconductsMagneticResonnanceMRprinciplesMRprinciplesFeaturesofMRmagneticfield3sortsofmagneticfieldsinMR

a,Static----atalltimes，magnetictorque；

b,gradient----scanning，framing；

c,RF----scanning，energyleveltransitionRadiofrequency(RF)：0～3000GHz

radar,television,phoneMR-RF----shortwave,ultrahighfrequencyRFheatingRF

heating

aoverallheating----heatstress

blocalheating----thermaldamageSAR：measuringthequantityof

RFenergythatisabsorbedbythebody,W/kg.influencedbyRFfrequency,type,coils,tissuemass,configuration,etc.

mass=50%RF

wavelenth，SAR

maxHeatingmechanismsofconducts1,Electromagneticinduction

probableinMR-DBS

closedcircuit（IPG-wire-lead-body）----changeofmagneticflux----inducedvoltage----inducedcurrent----JouleheatElectromagneticinductionHeatingofElectromagneticinduction

Artificialcochlea(<1°C),intracranialclips,artificialvessels(0-0.3°C),ECOG

contacts.2,Resonance

coilswillreceiveRFpowerandinducealternatingcurrents，producingmuchheat.HeatingmechanismsofconductsResonanceResonance:temperaturerise(max)>60°C.CaseforresonanceInsideMRcoil,LocalTEMPrise>60°C/30s,(Rcoil)

outsideMRcoil,TEMPrisenotmuch(T-Rcoil)Heatingmechanismsofconducts3,Antennaeffect

possibleinMR-DBS

WiresofDBSlead,oxymeter,ECG,EEGareall"antenna",receivingRFenergy.

Antenna=1/2wavelenth:maxreception.

PowerreceivedwillbereleasedonthetipAntennaeffectTEMPrise>60°CPhantomtests：electrodeofspinalstimulator2-11°C；ECG

contact69°C,intravescularGUIDING72°C。WillMRcauseTEMPrise?15volunteers:routineheadMR,multispotsTEMP(sublingualpocket,skin,rectum).

?Skin:0.2-2.0°C,?Core:0.Another,≤7.55T,AverageSAR≤6.0,multispot(esophagus,tympanic,dura,scrotum,

eyeball)

NodetrimentalTEMPrise(0.2-2.0°C)Eye,testis(worstcoolingorgan)

routineMR:

TEMP≤36°C

(widelyaccepteddamagingTEMP:41-55°C)WillMRcauseTEMPrise?Animal:SAR≤4.0,RF,

noelevationincore.

SAR>4.0,RF,slightrisenotsignificant,withchangeofheatdissipation,dogtonguesticking，rattailsecreting,whichoccurewhen>38-40°C.MechanismsofMR-DBSheatingMechanismsofMR-DBSheatingRFpower----antenna----closedcircuit----changeofmagneticflux----inducedvoltage----inducedcurrent----Jouleheat

similartoRFpallidotomyTEMPchangeofDBSleadRezai,phantom,1.5T,body:2.5-25.3,head:2.3-7.1body：6.1(extrawiresurroundingburhole)25.3(surroundingIPG)head：2.3Extrawiresintosmallloopswithchangingdiametersonthelevelofburhole.

Left:open,Right:filled.

1.5T,3.0T.

0-2.75loops

1.5T:1.8-10.3°C3.0T:0.8-7.3°CSmallloopsreduceheatingofMR-DBSNumericalmodelofMR-DBSheatingMaged,JNeuroengineer:Sumerizedplentyoftestsin-vitro,ex-vivoandin-vivo,constructednumericalmodel:DBS:M3389(1.5mm-0.5mm)andM3387(1.5mm-1.5mm).M3389

heatdistributionindifferentheatconductionrates（k=0.026,30,300）

k(diamond)800-2000,k(d-likecarbon)30-40?TofDBSelectrodeinnormaloperation(0-1.75v)andMR-RF(1.75-5v)Fourki3T,7TMR-DBS,gelphantom,SAR3,extrawire:loop;top,side,front.?T:3T>7T,?T:side>top>front,max:8.2/7.6°C

exceptforsideloop,7T?T<2°C,3T?T<4.5°C

6mm?Tslightlylessthancontacts.

BrainthermaldamageCellulardamageduetothermalinjuryChangeinmembraneconductance,enzymeactivity,actionpotentialthreshold.

Ionaccumulation,malfunctionofcellularorgan,enzymeinactivation.ThermaldamageofthebrainCEM43，cumulative

equivalentpermin

indicatingheatdamageofdifferentcouplesofTandtCEM43=t×R43-T，43°·1min=45°·15s=40°·1hThresholdforbrainthermaldamageDewhirst:

Threshold:43°C

43°C1min=heatdamage

17min=evidentlydamaged

60°C

severalseconds=necrosisHoops:43°C1h=deathofneuronsConfirmationofthermaldamagePathologicalchangesHeatsensitivity:neuron<glial<vesepithllReversibledamage:edema(ballon,lightlydyed）Irreversibledamage：

Necrosis:swelling,karyopyknosis,karyorrhexis,karyolysis

Apoptosis:shrinking,celldensitification,chromotinmargination,apoptoticbody.

Biochemistry—180-200bpDNALadder.Redneuron：acutenecrosis.DetectionofheatinjuryWholebodyheating:sensitivetissueapoptosislocaloverheat:acutedamage

necrosis-transition-normal

2h

apptssstart,24happtssmaxDetection:electronmicroscope,DNALADDER,TUNELdyeingMolecularbiology----HSP70HSP70：

constitutional:pr

molecularfolding

stress:wholebodyorlocal,heating,trauma,stressandseizure,decreasingcelldamage.LegalMedicine2012/EPResrch2011:

stressorlocaldamage

leadtoHSP70pr

andmRNA

risesignificantly.CasesWhenstickingtoMRguidelineKovacs:34MR-DBS

safeLarson:746DBS,1000MR,transientpain,safeChharbra:64,safeUllman:21DBS

head,9beforedeath1.5TMR，Notissuedamagearoundelectrodes.

4ex-vivo3.0TMR.NotissuedamageCases2003,JNeurosurgery,JorgSpiegel:

73y,F,PD,tremor,bilateralSTN-DBS,II

phasesM7428.

Externalstimulation:righttremordisappear,leftdecreasesignificantly,slightdysarthria,nomovementenhancement.

HeadMR(1.0T,T-R

head),externallead:outsidecoil,straight,

noinsulationdisorder.

AfterMR,distonia,

leftlegballisticmovement:leftfootcontinuousspasmicdorsalflexionandexternalextension.leftkneeballisticextension.

Whenrightstimulatorturnson,the