Application of autoregressive spectral analysis for ultrasound attenuation: interest in highly attenuating medium

A second-order autoregressive (AR2) model, whose parameters are estimated with the Burg algorithm, is used to estimate the center-frequency along echo signals and its evolution versus depth. Data simulation of independent A-lines reflected by a homogeneous medium of scatterers are generated by a computer model with attenuation values ranging from 1 to 5 dB/cm MHz and an ultrasonic frequency of 5 MHz. The performance of the estimator is evaluated for duration of time windows ranging from 5.12 to 0.32 μs and different spectral sampling. The comparison is made with the classical Fourier spectrogram technique (FFT). It is found that the AR model provides a better estimation of attenuation than the Fourier technique: the relative error of attenuation is below 5% for windows between 0.64 to 2.56 μs, while the one obtained with the Fourier technique lies between 10 and 70% for the same window sizes. These results offer promises for determining attenuation in biological medium which are highly attenuating either because of their structure, like bone, or because high frequencies are used