Radiation Exposure and Image Quality in X-Ray Diagnostic Radiology Horst Aichinger (cid:129) Joachim Dierker € Sigrid Joite-Barfuß (cid:129) Manfred Sabel Radiation Exposure and Image Quality in X-Ray Diagnostic Radiology Physical Principles and Clinical Applications Second Edition Authors Dr.HorstAichinger Dr.JoachimDierker UnterfarrnbacherStr.32 Hegenigstr.56 90766Fu¨rth 91056Erlangen Germany Germany [email protected] [email protected] Dipl.Phys.SigridJoite-Barfuß Prof.Dr.ManfredSa¨bel Friedhofstr.4a Universit€atsklinikumErlangen 91058Erlangen RadiologischesInstitut Germany Maximiliansplatz1 [email protected] 91054Erlangen Germany [email protected] ISBN978-3-642-11240-9 e-ISBN978-3-642-11241-6 DOI10.1007/978-3-642-11241-6 SpringerHeidelbergDordrechtLondonNewYork LibraryofCongressControlNumber:2011928414 #Springer-VerlagBerlinHeidelberg2012 Thisworkissubjecttocopyright.Allrightsarereserved,whetherthewholeorpartofthematerialisconcerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. 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Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface to the 1st Edition X-raydiagnosticradiologyisamajorworld-wideactivity.InEuropeapproximately250million X-rayexaminationsareperformedannually,andintheUnitedStatesofAmericaasimilarlevel of radiological activity is undertaken. This results in the fact that the largest contribution to radiation exposure to the population as a whole is known to be from man made radiation sources arising in the form of diagnostic X-rays (UNSCEAR 2000). It is also known that exposures vary widely, due to differences in X-ray techniques and the level of skill of the operator of the equipment. Consequently radiation protection of the patient is a major aim in modern health policy. The two basic principles of radiation protection of the patient as recommended by the International Commission on Radiological Protection (ICRP 1991) are justification of practice and optimisation of protection. Justification is the first step in radiation protection. It is generally accepted that no diagnostic exposure is justifiable without a valid clinical indication. In comparison to the associated radiation risk, every examination must result in a net benefit for the patient. Justification also implies that the necessary result cannot be achieved with other methods whichwouldbecombinedwithlowerrisksforthepatient. OnceadiagnosticX-rayexaminationhasbeenclinicallyjustified,thesubsequentimaging processmustbeoptimised.TheoptimaluseofX-raysinvolvestheinterplayofthreeimportant aspectsoftheimagingprocess(CEC1996): (cid:129) Thediagnosticqualityoftheradiologicalimage (cid:129) Theradiationdosetothepatient (cid:129) Thechoiceofimagingtechnique Inrespect ofdiagnostic radiology, the ICRP does notrecommend the application ofdose limitstopatientirradiationbutdrawsattentiontotheuseofdosereferencelevelsasanaidto optimisationofprotectioninmedicalexposure. The principles of justification and optimisation are largely translated into a legal frame- work by the Medical Exposure Directive (MED) 97/43/Euratom (CEC 1997). Concerning optimisationtheMEDstatesexplicitlyinArticle4,1(a)that: (cid:129) ‘All doses due to medical exposure for radiological purposes, except radiotherapeutic procedures, shall be kept as low as reasonably achievable consistent with obtaining the requireddiagnosticinformation,takingintoaccounteconomicandsocialfactors’. ThisconceptisknownastheALARAprinciple(aslowasreasonablyachievable). InArticle4,2.(a)theMEDstatesthat: (cid:129) ‘MemberStatesshallpromotetheestablishmentandtheuseofdiagnosticreferencelevels forradiodiagnosticexaminations’. DiagnosticreferencelevelsaredefinedinArticle2oftheMEDas: (cid:129) ‘Dose levels in medical radiodiagnostic practices for typical examinations for groups of standard-sizedpatientsorstandardphantomsforbroadlydefinedtypesofequipment.These levels are expected not to be exceeded for standard procedures when good and normal practiceregardingdiagnosticandtechnicalperformanceisapplied’. v vi Prefacetothe1stEdition The authors of this book have been engaged for a long time in the solution of problems concerning optimisation in X-ray diagnostic radiology, three of us (Aichinger, Dierker, Joite-Barfuß) as physicists in development working groups of Siemens Medical Solutions andone(S€abel)asamedicalphysicistinauniversityhospital.Duringthistimealotofdata material have been accumulated, which could be useful for physicists and engineers in the medicalradiodiagnosticindustry,formedicalphysicistsandfordiagnosticradiologistswork- ingatproblemsofimagequality,patientdoseestimationandespeciallytheestablishmentof diagnosticreferencelevels.InthisconnexionthepublicationoftheMEDwasthetriggerpoint forourdecisiontocollectandpublishthismaterial. Inparticularthefiguresandtablesincludedshouldenableamedicalphysicistto: (cid:129) Calculatethescatter-freecharacteristicquantitiesoftheprimaryradiationbeam (cid:129) Estimatepatientdoses(organdose,effectivedose) (cid:129) Optimise radiographic and fluoroscopic exposure parameters in relation to the medical indication (cid:129) Takeintoaccounttheinfluenceofscatteredradiationonimagequalityanddose The data provided for the solution of these tasks are partly based on X-ray spectra, measured on diagnostic X-ray tube assemblies, and supplemented by the results of measurementsonphantomsandsimulationcalculations. Takinginto consideration thatmammographyscreeningis increasingly establishedX-ray mammographyistreatedinsomedetail.Ontheotherhand,concerningcomputedtomography, thepresentationisconfinedtotheaspectofdoseestimation.Anessentialreasonforthisisthat one ofour colleagues (Kalender 2000) has written anexcellentbook on computed tomogra- phy,whichcoverstheaspectofimagequalityindetail. Ourbookconsistsofthreeparts: (cid:129) The ‘Physical Principles’ reviews some information on radiation physics, dosimetry and X-ray diagnostic technique, which will be useful for the understanding of the figures and tables, but it is not intended to replace standard books on the physics of diagnostic radiology. (cid:129) In the ‘Clinical Applications’ the material presented is applied to some clinical problems concerning radiation exposure of the patient, image quality and optimisation of imaging equipment. (cid:129) The ‘Supplement’ includes all the figures and tables, which are necessary for the calculations. It is complimented by a CD-ROM that includes the most important data of the‘Supplement’andalotofadditionalusefulfiles. A detailed description of the contents of the different parts of the book is given in the following‘Introduction’. In the preparation of this book we asked for and received the help of a number of well- qualified people: We are grateful to John H. Hubbell, Ph.D., from the National Institute of StandardsandTechnology,Gaithersburg,USA,forhissupportintheselectionofthemostup- to-datephotoninteractioncoefficientsandtoG.T.Barnes,Prof.Ph.D.,fromtheUniversityof AlabamainBirmingham,USA,forinformationinrespecttohisworkaboutscatteredradiation in mammography. Moreover we thank Tassilo v. Volkmann, Ph.D. from Kodak for the provision of the data of screen-film combinations and M.A.O. Thijssen, Ph.D. from the University Hospital in Nijmegen, Netherlands, for information about his CDRAD-phantom. LastbutnotleastwethankI.Aichingerforherpreparationofsomeofthefiguresinthisbook. HorstAichinger JoachimDierker SigridJoite-Barfuß ManfredS€abel Prefacetothe1stEdition vii References CEC(CommissionoftheEuropeanCommunities)1996.EuropeanGuidelinesonQualityCriteriaforDiag- nosticRadiographicImages.EUR16260(Luxemburg:CEC) CEC(CommissionoftheEuropeanCommunities)1997.CouncilDirective97/43/EURATOMof30June1997 onhealthprotectionofindividualsagainstthedangersofionisingradiationinrelationtomedicalexposure, OfficialJournaloftheEuropeanCommunities,NoL180/22 ICRP (International Commission on Radiological Protection) 1991. 1990 Recommendations of the ICRP, Publication60,AnnalsoftheICRP21No.1–3(NewYork:PergamonPress) KalenderWA(2000)ComputedTomography.(M€unchen:PublicisMCD) UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) 2000. Sources and EffectsofIonizingRadiation.(NewYork:UnitedNations) Preface to the 2nd Edition Sincethepublicationofthefirsteditionin2004X-rayimaginghasbecomealmostcompletely digitalinmoderndiagnosticradiologyinstitutes.OntheothersidetherearestillalotofX-ray unitsinoperationwhichusefilm-screencombinationsforradiographyandimageintensifiers for fluoroscopy. Therefore we have decided to leave the concerning material in the book essentially as it was. Furthermore for the full understanding of the new potentials in digital imaging,i.e.theadvantagesandfurtherdevelopmentpossibilitiesbutalsothecomplexity,the knowledge of the physics in conventional imaging is of great importance. In addition the frequency of computed tomography increases still rapidly, and – because it involves larger radiationdosesthanmostoftheconventionalimagingprocedures–obtainsgrowingattention also in radiation protection. Accordingly we have added to this edition some facts on the principlesofCTimaging. Indetailthefollowingimprovementshavebeencarriedout: (cid:129) More detailed consideration of the aspects of image quality and radiation exposure in digitalimagingandcomputedtomography (cid:129) Actualisationofthecitedreferences (cid:129) Removalofobsoletetextpassages,figuresandtables (cid:129) Correctionofdiscoveredprintingerrors We are grateful to Elke Nekolla, Ph.D., from the German Federal Office for Radiation Protection for placing Fig. 1.1 to our disposal. Furthermore we are grateful to Dr. Helmuth Schramm from Siemens Medical Solutions for his information about the functioning of fluoroscopywhenusingaflatpanelimagereceptorinmodernX-rayequipments. HorstAichinger JoachimDierker SigridJoite-Barfuß ManfredS€abel ix