High maneuverability guidewire with functionally graded properties using new superelastic alloys

Miniaturizing Floating Traps to Increase RF Safety of Magnetic-Resonance-Guided Percutaneous Procedures

OBJECTIVE

MRI in the area of cardiovascular catheter-based interventional procedures is an active field. A common intervention-revascularization of chronic total occlusions, requires a conductive guidewire for revascularization. The mechanical properties of guidewires are paramount to the successful execution of such procedures. Furthermore to benefit from MRI techniques, additional conductors are required to transmit signal from the tip of a catheter. Long thin conductors in MRI systems pose a safety risk in the form of RF heating due to induced RF currents on the conductors. Unfortunately many existing techniques to mitigate this risk require physical modification of the conductors, inevitably resulting in detrimental mechanical tradeoffs in the guidewire. This manuscript proposes a novel application and miniaturization of an existing device, the floating RF trap. The RF trap couples strongly to any thin conductor passing through the trap lumen inducing significant series impedance. This results in reduction of induced RF currents, and thus, heating.

METHODS AND RESULTS

This study shows theoretical and experimental analysis of induced impedance as well as theoretical reduction in heating due to various distributions of traps along the length of a catheter. Results of measuring induced current and heating in phantom experiments are also presented. Through comparison with commercial simulation packages and results of phantom experiments, it is shown that miniaturized RF traps can be modeled accurately, including their induced series impedance and effect on induced RF current.

CONCLUSION AND SIGNIFICANCE

It was demonstrated that floating RF traps present a feasible method to mitigate RF heating while maintaining important mechanical properties of guidewires.

Systematic evaluation of hybrid guidewires: shaft stiffness, lubricity, and tip configuration

OBJECTIVE

To conduct a comparison of physical and mechanical properties for 5 commonly used guidewires to assess advantages of wires for specific applications.

METHODS

Tests on guidewires (0.035" diameter; straight, flexible tip) included tip bending, shaft buckling, lubricity, and tip puncture measurements. Guidewires included 2 hybrid wires: the U-Nite (Bard Urological, Covington, GA) and the Sensor (Boston Scientific, Natick, MA). Our aim was to compare the stiffness of these hybrid wires with the standard Amplatz SuperStiff (Boston Scientific). Our second aim was to compare the hydrophilic tip of the hybrid wires with 2 traditional hydrophilic guidewires: the NiCore (Bard Urological) and RadiFocus glidewire (Boston Scientific).

RESULTS

The Amplatz SuperStiff had a significantly stiffer shaft than either hybrid wire, with a buckling force of 1.81 ± 0.91 N compared with the Sensor (0.80 ± 0.29 N, P = .0002) and the U-Nite (0.77 ± 0.29 N, P < .0001). The Boston Scientific guidewire tips were less stiff than the Bard guidewires, requiring up to 48% less force to bend when encountering resistance (P < .0001). The U-Nite had the highest lubricity (0.09 ± 0.03 N, P < .0001) and roundest tip of all the guidewires tested. The RadiFocus required the greatest puncture force (1.80 ± 0.27 N, P < .0001) of all the guidewires tested.

CONCLUSION

Hybrid wires offer a combination of a stiffer shaft and hydrophilic tip. The Amplatz SuperStiff remains the stiffest wire and as such is best suited for placement of ureteral access sheaths or larger stents. The Boston Scientific wires require less force to "bend" around a point of obstruction compared with the Bard wires. The Boston Scientific RadiFocus requires the greatest force to puncture aluminum foil.