Frequency dependence of average phase shift from human calcaneus in vitro.
If dispersion in a medium is weak and approximately linear with frequency (over the experimental band of frequencies), then it can be shown that the constant term in a polynomial representation of phase shift as a function of frequency can produce errors in measurements of phase-velocity differences in through-transmission, substitution experiments. A method for suppressing the effects of the constant phase shift in the context of the single-wave-model was tested on measurements from 30 cancellous human calcaneus samples in vitro. Without adjustment for constant phase shifts, the estimated phase velocity at 500 kHz was 1516+/-6 m/s (mean+/-standard error), and the estimated dispersion was -24+/-4 m/s MHz (mean+/-standard error). With adjustment for constant phase shifts, the estimated mean velocity decreased by 4-9 m/s, and the estimated magnitude of mean dispersion decreased by 50%-100%. The average correlation coefficient between the measured attenuation coefficient and frequency was 0.997+/-0.0026 (mean+/-standard deviation), suggesting that the signal for each sample was dominated by one wave. A single-wave, linearly dispersive model conformed to measured complex transfer functions from the 30 cancellous-bone samples with an average root-mean-square error of 1.9%+/-1.0%.
Wear
Keith A
KA
Center for Devices and Radiological Health, U. S. Food and Drug Administration, Silver Spring, Maryland 20993, USA. keith.wear@fda.hhs.gov
D000465:Algorithms; D002111:Calcaneus / Q000000981:diagnostic imaging*; D006801:Humans; D066298:In Vitro Techniques; D016018:Least-Squares Analysis; D016014:Linear Models; D008954:Models, Biological; D009757:Nylons; D019047:Phantoms, Imaging; D011076:Polycarboxylate Cement; D014463:Ultrasonography
D009757:Nylons; D011076:Polycarboxylate Cement; C005506:polycarbonate