ContentslistsavailableatScienceDirect
European
Journal
of
Radiology
jo u r n al ho me p a g e : w w w . e l s e v i e r . c o m / l o c a t e / e j r a d
Simultaneous
PET/MR
head–neck
cancer
imaging:
Preliminary
clinical
experience
and
multiparametric
evaluation
M.
Covello
a,∗,
C.
Cavaliere
a,
M.
Aiello
a,
M.S.
Cianelli
a,
M.
Mesolella
b,
B.
Iorio
b,
A.
Rossi
a,
E.
Nicolai
aaIRCCSSDN,ViaE.Gianturco,111-113–80143,Naples,Italy
bDepartmentofOtorhinolaryngoiatry,FedericoIIUniversity,Naples,Italy
a
r
t
i
c
l
e
i
n
f
o
Articlehistory: Received17March2014
Receivedinrevisedform26March2015 Accepted11April2015 Keywords: Hybridimaging PET/MR SUV DCE DWI
Headandneckcancer
a
b
s
t
r
a
c
t
Purpose:ToevaluatetheroleofsimultaneoushybridPET/MRimagingandtocorrelatemetabolicPETdata withmorpho-functionalparametersderivedbyMRIinpatientswithhead–neckcancer.
Methods:Forty-fourpatients,withhistologicallyconfirmedheadand neckmalignancy(22primary tumorsand22follow-up)werestudied.Patientsinitiallyreceivedaclinicalexamandendoscopywith directbiopsy.NextpatientsunderwentwholebodyPET/CTfollowedbyPET/MRofthehead/neckregion. PETandMRIstudieswereseparatelyevaluatedbytwoblindedgroups(bothincludedoneradiologist andonenuclearphysician)inordertodefinethepresenceorabsenceoflesions/recurrences.Regionsof interest(ROIs)analysiswasconductedontheprimarylesionatthelevelofmaximumsizeonmetabolic (SUVandMTV),diffusion(ADC)andperfusion(Ktrans,V
e,kepandiAUC)parameters.
Results:PET/MRexaminationsweresuccessfullyperformedonall44patients.Agreementbetweenthe twoblindedgroupswasfoundinanatomicallocationoflesionsbyPET/MR(Primarytumors:Cohen’s kappa0.93;Follow-up:Cohen’skappa0.89).TherewasasignificantcorrelationbetweenCT-SUV meas-uresandMR(e.g.,CT-SUVVOIvs.MR-SUVVOI:=0.97,p<0.001fortheentiresample).Therewas alsosignificantpositivecorrelationsbetweentheROIarea,SUVmeasures,andthemetabolicparameters (SUVandMTV)obtainedduringbothPET/CTandPET/MR.Asignificantnegativecorrelationwasobserved betweenADCandKtransvaluesintheprimarytumors.Inaddition,asignificantnegativecorrelationexisted
betweenMRSUVandADCinrecurrenttumors.
Conclusion:OurstudydemonstratesthefeasibilityofPET/MRimagingforprimarytumorsandrecurrent tumorsevaluationsofhead/neckmalignantlesions.WhenassessingHNC,PET/MRallowssimultaneous collectionofmultiparametricmetabolicandfunctionaldata.Thistechniquethereforeallowsforamore completecharacterizationofmalignantlesions.
©2015ElsevierIrelandLtd.Allrightsreserved.
1. Introduction
Headandneckcancers(HNC)accountforapproximately4–5%
ofallmalignantdisease.Ofthese,headandnecksquamouscell
car-cinoma(HNSCC)comprisesthevastmajority(90%)[1].Diagnosis
ofheadandneckcanceristypicallyachievedbyacombinationof
physicalexaminationandeithernasopharyngoscopyand/or
laryn-goscopywithdirectbiopsies.However,thefirstmanifestationof
the diseasecommonly involvesthe cervical lymph nodes, also
thepresenceofdistantmetastasesanddifferentprimariesmust
beconsidered.Followingdiagnosis,accuratestagingiscriticalfor
∗ Correspondingauthor.fax:+39081668841. E-mailaddress:echoplanare@gmail.com(M.Covello).
selectionoftheappropriatetreatmentstrategy.Forearly-stage
dis-ease,surgeryorradiotherapyarethemostcommontreatments,
withasuccessrateofabout80%[2].Postoperativeradiotherapyis
typicallyrecommendedwhentheriskforlocoregionalrecurrence
exceeds20%[3].Forpatientswhosediseaseisnotcontrolledwith
definitiveradiotherapy,salvagesurgeryisrecommended[3].For
regionallyadvancedHNSCC,concurrentchemo-radiotherapyhas
beenwidely used[4].Currently, positronemission tomography
(PET)andmagneticresonance(MR)arewell-establishedimaging
techniquesforthestaging[5]andfollow-upofHNC.MRtechniques,
suchasdiffusionweightedimaging(DWI)anddynamiccontrast
enhancement (DCE), along with fluorodeoxyglucose (FDG)-PET
are thebasilar imaging techniques usedto assess angiogenesis
andmetabolisminHNSCC.Developmentofnoninvasiveimaging
biomarkersmightassistinplanningoptimaltreatmentstrategies,
http://dx.doi.org/10.1016/j.ejrad.2015.04.010
whichmayleadtoa morefavorabletherapeuticoutcome [6,7].
