Safety limits & rapid scanning methods in magnetic particle imaging

Abstract

Magnetic Particle Imaging (MPI) is a new imaging modality that utilizes nonlinear magnetization of superparamagnetic tracers, with high sensitivity and zeroionizing radiation advantages. Since the introduction of MPI in 2005, there have been substantial contributions to pre-clinical applications such as cancer imaging, cell tracking, and angiography. These studies have promising implications for future clinical human-sized MPI systems. However, the time-varying magnetic fields that are used during image acquisition are subject to human safety concerns, especially in applications that require rapid imaging. By forming electric field patterns in the body, these fields may result in peripheral nerve stimulation, also known as magnetostimulation. To prevent potential stimulations; the effects of frequency, duration, and direction of the fields, as well as body part size were previously investigated. This thesis investigates the effects of duty cycle and fat/water tissue ratio on magnetostimulation thresholds for the drive field in MPI. Human subject experiments with in-house magnetostimulation setup were conducted at 25 kHz, followed by anatomical Magnetic Resonance Imaging (MRI) of the subjects. Accordingly, magnetostimulation thresholds first decrease then increase with increasing duty cycle and reach a maximum at 100% duty cycle. The results also show that the thresholds are strongly correlated with fat/water tissue ratio. Finally, this thesis also demonstrates that MPI image quality can be preserved for rapid scanning scenarios within the human safety limits.