1 CHARACTERIZATION OF TISSUE-MIMICKING MATERIALS USING MAGNETIC INDUCED SHEAR WAVE D. R. T. Sampaio, A. C. Bruno, F. W. Grillo, T. Z. Pavan and A. A. O. Carneiro Department of physics, FFCLRP – University of Sao Paulo, Ribeirão Preto, Brazil adilton@usp.br Abstract: Estimation of the tissues mechanical properties of is an important information to the pathologies diagnosis. A novel ultrasound-based methods use shear wave dispersion for this purpose. This paper describes the Magneto Motive Ultrasound (MMUs) implementation to evaluate mechanical parameters of paraffin phantoms. This technique can be applied in vivo as an alternative to biopsy. Ultrasound equipment was used with a magnetic system for generating seismic waves in paraffin phantom containing a magnetic inclusion. Consistent values of elastic and viscous modulus (μ1 = 8.4 ± 1.5 kPa; μ2 = 5.3 ± 2.2 Pa.s) were obtained. The evaluation of MMUs technique for estimating mechanical parameters of soft tissue was satisfactory, but for stiffer inclusions higher temporal resolution is needed. Keywords: Ultrasound, Magneto Motive Ultrasound, Shear Wave, Paraffin Gel Phantom Introduction Rheology characterization of soft tissues is an important indicator of pathologies, as cancer. Ultrasound elastography is a diagnostic tool used to distinguish between pathological and healthy tissues based on the stiffness, [1]. Elastography is an alternative to biopsy, which is the gold standard [2]. Recently, ultrasound-based shear wave elasticity imaging techniques have been used to investigate soft tissues elasticity and viscosity, [3], [4]. These methods use rheological mathematical models, as Voigt model, for mechanical characterization. The Voigt model depends on shear wave frequency (ωs), phase velocity (cs), and viscosity attenuation (αs) to obtain shear elasticity (μ1) and shear viscosity (μ2) of an viscoelastic medium with density (ρ), [5]: ଵ = ௦ ଶ ௦ ଶ ሺ మ − మ మ ሻ ( మ + మ మ ) మ (1) ଶ = ଶ మ మ ( మ + మ మ ) మ . (2) The magneto motive ultrasound (MMUs) uses the displacement induced by external magnetic force to locate magnetized targets inside tissue, [6]. In this case, the magnetic force produces mechanical oscillations, inducing seismic wave propagation perpendicular to the force direction, [7]. Paraffin-gel waxes have been used as promising tissue-mimicking materials. This material has speed of sound from 1425.4 ± 0.6 to 1480.3 ± 1.7 m.s -1 at room temperature (24ºC) and do not suffer dehydration, [8]. In this paper we present a MMUs use as alternative to obtain mechanical parameters using shear wave dispersion in paraffin tissue-mimicking phantoms. Materials and Methods The in vitro studies were performed in phantom at room temperature (24ºC). The phantom was a parallelepiped (80 x 80 x 25 mm) paraffin gel (ρg = 850 kg.m -3 ), [9] with a spherical (SP) (Ø = 10 mm) inclusion made of paraffin twice stiffer than the background. A second spherical (Ø = 7 mm) inclusion (SF), made of ferrite, was embedded in the phantom to be used as source to induce the seismic waves by being displaced due to the interaction with an external oscillating magnetic field. The SP is located at 35 mm of depth, and the SF at 50 mm (see Figure 1). Figure 1: MMUs system used to excite a paraffin tissue mimicking phantom with a ferrite inclusion positioned under a stiffer paraffin inclusion. A software interface, written in C++ and Qt4, was developed to load flexible sequences of acoustic acquisition synced with the magnetic excitation. The user interface runs on ultrasound equipment (Sonix RP, Ultrasonix @ 40 MHz), which also controls a function SP SF