Im1DepUni

IntrodSeparapower the coielectrocommeImagintemperheatingSNR STheoryPrevioubetweemeans make rthen bevoxels MethoImaginaroundCircuittuned a12cm d1.6% Corder Bfibre-owere acwas 38MRTI volumeData w90° (quwith idComplseries, from thdrift co−0.009were ccycle toresiduaprovidiMathwResultFiguresquadrathe SA2. Thethe thelocatiofunctioTable 1DiscusThermoindicatmeasursimilarHelmhSAR dpeak Sby the improvSAR mAcknofibre opRefereMRM;

mproving SNR

partment of Medicated Kingdom, 3Cen

duction ate labelling coil co

RF amplifier to dils can be high, themagnetic simulatiercial packages arng [3] (MRTI) usirature dependenceg from a pair of CAR maps. y: SAR Estimatious studies have asen the two measurethat only a small

regular MRTI meae calculated from experiencing SAR

od ng was performed d a re-cycled spects Inc. Brooklyn, Nand matched to 12diameter, 20cm loCuSO4 doped distiB0 drift correction ptic thermometer cquired every 33.8

840ms. Prior to MRmeasurements con

e acquisition, yieldwas acquired in fivuadrature) and 180dentical voxel posiex phase images to obtain phase i

he temperature cororrection. ∆T map97ppm, and the timalculated with theo obtain SAR mapals between the ming a measure of c

works Inc., Natick, ts s 1 and 2 show S

ature configurationAR all of the voxele y axis is logarithermometer probe (n (orange), and cl

ons, thin lines the 1 displays the peakssion and Conclusometer probe andting that the temprements. The fitter spatial distributioholtz maps match wdistributions betweAR in table 1 shoIEC[2]. To conclu

ve the SNR of the maps show consisteowledgements Davptic thermometer,

ences [1] Mildner, 63 1:218–223; 20

R in small tem

al Physics and Biontre for Neuroscie

ontinuous arterial sdeliver continuous erefore it is desirabions have becomere costly, and it caing the proton rese of the magnetisaCASL labelling co

on ssumed that the onements (2 minutestemperature rise o

asurements over anthe initial temper

R heating and therm

on a 3T Siemensctrometer (MR500NY, USA). Each c23.2MHz. A wholong cylindrical gelilled water cylindr[6]. Coils were po(ProSens with PS

84s with FOV = 21RTI measurementsnsisted of an initiding a time-series ve separate scannin0° (Maxwell). Twotions to the EPI vowere processed b

increment imagesrrected phase of ths were calculated

me series of each equation 1, where

ps at 100% duty cymeasured temperatu

confidence. ImageMA).

SAR maps at the n and the left hand ls within the imagihmic (base 10). F(blue) and in two lose to a transmittiactual data. Figurek SAR in each SARsion d MRTI measureerature compensatd functions closely

on; high local SARwell with superpoeen all configuratiow good agreemenude, presented is a initial measuremeency throughout a vid Carmichael, Jeand the MRC for T., et al.; MRM; 4

010. [5] Cline, H.,

mperature chaAaron Oliver-Ta

oengineering, Univnce, University of

spin labelling (CAwave (CW) poweble to obtain SARe the prevailing man be difficult to csonance shift allowation phase. Prese

oils using a 3D EP

nly contribution tos [5]), and if the ooccurs over this shn extended period ature change in thmal conduction, an

s Tim Trio (Erlan00, Surrey Medicachannel drove an ee-body birdcage cl phantom (2% agrical reference phaositioned at opposiSP-62 Modules an10 × 210mm, 2.5ms this sequence waial EPI volume acof 100 phase imagng sessions: each Ao MRTI datasets wolumes was run to by dividing by th, ∆φ. A first-orde

he reference phantoaccording to ∆T =voxel was fit to the c = 4200J/kg, anycle. In addition mure data and the me processing was p

centre of the ASLcoil only, respectiing volume with a

Figure 4 is a plot oregions of interesting coil (black). Tes 3 and 4 are fromR histogram.

ements show gooted B0 correction y match the data in

R close to the coilsositions of the indiions are also seen

nt, and the highest method for measunts, from which thrange of measurem

eff Hand and Olivefunding this resear49 5:791–795; 200et al.; MRM; 51 6

ange MR Theraylor1, Chris Randversity College Lonf Melbourne, Melbo

England

ASL) [1] typically uer to the neck. DesR maps to ensure thmethod for produccapture the nuancws 3D temperaturented is an optimPI acquisition and

o the temperature cbject is at thermalhort period, and cof heating, and to

he fitted data usingnd fibre optic therm

gen, Germany) wal Imaging Systemelement of an ASLcoil was used to trgar, 1.6% CuSO4 ,antoms were placedite sides of the phand OTP-A Sensorsmm slice thicknessas run for 2.5 hourcquisition, followeges. To avoid the sASL coil element

were collected in efacilitate precise l

he first image in ter 2D linear fit geoms was subtracte= ∆φ/αγB0TE[3], whe equation 1. SAnd divided by the

maps of the sum ofmodel fit were geperformed in Matl

L coil array, obtaiively. Figure 3 is aa sum of squares eof the temperaturet (ROI) positioned

Thicker lines represm the quadrature c

d agreement withproduces accurate

n both ROIs. SARs. The quadrature, ividual coil SAR mn in the SAR histmeasured SAR; 8

uring the SAR of ahe SAR is calculatments. Further woer Josephs for usefrch.

