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ID:58491950
大小:5.03 MB
页数:92页
时间:2020-09-21
《医学影像物理学课件:19yj-Ultrasound and Imaging.ppt》由会员上传分享,免费在线阅读,更多相关内容在行业资料-天天文库。
1、UltrasoundandImagingPropertiesofUltrasoundGenerationofUltrasoundUltrasoundpropagationinmediumBasicPrincipleofUltrasoundImagingImagingqualityandnoiseTheDevelopmentalTrendofUltrasoundSoundBasicConceptioninUltrasoundSoundPressureSoundIntensityAcousticImpedanceRange:2M---20MGenerationandDetectio
2、nofultrasoundTransducer:Adevicethatconvertselectricalenergyintomechanicalenergyorviceverseiscalledatransducer.Electric-magnetictransducerPiezoelectrictransducerElectric-magnetictransducerMagnet-FlextransducerInputloopPromptingloopBracketVibratingheadPiezoelectrictransducerCertainmetatarsalsh
3、avethepropertythattheapplicationofanelectricfiledcauseachangeinitsthicknessd,andviceversa.thisphenomenonisknownasthepiezoelectriceffect.PositivepiezoelectricandconversepiezoelectricResonantfrequencyContinualWaveandPulseWavePeakValueofamplitudePulsewidthAverageValuePulserepetitionperiodPulser
4、epetitionfrequencyResttimeDutyratioSinewavePulsewave(Dampedwave)UltrasoundPropertiesDirectionalityReflectionandRefractionPenetratingcapabilityandAbsorptionTheInteractionbetweenUltrasoundandMatterUltrasoundFieldThedirectionaldistributionofradiatedenergybyasoundsourcedependsontheshapeofthesour
5、ceanditsdimensionrelativetothewavelengthofultrasound.AngleDistributionPressureAngleDistributionAxesDistributionPressureAxesDistributionAngleDistributionPointsoundsource2PointUltrasoundFieldRoundnesssoundsourceManypointsoundsourceSamefrequencySamephaseSuperpositionDirectionalityFromHygens’spr
6、inciple,wecanknowthewavelengthoftheemittedsoundwaveissmallcomparedwiththediameterofthesource,theenergyofthesoundwavecanbeconcentratedinanarrowbeamNearfiledregionandFarfieldregionInfarfield,thebeamdivergeswiththeangleobeyfollowingrelationship:Nearfield:parallelityofsoundbeamareverygood,Itisfi
7、ttoImaging,distortionissmall..ButLislimited.Farfield:distributeuniform,Intensityisinverseproportionwithdistance.Example:Loudspeaker:UltrasoundtransducerNearfiled:Example:TheDiameterofultrasoundsourceis10mm,frequencyis10MHz,Whentheultrasoundbeamistr
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