Comparison of the Acoustic Streaming in Amniotic Fluid and Water in Medical Ultrasonic Beams

Zusammenfassung

Studienziel: Die akustische Strömung in Fruchtwasser wurde untersucht unter Bedingungen, wie sie bei der medizinischen Ultraschalldiagnose auftreten. Methode: Für die Messungen wurde eine Doppler-Methode eingesetzt. Der Vergleich mit der Strömungsgeschwindigkeit in Wasser wurde bei gleichen Expositionsbedingungen durchgeführt. Es wurden Laborgeräte verwendet, die Ultraschallstrahlen von Kliniksystemen nachahmen. Die Flüssigkeiten wurden in vitro mit 3,5-MHz-, 5-MHz-und 7,5-MHz-Transducern sowohl kontinuierlich als auch gepulst beschallt. Ergebnisse: Die akustische Strömung wurde in Fruchtwasser und in Wasser bei Leistungen von 50 mW und 140 mW gemessen. In beiden Flüssigkeiten konnte die Geschwindigkeitserhöhung aufgrund nichtlinearer Effekte in Pulsen hoher Amplitude nachgewiesen werden. Potenzial und Beschränkung gegenwärtig benutzter numerischer Methoden zur Vorhersage der akustischen Strömung wurden untersucht. Schlussfolgerung: Gepulster Ultraschall erzeugt in Fruchtwasser und in Wasser vergleichbare Strömungsgeschwindigkeiten, während kontinuierliche Schallstrahlen in Fruchtwasser eine deutlich schnellere Strömung als in Wasser bewirken.

Abstract

Aim: Acoustic streaming in amniotic fluid has been investigated under a variety of conditions relevant to the diagnostic use of ultrasound. Method: An ultrasonic Doppler method has been used for measurement. Streaming velocities have been compared with those generated in water for the same exposure conditions. Beams were generated by laboratory equipment simulating beams from clinical systems. The fluids were insonated in vitro using 3.5 MHz, 5 MHz and 7.5 MHz transducers in continuous wave (CW) and pulsed mode. Results: Acoustic streaming was measured in both amniotic fluid and water at the power levels 50 mW and 140 mW. Enhancement of velocities due to non-linear effects in high amplitude pulses was demonstrated for amniotic fluid as well as for water. The potential and limitations of present numeric methods for the prediction of acoustic streaming were explored. Conclusion: Pulsed ultrasound caused similar streaming velocities in amniotic fluid and water while continuous wave beams induced significantly faster streaming in amniotic fluid than in water.

Schlüsselwörter

Fruchtwasser - Ultraschall - Doppler-Methode

Key words

Amniotic fluid - ultrasonography - Doppler

References

• 1 Heling K S, Chaoui R, Bollmann R. Advanced dynamic flow - a new method of vascular imaging in prenatal medicine. A pilot study of its applicability.  Ultraschall in Med. 2004;  25 (4) 280-284
• 2 Schneider A. Normal values of blood flow velocity in the terminal vein of preterm infants.  Ultraschall in Med. 2004;  25 (2) 137-140
• 3 Atkins T J, Duck F A. Heating caused by selected pulsed Doppler and physiotherapy ultrasound beams measured using thermal test objects.  Eur J Ultrasound. 2003;  16 243-252
• 4 Starritt H C, Duck F A, Humphrey V F. An experimental investigation of streaming in pulsed diagnostic ultrasound beams.  Ultrasound Med Biol. 1989;  15 363-373
• 5 Duck, FA, Starritt H C. et al . The output of pulse echo ultrasound equipment; a survey of powers, pressures and intensities.  Br J Radiol. 1985;  58 989-1001
• 6 Duck F A. Acoustic saturation and output regulation.  Ultrasound Med Biol. 1999;  25 1009-1018
• 7 Muir T G, Cartensen E L. Prediction of nonlinear acoustic effects at biomedical frequencies and intensities.  Ultrasound Med Biol. 1980;  6 345-357
• 8 Cartensen E L, Law W, Mckay N D. et al . Demostration of nonlinear acoustics effects at biomedical frequencies and intensities.  Ultrasound Med Biol. 1980;  6 359-368
• 9 Duck F A, Sttaritt H C. Acoustic shock generation by ultrasonic imaging equipment.  Br J Radiol. 1984;  57 231-240
• 10 Tjøtta S. On some non-linear effects in sound fields, with special emphasis on the generation of vorcity and the formation of streaming patterns.  Arch Math Naturvidensk. 1959;  55 1-68
• 11 Wu J, Du G. Acoustic streaming generated by a focused Gaussian beam and finite amplitude tonebursts.  Ultrasound Med Biol. 1993;  19 167-176
• 12 Kamakura T, Matsuda K, Kumamoto Y. Acoustic streaming induced in focused Gaussian beams.  J Acoust Soc Am. 1995;  97 2740-2746
• 13 Zauhar G, Starritt H C, Duck F A. Studies of acoustic streaming in biological fluids with an ultrasound Doppler technique.  Br J Radiol. 1998;  71 297-302
• 14 Hartley C J. Characteristics of acoustic streaming created and measured by pulsed Doppler ultrasound.  IEEE Trans Ultrason Ferroelec Freq Contr. 1997;  44 1278-1285
• 15 Perkins M A. A versatile force balance for ultrasound power measurement.  Phys Med Biol. 1989;  34 1645-1651
• 16 Preston R C. The NPL ultrasound beam calibrator.  IEEE Trans Ultrason Ferroelec Freq Contr. 1988;  35 122-139
• 17 Zana R, Lang J. Interaction of ultrasound and amniotic liquid.  Ultrasound Med Biol. 1974;  1 253-258
• 18 Mitome H, Kozuka T, Tuziuti T. Effects of nonlinearity in development of acoustic streaming.  Jpn J Appl Phys. 1995;  34 2584-2589
• 19 Mitome H, Kozuka T, Tuziuti T. Development of acoustic streaming and its turbulent motion. Proceedings of 1995 World Congress on Ultrasonic. Berlin; WCU’95 September 3 - 7
• 20 Institute of Physical Sciences in Medicine .Testing of Doppler Ultrasound Equipment. York; IPSM Report No 70 1994

Appendix

The parameters used in the numerical solution are the following:

A) for calculation of streaming velocities in waterabsorption coefficient at 3.5 MHz 0.3099 Np/m
absorption coefficient at 5 MHz 0.6325 Np/m
absorption coefficient at 7.5 MHz 1.42 Np/m
sound speed 1500 m/s
kinematic viscosity 10 ^{- 6} m²/s
density of water 1000 kg/m³

B) for calculation of streaming velocities in amniotic fluidabsorption coefficient at 3.5 MHz 0.54 Np/m
absorption coefficient at 5 MHz 0.93 Np/m
absorption coefficient at 7.5 MHz 1.81 Np/m
sound speed 1510 m/s
kinematic viscosity 0.997 · 10 ^{- 6} m²/s
density of amniotic fluid 1010 kg/m³