Time-frequency-domain analysis: one-dimensional phantom studies.

Two methods have been adopted to date for investigating the interference effects resulting from the scattering of ultrasound by soft mammalian tissues; one involves the conversion of time-domain signals into the frequency-domain, where the broad spectral characteristics of a short acoustic pulse are utilised, whilst the other varies the orientation of the specimen with reference to the incident beam and analyses the interference effects at a specific frequency. It is shown both theoretically and experimentally that the two techniques are equivalent though the former is more seriously restricted by the equipment features. Results are presented on simple linear arrays of nylon monofilaments which indicate the ability of the respective techniques to evaluate scatterer separation. Furthermore a detailed examination of the limitations of the techniques concludes that the monofrequency orientation method is to be preferred and allows for the more accurate determination of scatterer separation. The significance of these findings is discussed with reference to the usage of these techniques for tissue characterisation.