A pulsed magnetomotive ultrasound imaging system for magnetic nanoparticle detection

Magnetomotive ultrasound (MMUS) imaging has been proposed to overcome the limitation of ultrasound to localize magnetic nanoparticles (MNP) within tissues. A harmonic magnetic field is commonly used; however, this approach can present drawbacks such as heating within amplifier and coil, frequency-dependent tissue mechanical response, and extended magnetic field rise time. Therefore, this study aimed to develop a pulsed electronic system to improve magnetic field application during MMUS. The system was capable of providing a pulsed magnetic stimulation, improving the magnetic field magnitude, and decreasing rise time by the optimization of the electrical properties of the coil used to generate the external magnetic field. The proposed system was evaluated to generate a magnetic field with different pulse durations ranging from 4 ms to 20 ms. Two coil configurations were tested, creating several MMUS images of phantoms, and evaluating their displacement behavior. In addition, the influence of the MNP magnetization on the pulsed MMUS output was studied, obtaining displacement saturation trends for zinc-ferrite MNPs, proving the relationship between the magnetization of MNPs and the displacement generated by the MMUS technique.