03. [2] IEC 6601-26:1129–1137; 2004

rmometry to adell2, Roger J Ordidndon, London, Engourne, Victoria, Aud, United Kingdom

utilises a close fittspite the low total hat local SAR limcing SAR maps. Hes/imperfections ore maps to be acq

mised method for aan image process

change within a vl equilibrium whenconsequently the mo then fit the tempg equation 2. Themometer probe da

whole-body scannems, Guildford, UKL labelling transmransmit the imagin, 0.9% NaCl) wasd equilaterally aroantom. The tempers, OpSens, Quebes, TE=32.86ms, TRrs, establishing a ded by 99 blocks osaturation of spins,pulsing individua

each scan session. location of the temthe time enerated d for B0 with α =

AR maps RF duty

f squares enerated, lab (The

ined from the a histogram of error less than e measured by d at the probe sent the fitted configuration.

h each other, e temperature

R maps show a Maxwell and

maps. Similar ograms. The

8.78±0.38W/kg fora transmitter RF coted. MRTI measurork will be to validful discussions, An

2-33, Edition 3; 204. [6] Poorter, J.D.

Right Left C

HelmhQuadra

Maxw

Table

acquire SAR Mdge3, and David Lgland, United Kinustralia, 4Institutem

ting surface coil copower (1-2W), lo

mits [2] are not excHowever the softwof ‘home-built’ coquired by taking acquiring an MRTsing technique for

voxel is from SARn heating commenmeasurements suffperature change to e fitting function wata from the same l

er, interfaced to a K), equipped withmit array, comprisinng RF pulses, ands positioned withinound the gel phanterature of each phaec, Canada). 3D gR=80ms, and GRAdynamic thermal eqof transmitting at f, RF heating was a

ally, and both coil After MRTI meas

mperature probe.

r the Helmholtz cooil, by acquiring a rements were validdate the SAR mapsntoine Lutti for pu

010. [3] Ishihara, Y, et al.; MRM; 33

Fig 3: Quadratur

Fi

SARmax (W/kg)

Coil 5.51±0.19Coil 7.79±0.69holtz 8.78±0.38ature 7.73±0.20well 7.89±0.78

e 1: Peak SAR

Maps of a pairL Thomas4 ngdom, 2PulseTeq Pe of Neurology, Un

oupled with a low ocal SAR close to ceeded. Full-wave ware is complex, oils. MR Thermal advantage of the

RTI time series of r calculating high

R [4, 5], valid onlynces. The low powfer from low SNRequation 1 on a v

was empirically folocations.

two-channel in-hh 1W nominal RFng of two 45mm i

d a 12 channel recn the head coil antom. The three refeantom was logged gradient echo EPI APPA 2× acceleratquilibrium to accofull power for 30sapplied at 100 kHzelements pulsing

surements had bee

onfiguration is wittime series of EPI

dated against a fibrs against full waveulse sequence code

Y., et al.; MRM; 341:74–81; 1995.

re SAR Histogram

Fig 1: Quadrature S

r of ASL Labe

Products Division,iversity College L

f

y if thermal conduwer level used in sR. To increase SNRvoxel-by-voxel basound to closely ma

house built transmF power amplifiersinner diameter cir

ceive-only head cond three 32mm diaerence phantoms wduring MRTI meavolumes of resolu

tion. The time to aount for heating ofs on the ASL coilz higher than the iwith phase shifts

en made a turbo s

thin the 10W/kg lI phase images andre optic thermomee electromagnetic e, Nikolaus Weisk

4 6:814–823; 1995

Tfit(1/2) te

c: voxel spe: time betw

Fig 2: LSAR Map

Fig 4: Quadratu

lling Coils

, Renishaw PLC, ondon, London,

uction is negligibleeparate coil CASLR it is proposed tosis. SAR maps canatch MRTI data in

mitter system baseds (ZHL-3A, Minircular surface coiloil for reception. Aameter, 30cm longwere used for firstasurements using aution 128×128×48

acquire one volumef the gradient coilsl array and an EPimaging frequencyof 0° (Helmholtz)pin echo sequence

ocal SAR limit sed fitting the data toeter, and calculatedsimulations. opf for lending the

5. [4] Oh, S., et al.

12 1 2emperature at 1st/2n

measurementecific heat capacit

ween measurement

Left Coil SAR Map

ure ΔT Plot

e L o n n

d -s

A g -a 8 e . I

y. , e

t o d

e

;

nd

t.yts

p

2665Proc. Intl. Soc. Mag. Reson. Med. 20 (2012)