Medical Imaging Systems · Ultrasound Imaging · 2 marks · Numerical answer
A PZT crystal has thickness 1 mm and sound speed 4000 m/s. Its longitudinal ultrasound beam meets blood flow at 30°. Blood speed is 10 cm/s and tissue sound speed 1540 m/s. Find Doppler shift in Hz.
The fundamental thickness resonance is f₀=cPZT/(2d)=4000/(2×.001)=2 MHz. Reflected Doppler shift is Δf=2f₀v cos30°/ctissue, with v=.1 m/s. Thus Δf=2×2×10⁶×.1×.866025/1540≈224.94 Hz, about 225 Hz. Both the thickness half-wavelength and echo factor two are required.
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