title: The evaluation of steerable ultrasonic catheters for minimally invasive MRI-guided cardiac ablation.
abstract: OBJECTIVE
  The purpose of this study was to develop steerable MR-compatible ultrasound catheters suitable for minimally invasive MRI-guided cardiac ablation therapies.
  
  
  METHODS
  MRI-compatible ultrasound steerable catheters were developed and tested for their overall tissue heating performance and safety. Ultrasound transducers were mounted on a monodirectional deflectable catheter tip that was made to be MRI-compatible. Catheter safety was assessed on the potential to form hot spots at the distal end of the catheter throughout fast spin echo and thermometry scans. Heating experiments were performed on phantoms and ex vivo porcine cardiac samples.
  
  
  RESULTS
  During catheter safety experiments, a maximum temperature increase of 11.35 ± 0.83°C was evident after a 12-min, 40-s fast spin echo scan with a whole body specific absorption rate (SAR) of 1.9 W/kg and 1.07 ± 0.22°C during thermometry scans (flip angle = 90°; scan time = 12 min, 41 s; whole body SAR = 0.34 W/kg). Temperature elevations induced by the sonication were shown to be on the order of 38.1 ± 5.2°C for phantom experiments and 49.3 ± 9.7°C for ex vivo cardiac samples.
  
  
  CONCLUSIONS
  Steerable ultrasound catheters have the potential to be safely placed in an MR system with little concern of catheter self-heating and driven to heat surrounding structures to cause ablations. In addition, these catheters have the added benefit of a deflectable tip that allows the treatment of multiple targets from within the bore of the MR scanner.
authors.affiliation: Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Toronto, Canada.
authors.forename: Mathew
authors.initials: M
authors.lastname: Carias
authors.forename: Kullervo
authors.initials: K
authors.lastname: Hynynen
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000502:physiology; D062906:Cardiac Catheters; D013504:Cardiovascular Surgical Procedures / Q000295:instrumentation*; D017115:Catheter Ablation / Q000295:instrumentation*; D019160:Endosonography / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006321:Heart / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*; D013552:Swine
keywords: cardiac ablation; interventional MRI; steerable catheters; thermometry; ultrasonic catheters