Measurements of phase velocity and group velocity in human calcaneus

Ultrasonic velocity in calcaneus correlates highly with bone mineral densit y, which is a good predictor of osteoporotic fracture risk. Several commerc ial bone sonometers perform a velocity measurement based on the transit tim e of a broadband pulse to assess skeletal status. This approach is somewhat problematic, however, because several authors have reported ambiguities in measurements in calcaneus, Phase velocity is an alternative that may be le ss dependent on device spectral characteristics. In addition, dispersion (t he frequency-dependence of phase velocity) is a fundamental property worth investigating to increase understanding of interaction between ultrasound a nd bone. To compare two group-velocity measurement methods and one phase-ve locity measurement method, a polycarbonate sample (for method validation) a nd 24 human calcanei were investigated in vitro. Phase velocity in calcaneu s at 500 kHz was 1511 m/s +/- 30 m/s (mean +/- standard deviation). Average phase velocity decreased approximately linearly with frequency (-18 m/s MH z). The two group velocity measurements were comparable and tended to be sl ightly lower than phase velocity, The magnitude of dispersion showed little correlation with bone mineral density. (C) 2000 World Federation for Ultra sound in Medicine & Biology.