Magnetically-Assisted Remote Controlled Microcatheter Tip Deflection under Magnetic Resonance Imaging

Summary

Current applied to an endovascular microcatheter with microcoil tip made by laser lathe lithography can achieve controllable deflections under magnetic resonance (MR) guidance, which may improve speed and efficacy of navigation of vasculature during various endovascular procedures.

Abstract

X-ray fluoroscopy-guided endovascular procedures have several significant limitations, including difficult catheter navigation and use of ionizing radiation, which can potentially be overcome using a magnetically steerable catheter under MR guidance.

The main goal of this work is to develop a microcatheter whose tip can be remotely controlled using the magnetic field of the MR scanner. This protocol aims to describe the procedures for applying current to the microcoil-tipped microcatheter to produce consistent and controllable deflections.

A microcoil was fabricated using laser lathe lithography onto a polyimide-tipped endovascular catheter. In vitro testing was performed in a waterbath and vessel phantom under the guidance of a 1.5-T MR system using steady-state free precession (SSFP) sequencing. Various amounts of current were applied to the coils of the microcatheter to produce measureable tip deflections and navigate in vascular phantoms.

The development of this device provides a platform for future testing and opportunity to revolutionize the endovascular interventional MRI environment.

Introduction

Endovascular procedures performed in interventional medicine use x-ray guidance as a tool for catheter navigation through vasculature to treat several major illnesses, such as brain aneurysm, ischemic stroke, solid tumors, atherosclerosis and cardiac arrhythmias targeting over one million patients per year worldwide^1-5. With the use of contrast media, navigation through vasculature is achieved through manual rotation of the catheter and mechanical advancement by the interventionist's hand⁶. However, navigation through small tortuous blood vessels around many vascular bends becomes increasingly difficult, elongating the time before reaching the ta....

Protocol

1. Microcoil Fabrication

1. Obtain a commercially available microcatheter (e.g. 2.3F Rapid Transit Cordis Neurovascular Catheter, Raynham, MA) for a substrate.
2. Ensure catheters have no ferrous components, are considered MR-safe, and range in size 2.3-3.0 F.
3. Sputter a titanium adhesion layer followed by a copper seed layer unto a 1 to 2 mm OD insulating tube. Possible materials include polyimide or alumina (Ortech Advanced Ceramics, Sacramento, CA).
4. Electrodeposit a positive photoresist layer using Shipley's PEPR-2400 (currently being sold by DOW Chemical under the name Intervia 3D-P). Electrodeposition results in a unifo....

Results

From the protocol described above, an angle of deflection between 0 and 90 degrees should be observed from application of 50-300 mA of current delivered simultaneously to both coils of a combined solenoid and Helmholtz coil microcatheter system (Figure 2E). An increase in applied current should result in an increase in microcatheter deflection angle, while a reversal in current polarity should result in deflection in the exact opposite direction as observed with positive current (Figures 5A-5C

Discussion

Here we describe the protocol for deflection of a microcatheter in a MR scanner. The key parameters for success are accurate application of current and measurement of deflection angle. Inaccurate measurement of deflection angle is the most probable error encountered in this protocol. The angles captured in MR images during the waterbath experiment may differ from actual values due to slight differences in the orientation by which the medium is positioned with respect to the bore of the magnet. To address this issue in th.......

Materials

Name	Company	Catalog Number	Comments
Name of Reagent/Material	Company	Catalog Number	Comments
GdDTPA Contrast Media (Magnevist)	Bayer HealthCare Pharmaceuticals Inc.	1240340	McKesson Material Number
Positive Photoresist	Shipley	N/A	PEPR-2400, Replacement: Dow Chemicals Intervia 3D-P
Copper Sulfate	ScienceLab	SLC3778	Crystal form
Sulfuric Acid	ScienceLab	SLS1573	50% w/w solution
Parrafin Wax	Carolina	879190
Potassium Carbonate	Acros Organics	424081000