Optimization of wireless lorentz force actuators inside MRI scanners

Interventional Magnetic Resonance Imaging (MRI) is getting popular due to the advantages of MRI as an imaging modality but the closed MRI bore makes it difficult for physicians to carry out procedures like biopsy by hand. In the scope of the project, which this thesis is a part of, a novel, MRI compatible, two-dimensional (2D) opto-electro-mechanical positioner is proposed. The rotors in the positioner uses wireless Lorentz force actuators which consists of a solar cell and a coil. The solar cells are used to convert optical power from LEDs or lasers to current which creates a magnetic moment when passing on the coil. This magnetic moment tries to align itself with the the high (1.5-7 T), DC magnetic field inside the MRI scanner, which yields a Lorentz torque exerted on the actuator, rotating the rotor. This thesis focuses on the optimization of the wireless actuation modules (WAM) such that, the rotor yields the maximum mechanical power for a given optical power input, under MRI conditions. To do that, a mathematical model of the rotor inside a uniform magnetic field is built, and the governing equations are used in a SPICE model to do numerical simulations of the rotor torque under different conditions. Using the simulation results, a WAM whose coil is optimized for 3 T magnetic field is designed. To characterize the rotor in lab, a Helmholtz coil is implemented which is able to generate 53 mT uniform magnetic field and a new WAM whose coil is optimized for this range is designed. Torque-rpm measurements of the rotor with this WAM, inside the Helmholtz coil, are done and compared with the simulation results. Lastly, fibers and lasers, together with electronics for drive and control, is assembled to test the complete 2D positioner system inside an MRI scanner.