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DOPPLER ULTRASOUND

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DOPPLER ULTRASOUND

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    1. DOPPLER ULTRASOUND Lee W. Goldman Hartford Hospital

    2. The Doppler Effect

    3. The Doppler Shift fD = (V1 +V2) fS /C where: fD = Doppler shift fS = emitted frequency V1 = velocity of emitter V2 = velocity of listener C = velocity of sound

    4. Doppler Techniques Continuous Wave (CW) Doppler accurate, no aliasing but not depth discrimination Pulsed Doppler Sacrifices accuracy for depth discrimination Duplex Doppler One line of Pulsed Doppler on B-mode display Multigated Doppler: Parallelprocessed sample volumes at several depths Color Flow: 2D flow information Can’t measure doppler shift: uses other indicators

    5. Continuous Wave (CW) Doppler

    6. Continuous Wave (CW) Doppler

    7. Doppler Shift fD = 2Vcos(?) fS/C where: ? = angle of insonation of vessel V = velocity of erythrocytes Example: fS = 5 MHz V = 35 cm/sec ? = 45o fD = (2)(5x106 /sec)(0.35 m/sec)(0.707) 1540 m/sec fD = 1600 Hz = 1.6 kHz

    8. Continuous Wave Doppler Uses two transducers: 1 transmit, 1 receive Advantages: Inexpensive Narrow spectrum ---> high measurement accuracy No “aliasing” allows high velocity measurement Drawbacks: Spectral broadening due to large “sample volume” Lack of depth selectivity Errors due to motion within path of CW US beam

    9. Pulsed Doppler Adds depth discrimination Longer pulse length narrow frequency band: 15-20 cycles (7-10 mm resolution) typical Samples doppler shift at PRF. 64-128 samples needed for accurate estimation. Max measurable shift=PRF/2 Larger shifts are aliased Multigating: parallel channels process different depth ranges

    10. Aliasing

    11. Duplex Doppler

    12. Pulsed Doppler Aliasing

    13. Pulsed Doppler Aliasing

    14. Pulsed Doppler Aliasing

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