医学影像技术：2X线摄影条件

X线摄影条件

exposurefactorX线摄影条件(exposurefactor)摄影电压：KV(仟伏）(PhotographicVoltage)摄影电流：mA（毫安）(PhotographicCurrent)摄影时间：S（秒）(Photographictime)距离：FFD（厘米）(Distances)

要获得一张优质的X线照片，除摆好正确的摄影位置，还需要掌握好X线摄影条件，照片受X线管焦点、被照体、影像转换介质、照片冲洗、激光照相机等多种因素的影响Toobtainahigh-qualityX-rayphotographs,inadditiontogracefullycorrectshootingposition,youalsoneedthepalmgoodgripX-rayphotographicconditions,photographsbyX-raytubefocus,thebody,theimagetransfermedium,photoprinting,lasercamerasandotherfactors感光效应Vn．i．t．s．f．zE=k

d.Z.ρ.r2

V：管电压，i：管电流，t：摄影时间，s：增感率，f：感光度，z：靶物质原子序数，d：被照体的厚度，Z：被照体的有效原子序数，ρ：被照体的密度，r：摄影距离，k：常数PhotographiceffectsVn．i．t．s．f．zE=k

d.Z.ρ.r2

V:tubevoltage,i:tubecurrent,t:photographytime,s:sensitizationrate,f:sensitivity,z:atomictargetsubstanceordinal,d:thicknessoftheilluminatedbody,Z:accordingtothebodyoftheeffectiveatomicnumber,ρ:densityoftheilluminatedbody,r:shootingdistance,k:constant1．管电压管电压(tubevoltage)是影响照片密度值、对比度、层次及信息量多少的重要因素。管电压的作用主要有二个方面：①在X线摄影中，管电压代表着X线的穿透能力，高的管电压可以穿透更厚和更高密度的结构；②管电压代表X线光子的能量，管电压越高，感光量越多。1.TubevoltageThetubevoltage(tubevoltage)thataffectthephotodensityvalues,Contrast,thelevelandamountofinformationthatmanyimportantfactors.Thetubevoltageappliedmainlytwoaspects:①IntheX-rayphotography,representingtheX-raytubevoltageofwearthroughcapacity,hightubevoltagecanpenetratethickerandhigherdensitystructure;②X-raytubevoltagerepresentativeofthephotonenergy,thehighertubevoltage,themoreamountoflight.VariouspartsofthebodyselectedreferencetubevoltagevaluetubevoltagePhotographypartsBreastThyroidFourlimbsshoulderJointCervicalvertebraMastoidChest(Bedside)SkullThoracicLumbarAbdomenChestcardiacandlargevessel2．管电流量管电流量代表X线量的多少，因而管电流量的大小直接影响探测器感光量的多少。管电流量增加探测器感光量增加，影像的量子斑点减少。但是对于屏-片组合而言，管电流量过高会使照片黑化度（光学密度）太大，组织结构不易观察。2.TubecurrentamountThetubecurrentamountrepresentstheamountofX-rays,andthusthethesizeoftubecurrentdirectlyaffectsthetheamountofthephotosensitivedetector.Whentheamountofcurrentdetectortubeincreases,theamountoflightincreasestoo,butthenumberofquantumdotdecreases.Butforscreen-filmportfolio,theoverhighamountofcurrentisleadtolargephotoblacktubedegree(Opticaldensity),anditisdifficulttoobservetheorganizationalstructure.3．摄影距离焦点至探测器的距离称为摄影距离，或称源像距（source-imagedistance,SID）焦点至胶片的距离，简称为焦-片距（focus-filmdistance；FFD）。在感光量计算公式中SID就是r。在摄影的有效范围内，探测器上得到的感光量与SID的平方成反比。3.PhotographyDistanceThedistancefromfocustodetectoriscalledphotographydistance,orthesource-imagedistance(source-imagedistance,SID)Thedistancefromfocustofilm,iscalledfocus-filmdistance(Focus-filmdistance;FFD).IntheamountoflightSIDistheformulaforcalculatingr.Intheeffectiverangeofphotography,theamountoflightonthedetectorisinverselyproportionaltoSIDsquare.4．成像探测器（1）屏-片组合（2）影像增强器-电视系统（3）成像板（4）平板探测器4.Imagingdetector(1)screen-filmportfolio(2)imageintensifier-televisionsystem(3)theimagingplate(4)flatpaneldetector（1）屏-片组合1）胶片（ⅰ）种类①一般摄影用X线胶片②多幅相机和激光打印机成像胶片结构（ⅱ）结构：主要由感光乳剂层、片基、保护层和底层构成。（ⅲ）感光特性：感光材料中直接决定和影响影像质量的因素统称为照相性能。包括：感光性能、物理性能、成像性能(1)screen-filmportfolio.1)Film.(Ⅰ)category.①generalphotographywithX-rayfilm.②multiplecamerasandlaserprinterimagingfilmstructure.(Ⅱ)Structure:Mainlycomposedbyaphotosensitiveemulsionlayer,afilmbase,aprotectivelayerandabottom..(Ⅲ)PhotographicFeatures:photosensitivematerialdirectlydetermineandshadowfactorsthataffecttheimagequalityreferredtoasphotographicproperties.Including:photographicproperties,physicalproperties,imagingperformance2）增感屏增感屏(intensifyingscreen)是X线摄影的重要器材之一。在X线摄影中，利用X线激发增感屏的荧光体所产生的荧光对胶片增加感光作用，大大减少X线曝光量。（ⅰ）种类：增感屏的种类根据其构成及用途分成三大类：①钨酸钙屏②稀土增感屏③特殊增感屏2)IntensifyingscreenIntensifyingscreenisoneoftheimportantequipmentinX-rayphotography.IntheX-rayphotography,theuseofX-rayexcitationphosphorintensifyingscreentorubberfluorescencegeneratedphotosensitivesheetincreaseseffect,greatlyreducingX-rayexposure.(Ⅰ)Type:thetypeofintensifyingscreenaccordingtoitscompositionandusesdividedintothreecategories:①calciumtungstatescreens②earthintensifyingscreen③specialintensifyingscreen（ⅱ）增感屏结构：主要有四层组成：①基层②荧光体层③保护层④反射层或吸收层（ⅲ）性能：增感屏的性能有二个方面：①增感率②对影像效果的影响(Ⅱ)intensifyingscreensstructure:Therearefourmaincomponents:①grassroots②phosphorlayer③protectivelayer④reflectororabsorberlayer(Ⅲ)Performance:Theperformanceoftheintensifyingscreenhastwoaspects:①sensitizationrate②effectontheimage暗盒背面观Tubeside

