title: Interventional device visualization with toroidal transceiver and optically coupled current sensor for radiofrequency safety monitoring.
abstract: OBJECTIVE
  The development of catheters and guidewires that are safe from radiofrequency (RF) -induced heating and clearly visible against background tissue is a major challenge in interventional MRI. An interventional imaging approach using a toroidal transmit-receive (transceive) coil is presented. This toroidal transceiver allows controlled, low levels of RF current to flow in the catheter/guidewire for visualization, and can be used with conductive interventional devices that have a localized low-impedance tip contact.
  
  
  METHODS
  Toroidal transceivers were built, and phantom experiments were performed to quantify transmit power levels required for device visibility and to detect heating hazards. Imaging experiments in a pig cadaver tested the extendibility to higher field strength and nonphantom settings. A photonically powered optically coupled toroidal current sensor for monitoring induced RF currents was built, calibrated, and tested using an independent image-based current estimation method.
  
  
  RESULTS
  Results indicate that high signal-to-noise ratio visualization is achievable using milliwatts of transmit power-power levels orders of magnitude lower than levels that induce measurable heating in phantom tests. Agreement between image-based current estimates and RF current sensor measurements validates sensor accuracy.
  
  
  CONCLUSIONS
  The toroidal transceiver, integrated with power and current sensing, could offer a promising platform for safe and effective interventional device visualization.
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Maryam
authors.initials: M
authors.lastname: Etezadi-Amoli
authors.forename: Pascal
authors.initials: P
authors.lastname: Stang
authors.forename: Adam
authors.initials: A
authors.lastname: Kerr
authors.forename: John
authors.initials: J
authors.lastname: Pauly
authors.forename: Greig
authors.initials: G
authors.lastname: Scott
mesh_terms: D002058:Burns, Electric / Q000209:etiology / Q000517:prevention & control*; D057785:Catheters; D004867:Equipment Design; D019544:Equipment Failure Analysis; D004869:Equipment Safety / Q000295:instrumentation*; D057918:Fiducial Markers; D006801:Humans; D053783:Magnetic Resonance Imaging, Interventional / Q000009:adverse effects / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011846:Radio Waves / Q000009:adverse effects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013817:Thermography / Q000295:instrumentation
keywords: RF current sensor; RF heating; RF safety; device visualization; interventional MRI; parallel transmit