Clinical grade active guidewire design for cardiovascular interventional MRI

In cardiovascular interventions, magnetic resonance imaging (MRI) can be used as an alternative to X-ray fluoroscopy to address problems such as soft tissue contrast and exposed ionized radiation. In recent years, advances in imaging techniques and innovative procedures have increased interest in using MRI guidance for minimally invasive procedure. An increasing number of procedures have been carried out on animals and quite a few studies have been conducted on humans. However, to accomplish a complete transition of MRI-guided therapies and treatments from animal experiments to clinic applications, some challenges need to be overcome. Chief among them is the fact that MRI-guided interventional procedures remain limited by a lack of availability of MR-compatible interventional instruments. In this study, the main goal is to close the gap between investigational studies in animal and clinical applications. First, an MRI-compatible active guidewire for a clinical application was designed and tested. A 0.035$''$ (128cm in length) active guidewire for MRI right and left heart catheterization at 1.5 T was manufactured in an ISO class 7 cleanroom. The design involved an internal fiberoptic temperature probe to monitor real-time temperature increases at the hottest spot of the guidewire to ensure patient safety during MRI scan. A solenoid coil at the distal end of the guidewire was also attached to change the current distribution of the guidewire and to create a conspicuous tip signal. Visualization of the exact location of the guidewire tip enhanced the safety and effectiveness of the right and left heart catheterization. And the mechanical requirements of the guidewire for right and left heart catheterization were met by using a taper nitinol wire as a core structure and thermoplastic elastomer material to support the entire structure. Second, the safety and effectiveness of the guidewire were evaluated through bench-top tests. The mechanical characteristics of the guidewire were compared to those of commercial counterparts. The guidewire design was modified until the mechanical requirements were met. The signal-to-noise ratio and imaging artifact were measured to evaluate the visibility of the guidewire. And a comprehensive in vitro heating test was conducted in an acrylic box filled with gel simulating human tissue conductivity. The longitudinal heating profile of the whole guidewire was acquired during these tests. In addition, the electrical safety of the guidewire was addressed by designing a leakage current blocking circuit to limit the leakage current. The preclinical in vivo studies were designed and conducted in swine animal models to assess the feasibility of the guidewire during right and left heart catheterization. The studies complied with Good Laboratory Practice (GLP) standards. The guidewire was navigated through the vascular structure and chamber of the heart and used to support the diagnostic catheter. Extensive heating tests were performed to evaluate the heating risk of the guidewire. It was determined that guidewire visualization and mechanical properties were sufficient to complete all the steps during the procedures. Finally, a proportional-integral-derivative (PID) controller was implemented to control the scan parameters during the MRI-guided procedure to ensure patient safety. The main aim was to reduce RF induced heating by dynamically adjusting the flip angle based on real- time temperature values coming from the guidewire shaft.