病人Screen–filmcombination胶片冲洗机照片X线管X-raytubepatientFilmProcessorPhoto3）屏-片组合屏-片组合成像性能的优劣表现在X线照片影像与输入的X线信息影像的差别上，差别越小，屏-片组合的信息传递功能就越好。屏-片组合的信息传递功能通过MTF的测定来客观评价。3)Screen-filmportfolioScreen-filmportfolioperformanceimagingperformancemeritsaccordingtotheX-rayfilmX-rayimagesandtheinputinformationonthedifferenceimage,thesmallerdifferencesinscreen-filmportfoliothebettermessagingfeaturepossibility.Screen-slicethroughacombinationofmessagingfeaturesMTFmeasurementtoobjectivelyevaluate.（2）影像增强器-电视系统影像增强器-电视（II-TV）摄像机系统中，增强器将X线转换成可见光，并将其强度增强放大数千倍，再用TV摄像机内转换为电子信号，影像用阴极射线管（CRT）显示。现代的系统已将输出信号数字化，影像可用阴极射线管或液晶屏显示。(2)imageintensifier-televisionsystemIntheimageintensifier-television(II-TV)CameraSystemtheX-rayintensifierconvertedintovisiblelight,anditsintensityamplifiedthousandsoftimes,andthenintheTVcameramachineconvertedtoelectronicsignals,imagesaredisplayedbyacathoderaytube(CRT).Modernsystemsmaketheoutputsignaldigitized,theimagecanbedisplayedbyacathoderaytubeorliquidcrystalscreen.Imageintensifierandmonitor(CRT)FocuselectrodePhotocathodeAnodeIncidentonthephosphorscreenIncidentplanesubstrateX-rayIncidentsurfaceFocusPowerFluorescentimageOpticalimageCathodepowersupply影像增强器（imageintensifier）数字遥控透视DigitalremoteperspectiveWhat’sthis?（3）成像板1）成像板结构①表面保护层②PSL物质层③基板④背面保护层2）特性：IP主要结构是荧光物质层，它对放射线、紫外线的敏感度远高于普通X线胶片。(3)theimagingplate1)Imagingplatestructure①surfaceprotectivelayer②PSLmateriallayer③substrate④backoftheprotectivelayer2)Features:IPmainstructureisafluorescentmateriallayer,whichtoradiation,ultravioletsensitivityismuchhigherthannormalX-rayfilm.保护层支持层成像层背衬层氟卤化钡ProtectivelayerSupportinglayerImaginglayerBackinglayerHalogenatedbariumfluoride激光源强度控制线束偏导装置线束成型光学装置传输环节集光器光学滤波器光电探测器模拟电子器件模数转化器图像缓冲器IP具有以下特性：（ⅰ）发射与激发光谱（ⅱ）时间响应特征（ⅲ）动态范围（ⅳ）存储信息的消退（ⅴ）天然辐射的影响IPhasthefollowingfeatures:(Ⅰ)emissionandexcitationspectra(Ⅱ)timeresponsecharacteristics(Ⅲ)DynamicRange(Ⅳ)Storinginformationregression(Ⅴ)Effectofnaturalradiation（4）平板探测器1）直接型平板探测器（ⅰ）组成：主要由导电层、电介层、Se(硒)层、顶层电极、集电矩阵层、玻璃衬底、保护层，以及高压电源和输入输出电路组成。