Frequency response of soft tissue displacements induced by the force on magnetic nanoparticles

摘要

In Magnetomotive Ultrasound (MMUS), tissue embedded magnetic nanoparticles (MNP) are mechanically excited by a magnetic field. Relatively small forces on the MNP result in small tissue displacements and a low SNR, when US-based displacement tracking is performed. From the application of elastography techniques it is known that the axial displacement of soft tissues shows a resonant behavior depending on the excitation frequency. Therefore, capturing the tissue's frequency response which is related to the corresponding stiffness, might allow to identify and apply appropriate MMUS excitation frequencies in order to increase displacement amplitudes and SNR. However, MMUS studies commonly utilize solenoid/yoke setups with excitation frequencies limited up to a few Hz. In this work, we present an MMUS setup which allows to measure the entire frequency range, relevant in elastography, by separating the gradient field from the excitation field. We further demonstrate the gain in displacement amplitudes when excitation at the resonance frequency is performed.