3D Magnetomotive Ultrasound using a Matrix Transducer to Visualize the Distribution of Magnetic Nanoparticles

Magnetic nanoparticles (MNPs) have shown significant potential for localized cancer therapies such as Magnetic Drug Targeting (MDT) and magnetic hyperthermia. Real-time monitoring of MNP distribution is essential to optimize drug perfusion and adjust applied magnetic fields accordingly. While magnetomotive ultrasound (MMUS) has been successfully employed to track MNP accumulation in MDT, conventional implementations are limited to 2D imaging. This study evaluates the feasibility of 3D MMUS using a matrix transducer for enhanced MNP displacement mapping. A polyvinyl alcohol cryogel phantom with an embedded ellipsoidal MNP inclusion (5mg/ml) was fabricated using two freeze-thaw cycles and positioned between a matrix ultrasound transducer (Vermon, 3 MHz, 32 x 32 elements, 0.3 x 0.3 mm pitch) and an electromagnet. The electromagnet generated a sinusoidal alternating magnetic field, inducing motion in the MNP-laden region. Plane wave imaging compounding (9 plane waves; volume rate 63 Hz; with compounding 7 Hz) was used to track tissue displacement, and a frequency- and phase-sensitive MMUS algorithm estimated axial displacement in three dimensions. The obtained 3D displacement maps clearly distinguished the MNP inclusion with maximum displacement of approximately 15μm. These findings demonstrate the feasibility of matrix transducer-based 3D MMUS, offering a promising approach for MDT monitoring. Future work will validate this technique in in vivo animal studies.