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a Chapter 2 Physical Principles of Doppler Ultrasonography 17
align an angle indicator cursor with the vessel axis
(the presumed flow axis) and determines the angle
it incurs with the beam path indicator cursor
(Fig. 2.14). The device computes this angle and produces
the velocity information in real time. The procedure
is subjective, and the precision of the measurement
obviously depends on operator skill.
Determination of the flow velocity may be clinically
useful during fetal echocardiographic examination,
as abnormal flow velocities in the pulmonary artery,
aorta, or ductus arteriosus may assist in identifying
structural or functional abnormalities. A reliable
measurement of the Doppler angle is also a requirement
for measuring volumetric blood flow and
inaccuracies in measuring the angle can introduce
significant errors in this measurement. Finally, an optimal
angle is important for an appropriate interpretation
of Doppler waveforms from the arteries that
demonstrate continuing forward flow during the enddiastolic
phase, as a large angle may artificially reduce
the magnitude of the end-diastolic frequency
shift. This point is of critical importance when assessing
an umbilical arterial circulation in which a reduced
or absent end-diastolic frequency shift may indicate
fetal jeopardy. The challenge of the angle of insonation
in Doppler sonography has prompted significant
research on the development of angle-independent
ultrasound technology for circulatory investigations;
this is further discussed in Chap. 4.
References
1. Wells PT (1977) Biomedical ultrasonics. Academic
Press, Orlando, FL
2. McDicken WN (1981) Diagnostic ultrasonics: ultrasonic
in tissue. In: Principles and use of instruments
(2nd ed). Wiley, New York, pp 54±70
3. Evans DH, McDicken WN, Skidmore R, Woodcock JP
(1989) Doppler ultrasound: physics, instrumentation
and clinical applications. Wiley, New York
4. Kremkau FW (1990) Doppler ultrasound: principles
and instruments. Saunders, Philadelphia
5. Goss SA, Johnston RL, Dunn F (1978) Comprehensive
compilation of empirical ultrasonic properties of mammalian
tissues. J Acoust Soc Am 64:423±457
6. Atkinson P, Woodcock JP (1982) Doppler ultrasound.
Academic Press, London
7. Lord Rayleigh (1871) Scientific papers 8 and 9. Philos
Mag 41:107, 274, 447
8. Van de Hulst HC (1982) Light scattering by small particles.
Dover, New York
9. Van de Hulst HC (1952) Scattering in the atmospheres
of the earth and planets. In: Kuiper GP (ed) The atmospheres
of the earth and planets. University of Chicago
Press, Chicago
10. Shung KK, Sigelman RA, Reid JM (1976) Scattering of
ultrasound by blood. IEEE Trans Biomed Eng BME-
23:460±467
11. Bascom PA, Cobbold RS (1996) Origin of the Doppler
ultrasound spectrum from blood. IEEE Trans Biomed
Eng 43:562±571
12. Fontaine I, Cloutier G (2003) Modeling the frequency
dependence (5±120 MHz) of ultrasound backscattering
by red cell aggregates in shear flow at a normal hematocrit.
J Acoust Soc Am 113:2893±2900