Pulmonary Nodule Size Evaluation With Chest Tomosynthesis

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Text of Pulmonary Nodule Size Evaluation With Chest Tomosynthesis

BJR 2015 TheAuthors.Publishedby the BritishInstituteof RadiologyReceived:7 January 2014Revised:29 December 2014Accepted:20 January 2015doi: 10.1259/bjr.20140040Citethis article as:ShimSS, Oh Y-W, Kong KA, Ryu YJ, KimY, Jang DH. Pulmonary nodule size evaluation with chest tomosynthesis and CT: a phantomstudy. Br JRadiol2015;88:20140040.FULL PAPERPulmonary nodule size evaluation with chest tomosynthesisand CT: a phantom study1S S SHIM,2Y-W OH,3K A KONG,4Y J RYU,1Y KIM and1D H JANG1Department of Radiology, Mokdong Hospital, Ewha WomansUniversity School of Medicine, Seoul, Republicof Korea2Department of Radiology, Korea University AnamHospitalandKoreaUniversityCollegeof Medicine,Seoul, Republic of Korea3Clinical TrialCenter, Ewha WomansUniversity Medical Center, Seoul, Republic of Korea4Departmentof Internal Medicine, Mokdong Hospital,Ewha WomansUniversity School of Medicine, Seoul, Republic of KoreaAddresscorrespondence to: Yu-Whan OhE-mail:yuwhan@kumc.or.krObjective: We compared digital tomosynthesis (TOMO) andchest CT in terms of assessing the sizes of nodules located inzones where evaluation by simple radiography is limited.Methods: Atotal of 48 images comprising phantomnodules of four sizes in six different locations were used.Nodule size measurement errors for measurements usingTOMOand CT images compared with the actual size fromeach observer were calculated. The inter- and intra-observer repeatabilityof themeasuredvaluesandtheagreement betweenthetwotechniqueswereassessedusing the method described by Bland and Altman.Results: The mean measurement errors for all of thenodules andfour observers were20.84mm[standarddeviation(SD), 0.60mm]onTOMOand20.18mm(SD,0.71 mm)onCTimages. Themeanmeasurementerrorsfor the different observers ranged from21.11 to 20.55mmfor TOMO andfrom20.39 to 0.08mm for CT.Assessingthe agreement between nodule size measurements usingTOMOandCTresultedinmeanmeasurementerrorsof20.65mm, witha95%limit of agreement of 22.53to1.22mm for comparison of TOMO with CT.Conclusion: Our results suggest that nodule sizes obtainedusing TOMOand chest CT are comparable, even fornoduleslocatedinareaswherethesizemeasurementislimited on simple radiography.Advances in knowledge: TOMOandCTcan be usedinterchangeably, even for nodules located in a blind areaon simple radiography.Solitarylungnoduledetectionhasincreasedowingtothewidespread use of CTimaging. Nevertheless, the mostcommonly used routine examination for lung nodulescontinuestobechestradiography,becauseituseslowra-diationdoses, is economical andis easytouse. Becausechest radiographic images are two-dimensional projectionsof three-dimensional structures, early lung cancer detectionon chest radiographs is often challenging. The projection ofpulmonary vessels, bones and part of the mediastinum onlungeldsoftenpartiallyorcompletelyobscuresthepul-monarynodules, resultinginfailurebytheradiologisttodetectlungnodules.1,2Digital tomosynthesis(TOMO)hasrecentlybeenappliedtochest imagingfor the detectionof subtlenodules onsimpleradiography, withpromisingresults.3,4Ithasbeenintroducedas a modality withthe potential toprovideimages similar to CT but at a comparably reduced cost andradiation exposure.4James et al5reported that 74% of lungnodules$4 mmindiameterthatcanbeidentiedonCTcanalso be detected using TOMO. Vikgrenet al6alsoreported that 92%of nodules $4 mmindiameter aredetectable using TOMO. In 2012, Johnsson et al7comparedthe ability of TOMOand CTto detect nodule size in20patients andfoundthat bothmethods couldbeusedinterchangeablyforthesemeasurements. Thisresult callsfor caution, however, because the limit of agreement (LOA)between the modalities is wider than for the intraobservervariabilityofeachmodality.Basedonthese studies, we hypothesizedthat TOMOiscomparabletoCTimagingfor thedetectionof noduleslocatedinareaswheresizemeasurement islimitedusingsimple chest radiography because of overlapping structures.The purpose of this study was to assess the size de-terminationof noduleslocatedinthesezonesbyTOMOandchestCT.METHODS AND MATERIALSThorax phantom and model nodule preparationThe thorax phantomN1 (Kyoto Kagaku Co., Ltd,Kyoto, Japan) was constructed fromsynthetic materials(i.e. polyurethane, epoxy resin, calciumcarbonate). Modelnodules witha homogeneous compositionof solid-type ure-thane foam nodules of four sizes (3, 5, 8 and 10 mm) were used.Nodules were placed in six lung zones: the right apex, middle ofthe right subpleural lungparenchyma, rightupper hilum, rightlowerhilum, rightdiaphragmaticangleoftheheart(rightcar-diophrenicangle)andtherightlowerretrohepaticlungparen-chyma(Figure1).Chest CTAtotal of48phantomsets, comprising4nodulesizes, 6loca-tions and2imagingmodalities, wereincludedinthepresentstudy. We used a 64-channel CT scanner (Somatom Denitionscanner; Siemens Healthcare, Forchheim, Germany) for chestCT. The scanning parameters were as follows: individual de-tector width, 0.625 mm; gantry rotation time, 0.5 s; tube voltage,120 kVp; tubecurrent, 30 mA; andpitch, 1. Axial imageswerereconstructedusing a sectionof 2 mminthickness, the B70kernel(SiemensHealthcare) anda345-mmeldofview.Digital tomosynthesisTOMOexaminations were performed using a commerciallyavailable unit (Sonialvision Sare II; Shimadzu Co., Kyoto,Japan)withaat-panel detectorsystem. WealteredthedigitalTOMO parameters to establish a lower radiation dose conditionthat was suitable for chest imaging. 