title: Segmented nitinol guidewires with stiffness-matched connectors for cardiovascular magnetic resonance catheterization: preserved mechanical performance and freedom from heating.
abstract: BACKGROUND
  Conventional 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.
  
  
  METHODS
  The 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.
  
  
  RESULTS
  The 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 1.1 ± 0.3 °C in vivo, using a flip angle of 45°. The guidewire was conspicuous during left heart catheterization in swine.
  
  
  CONCLUSIONS
  We 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.
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. burcu.basar@nih.gov.|Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey. burcu.basar@nih.gov.
authors.forename: Burcu
authors.initials: B
authors.lastname: Basar
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. toby.rogers@nih.gov.
authors.forename: Toby
authors.initials: T
authors.lastname: Rogers
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. ratnayakak@nhlbi.nih.gov.|Department of Cardiology, Children's National Medical Center, Washington DC, USA. ratnayakak@nhlbi.nih.gov.
authors.forename: Kanishka
authors.initials: K
authors.lastname: Ratnayaka
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. adrienne.campbell@nih.gov.
authors.forename: Adrienne E
authors.initials: AE
authors.lastname: Campbell-Washburn
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. mazaljr@nhlbi.nih.gov.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Mazal
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. schenkeb@nhlbi.nih.gov.
authors.forename: William H
authors.initials: WH
authors.lastname: Schenke
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. merdim.sonmez@nih.gov.
authors.forename: Merdim
authors.initials: M
authors.lastname: Sonmez
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. faranesa@nhlbi.nih.gov.
authors.forename: Anthony Z
authors.initials: AZ
authors.lastname: Faranesh
authors.affiliation: National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, Bethesda, MD, 20892-1538, USA. lederman@nih.gov.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lederman
authors.affiliation: Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey. kocaturko@nhlbi.nih.gov.
authors.forename: Ozgur
authors.initials: O
authors.lastname: Kocaturk
mesh_terms: D000497:Alloys / Q000737:chemistry*; D000818:Animals; D006328:Cardiac Catheterization / Q000295:instrumentation*; D062906:Cardiac Catheters; D004553:Electric Conductivity; D004867:Equipment Design; D004868:Equipment Failure; D005290:Ferric Compounds / Q000737:chemistry; D057918:Fiducial Markers; D006358:Hot Temperature; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D053783:Magnetic Resonance Imaging, Interventional / Q000295:instrumentation*; D008422:Materials Testing; D023421:Models, Animal; D019047:Phantoms, Imaging; D013552:Swine
chemical_list: D000497:Alloys; D005290:Ferric Compounds; C000499:ferric oxide; C013616:nitinol