Toward in vivo quantification of induced RF currents on long thin conductors

Abstract

Purpose: Most MR-guided catheter-based procedures, and imaging of patients with implanted medical devices, are currently contraindicated due to a significant risk of heating associated with induced RF currents. The induced RF current produces a corresponding artifact which can be used to remotely characterize current and safely predict RF heating. Application of this remote technique in vivo to safely quantify RF heating risk may allow for execution of many scans currently contraindicated. Sources of phase other than induced RF current may present difficulty in practical in vivo.

Methods: A custom ultra-short echo time (UTE) sequence was developed to minimize unwanted phase contributions. A phantom experiment was performed to compare current characterization using a stock gradient-echo (GRE) sequence and the custom UTE sequence following calibration of the temperature measurement apparatus using a previously published heating prediction technique. Animal experiments were used to investigate the feasibility of using the UTE sequence to quantify RF heating.

Results: Current characterization and heating prediction with a stock GRE sequence was equivalent to that with the custom UTE sequence. Heating measurements and image-based predictions in animal experiments agreed within error in all experiments.

Conclusion: Through comparison of measured heating and image-based prediction, feasibility of using a custom UTE sequence to quantify RF heating risk in vivo was demonstrated.

Keywords: RF heating; RF safety; UTE; cardiac MRI.