Metal artifact reduction for intracranial projectiles on post mortem computed tomography

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Metal artifact reduction for intracranial projectiles on

post mortem computed tomography

N. Douis, A.S. Formery, G. Hossu, L. Martrille, M. Kolopp, P.A. Gondim

Teixeira, A. Blum

To cite this version:

N. Douis, A.S. Formery, G. Hossu, L. Martrille, M. Kolopp, et al.. Metal artifact reduction for

intracranial projectiles on post mortem computed tomography. Diagnostic and Interventional Imaging,

Elsevier, 2020, 101 (3), pp.177-185. �10.1016/j.diii.2019.10.009�. �hal-03231120�

ORIGINAL

ARTICLE

/Forensic

medicine

Metal

artifact

reduction

for

intracranial

projectiles

on

post

mortem

computed

tomography

N.

Douis

,

A.S.

Formery

,

G.

Hossu

,

L.

Martrille

,

M.

Kolopp

_,

_P.A.

_Gondim

_Teixeira

_,

_A.

_Blum

a_{GuillozImagingDepartment,HopitalCentral,CHUNancy,54000Nancy,France} b_{ClaudeBernardClinic,57070Metz,France}

c_{ForensicInstitute,HospitauxdeBrabois,CHUNancy,54500Nancy,France} d_{ForensicInstitute,HopitalLaTimone,AP-HM,13005Marseille,France} e_{LorraineUniversity,Inserm,IADI,54000Nancy,France}

KEYWORDS Autopsy; Computed tomography(CT); Cadaver; Gunshotwounds; Artifacts Abstract

Purpose:To compare theimage quality ofcranial post-mortemcomputed tomography (CT)

obtainedwithandwithoutprojection-basedsingle-energymetalartifactreduction(SEMAR)in

cadaverswithintracranialmetallicballisticprojectiles.

Materialsandmethods:FromJanuary2017toJanuary2018,cadaverswithballisticprojectile

headwoundswithmetalfragmentsandwithoutmassiveheaddestructionwereinvestigated

usingpost-mortemCT.AllsubjectsunderwentCTusingaconventionaliterativereconstruction

(IR)andSEMAR.Toevaluatetheimpactofmetallicartifacts,thetotalintracranialarea(TA),

non-interpretable zone(NIZ),disturbedinterpretation zone (DZ),andartifact totalsurface

(ATS)weredelineated.Twoindependentreadersidentifiedextra-axialhemorrhage(EAH)and

subarachnoidhemorrhage(SAH).Autopsyreportswereusedasthestandardofreference.

Results:Elevencorpses(10males,1female;meanage,62.8±17.9[SD]years)wereevaluated.

SEMARshowedasignificantdecreaseintheATSratiowithrespecttoconventionalIR(72.1_±26.1

[SD]%[range:26.8-99.1]vs.86.4±17.8[SD]%[range:37.2-100];P<0.001)andNIZ/TAratios

(11.6±8.26%[range:0.95—33.4]versus42.5±30.5%[range:3.86—100];P<0.001).The

inter-observerreproducibilityindiagnosingEAHandSAHwasexcellentwithconventionalIR(0.82)

andgoodwithSEMAR(0.75).SEMARreduceduncertaindiagnosesofEAHin7subjectsforReader

1andin6forReader2,butdidnotinfluencethediagnosisofSAHforeitherreader.

Conclusion:SEMARreducestheinfluenceofmetallicartifactsandincreasestheconfidencewith

whichthediagnosisofEAHcanbemadeonpost-mortemCT.

©2019Soci´et´efranc¸aisederadiologie.PublishedbyElsevierMassonSAS.Allrightsreserved.

∗_{Correspondingauthor.}

E-mailaddress:douisnicolas@gmail.com(N.Douis).

https://doi.org/10.1016/j.diii.2019.10.009

178 N.Douisetal. Performingunenhancedpost-mortemcomputed

tomog-raphy (PMCT) has become a common practice during the forensicevaluationofdeceasedsubjects[1—3].PMCTallows subjectevaluation with no compromise tobody integrity andisparticularlyeffectiveatdetectingbonefracturesand foreignobjects, which arecrucial aspectsof the forensic investigation.Regardingballisticheadtrauma,various stud-ieshave demonstrated thatanalysis of native CT images, multiplanar reconstructions, and three dimensional (3D) volume-renderedreconstructionscouldguideandincrease theaccuracyofautopsies[4—13].Althoughentryandexit bullet wounds are best evaluatedby direct examination, PMCT can assist in the recovery of bullets and bullet fragmentsand providesa detailed evaluation of all bony structures,someofwhicharedifficulttoaccessatautopsy

[14—20].

