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ANEWAPPROACHTO ULTRAHIGHRESOLUTIONENDOSCOPIC MEDICALIMAGING By BONGSOOLEE ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1999 Tomywife,SeunghyunCho,andmyson,ChungwonLee. ACKNOWLEDGMENTS Iwouldfirstliketoacknowledgemysupervisorycommittee. ToDr. WesleyE. Bolch,myadviser,Iwouldliketogivethanksandappreciationforhissupportduringmy doctoralwork. IwouldalsoliketothankDr.JamesK.Walkerforhisvaluedadvice, support,andhelpthroughoutmydoctoralresearchinNanoptics,Inc. Inaddition,Iwould liketoextendmyappreciationtoDr.WonY.Choiforhissupportandguidance,which helpedinthecompletionofthisresearch. Iwouldliketoextendmygratitudetomyother committeemembers.Dr.AlanM.JacobsandDr.SamimAnghaieforalltheirinterestin myworkandtheirhelpfulsuggestion. IwouldliketothankNanopticsInc. forprovidingvariousresearchfacilitiesand fellowshipfor3years. IwouldalsoliketothankallNanopticsmembers,-Dr.Jacob Tymiansky,Dr.YongLi,Mr.JonathanCouch,andMr.StephanA.Tuchman-fortheir support,advice,andthegreattimeswehavehad. IwouldliketoextendmygratitudetotheKoreanGovernmentforawardingmea KoreanGovernmentOverseas Scholarship formydoctoral studyintheUniversityof Florida. Finally,Iamextremelygratefultomyparentsandparents-in-law. Withouttheir loveandsupport,thisworkwouldnothavebeenpossible. Iwouldalsoliketogive special thanks my wife, Seunghyun Cho, and my son, Chungwon Lee, for all their patience,unendinglove,andsupportofmeandmywork. iii TABLEOFCONTENTS page ACKNOWLEDGMENTS Hi ABSTRACT vii CHAPTERS 1 GENERALINTRODUCTION 1 1- 1I--l Fiber-OpticEndoscopes 1 1-2 PrinciplesofFiberOptics 3 1-2-1 TotalInternalReflection 3 2- 1-2-2 OpticalFiber 5 1-2-3 FiberBundle 10 1-3 2A-dvantagesofGRINFibersforUltrahighResolutionFiber-Optic 2- 2I-magingSystems 12 1-3-1 BackgroundtoGRINFiber 12 1-3-2 ImageBrightness 14 3- 1-3-3 ImageResolution 18 3-3-4 TimeResolution 19 4 DissertationOrganization 21 2 POLYMER-POLYMERMISCIBILITYSTUDYFORPLASTICGRADEDINDEX OPTICALFIBER 23 1 Introduction 23 2-2 Theory 27 2-3 ExperimentalandResults 28 3-1 Methods 29 3-2 Results 30 4 Summary 32 3 IMAGEASSESSMENTOFFIBER-OPTICIMAGINGSYSTEM 38 1 Introduction 38 3-2 ModulationTransferFunction(MTF) 39 2-1 PointSpreadFunction 42 IV 3-2-2 LineSpreadFunction 42 3-3-3 EdgeResponseFunction 43 3-3 3C-rosstalk 44 3- 3-3-1 Background 44 3-3-2 CharacterizationofCrosstalk 47 3-4 LeakyRays 55 4- 3-4-1 Background 55 4-2 CharacterizationofLeakyRays 56 5 Summary 62 4- 4 FABRICATIONOFPLASTICGRADEDINDEXIMAGEGUIDESFOR 4U-LTRAHIGHRESOLUTIONENDOSCOPES 64 1 Introduction 64 45--2 PreparationofGRINPreforms 68 4-3 VerificationofGRINProperties 73 4-4 FabricationofGRINImageGuides 77 5- 4-1 FirstDrawing,Stacking,andFusing 78 4-4-2 SecondDrawing,Stacking,Fusing,andFinalDrawing 80 4-4-3 SpecialCleanStackingProcess 82 6-5 Summary 84 5 FABRICATIONOFULTRAHIGHRESOLUTIONPLASTICGRADEDINDEX IMAGEFACEPLATES 85 1 Introduction 85 5-2 PreparationofGRINPreforms 87 5-3 FabricationofPlasticGRINFusedImageFaceplates 90 5-4 SpecialAbsorbentMaterial 91 5 Summary 93 6 OPTICALCHARACTERIZATIONOFULTRAHIGHRESOLUTIONPLASTIC GRADEDINDEXIMAGEGUIDESANDIMAGEFACEPLATES 95 1 Introduction 95 6-2 OpticalCharacterizationofUltrahighResolutionPlasticGradedIndex ImageGuides 96 6-2-1 ImageBrightness 96 6-2-2 ImageResolution 103 6-3 OpticalCharacterizationofUltrahighResolutionPlasticGradedIndexFused ImagePlates 112 6-3-1 Defects 112 6-3-2 ImageResolution 114 6-4 Summary 118 7 CONCLUSIONSANDSUGGESTIONSFORFUTUREWORK 120 7-1 Conclusions 120 7-2 SuggestionsforFutureWork 122 7-2-1 LargeNumericalApertureGRINFiber 122 7-2-2 PicosecondTissueImaging 123 REFERENCES 125 BIOGRAPHICALSKETCH 131 VI AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy ANEWAPPROACHTO ULTRAHIGHRESOLUTIONENDOSCOPICMEDICALIMAGING By BongsooLee August1999 Chairperson:WesleyE.Bolch MajorDepartment:NuclearandRadiologicalEngineering Existingfiber-opticimagingsystemssuchasthemedicalendoscope,horoscope, fusedimagefaceplate,imageconduit,andimageeonverteraremadefromglassstep index(SI)fibers. Thesefiber-optieimagingsystemshavelimitationsinbothimage qualityandmechanicalproperties. Inparticular,theimageresolutionoftheSIimage guideislimitedto5pm,andtheimagebrightnessrapidlydiminishesasthemicrofiber diameterdecreasesbelow5 pm. Thus, itis