Abstract
BackgroundCatheter visualization and tracking remains a challenge in interventional MR.Active guidewires can be made conspicuous in "profile" along their whole shaft exploiting metallic core wire and hypotube components that are intrinsic to their mechanical performance. Polymer-based catheters, on the other hand, offer no conductive medium to carry radio frequency waves. We developed a new "active" catheter design for interventional MR with mechanical performance resembling braided X-ray devices. Our 75 cm long hybrid catheter shaft incorporates a wire lattice in a polymer matrix, and contains three distal loop coils in a flexible and torquable 7Fr device. We explored the impact of braid material designs on radiofrequency and mechanical performance.ResultsThe incorporation of copper wire into in a superelastic nitinol braided loopless antenna allowed good visualization of the whole shaft (70 cm) in vitro and in vivo in swine during real-time MR with 1.5 T scanner. Additional distal tip coils enhanced tip visibility. Increasing the copper:nitinol ratio in braiding configurations improved flexibility at the expense of torquability. We found a 16-wire braid of 1:1 copper:nitinol to have the optimum balance of mechanical (trackability, flexibility, torquability) and antenna (signal attenuation) properties. With this configuration, the temperature increase remained less than 2°C during real-time MR within 10 cm horizontal from the isocenter. The design was conspicuous in vitro and in vivo.ConclusionWe have engineered a new loopless antenna configuration that imparts interventional MR catheters with satisfactory mechanical and imaging characteristics. This compact loopless antenna design can be generalized to visualize the whole shaft of any general-purpose polymer catheter to perform safe interventional procedures.
Highlights
Catheter visualization and tracking remains a challenge in interventional MR.Active guidewires can be made conspicuous in "profile" along their whole shaft exploiting metallic core wire and hypotube components that are intrinsic to their mechanical performance
Loopless antenna design using braiding layers The design of the loopless antenna was based on coaxial braiding layers that are separated by medical grade thermoplastic elastomer tubing (Pebax, Medical Extrusion Technologies, Murrieta, CA) and polyimide tubing (Microlumen, Tampa, FL)
We report the design and testing of a clinical grade active catheter for interventional MR that combines suitable mechanical performance with MR visibility
Summary
Catheter visualization and tracking remains a challenge in interventional MR.Active guidewires can be made conspicuous in "profile" along their whole shaft exploiting metallic core wire and hypotube components that are intrinsic to their mechanical performance. We developed a new "active" catheter design for interventional MR with mechanical performance resembling braided X-ray devices. Comparable devices for operation under MR are more complex They must be safe for use in the high magnetic field. They must not distort the surrounding magnetic field, which in turn distorts imaging of surrounding anatomy. They must preserve the mechanical properties expected by the interventional operator accustomed to X-ray operation. They must be conspicuous, from the tip throughout the length inserted in the body, for safe procedure conduct during especially complicated procedures
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