Althoughtheexactprevalenceisunknown,thepresence ofretainedmetalfragmentsintheheadfollowinggunshot woundsis frequent. Metallicforeignbodiesarean impor-tantsourceofartifactonCT,hamperingorevenprecluding imageinterpretation. Metallicartifactsarecaused mainly by beam hardening, photon starvation, and edge profile errors[21,22].Metallicartifactsareparticularly problem-atic,asbulletscomprisedofmetals andmetalalloys with high atomic numbers are responsible of considerable CT imagedegradation.

VariousCTimagereconstructionalgorithmsdesignedto reducemetalartifactsareavailableandhelpimproveimage qualityin thepresenceof metallicprosthesesindifferent body areas [23—29]. As firearm projectiles have a differ-entcompositionthanprostheticimplants,theperformance of thesealgorithms toevaluate gunshot woundsis uncer-tain.Ananimalstudyshowedthepotentialofmetalartifact reductiontechniques(iMAR)fortheassessmentofretained bullets in the head with CT [30]. Among the techniques availablefor metalartifact reductiononCT,single-energy metalartifact reduction (SEMAR, Canon Medical Systems) withrawdatainterpolationhasbeenstudiedinpatientswith considerable improvements in image quality [31,32]. We hypothesizedthatSEMARcouldincrease theimage quality ofPMCTimagesinheadgunshotwoundvictims,improving theanalysisofcranialhemorrhagiclesions.

Thepurposeofthisstudywastocomparetheimage qual-ityofPMCTobtainedwithandwithout SEMARincadavers withintracranialmetallicballisticprojectiles.

Material

and

methods

Subjects

FromJanuary2017toJanuary2018,126subjectsunderwent PMCTinourinstitution,requestedbyamagistrateaspart of the conventional judicial procedure. Subject age, sex, andcauseofdeathwereevaluated.Amongthesesubjects, therewere29gunshotwounds,21ofwhichwerelocatedin thehead.The exclusioncriteriawere:unanalyzable cere-bralparenchyma(putrefaction,headdestruction),absence of metallic projectile fragments in the head or impossi-bilitytoselectthe CTimagescontainingasinglemetallic body,andabsenceofiterativereconstructionwithSEMAR. Five subjects with no retained metallic fragments in the

Figure1. Flowchartdiagramofincludedandexcludedcadavers.

head and five subjects with available SEMAR reconstruc-tion were excluded. Thus, the final study population was composed of 11 cadavers (10 males and 1 female), with a meanage of62.8±17.9 (standard deviation[SD]years) (range:40—93 years).Fig.1shows subjects inclusioninto thestudy.Thecauseofdeathinallincludedsubjectswas suicide by gunshotwound to thehead. In our institution, ethicscommitteeapprovalisnotrequiredforretrospective, anonymizedstudiesbasedondeceasedsubjectsrequested aspartofajudicialprocedure.

Acquisition

protocol

CTimageswereacquiredwitha320detector-rowCT scan-ner(Aquilion® _{One,CanonMedicalSystems).Awhole-body}

acquisition wasperformed in allsubjects.The acquisition parametersforheadimagingwere:0.75stuberotationtime, 135 kVp, 450mA, 0.5mm slice thickness, FOV 24cm, and matrix512×512;foronesubject,slicethicknesswas1mm. Astandardheadreconstructionkernel(FC26)wasusedfor all reconstructions. For each study, two volumes of the head were reconstructed, one using an adaptive IR algo-rithm (AIDR3D, Canon Medical Systems)herein named as conventionalIRandanotherwithSEMAR.

Image

analysis

CTimage qualitywasassessedby aradiologist (N.D)with twoyearsofmedicalimagingexperience.OriginalCTimages of the brain in the axial plane were browsed to select images containing a single metallic fragment in order to avoidthecombinedeffectofmultiplefragmentsonimage quality. For five subjects, more than one image showing a single metallic body was available. These images were evaluatedindependently. The sameimages wereusedfor analysis with conventional IRand SEMAR reconstructions.

