Temperature Response of a Magnetic Resonance Imaging Coil Insert for the Navigation of Theranostic Agents in Complex Vascular Networks

The purpose of this paper is to provide some practical insights regarding the use of a commercially available imaging coil as a magnetic resonance navigation (MRN) propulsion actuator. MRN relies on magnetic resonance imaging (MRI) technology to navigate magnetic therapeutic or imaging agents to a target location. When such a target is accessible only through complex vessel pathways, an imaging gradient coil (IGC) insert can be used to generate high slew rate gradient pulses. Although temperature rise might not be an issue for imaging routines, knowing precisely the temperature coil response is of primary importance for MRN-assisted interventions as it may limit propulsion performance and ultimately lead to system breakdown. This paper reports the impact of four parameters, namely, duty cycle, frequency, amplitude, and gradient direction on the temperature behavior of an IGC with external diameter suitable to fit inside the bore of a clinical MRI scanner and internal diameter appropriate for small animals. A minimum rise time of 300 μs was measured and magnetic gradients up to 325 mT·m^-1 were generated. The insert can sustain burst-mode propulsion at maximum power for slightly less than 2 min before reaching its maximum admissible temperature. Temperature management is one of the future challenges in MRN research.