Therecentcommercialintroductionof hybridPET/MRscanners
offernewpossibilitiesforoncologicimaging,combiningthewide
rangeofphysiologicalinformation(glucosemetabolism,cell
prolif-eration,hypoxia,cellreceptorexpression)achievablebydifferent
PETtracerswiththehighspatialandcontrastresolutionofMRI.
Moreover, advanced MRI techniques (DWI, DCE and MR
spec-troscopy)yieldfunctionalinformationthatmaycomplementthe
findingsof PET imaging. Todate, severalPET/MRI studies have
shownpromisingresultsforclinicaloncologicapplications[8,9].
ThebestapplicationsforPET/MRIimagingexistforHNC.Duetothe
complexanatomyofthisregionthesuperbsoft-tissuecontrast
res-olutionofMRIisextremelyuseful.Forthisreason,PET/MRIseems
tobehighlyaccurateintheevaluationofprimaryextension
(T-staging).However,ithasnosignificantbenefitwithlymphnodes
involvement(N-staging)andlimitedimprovementformetastasis
detection(M-staging)whencomparedtoPET/CTexamination[10].
Therefore,theaims ofthestudy weretoevaluatefeasibility
ofsimultaneoushybridPET/MRimaginginpatientswithHNC.In
addition,metabolicdataobtainedfromPETandmorphologicand
functionaldata(DWI,DCE)obtainedbyMRIonprimarytumors
and recurrentlesionswere correlated.In this context, thenew
technologyofsimultaneousPET/MRscanningcanbesuitablefor
acomprehensivemultiparametricassessment.Wepresentour
ini-tialclinicalexperiencewithsimultaneousPET/MRimaginginthe
evaluationofpatientsaffectedbyHNC.
2. Materialsandmethods
2.1. PatientpopulationandImagingprotocol
InaccordancewiththeinstitutionalreviewboardandEthical
Committee,44consecutivepatients(meanage57±12;23males
and9females)withhistologicallyconfirmedheadandneck
malig-nancy(22primarytumorsand22recurrenttumors)werestudied
betweenMarch,2012toJune,2013.Exclusioncriteriaconsisted
of>150mg/dLbloodglucose,pregnancy,andstandard
contraindi-cationforMRI.Forprimarytumors,notherapyhasbeenstarted
atthetimeofMRimaging.Forrecurrentlesions,imagingsession
hasbeenperformed6–8weeksaftertheendoftreatment
(includ-ing12patientstreatedwithsurgery,4withradiotherapy,andthe
remainingwithacombination ofsurgeryand radiotherapy).All
patientsunderwent aonedaysingle-injectionimaging protocol
includingPET/CTandsubsequentPET/MR.
Briefly,patientswerefastedforatleast6hbeforescanning,
fol-lowedbybloodglucoseassessmentpriortoFDGinjection.Adoseof
406±40MBqof[18F]-FDGwasinjectedbasedonthepatient’sbody
weight.Followinganuptakeperiod(81±15min),patients
under-wentaPET/CTscan.AftercompletionofthePET/CTscan,patients
thenreceivedaheadandneckPET/MRexamination.
2.2. PET/CTacquisition
PET/CTacquisitionwasperformedonaGeminiTF(Philips
Med-icalSystems,Best,TheNetherlands)tomographdesignedwitha
multi-ringLYSOblockdetectorssystemandanominalaxial
reso-lutionnearthecenteroffieldofviewof4.8mm(FWHM)withan
absolutesensitivityof6.6kcps/MBq,aspreviouslyreported[11].
Accordingtoourroutineprotocolforoncologicalstudies,PET
data was acquired in sinogram mode for 15min with
ama-trix size of 144×144. PET data were reconstructed using the
LOR-TF-RAMLAalgorithm,therefore datawaspostfilteredwith
a three-dimensional isotropic gaussian of 4mm at FWHM.
CT-basedattenuationmaps werecreatedwitha low doseCTscan
(120kV,80mA)usingcommonlyemployedbi-linearscaling.The
acquisitiontimewas3minperbedposition(BP),with5\6BPs(each
21cm)coveringthetrunkofthepatientsstartingfromthepelvis
andmoveduptowardthehead.Followingwholebodyacquisition
anadditionalBPwasacquiredfocusingonthehead/neckregion.
Theresultwasatotalacquisitiontimeofapproximately18mins
perpatientforPET/CT.
Thepatientswerepositionedsupinewiththeirarmsbrought
togetherabovetheheadfortotalbodyacquisitionandwiththeir
armsrestingatthesidesforhead/neckacquisition.