Figure2. DescriptionofregionofinterestplacementonCTimagesina47-year-oldmalecadaver.HeadCTimagesreconstructedwith conventionaliterativereconstruction(A)andwithsingle-energymetalartifactreduction(SEMAR)(B)werebrowsedtoselectanaxialimage showingasinglemetallicforeignbody(CandD).Ametallicprojectilefragmentlocatedadjacenttotheinnersurfaceofthetemporalbone (arrow)generatingimportantmetallicartifacts.Thetotalcranialareaisdelineatedbyacontinuousblueline,theredarearepresentsthe zonethatisnon-interpretablezone,andthegreenarearepresentsthezonedisturbedbymetalartifacts.NotethatinDthenon-interpretable zoneismuchsmallerthaninC.

Themaximumdiameterofthetargetmetallicfragmentswas measured onconventionalIRusinga widewindowsetting (C1000/W9000 HU). The influence of metallic artifactsin theevaluationofcranialhemorrhagiclesionswasevaluated usinga40/80HUwindowsettingwithbothconventionalIR andSEMARCTimagesusingthefollowingprocedure(Fig.2). Afirstfreeform regionofinterest(ROI)wasusedto delin-eate the total intra-cranial area in mm2 _{in the selected}

slices(TA).AsecondfreeformROIwasusedtodelineatethe areainmm2_{completelyobscuredbymetallicartifacts}

(non-interpretablezone—NIZ).Athirdfreeform ROIwasusedto delineatetheareainmm2_{inwhichmetallicartifactswere}

present,butCTimageanalysiswasstillpossible(disturbed zone—DZ).Artifacttotalsurface(ATS)wascalculatedusing thefollowingequation:ATS=(NIZ+DZ).NIZ/TA,DZ/TA,and ATS/TAratiowerecalculatedforeachmetalfragment eval-uatedandforsubjectsconsideringallfragmentsevaluated ineachsubject.

Diagnostic performance for cerebral hemorrhage was evaluated by analyzing all CT images reconstructed with and without SEMAR.Two radiologists, with2-and 7-years ofmedicalimagingexperiencerespectively,independently evaluated PMCT images for the detection of extra-axial hemorrhage(EAH),includingepiduralhematoma(EDH)and acutesubduralhematoma(ASDH),aswellassubarachnoid hemorrhage (SAH). An EDH was diagnosed when a spon-taneously hyperattenuating elliptical lesion wasobserved betweenthe cranialvault andwhen cerebralparenchyma

wasidentified. An ASDH was diagnosed when a crescent-shaped spontaneously hyperattenuating CT image was observed at the location of the subdural space. SAH was diagnosedwhenthesubarachnoidspaceandcisternswere spontaneouslyhyperattenuating[33].Thediagnostic confi-dence for hemorrhagic lesions was graded using a Likert scale(1=definitelyabsent;2=likelyabsent;3=uncertain; 4=definitelypresent;and5=notanalyzable).

The locationof the entry and exit wounds was evalu-atedonimageswithandwithoutSEMARandcorrelatedwith autopsyfindings.

Standard

of

reference

Anautopsywasperformed usinga standardizedtechnique for all included cadavers. First, the body was externally examined.Acoronalscalpincisionfromoneretro-auricular regiontotheotherwasthenperformed,followedby reced-ingof the scalpforward and backward. The cranial vault wasopened usingan electricsaw. Photographsof autopsy findingswereavailableforallsubjectsexceptone.Autopsy reportsandphotographswerereviewedretrospectivelyby aforensicphysicianwith4yearsof clinical experienceto standardize the description and nomenclature of cranial lesions.Fortheautopsywithnophotographsavailable,the initialautopsyreportwasusedbecausethedescriptionwas deemedsufficientlyclear,usingasimilarlesion nomencla-ture.

180 N.Douisetal.

Statistical

analysis

StatisticalanalysiswasperformedusingRDevelopmentCore Teamsoftware(version3.2.02015).Quantitativedatawere presentedasmean±SD(range:minimum—maximumin%). RatiosbetweenNIZ,DZ,andATS withrespect toTAwere usedtoallowinter-subjectdatacomparison.Assome sub-jects presented multiple metallic fragments, these data werepresented in aper-fragment andper -subject basis. Apaired Wilcoxon test was usedto compare the sizes of thezonesmeasured with conventionalIRand SEMAR.A P

valueless than0.05wasconsidered toindicatestatistical significance.Kappatestwasusedtoevaluateinterobserver reproducibilityforthediagnosisofintracranialhemorrhagic lesions.Kappavaluesof0.00-0.20wereconsideredto indi-catepooragreement;0.21-0.4,fair;0.41-0.60,moderate; 0.61-0.80,goodand0.81-1,excellentagreement.Autopsy reportswereusedasthestandardofreferenceforthe eval-uationofintracranialhemorrhagiclesionsandFisherexact testwasusedtoevaluatediagnosticaccuracy.

