Measurement artifacts in sonometry of cancellous bone: the relative impact of phase cancellation and interference on measurements of phase-distorting phantoms

The goal of the present study is to demonstrate the relative effects of interference in the field and phase cancellation at the surface of a receiver on measurements of three increasingly more complex phantoms. Distinct from phase cancellation occurring at the surface of a phase-sensitive receiver, which results in an irrecoverable loss of energy, loss due to interference is only ostensible. Both apparent sources of loss have been shown by our lab to result in negative dispersion measured in cancellous bone. The transmitting transducer consisted of a single-element, planar, 2.9 cm diameter transducer centered at 500 kHz. The through-transmitted signals were received by a 0.6 mm diameter membrane hydrophone that was raster scanned in 0.04 mm steps over a 5.8 cm by 5.8 cm grid coaxial with the transmitting transducer. Signals received by the pseudo-array were processed offline to emulate a phase insensitive receiver of increasing aperture. Apparent attenuation coefficients were determined as functions of frequency for each configuration. Results suggest the potentially confounding role of time- and frequency-domain artifacts on measurements and illustrate the advantages of two-dimensional receiving arrays in determining the slope of attenuation (nBUA) for the clinical assessment of osteoporosis. This work was supported in part by NSF CBET 0717830 "Scholar in Residence at the FDA" and NIH HL 040302.