2.3. PET/MRAcquisition
PET/MRwasperformedontheBiographmMR(Siemens
Health-care,Erlangen,Germany).Thissystemconsistsofa3TMRIscanner
featuring high-performance gradient systems (45mT/m) and a
slewrateof200T/m/s.ThePET/MRsystemisequippedwithTotal
ImagingMatrixcoiltechnology(SiemensHealthcare),coveringthe
entirebodywithmultipleintegratedradiofrequencysurfacecoils.
Thecoils,patienttable,andcableshavebeenredesignedforPET/MR
inordertominimizetheirattenuationandtoallowunimpairedPET
acquisitionwiththecoilsinplace.AfullyfunctionalPETsystem
equippedwiththeavalanchephotodiodetechnologyisembedded
intothemagneticresonancegantry.
ThePETscannerhasaspatialresolutionof4.1mm(FWHM)at
1cmandof5.0mm(FWHM)at10cmfromthetransverseFOVand
asensitivityof11.72kcps/MBqatthecenteroftheFOV.
Onaverage,thePET/MRscanstartedabout20minafterthestart
ofthePET/CTacquisition.Bedpositionwasestablishedinorderto
getfullcoverageofthehead/neckregion.Aftercorrectpositioning
wasestablished,thecombinedPET/MRacquisitionwasperformed.
First,acoronal2-pointDixon3-dimensionalvolumetric
inter-polatedbreath-holdT1-weightedMRIsequencewasacquiredand
used for the generation of attenuationmaps and for anatomic
allocation of the PET results. The software of theMRI scanner
automaticallygenerates4differentimages:T1-weightedin-phase,
T1-weighted out-of-phase, water-only, and fat-only.
Simulta-neouslywiththestartoftheDixonMRIsequence,PETacquisition
began toensure correct temporal and regional correspondence
betweenMRIandPETdata.ThePETacquisitiontimewas4minand
consideringsimultaneousMRacquisitionthetotalPET/MR
exami-nationlastedabout30min.
2.4. PETdatareconstruction
PETdataobtainedonthePET/CTand PET/MRscannerswere
processed withcomparable reconstructionand correction
algo-rithms. For both modalities, emission data were corrected for
randoms, dead time, scatter, and attenuation. A 3-dimensional
attenuation-weightedordered-subsetsexpectationmaximization
iterativereconstructionalgorithm(AWOSEM3D)wasappliedwith
3iterationsand21 subsets,gaussiansmoothing of4mminfull
widthathalfmaximum,andazoomof1.Attenuationmapswere
obtainedfromtheCT databybilineartransformation,as
imple-mentedinthepost-processingsoftwareofthePET/CTscannerand
wereusedforattenuationcorrectionofthePET/CTdata.
2.5. MRI-basedattenuationcorrection
PETattenuationcorrection(AC)isacriticalissueforintegrated
PET/MRIscanners.Contrarily toX-rayCT, which inherently
pro-videsapatient-specificmeasurementoftheelectrondensity,MRI
signalisonlyrelatedtoprotondensity.Therefore,MRIis
intrinsi-callyunabletomeasureattenuationfactorsduetoelectrondensity.
Proposedsolutionsaresubstantiallybasedonthecombinationof
custom-tailoredMRIacquisitionswithimageprocessing,pattern
Inthiswork,clinicallyapprovedACisperformedbymeansofthe
attenuationmapsgeneratedonthebasisofthe2-pointDixonMRI
sequencesobtainedforeveryBP.Thisapproachhasrecentlybeen
demonstratedtoprovideresultscomparabletothoseof
conven-tionalattenuationcorrectionbylowdoseCT[12].Theprocedure
hasbeenimplementedinthepost-processingsoftwareofthe
scan-nerandoperatesautomatically.TheDixonfat-andwater-weighted
imageswereused tocreate anattenuationmap with4distinct
tissue-classes:background,lungs,fat,andsofttissue.Attenuation
ofthePETsignalcausedbyinstrumentation,suchasthepatient
bedandthefixedMRIcoils,isautomaticallyintegratedintothe
attenuationmaps[13].
It is worth noting that suchAC approach ignores the
pres-enceofbonystructures,thereforelimitingquantitativeaccuracyin
anatomicaldistrictscontaining(orcloseto)bones[14].Toaddress
thisissue,morerefinedACtechniquesarecurrentlyunder
investi-gationandclinicalvalidation[15].
2.6. MRacquisition
TheMRIprotocolwasperformedwithadedicated16channel
headandneckcoilincluding:coronalSTIR,axialFSET2-weighted,
axial FSET1-weighted,axial diffusion-weightedimaging (DWI),
andasingle-shotechoplanar2DSPAIR.Inthissequencethreeb
valueswereapplied:0,500and800s/mm2.
Perfusionstudiesweredynamicallyacquiredimmediatelyafter
intravenousadministrationofparamagneticcontrast(Magnevist®,
Bayer-Schering,Berlin,Germany)with50measurementsofvolume
InterpolatedGREprecededbytwopre-contrastmeasurementsof
thesamesequenceatavariableflipangle(2◦ and15◦).The
con-trastagentadministration(0.2ml/kgbodyweight)wasdonewith
aflow-rateof3.5ml/s,followedbysalineflush,usingapower
injec-tor.