Results

Amongthe11cadavers,20CTimageswithartifactsarising fromasinglemetallicforeignbodywereidentified(meanof 1.8±1.1[SD]imagesperCTstudy[range:1-4]).Themean metallicfragmentmaximum diameterswere5.9±2.5[SD] mm(range:3.15-12.05mm).

For all subjects, no additional elements contradicting deathbysuicidewerefoundafterautopsy.Theusedweapon andammunitioncalibervaried.Theriflemodelsusedwere: three carbines 5.56×15mm R (22 long rifle), one auto-maticwithunknowncaliber,onehuntingriflewithunknown caliber,twosingleshot rifleswitha 12mm caliber.Three handgunswerealsoused:oneautomaticpistol6.35mm(.25 AutomaticColtPistol,onesingleshotpistols5.56×15mm R (22 long rifle) and one revolver 9mm (0.38 special wadcutter). There was also a modified single shot pistol 5.56×15mmR(22longrifle)caliber.Theusedammunition typewasunknown.

A significant decrease in mean ATS ratios per frag-ment was found with SEMAR (72.1±26.1 [SD] % [range: 26.8-99.05%]) compared to conventional IR (86.4±17.8 [SD]% [range: 37.2-100%]) (P<0.001). A similar variation was found with ATS ratios per subject with and without SEMAR (75.41±21.69 [SD] % [range: 39.95—98.28%] and 87.94±19.13 [SD] % [range: 37.22-100], respectively). A significantdecreasemeanNIZratiowasfound withSEMAR compared to conventional IR (P<0.001). The mean NIZ ratiowithandwithoutSEMARperfragmentwas11.6±8.26 [SD]%(range:0.95—33.39%)and42.5±30.5[SD]%(range: 3.86—100%),respectively,andpersubjectwas13.15±9.43 [SD] % (range: 0.95—33.39%) and 52.66±31.40% (range: 3.86-100%), respectively. No significant difference in DZ ratiosperfragmentbetweenconventionalIRandSEMARCT imageswasobserved(P=0.07).Arelativeincreaseinmean DZ ratios per fragment with SEMAR with respect to con-ventionalIRwasobserved(meanDZratiowithandwithout SEMAR60.4±24.4[SD]%[range:13.9-92.5%]and43.7±[SD] 24% [range: 0-75.64%], respectively) (Table 1). DZ ratios persubjectvariedwithandwithout SEMAR(62.29±20.88

[SD]%[range:39—89.22%]and35.01±21.0 [SD]%[range: 0—63.07%],respectively).

The interobserver variability for the diagnosis of EAH andSAHwasexcellentwithconventionalIR(Kappa=0.82, IC 95%[0.99-0.64]) andgood withSEMAR (Kappa=0.75, IC 95%[0.96-0.54]) [34]. In two subjects, the evaluation of intracranial hemorrhagic lesionswas not feasible both on imagingandonautopsyduetoheaddestruction.

Atotalof13 hemorrhagiccranial lesionswere deemed presentatautopsy,includingSAHineightsubjectsandEAH infivesubjects.Ifgrade1wasconsideredasanegative diag-nosisandgrade4asapositivediagnosis,tenoftheselesions werecorrectlydiagnosedbybothreaderswithconventional IR and SEMAR. For both readers, 100% (8/8) of the SAH werecorrectly diagnosedwhile only40% (2/5)of theEAH werecorrectlydiagnosed.Regardingdiagnosticconfidence, the numberof uncertain diagnosesdecreased withSEMAR forboth readers.Infiveandfoursubjectsrespectivelyfor Readers1and2,thediagnosticconfidenceforEAHchanged fromuncertain withconventional IRtolikely absentwith SEMAR,andintwolesionsforbothreaders,thediagnostic confidenceforEAHchangedfromlikelyabsenttodefinitely absent(Fig.3).Inallthesesubjects,anautopsyconfirmed theabsenceoftheselesions.WhenSEMARwascomparedto IR,asignificantincreaseinthediagnosticaccuracyofASDH wasfoundforReader1(P=0.012).Nosignificantdiagnostic accuracydifferenceswerefoundforEDH(P=0.175)forthis reader.ForReader2,thedifferencesindiagnosticaccuracy for EAH between SEMAR andIR werenot statistically sig-nificant(P=0.0615andP=0.175,respectivelyforEDHand ASDH).