impossibletodevelopbrightultrahigh resolution(below5pm)fiber-opticimageguideswithconventionalSIfibers. Inthisstudy,ultrahighresolutionimageguidesandfusedfiber-opticfaceplates withpixelsizebetween5 pmand2.5 pmwerefabricatedwithplastiegradedindex vii (GRIN) fibers. The image brightness and image resolution were measured and comparedwiththoseofexistingglassSIimageguides. TheimagebrightnessofplasticGRINimageguideswasmorethanafactoroftwo higherthanthatofglassSIimageguideswiththesamenumericalapertureandthesame microfiberdiameter. ThereisanimprovementinresolutionoftheplasticGRINimage guidesasthemicrofiberdiameterisreducedfrom5pmto2.5pm. Themodulation transferfunction(MTF)oftheGRINimagefaceplatesalsoimprovedasthediameterof microfibersdecreasesbelow5pm. Throughthis feasibility study, ithas been shownthat fiber-optic image guides madefrompolymericgradedindexfiberscanachieveultrahighimageresolution,i.e., below5pmwithbetterimagebrightnessthanthatofSIimageguides. Thefundamental limitationontheresolutionofallpreviousfiber-opticimageguidesimposedbythe thicknessofstepindexcladdingmaterialscanbeovercome. Thisnewdesignofoptical systemscouldhaveamajorimpactonawidearrayoffutureopticalsystemsusedin defense,industrial,andmedicalapplications. viii CHAPTER 1 GENERALINTRODUCTION 1-1 Fiber-OpticEndoscopes ThenameendoscopeisderivedfromtwoGreekwordswhichareendom(within) andskopein(view)(Haubrich1989). Endoscopeisthusanopticalinstrumentusedfor viewinginternalorgansthroughnaturalopenings(ear,throat,rectum,etc.)orthrougha smallincisionintheskin. Generally,aflexibleendoscopeisreferredtoasafiberscope. Inflexibleendoscopesabundleofpreciselyalignedflexibleopticalfibersisused,while inrigidendoscopestheimageisconveyedbyarelayoflenses. Theclassicalrigid endoscopeshaveanumberofperiscopicandfieldlensinordertoconveytheimage fromdistalendtotheeyepiece. Insomecase,asmanyas40-50lensesmaycause considerableoptical aberration, light lossesandghostimages. Inaddition,the off- centeringoflensescanalsocausesignificantvignettingandimagedeteriorationunless great care is taken in the system design. The demands on the performance of endoscopicinstruments,whichincludehavingaverysmalldiameterandbeingflexible, havealsobeenincreasedoverthelastthirtyyears. Fiber-opticendoscopespermitthe visualizationofinaccessibleregionsinthebodywithoutpainanddiscomforttothe patient. Aflexibleendoscopeisessentialformanycasesbecauserigidendoscopesonly have a limited use in digestive endoscopy (Salmon 1974). Nearly all current endoscopesoftenincludetwokindsofopticalfibersforimageguideand lightguide. 1 2 andancillarychannelsforpassageofair,water,andimplementssuchasbiopsyforceps, cytologybrushes,orvarioustoolswhichcanberemotelycontrolled(Katzir1987). Althoughtheoriginalconceptofendoscopystartedfromtheearly19**’century,the firstendoscopemadeofopticalfibers(fiberscope)wasusedforviewingthestomach andesophagusintheUniversityofMichiganSchoolofMedicinein1957(Hirschowitz 1979). Afterthattime,therehasbeenrapidprogressinthedevelopmentofendoseopes. Endoscopes can be divided into two eategories according to their medical applications(Katzir1989),althoughtheprinciplesofoperationandbasicfeaturesofthe various kinds offiber-optic endoscopes are similar. The firstone includes regular endoseopessuchasthegastroscope,colonoscope,andbronchoscope. Gastroscopesare endoscopesforviewingtheupperpartofthegastrointestinaltract,stomach,esophagus andbilechannels. Colonoscopesandbronchoscopesareusedforexaminingthecolon andbronchi,respectively. Theseeondcategoryincludesultrathinendoscopessuchas needlescopes,ophthalmicendoscopesandangioscopes. Inthe1980’s,ultrathinfibers werefabricatedandthediameterofanendoscopewasreducedto lessthan 1 mm. Thesekindsofultrathinendoscopesareusedtoexamineverysmallpartsofinternal organs. Inrecentyears,ultrathinsilica-basedneedlescopeshavebeendevelopedfor medical applications such as imaging and clinical diagnostics. The ultrathin needlescopeshave2000to6000pixelsandthediameterofthemareabout0.2mmto 0.5mm. Ithasbeenfoundthatitiseasytoinserttheultrathinneedlescopestothe mammaryglandsandtodetect breastcanceratanearlystage(Tsumanumaetal.1991). Inaddition,thiskindofneedlescopemakesitpossibletoobtainreal-timeimagesof inaccessiblelocationswithinthehumanbody(Kiatetal. 1992). Also,theophthalmic