Inaddition,afterdynamicacquisitions,avolumeInterpolated
GREisotropicathighresolutionandaT1-weightedturbospinecho
withfatsuppressionwereacquired.
Table1 shows technicaldetails of theabove-mentionedMR sequences.
InordertoobtaingoodMRIimagequality,allpatientswere
care-fullyinstructedtorefrainfromvigorousswallowingorbreathing
duringimageacquisitionespeciallyduringtheacquisitionofDWI
sequences.Smallbreaksweremadebetweenindividualsequences
toallowpatientstoclearthethroatofmucoussecretions,cough,
orswallow.
2.7. Dataprocessingandmultiparametricanalysis
PETdataobtainedsimultaneouslywithCTandMRexamination
wereprocessed withcomparable reconstruction and correction
algorithms.Forbothmodalities,emissiondatawerecorrectedfor
randoms,deadtime,scatter,andattenuation.
Tumortissuewasidentifiedasanyvoxelinthe3Ddatasetwith
countsgreaterthana fixedthresholdfractionofthepeak
activ-ityinthetumor.Thethresholdlevelfortumorcharacterization
wasselectedasa StandardizedUptake Value(SUV)equal toor
higher than 3.5 [16]. The SUVs were calculated automatically
by the software (Syngo.via, Siemens Medical Systems) using
the body weight method: SUV=[decay corrected tissue
activ-ity (kBq/ml)]/[injected18F-FDG doseper body weight(kBq/g)].
ThemaximumSUV(SUVmax)andmeanSUV(SUVmean)ofthe
tumortissuewerederivedautomaticallybythesoftwareusinga
voxel-of-interest(VOI)methodoftissuedelineationforboththe
acquisitions.Moreover,basedonSUVvalues,avolumetric
charac-terizationoflesionburdenwasmadeassuggestedinaprevious
study[17]consideringametabolictumorvolume(MTV)witha
thresholdof40%ofthemaximumsignalintensity(MTV40).
Twogroupsofoneseniorradiologistexperiencedinheadand
neckimaging(8and10yearsexperience)andonenuclearmedicine
specialist(9and7yearsexperience)wereblindedtothePET/CT
findings and consensuallyreviewed tumor findings on PET/MR
imagesinconsensus.Primarytumorsizeandinfiltrationof
neigh-boringstructureswereassessed(Fig.1A).Acomparisonbetween
PET/CTandPET/MRfindingshasnotbeenperformedconsidering
thatCTexaminationwaswithoutcontrastagentinjectionandthis
couldbiastheanalysisbyunderestimatingCTdiagnosticaccuracy
(Fig.1B).
Subsequently,theDCE-MRimagesweretransferredfor
post-processing to a workstation running commercially available
softwarefortissueperfusionestimation(Tissue4D,Siemens
Med-icalSystems).Aftermotioncorrectionandregistrationofthe
pre-and post-contrast acquisitions, T1 mapping was automatically
performed and a freehand region-of-interest (ROI)was plotted
aroundthetumorincludingtheneighboringvessels(carotid
arter-ies,jugularvein). Thepharmacokineticmodeling wasbased on
atwo-compartmentmodelthatallowsforthecalculationofthe
following:transferconstantbetweenvascular,extravascular,and
extracellularspace(EES)(Ktrans);thevolumeofEES(
v
e);the
con-stantbetweenEESandbloodplasma(kep);theinitialareaunder
theconcentrationcurve(iAUC)[18].Ktransisaparameterrelated
tovesselpermeabilityandtissuebloodflow.TheleakagespaceVe
isamarkerofcelldensity,thekepisatransferconstantfromthe
extracellular/extravascularspacetoplasma,and iAUC isrelated
tothebloodvolumeinthetissueofinterest[18].Arterial input
function(AIF)wasrelated togadolinium doseinjectedand was
modeledbyabi-exponentialfunctionusinganintermediatemode
providedbythesoftware.For thesubsequenttumorROI
analy-sis,PET/MRdatasets(PETacquisition,axialT1post-contrastand
axialT2sequences,axialADCmap,andsingleperfusionmapsfor
Ktrans,
v
e,kep andiAUC)wereevaluatedintoaunified
measure-mentsframeworkcustomizedintotheSyngo.viasoftwareplatform
(SiemensMedicalSolutions)allowingavisualcomparisonofthe
multiparametric data.Post-contrast T1-weightedas wellas
T2-weightedimageswereutilizedtodrivethetumoroutlineinmajor
diameterlesionslice,whichavoidsnecroticareasandlarge
feed-ingvessels.Therefore,ROIareavalue,referredasthetumorsize
inthemajordiameterlesionslicewasextractedforeachpatient.
Formultiparametriccomparisons,theROIoutlinewasdrawnwith
thesamepositionandextentoneachmaptoautomaticallyextract
maximum and mean values for each parameter (SUVmax and
SUVmeanforthePET; ADCmaxandADCmeanforthediffusion;
Ktrans,k
ep,
v
e,andiAUC,respectivelymaxandmeanforperfusionmaps)(Fig.1A).