顶电极a-Se转换层TFT阵列(4)flatpaneldetector1)Direct-typeflatpaneldetector(Ⅰ)components:mainlycomposedbyconductivelayer,adielectriclayer,Se(selenium)layer,thetopelectrode,acollectormatrixlayer,aglassSubstrate,aprotectivelayer,andahighvoltagepowersupplyandinputandoutputcircuit.Topelectrodea-SeconversionlayerTFTarray（ⅱ）特性：①直接光电转换②直接读出X线曝光过程中的电荷分布③量子检测效率（DQE）④曝光宽容度大⑤X线敏感度和响应特性⑥空间分辨力⑦调制传递函数（MTF）(Ⅱ)Features:①directphotoelectricconversion②directlyreadouttheX-rayexposureprocessoftheelectricalchargedistribution③detectivequantumefficiency(DQE)④exposurelatitude⑤Xlinesensitivityandresponsecharacteristics⑥spatialresolution⑦modulationtransferfunction(MTF)2）间接型FPD：是一种以a-Si（非晶硅）光电二极管阵列为核心的X线影像间接型FPD。（ⅰ）基本组成：a-SiFPD基本组成是由CsI闪烁体（cesiumiodidescintillator）层、a-Si光电二极管阵列、行驱动电路、列读取电路以及图像信号读取电路等部分构成。2)IndirectFPD:isakindofa-Si(amorphoussilicon)PhotodiodewiththecoreofX-rayimagesindirectFPD.(Ⅰ)basiccomponents:a-SiFPDbasiccompositionisCsI​​scintillator(cesiumiodidescintillator)layer,a-Siphotodiodearray,thelinedrivercircuit,column,readcircuitaswellasotherpartsoftheimagesignalreadcircuit.闪烁体非晶硅传感器读出电路外壳驱动电路DrivecircuitShellAmorphoussiliconsensorReadoutcircuitScintillator（ⅱ）性能参数：①调制传递函数（MTF）较高。②FPD的噪声主要来源于X线量子噪声、探测器电子学噪声。在普通条件下，电子学噪声要远小于量子噪声。③量子检测效率（DQE）也较高。④其他品质因素，有灵敏度、线性、记忆效应、探测器图像获取时间、探测器的温度稳定性（stability）等。(Ⅱ)Performanceparameters:①modulationtransferfunction(MTF)ishigher.②FPDnoisecomesmainlyfromtheX-rayquantumnoise,detectorelectronicnoise.Innormalconditions,detectorelectronicnoiseisfarlessthanthequantumnoise.③detectivequantumefficiency(DQE)ishigher.④otherqualityfactors,thereissensitivity,linearity,memoryeffect,theprobeimageacquisitiontime,thedetectortemperaturestability(stability)andsoon.3）电离型探测器：电离型DR系统的成像探测器为线状结构，采用动态线扫描技术直接接收X射线光子。有两种形式：①多丝正比室②电离室3)Ionizationdetector:IonizingimagingdetectortypeDRsystemislinearjunctionstructure,theuseofdynamiclinescantechnologytodirectlyreceiveX-Rayphoton.Therearetwoforms:①multi-wireproportionalchamber②ionizationchamber碘化铯/非晶硅与非晶硒的比较电荷收集电极E-----++TOP电极绝缘层Selenlum硒X线半导体电子阻断层偏压电场

