Valuation of responses in spectral techniques for thermal estimation into biological media, from ultrasonic echo-signals contaminated with increasing noise levels

The objective of this work is to define the preliminary bases needed for achieving an evaluation of responses of the spectral analysis technique for non invasive temperature estimation, when applied to multi-echo ultrasonic signals contaminated with increasing noise levels. Power Spectral Density (PSD) of an ultrasonic signal is calculated in order to obtain accurate information about signal frequency components. The frequency of interest in non invasive thermal estimation is the one associated to the average distance among internal scatterers, which defines a fundamental resonance mode. This fundamental frequency is also associated with the speed of the ultrasound in the propagation media and with its variations versus the temperature. The final objective of this on-going study is to determine potential disturbances on that fundamental resonance frequency, and mainly on its harmonics related to the indirect detection of temperature increments or decrements, for the realistic case of be working with ultrasonic echo-signals contaminated with different noise levels.