CT(设备构成)

ComponentsofaCTscannerCT扫描仪组成计算机操作台监视器X发生器X-RAYTUBECOLLIMATOR探测器DAS扫描架BODY扫描床§3.1ComponentsofaCTscannerCT扫描仪组成ComponentsofaCTscannerCT扫描仪组成•数据采集阶段包括：X射线管、探测器、准直器、滤过器、对数放大器、模数转换器（A/D）、接口电路等•图像重建阶段包括：计算机、D/A转换器等•图像显示阶段包括：图像显示器、相机、接口电路等等•整个系统由中央系统控制器操纵，加上检查床便构成一台完整的X-CT系统ComponentsofaCTscannerCT扫描仪组成24§3.2X-RayTubeI.球管的发展II.球管功能及构成III.球管特性IV.球管新技术V.球管的高压发生器§3.2X-RayTubeI.球管的发展–固定阳极（stationaryanode）X线管（I、II代CT、牙科CT等）–旋转阳极(rotatinganode)X线管（全身CT）II.X-Raytubecomponentsandfunctions球管构成及功能•球管组成•Envelope外壳•Cathode阴极•Anode阳极•ProtectivehousingX射线管防护罩II.2.1Envelope球管外壳•Function：maintainvacuum真空状态~保证电子在真空管内的自由加速•Demand：withstandtremendousheat(耐受高温),MinimizeXrayabsorption(降低X线吸收)•MadeofPyrexglass（耐热玻璃）ormetalFrame–Pyrexglass：较好的隔热、绝缘性能–Metal：绝缘性能提高、冷却好、耐用（适于CT）Tubewindow：Asegmentofglassthatisthinnerthantherestoftheglassenvelope.Contributestoinherentfiltration：0.5mmAlequivalency.II.2.2Cathode阴极•Twoprimaryparts:–Filament灯丝–Focusingcup聚焦杯•TheFilamentfunction灯丝功能–Whencurrent(mA)isappliedtothecoilofwire,electronareejected.发射电子•TheFilamentmaterials灯丝材料–usuallymadeoftungsten钨材料•higherthermionicemission高的热电子发射率•highmeltingpoint高熔点–AppendThorium（钍）~增加电子发射率和延长灯丝寿命Focusingcup聚焦杯•Containsanegativecharge.负极–Designedtorepel(排斥)electronsandcondenseelectronbeamtosmallareaononfocaltrack.聚焦到达阳极的电子；II.2.3TheAnodeAssembly阳极组件•Function：电子在阳极受阻，韧致辐射产生X线•Type–Stationaryanode固定阳极–Rotatinganode旋转阳极StationaryAnodeX-rayTube固定阳极X线管•Usedfordentalx-rays,someportableimaging牙科X射线、部分便携式成像设备•Usedwhenhightubecurrentandpowerarenotrequiredbecausetheyarenotcapableofproducinghigh-intensityx-raybeamsinashorttime不需在短时间内产生高强度X射线，因此用于球管电流和功率要求不高时RotatingAnodeX-rayTube旋转阳极X线管•Tungsten-rheniumalloy(铼钨合金)：弹性、寿命•Molybdenum（钼）：高热容量•Graphite（石墨）：更高热容量Theadvantageoftherotatinganode旋转阳极的优点•HighPower功率大•TheeffectivesizeofFocusdecrease有效焦点变小II.2.4ProtectiveHousingX射线管防护罩•Madeoflead&steel由铅和钢制成ThefunctionofProtectiveHousing：•UsefulX-Raybeam产生有用X线•Providesmechanicalsupport（支撑）forthetubeandprotectsfromroughhandling•Sometubescontainoilthatservesasaninsulatoragainstelectricshockandasathermalcushion-dissipateheat•Someprotectivehousinghascoolingfantoair-coolthetubeandoil•Whenx-raysareproduced,theyareisotropicemitted各向同性发射X线•usefulorprimarybeam•leakageradiationII.3Thecharacteristicsofx-raytube球管特性Focalspot焦点anodeangle阳极倾角heatcapacity热容量Heatdissipation散热率II.3.1Focalspot焦点•Theareaoftheanode’stargetwherex-raysareemitted•ThesmallerthefocalspotthebettertheresolutionoftheresultantimageDualFocusArrangements双焦点Mostdiagnostictubeshavetwofocalspots;large&small大焦点和小焦点Dual-focustubes双焦点largesmall•大焦点:软组织或对比度分辨率的大容积扫描•小焦点:薄层和高分辨率扫描Focalspot–penumbraeffect焦点与半影焦点尺寸、焦点到扫描物体距离~半影SharpimageBlurredimagePenumbraeffectFlyingspotsize飞焦点•Philips：电场偏转•Siemens：磁场偏转Flyingspotsize飞焦点•控制电子束的位移，在很短的时间内在两个位置间移动发射X线，相当于多了一次采集或采集数量的加倍；•采样增加、空间分辨力增加II.3.2Anodeangle阳极倾角ANODEANGLEBOMBARDINGELECTRONSANODEANODESHAFT有效焦点大小与靶面倾角effectivefocalspotsizevsanodeangleELECTRONSanodeFocalspotEFFECTIVEFOCALSPOTEYEcathodeII.3.3Heatcapacityandheatdissipation热容量和散热率（冷却速率）•Heatunitishowmuchheatananodecanstorebeforedamageoccurs热容量表示阳极损坏之前的储热能力•单位：HUkVpmAtimerectificationconstant•Heatdissipationmeanshowfastatube’sanodecoolsdown散热率表示阳极冷却时间•单位：HU/minHeatcapacityvs.anodeangle热容量与靶面倾角•Forthesameeffectivefocalspotsize,theheatcapacityincreasesastheanodeangledecreases有效焦点一样时，热容量增大，阳极角度减小；HEATHEATEFFECTIVEFOCALSPOTSIZEEFFECTIVEFOCALSPOTSIZEELECTRONSELECTRONSANODEANODE450300II.4NewCTxraytube（Straton®x-raytube）MedicalPhysics--September2004--Volume31,Issue9,pp.2699-2706•Anovelcoolingprincipleononehand，anovelbeamcontrolsystemontheotherhand.全新的冷却原理和射束控制技术Straton®x-raytube•Providesdirectcoolingoftheanodewithallbearingslocatedoutsidethevacuum.阳极和轴承置于真空之外，对阳极直接冷却；•Eliminatestheneedforwaitingtimesduetoanodecoolinginclinicalworkflow.（无需等待冷却）•Straton球管与传统球馆的不同在于阴极和阳极一起固定在绝缘油中–球管工作时，不单是阳极旋转，而是在马达的带动下整个球管的旋转；–阳极的背面直接靠在管壁上极易散热，冷却油通过循环直接将热带走；•偏转线圈的作用是使电子束达到适当的阳极位置，轰击靶面产生X线；通过偏转线圈的信号控制可改变焦点位置~飞焦点。Straton®x-raytubeTubeFailure球管损坏•Tubearcing打火•Filamentbreakage灯丝击穿•Statorfailure定子损坏•NormalAnodeWear阳极击穿IV.1Generatorpurpose高压发生器作用•Thegeneratorproduceshighvoltageandtransmitsittothex-raytube.Thishighvoltagepropelstheelectronsfromthex-raytubefilament(灯丝)totheanode发生器提供高压并将其传输到X线管，使得电子从球管灯丝到达阳极•Providetheheatcurrentoffilament灯丝加热电流•TimeControl控制X线曝光时间IV.2Generatorform发生器形状•Inthepast,thehigh-voltagegeneratorwasabulkypieceofequipmentlocatedinacornerofthex-rayroom过去高压发生器是大体积的设备，安置在X线室的一角。•CTscannernowusehigh-frequencygenerators,whicharesmall,compact,andmoreefficient.ItislocatedinsidetheCTgantry如今CT扫描仪使用高频发生器，它的体积更小，更紧凑，效率更高。安装在CT机架内•Insomescanners,thehigh-frequencygeneratorismountedontherotatingframe安放在旋转架内•Whereasinothersitislocatedinonecornerofthegantryanddoesnotrotate安放在机架的一角固定不动IV.3SinglekVporvariablekVp单项kVp和可变kVp•AgeneratorcanhaveasinglekVporvariablekVpoutput–kVpaccuracyismoreeasilyachievedinsinglekVpsystems单kVp输出系统的kVp更精确–VariablekVpsystemsdoallowforanincreasedcapabilitytodiscriminatedifferenttissuesVariablekVp输出系统区别不同组织的能力提高•Generatorshavedifferentpowerrati