Magnetic Nanoparticle-Guided Blind Focusing of the Electric Field for Microwave Hyperthermia

This paper deals with microwave hyperthermia, presenting a novel way to achieve the blind focusing on the tumor of the electric field radiated by an array of antennas. As in a recently proposed approach, the idea is to determine the antenna excitations by measuring the variation of the electric field arising from a localized variation of the electromagnetic contrast, without requiring any a priori knowledge of the geometry and of the electric properties of the tissues wherein the electromagnetic field propagates (thus, the adjective “blind”). The first novelty of the new approach is the use of magnetic nanoparticles as contrast agents, which, in addition to being biocompatible, are appealing thanks to the possibility of changing their magnetic contrast, in a fast, remote, and reversible way, by applying an external magnetic field. This allows a reconfigurable focusing through a continuous tuning of the antenna excitations, thereby enabling one to counteract the possible loss of focusing that could occur during the treatment. However, the magnetic nature of the induced contrast variation requires the development of ad hoc strategies for the synthesis of the excitations, which represent the other novelty of the new approach. Its effectiveness has been thoroughly investigated with an exhaustive 2-D numerical analysis, considering as case study that of breast cancer, and further assessed through 3-D realistic numerical simulations.