TY - JOUR

T1 - Theoretical Analysis of the CW Doppler Ultrasonic Flowmeter

AU - Brody, William R.

AU - Meindl, James D.

PY - 1974/5

Y1 - 1974/5

N2 - The widespread application of ultrasonic techniques for the measurement of pulsatile blood flow has been hampered by the lack of a detailed theoretical understanding of the Doppler ultrasonic flowmeter. A general model for the Doppler flowmeter based upon stochastic considerations of the scattering of ultrasound by blood is introduced in this paper. The model characterizes the backscattered ultrasound as a Gaussian random process and the expression for the autocovariance function is derived. For the CW Doppler flowmeter, the power spectral density function is computed, and its significance is emphasized: measurement of blood flow velocity corresponds to estimation of the average frequency of the Doppler power spectrum. The CW Doppler flowmeter, if properly constructed, can measure either local velocity of flow averaged over one small portion of the vessel cross section, or it can detect the average velocity of flow (and hence estimate volume blood flow) over the entire vessel lumen. In either instance, the requirements for proper operation of the CW flowmeter are: a) uniform illumination of the region of the blood vessel of interest by the transducers; b) estimation of the mean or average Doppler frequency (first moment) of the Doppler power spectrum. For volume flow estimation, these requirements are absolutely essential. For local velocity measurements, a narrow Doppler spectrum is produced, and conventional FM demodulators [such as the zero-crossing counter (ZCC)] can be substituted for the average frequency detector with only a minimal degradation in system performance. When operated in the average velocity or volume flow mode, the CW Doppler flowmeter behaves similarly to the electromagnetic flowmeter in that both require uniform vessel illumination and both estimate average velocity. The Doppler system has two important advantages, however. 1) It does not require in vivo calibration. 2) It has a stable zero-flow reference.

AB - The widespread application of ultrasonic techniques for the measurement of pulsatile blood flow has been hampered by the lack of a detailed theoretical understanding of the Doppler ultrasonic flowmeter. A general model for the Doppler flowmeter based upon stochastic considerations of the scattering of ultrasound by blood is introduced in this paper. The model characterizes the backscattered ultrasound as a Gaussian random process and the expression for the autocovariance function is derived. For the CW Doppler flowmeter, the power spectral density function is computed, and its significance is emphasized: measurement of blood flow velocity corresponds to estimation of the average frequency of the Doppler power spectrum. The CW Doppler flowmeter, if properly constructed, can measure either local velocity of flow averaged over one small portion of the vessel cross section, or it can detect the average velocity of flow (and hence estimate volume blood flow) over the entire vessel lumen. In either instance, the requirements for proper operation of the CW flowmeter are: a) uniform illumination of the region of the blood vessel of interest by the transducers; b) estimation of the mean or average Doppler frequency (first moment) of the Doppler power spectrum. For volume flow estimation, these requirements are absolutely essential. For local velocity measurements, a narrow Doppler spectrum is produced, and conventional FM demodulators [such as the zero-crossing counter (ZCC)] can be substituted for the average frequency detector with only a minimal degradation in system performance. When operated in the average velocity or volume flow mode, the CW Doppler flowmeter behaves similarly to the electromagnetic flowmeter in that both require uniform vessel illumination and both estimate average velocity. The Doppler system has two important advantages, however. 1) It does not require in vivo calibration. 2) It has a stable zero-flow reference.

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U2 - 10.1109/TBME.1974.324381

DO - 10.1109/TBME.1974.324381

M3 - Article

C2 - 4277736

AN - SCOPUS:0016055733

SN - 0018-9294

VL - BME-21

SP - 183

EP - 192

JO - IEEE Transactions on Biomedical Engineering

JF - IEEE Transactions on Biomedical Engineering

IS - 3

ER -