Towards the Integration of an MPI Compatible Ultrasound Transducer

Abstract

Magnetic particle imaging (MPI) is a tracer based modality and thus lacks anatomical information. Medical ultrasound (US) imaging provides the desired morphological data in real-time that could complement functional MPI images. However, most customary US devices will certainly be damaged by the strong alternating magnetic fields inside the MPI bore. Moreover, US equipment might degrade MPI signal quality. In this work, US components that are prone to eddy current heating were pointed out by presenting the major components of a medical US transducer. A theoretical model was utilized to derive maximum applicable sizes for conducting parts like electrode surfaces and cables. Heating experiments inside the MPI bore showed that heating can be managed by dispensing extensive electric shields and keeping conducting structures reasonably small. Further, transducer dummies that were placed inside the MPI scanner bore and actively driven with US signals were used to assess the interferences between both modalities. The MPI signals showed a minor increase in the noise level when transducer dummies were present, while serious interferences were recognized when a dummy comprising a tuning inductor was  electrically driven. The US signals showed strong disturbances in the frequency range of the MPI drive fields during MPI acquisition, which was decades lower than the relevant US frequency range. It is concluded that the combination of an MPI scanner and adapted US hardware is feasible. Future work needs to address the suppression of interferences and their impact on image quality of both modalities.