title: RF Heating of MRI-Assisted Catheter Steering Coils for Interventional MRI.
abstract: OBJECTIVE
  The aim of this study was too assess magnetic resonance imaging (MRI) radiofrequency (RF)-related heating of conductive wire coils used in magnetically steerable endovascular catheters.
  
  
  METHODS
  A three-axis microcoil was fabricated onto a 1.8Fr catheter tip. In vitro testing was performed on a 1.5-T MRI system using an agarose gel-filled vessel phantom, a transmit-receive body RF coil, a steady-state free precession pulse sequence, and a fluoroptic thermometry system. Temperature was measured without simulated blood flow at varying distances from the magnet isocenter and at varying flip angles. Additional experiments were performed with laser-lithographed single-axis microcoil-tipped microcatheters in air and in a saline bath with varied grounding of the microcoil wires. Preliminary in vivo evaluation of RF heating was performed in pigs at 1.5 T with coil-tipped catheters in various positions in the common carotid arteries with steady-state free precession pulse sequence on and off and under physiologic-flow and zero-flow conditions.
  
  
  RESULTS
  In tissue-mimicking agarose gel, RF heating resulted in a maximal temperature increase of 0.35°C after 15 minutes of imaging, 15 cm from the magnet isocenter. For a single-axis microcoil, maximal temperature increases were 0.73°C to 1.91°C in air and 0.45°C to 0.55°C in saline. In vivo, delayed contrast-enhanced MRI revealed no evidence of vascular injury, and histopathologic sections from the common carotid arteries confirmed the lack of vascular damage.
  
  
  CONCLUSIONS
  Microcatheter tip microcoils for endovascular catheter steering in MRI experience minimal RF heating under the conditions tested. These data provide the basis for further in vivo testing of this promising technology for endovascular interventional MRI.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Avenue, L-352, San Francisco, CA 94143-0628, USA.
authors.forename: Fabio
authors.initials: F
authors.lastname: Settecase
authors.forename: Steven W
authors.initials: SW
authors.lastname: Hetts
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Martin
authors.forename: Timothy P L
authors.initials: TP
authors.lastname: Roberts
authors.forename: Anthony F
authors.initials: AF
authors.lastname: Bernhardt
authors.forename: Lee
authors.initials: L
authors.lastname: Evans
authors.forename: Vincent
authors.initials: V
authors.lastname: Malba
authors.forename: Maythem
authors.initials: M
authors.lastname: Saeed
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Arenson
authors.forename: Walter
authors.initials: W
authors.lastname: Kucharzyk
authors.forename: Mark W
authors.initials: MW
authors.lastname: Wilson
mesh_terms: D002058:Burns, Electric / Q000209:etiology / Q000517:prevention & control; D002406:Catheterization, Peripheral / Q000009:adverse effects / Q000295:instrumentation*; D057785:Catheters; D017097:Electric Impedance; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D006801:Humans; D053783:Magnetic Resonance Imaging, Interventional / Q000009:adverse effects / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D011846:Radio Waves; D025321:Surgery, Computer-Assisted / Q000009:adverse effects / Q000295:instrumentation*