Design and Fabrication of Wireless Multilayer Tracking Marker for Intraoperative MRI-Guided Interventions

This article presents the design, fabrication, and evaluation of miniature magnetic resonance (MR) compatible wireless markers, which can provide three-dimensional (3-D) positional tracking under magnetic resonance imaging (MRI). To achieve the small size of such markers, rectangular spiral planar coils were stacked in multiple layers, which can be fabricated on a flexible printed circuit board. Finite-element-based simulations and analytical modeling were applied to ensure the proper adjustment of the MRI scanner resonant frequency while maintaining a high circuit quality factor. A four-layer planar tracking coil was prototyped with a size of 6.7 × 1.5 × 0.3 mm
³
, and a quality factor of 28.5. This design and fabrication approach is reportedly the first design to initiate wireless markers in such a small size, enabling straightforward integration with interventional tools. When validated under MRI, the tracking marker appeared as a very high contrast spot on the MR images. For a 48 mm distance from the isocenter, the estimated maximum errors in 3-D position was 0.48 mm. And the inherent standard deviation of marker localization was 0.12 mm. With the high MR contrast signal generated, the presented markers enable automatic and real-time tracking in 3-D but without MR image construction. In combination with the small form factor, this marker would facilitate the MRI-guided navigation of interventional tools, in particular for those assisted by teleoperated robots.