欢迎来到天天文库
浏览记录
ID:62046118
大小:5.15 MB
页数:116页
时间:2021-04-13
《最新(医学影像物理学)19Ultrasound and Imaging课件ppt.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、(医学影像物理学)19UltrasoundandImagingSoundBasicConceptioninUltrasoundSoundPressureSoundIntensityAcousticImpedanceRange:2M---20MGenerationandDetectionofultrasoundTransducer:Adevicethatconvertselectricalenergyintomechanicalenergyorviceverseiscalledatransducer.Ele
2、ctric-magnetictransducerPiezoelectrictransducerUltrasoundPropertiesDirectionalityReflectionandRefractionPenetratingcapabilityandAbsorptionTheInteractionbetweenUltrasoundandMatterUltrasoundFieldThedirectionaldistributionofradiatedenergybyasoundsourcedepend
3、sontheshapeofthesourceanditsdimensionrelativetothewavelengthofultrasound.AngleDistributionPressureAngleDistributionAxesDistributionPressureAxesDistributionAngleDistributionPointsoundsource2PointUltrasoundFieldRoundnesssoundsourceManypointsoundsourceSamefr
4、equencySamephaseSuperpositionDirectionalityFromHygens’sprinciple,wecanknowthewavelengthoftheemittedsoundwaveissmallcomparedwiththediameterofthesource,theenergyofthesoundwavecanbeconcentratedinanarrowbeamNearfiledregionandFarfieldregionInfarfield,thebeamdi
5、vergeswiththeangleobeyfollowingrelationship:Nearfield:parallelityofsoundbeamareverygood,ItisfittoImaging,distortionissmall..ButLislimited.Farfield:distributeuniform,Intensityisinverseproportionwithdistance.Example:Loudspeaker:UltrasoundtransducerNearfiled
6、:Example:TheDiameterofultrasoundsourceis10mm,frequencyis10MHz,Whentheultrasoundbeamistransmittedinwater,Whatisthespreadingangleandthelengthofnearfiled.(Thespeedofsoundinwateris1500m/s.)Solution:Accordingtherelationshipoffrequencyspeedandwavelengthlengthof
7、nearfieldspreadingangleFocusofUltrasoundBeamSoundLensFocusSoundreflectorFocusCurvedsurfacetransducerElectronicFocusSoundLensFocusUltrasoundbeamislikeopticbeam,wecanfocusthemwithlens.Becausethespeedinlensisfasterthanthespeedinmaterialoutsideoflens,soweadop
8、tconcavelens.Forreducingthelossofintensity,thethicknessoflensisverysmall,anditsmaterialusuallyisethoxylineororganicglassSoundreflectorFocusThisisalsoliketheprincipleingeometricaloptics,itadoptreflectionmethod.Curved
此文档下载收益归作者所有