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Lecture 1 Notes

Vcosc transducer fo fofd doppler equation

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Unformatted text preview: quency, fd Doppler Ultrasound: Basic Concepts Transducer Target (stationary): fd = 0   Target moves towards transducer: –  More compressions per unit time: fd > 0   Target moves way from transducer: –  Fewer compressions per unit time: fd < 0 Doppler Ultrasound: Concepts   Doppler Equation: fd = 2fo.v.cosθ/c Transducer fo fo+fd θ Doppler Equation: Consequences Shift frequency is proportional to blood velocity   fo = 2-10 MHz, v = 0-5 m/s fd = 0-15 kHz (Audio frequencies)   fd is maximized when blood flow is in-line with ultrasound beam (θ=0)   fd = 0 when flow is perpendicular to the beam   Blood flow –  fo is the frequency transmitted –  v is the velocity of the moving blood –  c is the sound speed in the medium (blood, ~1600 m/s) Doppler Data Processing UBM-Doppler analysis is sensitive to blood flow abnormalities Blood Velocity Flow reversal in mouse mutants with defective cardiac valves E13.5 Wildtype NFATc1-/- Time (Aristizabal, Ultrasound in Medicine & Biology 1998) Schematic: Ultrasound Imaging System Functions of the transducer       Single Element Transducer Used both as Transmitter And Receiver Transmission mode: converts an oscillating voltage into mechanical vibrations, which causes a series of pressure waves into the body Receiving mode: converts backscattered pressure waves into electrical signals Piezoelectric Material               Converts electrical voltage to mechanical vibration and vice versa The thickness of the crystal varies with the applied voltage When an AC voltage is applied across the crystal, the thickness oscillates at the same frequency of the voltage Examples of piezoelectric Materials: –  Crystalline (quartz), Ceramic (PZT, lead zirconium titanate), Polymers (PVDF), Composite materials –  PZT is the most efficient material The crystal vibrates sinusoidally after electrical excitation has ended...
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