Analysis of the error in measurement of ultrasound speed in tissue due to waveform deformation by frequency-dependent attenuation.

A systematic error exists in measurement of ultrasound speed in tissue with pulse methods. Frequency-dependent attenuation distorts the incident waveform as it passes through tissue causing an error in determination of speed when the time interval between fixed points on the incident and transmitted waveforms is measured. Two equations have been derived for a generalized pulse in a non-dispersive medium that enable calculation of this error when the peaks of the waveforms or the zero-crossings are used as reference points in the speed measurement. The errors have been calculated for measurement of speed in muscle, liver and fat for path lengths of 5, 10, an 15 cm for two incident pulse shapes. In general, the magnitude of this error is small compared to the biological variation, but may be significant compared to experimental error.