Magnetically‐assisted remote control (MARC) steering of endovascular catheters for interventional MRI: A model for deflection and design implications

Abstract

Current applied to wire coils wound at the tip of an endovascular catheter can be used to remotely steer a catheter under magnetic resonance imaging guidance. In this study, we derive and validate an equation that characterizes the relationship between deflection and a number of physical factors: theta/sin(gamma-theta) = nIABL/EI(A) where theta is the deflection angle, n is the number of solenoidal turns, I is the current, A is the cross-sectional area of the catheter tip, B is the magnetic resonance (MR) scanner main magnetic field, L is the unconstrained catheter length, E is Young's Modulus for the catheter material, and I(A) is the area moment of inertia, and y is the initial angle between the catheter tip and B. Solenoids of 50, 100, or 150 turns were wound on 1.8 F and 5 F catheters. Varying currents were applied remotely using a DC power supply in the MRI control room. The distal catheter tip was suspended within a phantom at varying lengths. Images were obtained with a 1.5 T or a 3 T MR scanner using "real-time" MR pulse sequences. Deflection angles were measured on acquired images. Catheter bending stiffess was determined using a tensile testing apparatus and a stereomicroscope. Predicted relationships between deflection and various physical factors were observed (R2 = 0.98-0.99). The derived equation provides a framework for modeling of the behavior of the specialized catheter tip. Each physical factor studied has implications for catheter design and device implementation.

Safety evaluation of magnetic catheter steering with upgraded magnetic resonance imaging system

“…Once magnetized, forces can be applied to the sphere with magnetic gradient field. Contrary to methods [2], [3], this method do not present risks of locally heating blood and tissue.…”

“…Compared with fluoroscopy, Magnetic Resonance Imaging (MRI) offers improved soft tissue resolution and eliminates ionizing radiation exposure [1]. Moreover, recent efforts [2], [3] have been put in to use the magnetic properties of the MRI apparatus for catheter manipulations. Using coils at the distal end of a catheter, different currents are applied to steer the tip of the catheter [2], [3].…”

“…Moreover, recent efforts [2], [3] have been put in to use the magnetic properties of the MRI apparatus for catheter manipulations. Using coils at the distal end of a catheter, different currents are applied to steer the tip of the catheter [2], [3]. Current is provided from a power supply or from the MRI radio-frequency subsystem.…”

Endovascular image‐guided interventions (EIGIs)

“…70 The use of the existing magnetic field in MRI systems is being reported for steering catheters. 71 There is the beginning commercial availability of remote catheter steering systems, such as the one by Hansen Medical (Hansen Medical Inc., Mountain View, CA) 72,73 designed for EP. However, these appear to be implemented with wires tied to external motors and hence are hard to project to the full range of EIGI, which may require navigation through a tortuous vessel.…”

New-Generation Laser-lithographed Dual-Axis Magnetically Assisted Remote-controlled Endovascular Catheter for Interventional MR Imaging: In Vitro Multiplanar Navigation at 1.5 T and 3 T versus X-ray Fluoroscopy

“…Third, laser lithography has permitted further miniaturization of our catheter tips, which is especially important for future applications in the smaller vessels of the brain, liver, and heart. Laser lithography has enabled fabrication of multiple coil tips that are both precise and consistent, allowing predictable catheter tip deflections and equations that describe correlation between applied current and catheter tip movements (15)(16)(17)(18).…”