读出电路

+_X-Ray光子碘化铯闪烁体(CsI)可见光不定型硅阵列电信号数字信号读出电路X-Ray光子数字信号Cesiumiodide/amorphoussiliconandamorphousseleniumcomparisonChargecollectionelectrodesE-----++TOPelectrodeInsulatinglayerSelenlum硒X-raysemiconductorElectronblockinglayerBiaselectricfieldReadoutcircuit

+_X-RayphotonsCesiumiodidescintillator(CsI)VisiblelightAmorphoussiliconarraysElectricsignalDigitalsignalReadoutcircuit

X-RayphotonsDigitalsignal碘化铯/非晶硅与非晶硒的比较

Cesiumiodide/amorphoussiliconandamorphousseleniumcomparison间接（碘化铯）转换方式Indirect(CsI)conversion高纯度非晶硒绝缘片HV直接转换（非结晶硒）方式Directconversion(non-crystallineselenium)mode+-a-SiPhotoDiodeCsILightIncidentX-raysOutput碘化铯

非晶硅光电二极管可见光碘化铯/非晶硅与非晶硒的比较非晶态硒CR传统胶片非晶态硅(143微米)碘化铯/非晶硅与非晶硒的比较量子捕获效率高（DQE）刷新速度快照射剂量低应用设备广泛（DR，DSA等）平板生产商

GE（整板）

TRIXELL（四块拼接）设备生产商

GE，SIEMENS，PHILIPS……量子捕获效率较低（DQE）刷新速度慢照射剂量高在DR上应用平板生产商

HOLOGIC设备生产商

KODAK，友通Cesiumiodide/amorphoussiliconandamorphousseleniumcomparisonHighquantumcaptureefficiency（DQE）HignrefreshspeedLowdoseApplicationequipmentiswide（DR，DSA

edc）Theflat-panelmanufacturers

GE（fullboard）

TRIXELL（fourstitching）Theequipmentmanufacturer

GE，SIEMENS，PHILIPS……Lowquantumcaptureefficiency（DQE）LowrefreshspeedHighdoseIntheapplicationofDRTheflat-panelmanufacturers

HOLOGICTheequipmentmanufacturer

KODAK，DFI5．滤线栅X线摄影时，被照体产生散射线，使照片影像上形成灰雾（fog），使影像的对比度减小，减少散射线到达胶片最有效的方法是利用滤线栅(grid)。一般认为肢体厚度超过10cm就应用滤线栅。滤线栅不仅吸收了散射线，而且还吸收掉一部分原发X线。因此，在制定摄影条件时，必须考虑到滤线栅的曝光系数B5.GridsX-rayphotography,thescatteredradiationproducedaccordingtothebody,makephotoImageformingfog(fog),sothattheimagecontrastdegreeofreduction,reducingthescatteredradiationreachingthefilmthemosteffective.Methodistheuseofgrids(grid).Generallybelievedlimbthickerthan10cmontheapplicationofgrids.Gridsnotonlyabsorbedthescatteredradiation,butalsoabsorboutpartoftheprimaryX-ray.Therefore,informulatingphotographingpiecesmustbetakenintoaccountgridsexposurefactorBFocusX-raytubeTheprimaryX-rayThespecimenScatteredradiationpassthroughX-rayOrganicintermediatefillerParallelFocusGridsstructure散射线原发射线Originalemissionlines滤线栅的作用散射线Scatteredradiation照片密度大