Withboth SEMAR andconventional IR,there weretwo false-positivediagnosesofEAHfor Reader1andthreefor Reader 2, as well as one false-negative diagnosis of EAH foreachreader(Fig.4).Moreover,withSEMARCTimages, there was one additional EAH false-positive diagnosis for eachreaderandoneEAHfalsenegativeforReader2.

Thelocationoftheentryandexitwoundwascorrectly identifiedinallcaseswithbothSEMARandconventionalIR images.

Discussion

AsignificantreductioninmetalartifactinfluenceonPMCT withSEMARwasobservedcomparedwithconventionalIR, witha significantdecrease inboth ATS andNIZratios per fragment. A similar variation was seen withATS and NIZ ratiosperpatient.Theseresultsareinaccordancewith pre-viousliteraturereportsonCTmetalartifactreductioninlive patients[23,24,26,31,35—37].Inaddition,SEMAR significan-tly increased the diagnostic accuracy for aSDH compared to IR for reader 1. However, there were no significant changes in accuracy for reader 2 norfor thediagnosis of EDH for reader1, which might be explainedby thesmall sample size. The diagnostic confidence in cranial hemor-rhagiclesionidentification increasedwithalowernumber of uncertain diagnosis for both readers with SEMAR. The interobservervariability, however,wasslightly worsewith SEMAR,whichislikelyrelatedtothedecreaseinthenumber of uncertain diagnoses. Although SAH was correctly iden-tified inall subjects withboth algorithms,the number of

artifact reduction for intracranial projectiles 181

Table1 MetalartifactmeasureswithoutandwithSEMARandcalculationofNIZ,DZ,andATSratios.

Subject IS Tfm(mm) TA(mm2_{) NIZ(mm}2_{) NIZ/TA(%) DZ(mm}2_{) DZ/TA(%) ATS/TA(%) NIZ(mm}2_{) NIZ/TA(%) DZ(mm}2_{) DZ/TA(%) ATS/TA}

(%) 1 1 7.72 12255.01 9552.62 77.94 2269.75 18.52 96.47 793.85 6.48 9967.89 81.34 87.82 2 2 6.25 2448.08 1992 81.37 317.8 12.98 94.35 631.51 25.80 959.67 39.20 65.00 3 3 9.24 11564.23 5230.74 45.23 5962.82 51.56 96.79 1489.85 12.88 1612.94 13.95 26.83 3 4 8.66 9647.06 9647.06 100 0.00 0.00 100 1675.48 17.37 7396.05 76.67 94.03 4 5 3.03 15383.92 963.19 6.26 10736.91 69.79 76.05 242.40 1.58 4285.25 27.86 29.43 4 6 8.07 11328.69 5740.40 50.67 4240.38 37.43 88.10 1433.08 12.65 8160.40 72.03 84.68 4 7 3.61 9393.99 969.35 10.32 4499.30 47.90 58.21 192.94 2.05 2493.11 26.54 28.59 5 8 8.82 7943.68 5950.94 74.91 1992.74 25.09 100.00 2652.55 33.39 4502.71 56.68 90.07 6 9 4.69 8631.10 3344.54 38.74 5038.38 58.37 97.12 1421.59 16.47 6073.27 70.36 86.84 6 10 6.48 8385.72 2722.58 33.92 5303.14 63.24 100.00 1393.20 16.61 6621.83 78.97 95.58 7 11 4.21 13311.42 1519.68 11.41 9419.77 70.76 82.18 925.59 6.95 6539.18 49.12 56.08 7 12 4.54 11522.6 2347.98 20.37 8715.71 75.64 96.02 1409.73 12.23 5992.23 52.00 64.24 7 13 3.54 8292 2619.41 31.59 1952.10 23.54 53.56 1447.74 17.46 2830.47 34.13 51.59 7 14 3.15 7779.99 960.87 12.35 4691.02 60.30 72.65 227.52 2.92 4127.30 53.05 55.97 8 15 4.23 9853.87 3024.87 30.70 5977.60 60.66 91.36 382.98 3.89 9119.52 92.55 96.43 8 16 4.93 10154.67 3292.56 32.42 6069.10 59.77 92.19 993.16 9.78 8770.5 86.37 96.15 8 17 4.89 8534.53 2506.5 29.36 5870.92 68.79 98.16 880.22 10.31 7573.31 88.74 99.05 9 18 1.95 9439.81 364.41 3.86 3149.09 33.36 37.22 89.96 0.95 3681.42 39.00 39.95 10 19 8.8 8079.12 8079.12 100 0.00 0.00 100.00 1107.46 13.71 6569.30 81.31 95.02 11 20 10.5 11820.06 7207.36 60.97 4296.41 36.35 100.00 1114.47 9.43 10502.42 88.85 98.28 mean±SD [range] 5.86±2.49 [1.95—10.5] 9788.48±2658.25 [2448.08—15383.92] 3901.81±2894 [364.41—9552.62] 42.55±30.52 [3.86—100] 4525.147±2975.12 [0—109419.7] 43.70±23.96 [0—75.64] 86.38±17.78 [37.22—100] 1025±630.63 [89.96—2652.55] 11.64±8.26 [0.95—33.39] 5888.94±2756.19 [959.67—10502.42] 60.44±24.35 [13.9—92.5] 72.08±26.09 [26.82—99.05]

