1TT Liu, BE280A, UCSD, Fall 2006Bioengineering 280APrinciples of Biomedical ImagingFall Quarter 2006Ultrasound Lecture 3TT Liu, BE280A, UCSD, Fall 2006Focusing with Phased ArrayAnderson and Trahey 20002TT Liu, BE280A, UCSD, Fall 2006Focusing and SteeringPrince and Links 2005TT Liu, BE280A, UCSD, Fall 2006Dynamic FocusingPrince and Links 20053TT Liu, BE280A, UCSD, Fall 2006 Doppler Effecthttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htmTT Liu, BE280A, UCSD, Fall 2006 Doppler Effect ! "f =2vf0c # v$2vf0cExamplev = 50 cm/sc = 1500 m/sf0 = 5 MHz2vf0c= 3333 Hz4TT Liu, BE280A, UCSD, Fall 2006Dopplerhttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htmTT Liu, BE280A, UCSD, Fall 2006CW Dopplerhttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htm5TT Liu, BE280A, UCSD, Fall 2006CW Dopplerf0f0+Δf-f0-f0-Δf*Effective width = 1/TobsTT Liu, BE280A, UCSD, Fall 2006CW Doppler ! Resolution "f =1/Tobs"v =c"f2 f0=c2Tobsf0ExampleDesign goal : "v = 5 cm /s; f0= 5 MHzTobs=c2"vf0=1500m /s2 0.05m / s( )5 #106( )= 3msNote that for a depth of 15 cm, it takes only200 usec for echos to return.6TT Liu, BE280A, UCSD, Fall 2006PW Dopplerhttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htmTT Liu, BE280A, UCSD, Fall 2006PW Dopplerhttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htm7TT Liu, BE280A, UCSD, Fall 2006Siemens Medical Systems; jnormal common carotid arteryTT Liu, BE280A, UCSD, Fall 2006Aliasing! Measure Doppler shifts at a specified rangeFor unambiguous range, one pulse at a time.TPR=2rmaxc (e.g. 200 usec for 15 cm depth)To avoid aliasing require1TPR> 2"fmaxΔf-Δf*1/TPR=Δf-ΔfAliasedΔf-Δf8TT Liu, BE280A, UCSD, Fall 2006Aliasinghttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htmTT Liu, BE280A, UCSD, Fall 2006Aliasinghttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htm9TT Liu, BE280A, UCSD, Fall 2006Aliasinghttp://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-htmłchapter_01.htmTT Liu, BE280A, UCSD, Fall 2006PW Doppler! Velocity Resolution (same as with CW) Tobs>1"f=c2"vf0Range ResolutionWant to interrogate velocities from a small region "z =cTpulse2We also need to make sure that particles remain within this regionover the observation time TobsvmaxTobs< "z # Tobs<"zvmax=cTpulse2vmax10TT Liu, BE280A, UCSD, Fall 2006PW Doppler! Design ExampleRmax= 6 cm " TPR=2(0.06m)1500m /s= 80 µsec1TPR> 2#fmax=4vmaxf0cc4TPRf0> vmax" for f0= 5MHz we find that vmax< 93.75cm /sIf we choose #v = 1cm / s then Tobs=c2#vmaxf0= 15msRange resolution : #z > vmaxTobs= 1.4cmTpulse=2#zc=
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