Table1
SummaryofMRacquisitionprotocolandsequences.
Sequencename Orientation Repetitiontime(ms) Echotime(ms) Flipangle(◦) Voxelsize(mm3) Acquisitiontime(min:s)
STIR Coronal 5000 84 125 1.1×0.8×3.5 2:02
FSET2-w Axial 5000 117 90 0.7×0.7×3.0 3:10
FSET1-w Axial 590 9.9 150 0.9×0.6×3.0 4:32
DWI Axial 13,800 70 2.8×2.8×4.0 2:11
VolumeInterpolatedGRE Axial 5.37 1.78 15 1.7×1.2×3.6 0:10
VolumeInterpolatedGREISO Axial 4.93 2.29 9 1×1×1 4:41
Fig.1.InA,ROIplacementformultiparametricanalysisina70y.o.malewithHNSCClesioninprimarystaging.ROI(inred)wasmanuallyoutlinedonpost-contrast T1-weighted(T1+C)andT2-weighted(T2)imagesinmajordiameterlesionslice,andfollowingdrawnwithsamepositionandextentoneachmap.InB,acoronalviewofthe samepatientfrombothPET/MRandPET/CTacquisitions.
Moreover, standardized ROIs (1cm2) were placed in the
paraspinalmuscleofeach patientin order toobtainSUV,ADC, andDCE-MRIestimatesinthenormaltissueandprovidesignificant differencescomparedwiththetumortissue.
2.8. Statisticalanalysis
Multiparametricdata wereexportedand analyzedusingthe Sigmaplotv10.0programwithSigma-Statintegrationv3.2(SPSS,
Erkrath,Germany).Ap-valueoflessthan0.05wasconsidered sta-tisticallysignificant.Thevaluesarepresentedasmean±standard deviation(SD).
TheKolmogorov–Smirnovtestwasfirstusedtoexamineifthe datawasnormallydistributed.Cohen’skappawasusedto eval-uateagreementforprimarytumordetectioninPET/MRbetween thetwogroupsofobservers,withoutaccountingforlymphnodes involvementandputativedistantmetastases.Anydifferencesin theparametersestimationsbetweenthenormalandtumortissue andbetweentheprimarytumorsandrecurrentlesionswere deter-minedwitha t-studenttest. Spearman’scorrelationcoefficients werecalculatedtocompareMRIandCTbasedSUVvaluesandto comparemetabolicdiffusionandperfusionparameters.A correla-tioncoefficientof≤0.35wasconsideredlow,0.36–0.67moderate, 0.68–0.90high,and≥0.90tobeexcellentcorrelations[19].
3. Results
3.1. Feasibilityandinterobserveragreement
AllPET/CTandPET/MRstudieswereacquiredsuccessfullyand
weresuitableforfurtherevaluation.
Satisfactoryagreementbetweenthetwoobservergroupswas
foundinanatomicallocationoflesionsbyPET/MR(T-staging)with
nosignificantdifferencesbetweenthetwoclinicallydefinedgroups
(Primarytumors:97%,Cohen’skappa0.93;Recurrenttumors:93%,
Cohen’skappa0.89).
3.2. Multiparametriccomparisonintheoverallsampleand
subgroupsdefinition
ThesummarystatisticsfortheFDG-metabolism,diffusion,and
perfusion measurements in the healthy muscle tissue and the
tumorsaredemonstratedinTable2.
Representativecasesofmultiparametrichead–neckimagingare
showninFigs.2and3.
Whengroupingallpatientstogether(n=44)therewasa
signifi-cantpositivecorrelationsbetweentheROIarea,theSUVmeasures,
and the SUV estimations. Conversely, there was a significant
negativecorrelationbetweenMRSUVROI,andADCMean.There
wasalsoasignificantnegativecorrelationbetweenADCMeanand
KtransMean(Table3).
Inparticular,thereweretwosubgroupsidentifiedforpatients
inprimaryorrecurrenttumors.Primarytumors(n=22)included
11laryngeal,3oral,1sinonasal,2oropharingeal,3parotid,and2
rhinopharingealcancers.
Recurrenttumors(n=22)included14casesoflaryngeal,3oral,
2sinonasal,1parotid,and2rhinopharingealcancers.Inparticular,
11patientsreceivedonlysurgicaltreatment,4radiotherapy,and7
bothchemo-andradiotherapy.
3.3. Multiparametriccomparisoninprimarytumors
Asforasprimarytumorsthecorrelationanalysisdemonstrated
asignificantcorrelationbetweentheROIarea,theSUVmeasures,
andtheSUVestimations.
Conversely,therewasasignificantnegativecorrelationbetween
ADCMeanandKtransMean(Fig.2;Table3).
3.4. Multiparametriccomparisoninrecurrenttumors
Asforasrecurrenttumors,theSpearman’scoefficientanalysis
amongthedifferentparametersinthetumorsitesdemonstrateda
significantcorrelationbetweentheROIareaandtheMRSUVROI.
