Instantaneous Spectral Analysis for a Quantitative Measurement of Ultrasonic Attenuation in Biological Tissue*

The aim of quantitative echography is to provide numerical estimates of biological tissue parameters, such as attenuation, scattering strength, sound velocity, which can be clinically significant. In this domain, it has become clear that a careful modelling of the echogram formation process is necessary because, as the probing ultrasonic pulse propagates and interacts with biological structures, it undergoes diffraction effects as well. Hence the meaningful information about the propagation medium is intricately altered by diffraction phenomena induced by finite size transducers. By using a time-frequency formalism, we show that a non-stationnary 'diffraction filter' depending only on the imaging transducer can be defined which allows diffraction unbiasing. Theoretical, numerical and experimental evidence is presented for the need for diffraction correction and for the validity of the proposed solution.