Active microcoil tracking in the lungs using a semisolid rubber as signal source

A new method to localize and track medical devices in air‐filled body cavities is proposed that uses active microcoils with a semisolid filling. In air spaces, e.g., the lung, microcoils require an independent signal source, which should be made of a biocompatible, solid and sterilizable material with a long shelf time. In a measurement of the T 1 and T * 2 and the relative spin density of several semisolid materials, latex was identified as a suitable material from which a prototype catheter was constructed with a microcoil at its tip. In a dual‐echo tracking pulse sequence, the very short T * 2 of the rubber material allowed suppressing the background signal from surrounding tissue with a subtraction technique and additional dephasing gradients. With a roadmapping reconstruction, the microcoil's trajectory could be visualized on a previously acquired reference image set with a tracking rate of up to 60 Hz at a spatial resolution of better than 2mm. In a real‐time tracking implementation, an image update rate of 4 Hz was achieved by combining the tracking with a fast real‐time imaging sequence. Both methods were successfully applied in vivo to track the catheter in the lung of a pig. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.