However,thecorrelationwasnotsignificantwithCTSUVVOIorMR
SUVVOI(p=0.35and.23,respectively),whichwasdemonstratedin
primarytumors.Asignificantcorrelationwasalsofoundbetween
theSUVmeasures,MRSUVVOI,andMRSUVROI.Finally,a
signifi-cantnegativecorrelationwasfoundbetweenMRSUVROIandADC
mean(Fig.3;Table3).
No significant differences were detected between the two
groupsformetabolic,diffusionandperfusionparameters.SUV
esti-mationandallperfusionparameters(Ktrans,k
ep,
v
e,andiAUC)intumorsweresignificantlyhighercomparedtonormalmuscletissue
inboththegroups(Primarytumors:p<0.001;Recurrenttumors
p<0.001)(Figs.1and2,Table2).Conversely,theADCmeanvalue
intumorswassignificantlylowercomparedtonormalparaspinal
Table2
Summaryofmetabolic,diffusionandperfusionparametersinboththegroups.
Parameter Overallsample Primarytumors Recurrenttumors Muscle
Mean SD Mean SD Mean SD Mean SD
AGE 60.94 2.23 62.52 12.35 59.36 12.93
AREA–Tumorsize (cm2) 2.73 0.37 2.99 4.90 2.47 1.73 1 0 CTSUVMean 5.77 1.76 4.53 4.53 7.01 5.75 0.715** 0.065 CTMTV (cm3) 14.42 1.62 15.56 19.48 13.27 14.24 MRSUVMean 7.78 2.39 6.09 5.05 9.47 8.91 0.721** 0.077 MRMTV (cm3) 11.92 1.58 13.03 16.59 10.81 11.78 SUVMean2D 20.36 1.35 19.40 24.10 21.32 17.66 0.724** 0.079 ADCMean (m2/s) 1193.26 0.14 1193.14 481.68 1193.4 187.09 1483.58* 108.2
KtransMean(min−1)
(×1000) 268.09 13.60 277.71 167.29 258.48 150.82 51.18* 10.36 kepMEAN (min−1)(×100) 83.99 5.98 88.22 62.30 79.76 31.73 51.59* 14.36 iAUCMean (mMmin)(×50) 901.54 17.73 914.08 472.24 889.01 539.96 166.21* 30.27 veMean (×1000) 326.35 25.84 308.08 124.99 344.62 133.11 103.52* 22.03
Abbreviations:CT:computedtomography;SUV:standardizeduptakevalue;MR:magneticresonance;MTV:metabolictumorvolume;ADC:apparentdiffusioncoefficient; Ktrans:transferconstantbetweenvascularandEES;kep:constantbetweenEESandbloodplasma;iAUC:initialareaundertheconcentrationcurvein60s;ve:thevolumeof
EESperunitofvolumeoftissue.
*p≤0.05; **p≤0.01.
Fig.2.Multiparametricevaluationofmorphological(T1,andT1+C),metabolic(PET)andfunctional(DWI,ADC,iAUC,ve,kep,andKtrans)ina57y.omalewithrightvocalcord
HNSCCandanteriorcommissureinfiltrationinprimarystaging.Theincreaseofthicknessandenhancementofthetumorsiteinthemorphologicalacquisitions,theincrease ofFDG-uptake,andthereduceddiffusivityinADCwithanincreaseofperfusionparametersweredetected.
Fig.3. Multiparametricevaluationofmorphological(T1,andT1+C),metabolic(PET)andfunctional(DWI,ADC,iAUC,ve,kep,andKtrans)ina69y.o.malerecurrencyafter
surgeryforaHNSCCofthelarynx.Theincreaseofthicknessandenhancementofthetumorsiteinthemorphologicalacquisitions,theincreaseofFDG-uptake,andthe reduceddiffusivityinADCwithanincreaseofperfusionparametersweredetected.
Table3
Significantcorrelationsinmultiparametricanalysis.
Parameters Spearman’s
coefficient
Significance(p value) Overallsample
ROIareavs.CTSUVVOI 0.66 <0.001
ROIareavs.MRSUVVOI 0.61 <0.001
ROIareavs.MRSUVROI 0.61 <0.001
CTSUVVOIvs.MRSUVVOI 0.97 <0.001
CTSUVVOIvs.MRSUVROI 0.88 <0.001
MRSUVVOIvs.MRSUVROI 0.91 <0.001
CTMTVvs.MRMTV 0.94 <0.001
MRSUVROIvs.ADCMean −0.36 0.04
ADCMeanvs.KtransMean −0.5 <0.001
Primarytumors
ROIareavs.CTSUVVOI 0.51 0.04
ROIareavs.MRSUVVOI 0.45 0.04
ROIareavs.MRSUVROI 0.53 0.01
CTSUVVOIvs.MRSUVVOI 0.95 <0.001
CTSUVVOIvs.MRSUVROI 0.81 <0.001
MRSUVVOIvs.MRSUVROI 0.83 <0.001
CTMTVvs.MRMTV 0.93 <0.001
ADCMeanvs.KtransMean −0.42 0.04
Recurrenttumors
ROIareavs.MRSUVROI 0.61 0.04
MRSUVVOIvs.MRSUVROI 0.99 0.01
MRSUVROIvs.ADCmean −0.72 0.01
Abbreviations:ROIarea:tumorsizein2Dmajorlesionsize;Abbreviations:CT: computedtomography;SUV:standardizeduptakevalue;MTV:metabolictumor volume;ADC:apparentdiffusioncoefficient;Ktrans:transferconstantbetween vas-cularandEES.
muscle(Primarytumors:p<0.001;Recurrenttumors:p<0.001) (Table2).
