Ozgur Kocaturk

Segmented nitinol guidewires with stiffness-matched connectors for cardiovascular magnetic resonance catheterization: preserved mechanical performance and freedom from heating

BackgroundConventional guidewires are not suitable for use during cardiovascular magnetic resonance (CMR) catheterization. They employ metallic shafts for mechanical performance, but which are conductors subject to radiofrequency (RF) induced heating. To date, non-metallic CMR guidewire designs have provided inadequate mechanical support, trackability, and torquability. We propose a metallic guidewire for CMR that is by design intrinsically safe and that retains mechanical performance of commercial guidewires.MethodsThe NHLBI passive guidewire is a 0.035” CMR-safe, segmented-core nitinol device constructed using short nitinol rod segments. The electrical length of each segment is less than one-quarter wavelength at 1.5 Tesla, which eliminates standing wave formation, and which therefore eliminates RF heating along the shaft. Each of the electrically insulated segments is connected with nitinol tubes for stiffness matching to assure uniform flexion. Iron oxide markers on the distal shaft impart conspicuity.Mechanical integrity was tested according to International Organization for Standardization (ISO) standards. CMR RF heating safety was tested in vitro in a phantom according to American Society for Testing and Materials (ASTM) F-2182 standard, and in vivo in seven swine. Results were compared with a high-performance commercial nitinol guidewire.ResultsThe NHLBI passive guidewire exhibited similar mechanical behavior to the commercial comparator. RF heating was reduced from 13 °C in the commercial guidewire to 1.2 °C in the NHLBI passive guidewire in vitro, using a flip angle of 75°. The maximum temperature increase was 1.1u2009±u20090.3 °C in vivo, using a flip angle of 45°. The guidewire was conspicuous during left heart catheterization in swine.ConclusionsWe describe a simple and intrinsically safe design of a metallic guidewire for CMR cardiovascular catheterization. The guidewire exhibits negligible heating at high flip angles in conformance with regulatory guidelines, yet mechanically resembles a high-performance commercial guidewire. Iron oxide markers along the length of the guidewire impart passive visibility during real-time CMR. Clinical translation is imminent.

A NOVEL ACTIVE DEVICE FABRICATION METHOD FORINTERVENTIONAL MRI PROCEDURES

Magnetic Resonance Imaging (MRI) is a promising candidate compare to X-Ray fluoroscopy for interventional cardiovascular procedures due to its ionizing radiation free mechanism and superior soft tissue contrast. However, Interventional MRI field lacks dedicated clinical grade MRI safe and visible devices. In this study, we designed and developed a Computer Numerical Control (CNC) based thin film conductive ink printing system for developing low profile “active” interventional devices for cardiovascular procedures under MRI. The proposed automated system allows forming three-dimensional receiver antenna configurations automatically onto non-planar surfaces. The developed system decreased the process time and increased reproducibility significantly compared to alternative lithography-based techniques also used for low profile active device development. The validation and calibration test results showed that the motion control system worked within a tolerance of 2 μm and the dispenser unit had more than 90% accuracy. As a part of this study, a loop RF antenna was designed and formed on an MRI-compatible needle using biocompatible heat shrink polymer. MRI visibility and RF induced heating tests were performed successfully for the prototype active needle. An identical active needle was fabricated using conventional methods to compare the overall device profile and MRI visibility performance.

Erratum to: Thin film based semi-active resonant marker design for low profile interventional cardiovascular MRI devices

Objectives nA new microfabrication method to produce low profile radio frequency (RF) resonant markers on catheter shafts was developed. A semi-active RF resonant marker incorporating a solenoid and a plate capacitor was constructed on the distal shaft of a 5 Fr guiding catheter. The resulting device can be used for interventional cardiovascular MRI procedures.

Lithography based resonant marker design for MRI catheter visualization

Background The unavailability of safe, conspicuous devices remains the chief barrier to wider clinical adoption of interventional cardiovascular magnetic resonance imaging. Active catheter receiver coils are conspicuous but their metallic transmission lines risk heating and their manufacture requires excessive device size. We have designed a clinical grade 5 Fr radio frequency (RF) resonator marker embedded directly into the catheter shaft using novel lithography techniques. We developed special manufacturing techniques to impart these circuits onto non-planar catheter surfaces. This approach eliminates (1) the bulky circuit components such as wire-wound coils and rigid capacitors as well as (2) long conductive cables, required for receiver coil-based visualization, that are subject to heating.