Propagation speed

Radiopaedia • CC-by-nc-sa 3.0 • de

The propagation speed of sound waves through tissue is an important element of ultrasound scans. Ultrasound machines assume sound waves travel at a speed of 1540 m/sec through tissue . In reality, the speed of sound is affected by the density and elasticity of the medium through which it is traveling and these factors are not constant for human tissues. The propagation speed of sound is higher in tissues with increased stiffness and density .

Examples of propagation velocities in different tissues are given below :

air: 330 m/sec
fat: 1450 m/sec
water: 1480 m/sec
liver: 1550 m/sec
kidney: 1560 m/sec
blood: 1570 m/sec
muscle: 1580 m/sec
bone: 4080 m/sec

Ultrasound machines use echo-ranging to determine the distance between the transducer and reflective interfaces . As the machine assumes a constant propagation speed of 1540 m/sec, speed displacement artifact can occur if the sound wave traverses tissues of differing propagation speeds .

Differences in propagation speeds are also relevant in causing refraction and the formation of refraction artifact .