Does size play a role in induced displacement in magneto-motive ultrasound imaging? Saeideh Arsalani Department of Physics, FFCLRP, University of São Paulo ORCID: 0000-0001-9451-8254 Oswaldo Baffa Faculdade de Engenharia Elétrica Universidade Federal de Uberlândia Uberlândia, Brazil ORCID: 0000-0002-0622-2814 Yaser Hadadian Department of Physics, FFCLRP, University of São Paulo ORCID: 0000-0003-2176-2891 Theo Z. Pavan Faculdade de Engenharia Elétrica Universidade Federal de Uberlândia Uberlândia, Brazil ORCID: 0000-0002-9931-8558 Soudabeh Arsalani Department of Physics, FFCLRP, University of São Paulo ORCID: 0000-0002-1957-7956 Antonio Adilton. O. Carneiro Faculdade de Engenharia Elétrica Universidade Federal de Uberlândia Uberlândia, Brazil ORCID: 0000-0002-1752-7170 Abstract— Over the past decade, a technique called magneto- motive ultrasound imaging (MMUS) has been established to obtain displacement of magnetic nanoparticles (MNPs) due to the interaction between MNPs and the magnetic field. Recently, shear wave dispersion magneto-motive ultrasound imaging (SDMMUS), which is a subdivision of MMUS modality, has been introduced as a novel elasticity imaging to obtain viscoelastic properties of soft tissue mimicking phantoms labeled with iron oxide nanoparticles. In this technique, an alternating external magnetic field applied to induce displacements in order of micrometers and the mechanical properties of the medium results from these movements. Here, two different iron oxide MNPs synthesized by co-precipitation method, having the same saturation magnetizations but two different mean particle sizes were used as contrast agent in MMUS. Gelatin tissue mimicking phantoms were prepared containing inclusion with the MNPs to perform the experiments. According to the obtained results, the induced displacements were almost the same for both samples, suggesting in MNPs with the same magnetization and the mean size ranges studied here, the effect of size on the induced displacement can be neglected. Moreover, the mechanical properties of phantoms were reported the same values for both MNPs used. Keywords—Magneto-motive ultrasound, shear wave, magnetic nanoparticles, mechanical properties. I. INTRODUCTION Over few decades, elastography has been known as a well- known imaging modality due to mapping mechanical properties of tissues. Some diseases in different tissues including breast, liver, and so on have been recognized through changes of mechanical properties. Since the viscoelasticity of soft tissues is often associated with pathological state, they can be used as a diagnostic tool in medicine [1]. Ultrasound-based methods have been widely used compared to other techniques including magnetic resonance imaging (MRI), Single-photon emission computed tomography (SPECT) and so forth due to many inherent advantages, including real time, cost effectiveness, portability and non-ionizing radiation[2]. However stand-alone ultrasound imaging has a poor contrast for magnetic nanoparticles. Currently, magnetic nanoparticles have become a promising tool in the clinical diagnostic and therapeutic techniques as their capacity to function at the cellular and molecular level of biological as well as their physical properties. MNPs in the form of superparamagnetic iron oxides (SPIO) have been established as a contrast enhancement for MRI imaging as MR imaging [3, 4]. As mentioned above, magnetic nanoparticles have shown weak contrast agents to ultrasound imaging. While, a novel remote elastogarphy called MMUS method has been introduced by oh et al. [5] to deal with this issue. MMUS is one of the recent modalities which benefits from superparamagnetic nanoparticle as contrast agent to visualize molecular and cellular levels through ultrasound imaging. In this technique, an external magnetic excitation is applied to induce a motion within tissue labeled with magnetic nanoparticles and this movement is detected by ultrasound technique (ref). Later, many