Emerging Applications of Color Magnetic Particle Imaging

Color Magnetic Particle Imaging (MPI) is a rapidly developing area within MPI, promising numerous important applications such as identifying the properties of the MNP environment and catheter tracking during cardiovascular interventions. Different MNPs are expected to induce different MPI signals based on factors such as their magnetic material and core diameter. Furthermore, the relaxation behaviors of MNPs are affected by the differences in their environmental conditions, such as temperature or viscosity. This talk will discuss recent techniques in color MPI that leverage these differences to distinguish different MNP types and/or their environmental conditions. Specifically, the presentation will concentrate on calibration-free x-space-based relaxation mapping for color MPI.

Control and Detection Strategies for Magnetic Microrobots Inspired by Magnetic Particle Imaging

In addition to underpinning several minimally invasive biomedical imaging modalities, magnetic stimuli offer a compelling means to control and power medical microrobots deployed within the body. The variety of forms that these magnetically responsive microrobots can take is continuously expanding, ranging from fabricated structures designed to efficiently locomote in response to applied magnetic fields, to naturally magnetic organisms repurposed as biohybrid microrobots. In the past, the magnetic stimuli most frequently applied to these microrobots have been directable uniform magnetic fields that can steer their intrinsic motion or gradient fields that apply forces to pull them. However, these methods entail serious practical challenges, since control often requires a complimentary form of live imaging, and the feasibility of producing adequate gradients in patients diminishes as the microrobots shrink in size. Rotating magnetic fields (RMFs), in which magnitude remains constant while direction is swept around one or more planes of rotation, offer a promising alternative for actuation. Not only do RMFs deliver mechanical energy through magnetic torque-based actuation schemes that more readily scale to patients, but our work has also shown that concepts inspired by magnetic particle imaging present unique possibilities for control and feedback when adapted to RMFs. Actuating microrobots with RMFs permits simultaneous actuation and inductive detection, which we demonstrate with setups adapted for low frequencies (Hz to 10s of Hz) and physical phase cancellation. Moreover, we have shown that a superimposed magnetostatic selection field can spatially restrict torque-based actuation to a single point. By combining these ideas, and employing signal processing techniques focused on phase decomposition, we show that spatially selective inductive signal acquisition is possible in a gating field and that the resolution is set by the relative magnitude of the magnetostatic field and RMF. These principles build toward improved methods for drug targeting with live feedback and show how concepts from MPI can be fruitfully extended to magnetic microrobotic control.