照片密度小高栅比低栅比tightloose6.照射野通过X线管窗口的X线束(X-raybean)入射于被照体的曝光面的大小称为照射野（radiationfield）。照射野的大小，与X线照片的对比度、影像密度都有很重要的关系。6RadiationfieldSizeofexposureinthesurfaceofthebodycausedbyX-raybeanwhichpassthroughX-raytubewindowcalledirradiationfield(radiationfield).Thesizeoftheradiationfield,hasimportantrelashionshipwiththeX-rayphotographandimagedensity.据研究照射野在100cm2～200cm2以上时，散射线(scatteredradiation)含有率急剧增加。照射野在600cm2～700cm2时，散射线含有率趋于饱和。X线摄影时，应将X线的照射野的大小减少到能包含被照部位最小程度，以起到对患者和工作人员的辐射防护(radiationprotection)作用及提高照片的清晰度。Accordingtostudytheradiationfieldin100cm2~200cm2ormore,scatteredradiation(scatteredradiation)contenturgentincreasesharply.Radiationfieldin600cm2~700cm2,thebulkraycontentsaturated.WhenX-rayphotography,X-rayradiationfieldshouldreducetothesizeoftheleastpartthatilluminatedportioncancontaintoplayforpatientsandstaffradiationprotection(radiationprotection)foruseandenhanceyourphotos.照射野和胶片大小相同照射野大于胶片散射线7．其他因素当使用传统的屏-片组合进行摄影时，胶片处理条件影响着照片的密度值，显影液就是影响感光效应的重要因素。显影液的性能取决于显影液的配方、pH值、显影时间和显影温度。一般讲，显影液浓度高、pH值高、温度高相对感度高。在激光打印技术中，照片的密度与照射激光的强度有正相关关系。7.OtherfactorsWhenusingconventionalscreen-filmportfoliophotography,plasticwaferprocessingconditionsaffectthedensityofthepicture,thedevelopingliquidisanimportantfactoraffectingthephotosensitiveeffect.Developmentperformancedependsonthedeveloperliquidformulations,pH,developmenttimeanddevelopmenttemperature.Generallyspeaking,thedeveloperconcentration,pHvalue,temperatureandhighrelativesensitivity.Inlaserprintingtechnology,thepicturedensityandirradiationintensityofthelaserhasapositivecorrelation.X线影像的形成X线成像的途径X线对比度光学密度光学对比度X-rayimageformationX-rayimagingapproachXlinecontrastTheopticaldensityOpticalContrastX线成像的途径X线被照体X线对比度增强器、荧光屏、荧光板显定影照片观片灯

IP影像板（或平板探测器）光学对比度人眼人脑加以判断X-rayimagingapproachX-ray

body

X-raycontrast

booster、screen、board

fuser

photo

light

IP

board（flatpaneldetector）Opticalcontrast

eyes

DeterminebythebrainX线X线对比度1.X线对比度KXX线穿过被照体两部分产生不同线量之比

II0KX=I´II´X-raycontrast1.X-raycontrastKXTheratiooftheX-raypassthroughtwodifferentparts

II0KX=I´II´X-raycontrast

X线对比度2.四种状态下产生的X线对比度⑴.被照体的衰减系数和厚度均不同

II0e－μdKX===eμ´d

´－μdI´I0e－μ´d´⑵.被照体的衰减系数相同,厚度不同

II0e－μdKX===eμ(d

´－d)I´I0e－μd´2.FourstatesarisingundertheX-raycontrast⑴.attenuationcoefficientandthicknessaredifferent

II0e－μdKX===eμ´d

´－μdI´I0e－μ´d´⑵.sameattenuationcoefficientdifferentthickness

II0e－μdKX===eμ(d

´－d)I´I0e－μd´⑶.被照体的衰减系数不同,厚度相同

II0e－μdKX===ed(μ

´－μ)I´I0e－μ´d⑷被照体内部含有不同衰减系数的物质

II0e－μdKX===ed

´(μ´－μ)I´I0e－μ(d－d´)－μ´d´⑶.Different

attenuationcoefficientsamethickness

II0e－μdKX===ed(μ

´－μ)I´I0e－μ´d⑷containsubstancewithDifferentattenuationcoefficient

II0e－μdKX===ed

´(μ´－μ)I´I0e－μ(d－d´)－μ´d´三、对比度指数1.μ值的大小

μ值的大小与物质的成分有关

μ=bZ4λ3

骨骼:μb=2.09λ3+0.342

肌肉:μm=2.2λ3+0.18

脂肪:μf=1.692λ3+0.1692

空气:μa=0.00338λ3+0.000234Third、thecontrastindex1.μ

size

sizeofμhasrelationshipof

compositionoftherelevantmaterial

μ=bZ4λ3bones:μb=2.09λ3+0.342mucles:μm=2.2λ3+0.18fatty:μf=1.692λ3+0.1692air:μa=0.00338λ3+0.000234Contrastindexandtubevoltagerelationship

对比度指数与管电压的关系2.对比度指数

X线摄影中常见

KX=ed

´(μ´－μ)

