1. Supercapacitor Energy Storage for Magnetic Resonance Imaging Systems
By SARIN S ABRAHAM
Indroduction
Magneticresonance imaging(MRI) isone of the most importantmedical imagingmodalities.
In MRI the harmful ionizingradiationsare absent
The powersupplyratingforMRI istypicallyseveral hundredkilovoltamperes.
Supercapacitorsoffermuchhigherpowerdensitiesandsufficientlylonglife cycle toMRIsystem
MRI SYSTEM
1. MRI reliesonthe principlesof nuclearmagneticresonance.
2. The three fieldgradientsare producedbythe correspondingcoppercoil.
3. Each gradientcoil isindependentlypoweredbyaseparate amplifier
4. To produce anatomical images,MRIemploysspatial encoding
Power profile
For the analysisof the powerusage bythe MRI system,pulsesequence relatingtothe three
gradientcoils,whichdefinetheircurrentprofile i(t).foragradientcoil of inductance L& resistance R,
the correspondingvoltage isgivenby
v = L(di/dt)+R*i
AssumingthatRais internal resistanceof gradientamplifier,powersuppliedtogradientaxisis
p = v * i=L(di/dt)+(R+Ra)*(i^2)
total gradientpower suppliedtothe MRI systemis
p = pSS+ pPE+ pFE
SUPERCAPACITOR
Alsoknownasultracapacitor
Familyof electrochemical capacitor
The capacitance value of an electrochemical capacitorisdeterminedbytwostorage principles
Supercapacitorsare dividedintothree families,basedonelectrode design(Double-layercapacitors,
Pseudocapacitors,Hybridcapacitors)

2. PreliminarySupercapacitor selection
The prescribedsetof imagingsequences(Table II),whichdefinethe currentprofilesforthe three
gradientcoils
The total energyusedforthe whole protocol isdeterminedbythe resistive lossesinthe gradientcoil
windings,anditwasestimatedtobe 449 kJ.
From this,itwas concludedthatusingaseriescombinationof twostandardsupercapacitormodules
BMOD0063-P-125
The available storedenergywasestimatedas620KJ
Experimental SupercapacitorParameter Estimation
Parameters Racc,R, Cacc,C, and Ls were estimated usingEIS.
 Racc = .0129Ὠ
 R = .03Ὠ
 Cacc = .91 F
 C = 7.77 * V + 42.7
 Ls = 2.7 nH
PERFORMANCEANALYSIS
A. The equivalentcircuitmodeldevelopedearlierwasusedto simulate the energyusage
throughoutthe stroke examinationandto analyse the supercapacitorperformance within
the target system.
B. The gradientcurrentprofiles(pulse sequences)forthe complete examinationwere
generatedusingthe available MRIspectrometerandrecorded.
C. Usingthe electrical parametersof the gradientcoilsandthe amplifiers,these wereusedto
generate the correspondingpowerprofilesexperiencedbythe powersupplythroughoutthe
examination.
A. Energy Used
 The resultsare summarizedinTable IV,whichshowsvoltagesandenergyusedineachof
the image acquisitionsdetailedinTable II.
 Fig.13 additionallyshowsthe resultsasaplotof voltage versusenergyremainingatvarious
stagesof the examination.
 It can be seenthatthe supercapacitorbanksdomeetthe requirementof thisapplicationin
termsof the overall energyusedandthe voltage range,whichremainsabove the bottom
limitof 150 V.

3.  It shouldbe notedthatthese figuresconservativelyassume thatthe supercapacitoris
chargedonlybefore andnotduringthe examination.
B. Overall SystemImpact
The proposedsupercapacitormoduleshave acombinedweightof around120 kg and occupy1.0 ×
0.7 × 0.6 m3, considered suitable forbothmobile and stationaryuse
The gradientamplifiersneededahighervoltage ratingthan150 V requiredbythe gradientcoils
alone.
The proposedgradientsysteminterface withthe local powersource replacesthe usual switch-mode
powersupply
Advantage
 Inpractice,the supercapacitorswill be replenishedata constantrate bythe charger.
 The time available toreplenishthe storedenergymaybe assumedtobe 30 min,on the basis
that thisisthe durationof an examinationappointmentforone patient.
 Half of that time maybe takenby the patientsetupinthe scanner.Clearly,charge current
may be tradedagainstchargingtime.
CONCLUSION
 The studyhas analyzedthe suitabilityof supercapacitors asenergystorage foruse withMRI
systems,asthe meansof reducingthe powersupplyrating,tomeetneedsof mobile units
and to reduce the capital costsof permanentinstallations.
 The additional costsassociatedwithsupercapacitorsare well exceeded bythe savings
achievedonotheraspectsof the proposedsystem.
 In case of the lessefficientshieldedgradients,the increasedpowerconsumptioncanbe
readilymetwithalargersupercapacitorbank.