Speed of Sound

Published on 06/02/2015 by admin

Filed under Anesthesiology

Last modified 22/04/2025

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2 Speed of Sound

The speed of sound is determined by properties of the medium in which it propagates. The sound velocity equals , where B equals the bulk modulus, and rho equals density. The bulk modulus is proportional to stiffness. Thus stiffness (change in shape) and wave speed are related. Density (weight per unit volume) and wave speed are inversely related. The speed of sound in a given medium is essentially independent of frequency.

Because the velocity of sound in soft tissue is 1540 m/sec, 13 microseconds elapse for each centimeter of tissue the sound wave must travel (the back-and-forth time of flight). Speed of sound artifacts relates to both time of flight considerations and refraction that occurs at the interface of tissues with different speeds of sound.¹^–³

FIGURE 2-1 Bayonet artifacts during popliteal block (A and B). Because the speed of sound is not necessarily homogeneous in soft tissue, the needle can sometimes appear to bend, similar to a bayonet. Actual mechanical bending of the needle typically appears as gentle bowing of the needle (C).

1 Scanlan KA. Sonographic artifacts and their origins. AJR Am J Roentgenol. 1991;156:1267–1272.

2 Fornage BD. Sonographically guided core-needle biopsy of breast masses: the “bayonet artifact”. AJR Am J Roentgenol. 1995;164:1022–1023.

3 Gray AT, Schafhalter-Zoppoth I. “Bayonet artifact” during ultrasound-guided transarterial axillary block. Anesthesiology. 2005;102:1291–1292.

Atlas of Ultrasound-Guided Regional Anesthesia 2e