IS:Selectedimages;Tfm:Metalfragmentsize;TA:Totalintracranialarea;NIZ:Non-interpretablezone;DZ:Disturbedinterpretationzone;ATS:Artifacttotalsurface;IR:Conventional iterativereconstruction;SEMAR:Single-energymetalartifactreduction.

182 N.Douisetal.

Figure3. A 67-year-old manvictim ofa headgunshotwould. A, CT imagein theaxial planeobtainedwith conventionaliterative reconstructionattheleveloftemporo-occipitallobeswithmetallicprojectileagainstinneroccipitalbone(largearrow)generatingartifacts, whichhampertheanalysisofthecerebralparenchyma.B)Axialcomputerizedtomographyimagereconstructedwithsingle-energymetal artifactreduction(SEMAR)atthesamelocationshowsmarkedreductioninmetallicartifactsenablingbetteranalysisofcerebralparenchyma andmeninges.Spontaneoushyperattenuatingareaofthefalx(thinarrow)indicativeofsubarachnoidhemorrhage(SAH)canbeseen.C) PhotographobtainedduringautopsyconfirmsvariousfociofSAH(arrows).

Figure4. A78-yearoldmanvictimofaheadgunshotwound.AandB,CTimagesintheaxialplaneobtainedwithconventionaliterative reconstructionandsingle-energymetalartifactreduction(SEMAR)respectivelydemonstrateametallicforeignbody(fatarrows). Sponta-neoushyperdensitycanbeseeninbothimages(thinarrows)andwasinterpretedasanacutesubduralhematoma(ASDH)bytworeaders. Withsingle-energymetalartifactreduction(B)andalinearimagedelineatingacrescent-shapedfluidcollectionisseenadjacenttothe skullfracture(arrowhead).Thisimagewasverydifficulttoidentifywithconventionaliterativereconstruction(arrowheadinA)andwas interpretedasanepiduralcollectionbyReader1.CandD,Photographsobtainedduringautopsyconfirmdiffusesubarachnoidhemorrhage (arrowsinC)andrightASDH(arrowinD).Theleft-sidedcrescentimageseeninBwasmisinterpretedbythereaderandcorrespondedto anASDH.

false positive andfalse negativeEAH diagnoses increased withSEMARcomparedtoconventionalIR.This observation couldbe relatedto therelative increase inthe DZratios per fragment and per patient, despite the overall reduc-tioninATS;thusindicatingthatdespiteimprovedCTimage quality, characterizingEAH in subjects withhead gunshot woundswithPMCTremainschallenging.SEMARdidnot influ-enceDZratiosperfragmentcomparedtoconventionalIR. TheseresultssuggestthatSEMARismoreeffectivein redu-cing the NIZ compared DZ. Thus, NIZ decreases as it is partiallysubstitutedby DZ,increasingtheDZ/TA ratio.As the ATS is significantly reduced with SEMAR compared to conventional IR, despite the paradoxical increase in DZ-TA ratio, the end result is an increase in the analyzable cerebralparenchymaarea.AlthoughSEMARcanbe recom-mendedtoevaluatesubjectswithgunshotheadwoundsas it improves global CTimage quality comparedto conven-tionalIR,residualartifactshinderingCTimageanalysisstill remain.