74 low-dose projectionimages were acquired within 4.85 s using a tube voltage of120 kVpand0.04 mA. The detector was xedintoposition,whereas the X-ray tube was subjectedtovertical continuousmovement, from220 to 120, around the standard orthogonalposteroanterior position, and image data were acquired. A totalof 74 projection images were obtained from 1 examination andwereusedtoreconstruct 84coronal images witha2-mmre-constructioninterval.Radiation doseFor the radiation dose assessment in TOMO, a dosemeter(UnforsThinXIntra; Unfors Instruments AB, Billdal, Sweden)that was attached to the centre and surface of the chest phantom(N1)recordedtheabsorptiondose. Theabsorbeddoseat thephantomsurface for TOMOwas 0.7 mGy, andthe absorbeddoseatthephantomcentre was0.2 mGy.Pulmonary nodule measurementFour radiologists with 15, 4, 3 and 1 years experience in chestimage interpretation participated in the study. Atotal of48images, comprisingnodulesof4sizesin6differentloca-tions andarrangedinrandomorder bytheViewDEXsoft-ware(S odraAlvsborgs Sjukhus, SahlgrenskaUniversityandUniversityofGothenburg, Gothenburg, Sweden), wereused.Observers were blinded to the location and size of the nodulesin the phantom model (Figure 2). They measured the left-to-right diameter andrecordedthelongest length. Theuseofzoomor enlarge tool was freelyavailable, andthe windowFigure 1. Six locations of phantomnodules: (1) right apex;(2)middleoftherightsubpleural lungparenchyma; (3)rightupper hilum; (4) right lower hilum; (5) right cardiophrenicangle; and (6) right retrohepatic lung parenchyma.Figure 2. Images of the thorax phantom performed with chesttomosynthesis (TOMO) (a, c) and chest CT (b, d) witha phantom nodule (arrows). (a, b) A 3-mm nodule in the rightapexisobservedonTOMO(measuredas2.38mm)(a)andalsonotedonCT(2.28mm)(b). (c, d)A5-mmnoduleinthemiddleof theright subpleural lungparenchymais seenonTOMO (4.36mm) (c) and CT (5.00mm) (d).BJR SSShimet al2 of 8 birpublications.org/bjr Br J Radiol;88:20140040centre/width for CT was 2750/1500 HU, whereas the windowwidthforTOMOwas30004500 HU. Thesevaluesareclin-icallyrelevant.Allofthemeasurementswererepeatedat20-dayintervalstoassessintraobservervariation.Statistical analysisNodulesizemeasurement errors formeasurement onTOMOandCTimages comparedwiththeactual sizefromeachob-server were calculated. The results are presentedas means 6standard deviations (SDs) and 95% condence intervals (95% CI)ofthemean. Fortheinter-andintraobserverrepeatabilityofthemeasured values,theagreementbetweenthetwotechniqueswas assessed using the method described by Bland and Altman.8The 95% LOA was calculated as the mean difference 61.96 SD ofthe difference.RESULTSUponinitial measurement, oneobserver judgedtwoof the3-mm nodules as beingmissedon the TOMO modality; oneobserverjudgedthreeofthe3-mmnodulesasbeingmissedontheCTmodality; whileanotherobserver judgedoneofthese nodules as being missedonCT. Upontheir secondevaluation, one observer judged two of the 3-mm nodules asbeing missed on TOMOand one 3-mmnodule as beingmissedonCT.ThenumberofmeasuredphantomnodulesandmeanrelativeerrorsforCT andTOMOmeasurementsforeachobserverareTable 1. Number of detected nodules, mean relative error and standard deviation (SD) for each observer regarding measurementson tomosynthesis (TOMO) and CT imagesObserver Observer1 Observer2 Observer 3 Observer4TOMO imagesDetected (n) 24 24 24 22Meanmeasurement error (mm) 20.55 20.75 20.94 21.11SD(mm) 0.38 0.22 0.43 0.98CT imagesDetected (n) 24 24 23 21Meanmeasurement error (mm) 0.08 20.36 20.07 20.39SD(mm) 0.28 0.27 0.66 1.16Figure 3. Measurement error for each observer and eachnoduleontomosynthesisimagescomparedwiththeknowndiameter of thenodule. Dashedline(centre) representsthemeanmeasurementerror forallnodules andobservers.Smalldashedlines(topandbottom)representthemeanmeasure-ment error 62 standard deviation.Figure 4. Measurement error for each observer and eachnoduleonCTimagescomparedwiththeknowndiameterofthe nodules. Dashed line (centre) represents the meanmeasurement error for all nodules and observers. Small dashedlines (top and bottom) represent the mean measurement error62 standard deviation.Full paper: Pulmonary nodule sizeevaluation withTOMOand CT BJR3 of 8 birpublications.org/bjr Br J Radiol;88:20140040Figure 5. Plots show (a) manual measurement data from tomosynthesis (TOMO) images for the diameters of all nodules andobserversplottedagainsttheactual sizeand(b)manual measurementdatafromCTimages. Intheplots, the45lineofequalityisdrawntohelpassesstheagreement betweenthemeasurements. Plotsillustratethat th