Velocity dispersion of acoustic waves in cancellous bone

摘要

Measurement of ultrasonic attenuation and velocity in cancellousnbone are being applied to aid diagnosis of women with high fracture riskndue to osteoporosis. However, velocity dispersion in cancellous bone hasnreceived little attention up to now. The overall goal of this researchnwas to characterize the velocity dispersion of human cancellous bonenbased on a spectral analysis of ultrasound transmitted through the bonenspecimens. We have followed a systematic approach, beginning with theninvestigation of a test material, moving on to the investigation of bonenspecimens. Particular attention is given to diffraction effect, anpotential source of artifacts. Parametric images of phase velocityn(measured at the center frequency of the pulse spectrum), slope ofnattenuation coefficient (dB/cm/MHz) and velocity dispersion werenobtained by scanning 15 bone specimens. We have demonstrated that thendiffraction effect is negligible in the useful frequency bandwidth, andnthat the ultrasonic parameters reflect intrinsic acoustic properties ofnbone tissue. The measured attenuation showed approximately linearnbehavior over the frequency range 200 to 600 kHz. Velocity dispersion ofncancellous bone in the frequency range 200 to 600 kHz was unexpectedlynfound to be either negative or positive and not correlated with thenslope of attenuation coefficient. There was a highly significantncorrelation between the slope of attenuation coefficient and phasenvelocity at the center frequency of the spectrum. This behaviorncontrasts with other biological or nonbiological materials where thenlocal form of the Kramers-Kronig relationship provides accuratenprediction of velocity dispersion from the experimental frequencyndependent-attenuation for unbounded waves