μ´－μ为被照体内的衰减系数之差叫对比度指数。随电压升高，对比度指数下降2.Contrastindex

commoninX-rayphotography

KX=ed

´(μ´－μ)

μ´－μistheattenuationcoefficientoftheilluminatedbodycalledthedifferencecontrastindex.Withthevoltageincreases,thecontrastindexdeclines四、X线对比度观察法1.透视法①.X线被照体荧光板影像

(浅淡、须在暗房)②.X线被照体倍增管监视器影像(明亮)

Four、X-raycontrastobservation1.Perspective①.X-ray

body

board

image

(lightshouldbeinthedark)②.X-ray

body

tube

Supervise

image

(bright)2.摄影法①.直接摄影法

X线荧光物质照片②.间接摄影法

X线倍增管光学成像系统照片(35、70、100mm）2.PhotographyFrance①.DirectphotographicmethodX-ray

fluorescencesubstance

photos②.IndirectphotographicmethodX-ray

tubeopticalimagingsystem

photos(35、70、100mm）五、影响X线对比度的因素1.被照体的原子序数Z2.被照体的密度ρ3.X线的波长λ4.被照体的厚度d5.散射效应Fifth、thefactorsthataffecttheX-raycontrast1AccordingtothebodyoftheatomicnumberZ2Beaccordingtothedensityρ3X-linewavelengthλ4Accordingtothebodythicknessd5Scatteringeffect光学密度透光率阻光率光学密度OpticalDensityTransmittanceLightratioOpticalDensity一、透光率透过光与入射光之比，表示物体的透光程度

入射光

I透过光

T=I0I0IFirst、thetransmittanceTheratiooftheincidentandtransmittedlight,whichmeanstheobjectlightdegree

IIncidenttransmitted

T=I0

I0I二、阻光率入射光与透光之比，表示物体的吸光能力

I01O==IT

当O接近1时，即I≈I0，表示物体的吸收光的能力很小，对于照片来说，此处显得几乎为透明，则所接受的X线曝光量就越小Second、thelight-blockingratioTheratioofthetransmittedandincidentlight，whichrepresenttheabilityoflightabsorption

I01O==ITWhenOiscloseto1,I≈I0，meanstheabilityoflightabsorptionislow，tophotos,thispartisalmosttransparent，thenthereceivedX-rayexposureissmall三、光学密度1.光学密度D

光学密度D是阻光率的对数

D=lgO

特点:

①.O=I0/I是阻光率，是一个不变的比值，D不随入射光的变化而变化②.D是无量纲的Third、theopticaldensity1.OpticaldensityDOpticaldensityDisthelogarithmofthelight-blockingrate

D=lgOFeatures:①.O=I0/Iisthelight-blockingratioisaconstantratio,Ddoesnotchangewiththeincidentlight②.D

isdimensionless2.密度、黑化度光学密度又称黑化度、简称密度∑D=D1+D2+D3+……+Dn照片密度=片基本底灰度+两面药膜密度3.光学密度的测量

直射密度D"①.透射式密度计漫射密度D#

2.Density,degreeofblackeningOpticaldensityisalsoknownasblackdegree,referredtoasdensity∑D=D1+D2+D3+……+DnThephotoDensity=gray+sidesofthebottompieceofbasicmembranedensity3.Opticaldensitymeasurement

DirectdensityD"①.Transmissiondensitymeter

DiffusedensityD#D"Q=D#

Q是Callier系数,与照片的银粒子大小有关，极小时为1，否则都大于1测量直径：1～3mm（光电式）D"Q=D#QisCalliercoefficient,whichrefertothesizeofthesilverparticlesinthephotos,extremelysmallas1orgreaterthan1Measuringdiameter：1～3mm（photoelectric）②.显微密度计带微机处理，打印系统

测量直径：

5～200μm应用：屏胶系统调制传递函数MTF(modulationtransferfunction)的测试焦点的MTF的测试照片的颗粒度(graininess)MRS的测试观测者操作特性曲线ROC的曲线②.MicroscopicdensitymeterWithcomputerprocessing,theprintingsystemMeasuringdiameter:5~200μmApplication:TestofscreendispensingsystemmodulationtransferfunctionMTF(modulationtransferfunction).FocusMTFtestThephotooftheparticlesize(graininess)MRStestObserveroperatingcharacteristiccurveROCcurve光学对比度光学对比度影响光学对比度的因素Opticalcontrast

