Abstract
Pulsed Doppler flowmeters are considered to estimate the velocity of blood flow by measuring the frequency shift of echoes, due to the Doppler effect1. Typical frequency shifts of the echoes are of the order of kHz. However, the time and frequency domain properties of ultrasound pulses travelling in tissue also undergo changes due to propagating and scattering effects. For example, the attenuation coefficient for a soft tissue such as liver 2 is α.(f) = 0.4f 1.14. If the emitted pulse is assumed to be Gaussian, with a centre frequency of 5 MHz and a 3 dB bandwidth of 0.8 MHz, the shift in mean frequency with depth for such a medium is calculated to be 0.11 MHz cm-1 . Hence, if pulsed Doppler flowmeters assess velocity by estimating a shift in frequency of the echoes, then attenuation should have a dramatic influence on the measurement outcome. Such a severe effect is not seen 1,3,4 and, although several investigators have considered the influence of attenuation, no clear reason for this discrepancy has been proposed and there is disagreement as to the size of the effect.
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Thomas, N., Leeman, S. (1995). The Attenuation Effect in Pulsed Doppler Flowmeters. In: Jones, J.P. (eds) Acoustical Imaging. Acoustical Imaging, vol 21. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-1943-0_58
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DOI: https://doi.org/10.1007/978-1-4615-1943-0_58
Publisher Name: Springer, Boston, MA
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