Drive field coil design in a MPI scanner

Magnetic Particle Imaging (MPI) is a new quantitative tomographic imaging technique based on the non-linearity of the magnetization curves of ferromagnetic material. It measures the magnetic field generated by iron-oxide magnetic nanoparticles which are located at a field-free point in space. The drive field coils (DFC) are responsible for the movement of this point throughout the field of view, as well as for the recording of the signal induced by nanoparticles. This paper summarizes a six months research accomplished at Philips Laboratories Hamburg. It proposes a suitable structure for the DFC, achieving a high signal to noise ratio and providing a self-resonant frequency higher than the MPI work frequency range. Additionally, this study suggests a favorable design for a human-size scanner and follows the consequent modification of the DFC allowing low power dissipation. The key-methodology adopted for problem solution has been computer simulation. After defining the connection between the signal to noise ratio of the system and DFC resistance, a power losses analysis based on proximity effect in a litz wire coil has been used to identify the structure which allows working under the condition of body noise limitation. It has been demonstrated through estimation, performed by combining both, an inductive and a capacitive analysis of the coil behavior in a single model, that such a structure further meets self-resonant frequency requirements. These results have been verified additionally by experimental setup. An analysis of important issues related to the construction of a human-size scanner -- as power dissipation and shielding influence -- has been performed, providing eventually an ultimate structure for both, the DFCs and the human-size scanner. Moreover, a possible scanner configuration capable of three-dimensional movements of the field-free point throughout the field of view is presented. The DFC designed in this study does not increase the noise in the system, thus it does not affect signal to noise ratio. Estimated self-resonant frequency fits to MPI applications and coil power consumption meets all previous project estimations. The design of an adequate DFC represents an essential step towards the construction of the first prototype of a human-size scanner, hence, towards the application of this promising MPI imaging technique to human patients.