4. Discussion
ThisstudydemonstratedthefeasibilityofPET/MRexamination
fortheevaluationoftheT-stadiuminpatientswithheadandneck
cancerduringstagingorfollow-up.ThisstudyalsofoundPET/MR
examinationtohaveahighinter-observeragreementforlesion
detectionandsignificantrelationshipsamongseveralmetabolic,
diffusion,andperfusionparametersintheprimarytumor.
InthepastthreedecadesPEThasdemonstrateditsvaluein
pro-vidingnon-invasiveinformationoftissueatthemolecularlevel.
The valueof PET lies in itshigh sensitivity tracking of in vivo
biomarkers, however it lacks precise anatomical information,
whichhasbeenovercomewiththeintroductionofthePET/CT
scan-ners.18F-labeledfluorodeoxyglucosepositronemission
tomogra-phy([18F]FDGPET)iscommonlyusedinHNSCCfortumorstaging,
monitoringoftreatmentresponses,detectionofrecurrences,and
radiotherapyplanning[5].AlthoughPET/CTiscurrentlythegold
standardforoncologicalimaging,severallimitationsexist,which
include:substantialamountsofionizingradiationfromrepeated
PET/CTscansduringdiagnosticandfollow-upexaminations;the
anatomicalcontributionofCTislimitedinsofttissuesandareas
withcomplexanatomy(i.e.theheadandneck&pelvisregion).
Theseissuescanbeovercomewithrecentlylaunchedfully
inte-gratedhybridPET/MRscanners,whichcanperformsimultaneous
acquisitionofPETandMRI.BycombininganatomicalMRI,DW-MRI,
DCE-MRIandPETimagingtoobtainconcertedinformationabout
cellularity,perfusionandbiologicalactivityofthetumor(i.e.byuse
ofFDG,FLTorCholine),wehypothesizethatthesensitivityandthe
specificityinoncologystagingcanbeimproved.However,currently
nospecificclinicalindicationforPET/MRhasbeenestablished.
PET/CTand PET/MRstudieswereacquiredin all44 patients
without side effects and were suitable for further evaluation.
Althoughseveralstudieshavedemonstratedthefeasibilityofthis
new powerful tool in oncological imaging, the head and neck
regionincludescomplexanatomywithmanydifferenttissuesin
asmallregionandisoftenaffectedbyinvoluntarymotionartifacts
duringimagingacquisition.Theabilitytoperformsimultaneous
acquisition decreases the acquisition time bypassing putative
co-registrationproblems,especiallyforhigh-temporalresolution
phenomenalikeperfusion.
Indeed,softwarefusionofPETandMRIdataischallenginginthe
neckandthesimultaneousacquisitionoftheMRIandPETdata
pro-videsimprovedcoregistration.ThefeasibilityofPET/MRinthehead
andneckregionhasalsobeenreportedbyothergroups,
demon-stratingagoodMRimagequalitywithoutimpairmentofthePET
signal[20,21].
ThehighcontrastresolutionofMRIcomparedtoCTcreateda
morefinedifferentiationofheadandnecktissues,whichprovideda
correctstagingandfollow-upofHNSCC,mainlyforTstadium
char-acterization[10].Arecentarticlethatexaminedthirtypatientswith
HNCcanceratprimarytumorsfoundahigherdiagnosticaccuracy
forTevaluationsfromretrospectivelyfusedPET/MRcomparedto
PET/CTandacomparableaccuracyforN-staging[22].Ourcurrent
studyalsosupportsthispreviousreportbydemonstratingexcellent
agreementbetweenthetwoobservergroupsfortheanatomic
allo-cationoflesionsbyPET/MR(T-staging).Thishasalsobeenfound
inotherstudies,examiningdifferenttypesofcancer(lymphnodes
anddistantmetastases)revealinginter-readeragreementbetween
observersofabout0.5[23]and0.7[24].
