Parametric vs nonparametric measurements in tissues with nonlinear frequency dependent attenuation.

The relationship between the attenuation parameters of tissue and the linear regression slope derived from nonparametric estimates of tissue attenuation is investigated. It was found that if the attenuation in the tissue possesses a nonlinear frequency dependence, the linear regression slope parameter becomes dependent on center frequency and on the bandwidth of the measurement. Moreover, it was found that the slope estimate is numerically close to the parameter derived from parametric attenuation measurements in such cases.