Ultrasound harmonic behaviour of artificial tissues

The characterization of the acoustical behavior of a new tissue mimicking phantom for flowing microbubble contrast agent investigations is addressed in this paper. Since harmonic images nowadays represents the key methodology in contrast ultrasound imaging, particular attention is dedicated to the analysis of harmonic components of backscattered ultrasound signals in the matter. As a first part of this study we compare the acoustic properties of a pig liver tissue with the corresponding ones of a hydrogel polymeric material, having chosen the first as the reference tissue in the preparation of the phantom. This latter is composed by a cellulose derivate based material in which a specific concentration of the components was found in order to mimic liver acoustical behavior. The second part of the study compares the harmonic analysis results of the liver and the hydrogel sample. The analysis was carried out by using a commercial echograph (Megas GPX, Esaote SpA, Florence, Italy) equipped with a linear transducer LA532 (Esaote SpA, Florence, Italy). Three different insonifying frequencies were employed (2, 2,5 and 3,3 MHz), each one with four echograph electrical power (EEP) settings (15%, 35%, 60%, 80%), in order to obtain four different mechanical indices (MIs) for every adopted frequency. By plotting the fundamental (1H), sub-harmonic (1/2H) and second harmonic (2H) components of backscattered signal rising from liver and hydrogel versus MI values, a very similar behaviour is observed, demonstrating that the new phantom is a suitable candidate in ultrasound contrast imaging studies.