OpticalcontrastFactorsaffectingopticalcontrast一、光学对比度1.光学对比度K

照片上相邻两处的密度值之差称为光学对比度

K=D1－D2I0I0I2

=lg－lg=lgI1I2I1

First、theopticalcontrast1.KopticalcontrastThephotoonthedensityvalueofthetwoadjacentdifferenceiscalledopticalcontrast

K=D1－D2I0I0I2

=lg－lg=lgI1I2I1

2.照片上的光学对比度(opticalcontrastinphotos)

D1－D2ν=lgI2－lg

I1

K=D1－D2I1=νlgI2

=lgKX

=ν（μ2d2－μ1d1）

Formationofopticalcontrast

光学对比度的形成

Opticalcontrastonfilm

胶片上的光学对比度二、影响光学对比度的因素1.胶片反差系数ν值的影响

ν值大，照片对比度好

ν值小，照片对比度差

应用：腹部用ν值大的胶片胸部用ν值小的胶片

Second、thefactorsthataffecttheopticalcontrast1FilmgammavalueofνΝvalueislarge,goodcontrastphotosΝvalueissmall,poorcontrastphotoApplication:AbdominalfilmwithalargevalueνThechestfilmwithasmallvalueνDifferentgammacontrasteffectsonthephotofilm

不同反差系数胶片对照片对比度的影响2.线质的影响低KV时，照片对比度好高KV时，照片对比度差高KV,ν值小胶片特性曲线在直线部分低KV,ν值大胶片特性曲线在肩部或趾部

为了获得良好的对比度，可采用不同管电压进行摄影

软组织摄影：25～35KVp

普通摄影：40～100KVp

高仟伏摄影：100KVp以上2LinequalitativeimpactLowKV,thephotogoodcontrastHighKV,picturespoorcontrastHighKV,νissmallpartofthefilmcharacteristiccurveinastraightlineLowKV,νislargerfilmcharacteristiccurveintheshoulderortoeInordertoobtaingoodcontrast,canbephotographedindifferenttubevoltageSofttissuePhotography:25~35KVpGeneralphotography:40~100KVpHighkVPhotography:100KVpmoreDifferentlinequalitativeimpactonthefilmcontrast

不同线质对胶片对比度的影响3.线量的影响

mAS对X线照片对比度没有直接的影响，但线量增加了，使低密度区增高，影像密度值在特性曲线的直线部分，使这部分影像可以辨认3TheamountoflineMAScontrasthavenodirectlyeffecttotheX-rayphotographs,butthelinecapacityincreased,thedensityareaincreased,theimagedensityvalues​​ofthecharacteristiccurveSsraightsection,sothatyoucanidentifywhichpartoftheimageEffectsofradiationqualityinvariantlineamounttocontrastratio

线质不变线量对

对比度的影响4.灰雾的影响Fogeffects片基灰雾Filmbasefog乳剂灰雾引起照片对比度下降Emulsionfogcausedcontrastdegradation散射灰雾Scatteringfog优质X线照片影像锐利度影像分辨率优质X线照片的条件High-qualityX-rayphotographImagesharpnessImageresolutionHigh-qualityX-rayphotographoftheconditions一、影像锐利度表示阅片时的难易程度，照片上指相邻两个器官组织影像清楚的程度

KS=HS是一个模糊数学概念，与对比度K成正比，与模糊值H成反比，是衡量照片质量的一个模糊概念First、theimagesharpnessExpressesthedegreeofdifficultyreadingfilms,photographsontheadjacentfingertwoimagesclearlytheextentoforganandtissue

KS=HSisafuzzyconcept,withapositivecontrastKandinverselyproportionalwiththefuzzyvalueH,isafuzzymeasureofpicturequalityImagesharpness

影像锐利度二、影像分辨率当半影H=2d时，照片对比度为0，影像消失，这时R=1/2d，称为极限分辨率多个成像单元组成的成像系统的影像分辨率

1R=1111+++……+R1R2R3RnSecond、theimageresolutionWhenH=2dpenumbra,thepicturecontrastis0,theimageeliminationmissing,thenR=1/2d,calledlimitingresolutionApluralityofimageformingunitsoftheimageoftheimagingsystemresolution

1R=1111+++……+R1R2R3RnImageresolution

影像分辨率例：用1.0mm焦点的X线管，10cm的肢－片距，焦－片距FFD为110cm的条件摄影时，焦点所产生的半影为：

10H=F×=0.1(mm)