A hemorrhagic cranial lesion of anykind is relevantin forensicinvestigationsbecauseitindicatesthatthevictim wasaliveatthetimeofthegunshot.Althoughthe distinc-tion between intra or EAH is of negligible importance in forensic investigation,this informationcould beuseful to evaluate victims of non-lethal head gunshot wounds and patients with therapeutic cranial metallic foreign bodies (e.g., aneurysmcoils). Internal ballistics findingsare also paramount for head gunshot wound evaluation on PMCT. Althoughallentryandexitwoundswerecorrectlyidentified withPMCT,thesmallnumberofsubjectsandlackof stan-dardization inautopsyreports precluded bullet trajectory assessment in this study. Finally, dual-energy applications onPMCT could beused toassess metal fragment compo-sitionbased onatomicnumbers that coulddetermine the ammunitiontype[38,39].

Severallimitationsofthisstudymustbeacknowledged. First, as a retrospective study with a small number of cadavers,itdoesnotdefinitelydemonstratethesuperiority of SEMAR. Furthermore, a single metalartifact reduction algorithm was evaluated. Although other metal artifact reduction algorithms, particularly those using monochro-maticimaging, werenottested, previous studies indicate thattheperformanceofSEMARisslightlysuperiortothese algorithms[40].Also,themetalcompositionofthebullets evaluatedwasunknown,whichmayinfluencethe effective-nessofSEMAR.Furtherinvestigationiswarrantedtoassess theeffectofbulletcompositiononmetalartifactreduction. ThemeasurementsofNIZ,DZ,andTAwithafreehandROI couldleadtosmallreaderinducedvariations.Finally,only headgunshotwoundswereevaluatedinthisstudy,andthus furtherstudiesarenecessarytoassesstheefficacyofSEMAR onothertypesofmetallicforeignbodiesinotheranatomic locations.

In conclusion, SEMAR significantly improves CT image quality of PMCT cerebral parenchyma with a significant decrease in NIZ and ATS ratios. This technique leads to increased diagnostic confidence for EAH lesions allowing the identification of all SAH studied. SEMAR led to a slight decrease in interobserver agreement and did not improve the performance of the identification of EAH, which remained poor. Thus, SEMAR can be recommended fortheevaluationofheadgunshotwounds,buttherewasno

improvementinthediagnosticperformanceofintracranial hemorrhagiclesions.

Informed

consent

and

patient

details

Funding

Thisworkdidnotreceive anygrantfromfundingagencies inthepublic,commercial,ornot-for-profitsectors.

Author

contributions

AllauthorsattestthattheymeetthecurrentInternational Committeeof Medical JournalEditors (ICMJE)criteria for Authorship.

Douis,Nicolas:Methodology,FormalAnalysis, Investiga-tion,validation,Writing—OriginalDraft,Writing—Review &Editing.

Formery,Anne-Sophie:Investigation.

Hossu,Gabriela:Methodology,FormalAnalysis. Martrille,Laurent:Resources,supervision. Kolopp,Martin:Methodology,Investigation.

Gondim Teixeira, Pedro Augusto: Methodology, Formal Analysis,ProjectAdministration,Validation,Writing— Orig-inalDraft,Writing—Review&Editing.

Blum, Alain: Conceptualization, Methodology, Project Administration,Validation.

Acknowledgments

WeareindebtedtoBrunoPuyssegur,JorisHoude,andValérie LamyfortheireffortsincaseselectionandCTimage recon-struction.We arealsogratefulfor thesupportofforensic institutepersonnel.

Disclosure

of

interest

The authors declare the following financial or personal relationships that could be viewed as influencing the work reportedin this paper: twoauthors involved in this work(P.A.G.T.andA.B.)participateonanon-remunerated researchcontractwithCanonMedicalsystemsforthe devel-opmentandclinicaltestingofpostprocessingtoolsforMSK CT.Theotherauthorshavenopotentialconflictsofinterest todisclose.

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