Asfor the correlationanalysis, there wasa significant
posi-tiverelationshipbetweentheROIarea(tumorsizeinthemajor
axiallesion diameter)and theSUV.Thiscorrelationshowsthat
biggerlesionshavehighermetabolicactivity,althoughthe
pres-enceofnecroticintralesionalregionscanbiasSUVestimation.In
this study, we limit this bias performinga manual tumor
out-linein majordiameterlesion slice, avoiding necrotic areasand
largefeedingvessels.Althoughtherearecontroversialresultswith
respecttothecorrelationbetweenthelesionsizeandSUV
measure-ment[25,26]thedifferencesfoundbetweenprimaryandrecurrent
tumors couldbealsodue totheeffect of differenttherapies on
lesionhomogeneity.Fruehwald-Pallamaretal.[26] reportedno
significantdifferences in ADCvalues andSUVmax betweenthe
variousTstagesin31patients.Thepossibleinclusionof
inflamma-tion,fibrosisand/ornecrosiswithintheROIlesionareameasured
alongthemajoraxisisalikelyconsequenceofsurgery,
radiothe-rapy,chemotherapyordifferentcombinedtherapeuticapproaches
duringthefollow-up.Forthesereasons,inordertoreduceeffects
related to treatments, 6–8 weeks from the end of treatment
passedbeforetheimagingstudyofrecurrentlesions.Alsoprevious
reportsandthecurrentstudyhavefoundcomparableestimatesof
metabolicparameters(SUVandMTV)betweenPET/CTandPET/MR
mainly in primary tumors and theoverall sample. In a recent
report[23],averyhighcorrelationbetweentheSUVvaluein
18F-FDG-PET/MRand18F-FDG-PET/CTimaginghasbeendetectedfor
primarytumors,lymphnode,anddistantmetastasesin14patients.
Otherauthors[12,24]foundnostatisticallysignificantdifferencein
diagnosticcapabilitybetweenPET/CTandPET/MRin17patients.
AlthoughMRI-basedACisstillunderdebate[14],2-pointDixon
approachforMRIattenuationhasrecentlyprovidedresults
com-parable tothose of conventional attenuationcorrectionby low
doseCT[12].HighcorrelationbetweenSUVestimatedbyPET/CT
andPET/MRresultingfromthisstudysupportstheseconclusions,
accordingtoapreviouswork[14].Inthecurrentstudywhen
exam-iningmetabolic(SUV),diffusion(ADC)andperfusionparameters
(Ktrans,k
ep,iAUC,
v
e),wedemonstratedasignificantnegativecorre-lationbetweenMRSUVROIandADCMeaninrecurrenttumorsand
theoverallsample.Althoughthecelldensity(estimatedbyADC)
andglucosemetabolism(estimatedbySUV)ofatumoraredifferent
physiologicalparameters,onerecentreporthasshownapositive
[26,28]haveobservednosignificantcorrelationbetweenthesetwo
parameterswithMRIandPET/CT.Thenegativecorrelationresulting
fromthisstudyshowsthathighercellularityofthelesions,
reflect-ingonalowADC,parallelswithanincreasedglucoseuptakeand
cellularmetabolism.Controversialresults[26–28],instead,canbe
duetotumorinhomogeneityandcontextualnecroticareas,where
thefreediffusionofwaterprotonsresultsinnoADCrestriction[26].
Inaddition,therewasasignificantnegativecorrelationbetween
ADCMean and Ktrans Mean in primary tumors and the overall
sample. Although few studies have investigated the
relation-ship among these parameters, the resultsappear controversial
[26–28].AninversecorrelationbetweenADCandKtranshasalso
beendetectedfor othertumors(i.e.brain)[27],whichsuggests
anintricaterelationshipbetweenvascularpermeability andthe
tumormicroenvironment.Inthis context, twotumoral features
mayexplainthenegativecorrelationbetweentheseparameters.
Fromoneside,tumorproliferationincreasescelldensityandADC
restrictionwhile,fromtheotherhand,neoangiogenesisincreases
immature tumoral vessels and, thereby, vascular permeability
expressedbyKtrans.
Finally,perfusionparameterssuchasKtranshavebeen
demon-stratedtobepotentiallypredictiveofpatientresponsetotherapy,
howevercontroversialresultscanbedebated[29].Anydifferences
maybeattributedtotheappliedpharmacokineticmodelling(e.g.
(extended)Toftsmodelormoreelaboratedmodelslikethe
shutter-speedone)[18].Inanycase,Ktransseemstobesuitabletomonitor
therapy(relative)changesintumorsthoughthecorrectnessofthe
absolutevaluesmaybenotalwaysclaimed[30].
5. Conclusions
OurstudydemonstratesthefeasibilityofPET/MRimaging in
theT-stadiumevaluationofHNClesionsduringstagingor
follow-up.Thisintroducesamorecompletecharacterizationofmetabolic,
diffusion,andperfusioncharacteristicsofprimarylesions.
The strength and the originality of this study exists in the
involvementofmultiparametricMRI,whichincludebothdiffusion
andperfusionevaluationsthatarecollectedsimultaneouslyduring
PET/MRacquisition.
Although further improvements should be performed to
increasethevalueofhybridacquisitionofPET/MR(improved
atten-uationcorrectionalgorithmfor bone segmentation,and surface
dedicatedcoilsforheadandneckregion),webelievethis
analy-sismayplayacrucialroleinprognosisandtreatmentofpatients
whenconsideringthepredictivevalueoftheseparameters[29].
Conflictofinterest
Allauthorshavenoconflictsofinterestandnodisclosuresof
financialinteresttoreport.
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