title: Influence of geometric and material properties on artifacts generated by interventional MRI devices: Relevance to PRF-shift thermometry.
abstract: OBJECTIVE
  Magnetic resonance imaging (MRI) is capable of providing valuable real-time feedback during medical procedures, partly due to the excellent soft-tissue contrast available. Several technical hurdles still exist to seamless integration of medical devices with MRI due to incompatibility of most conventional devices with this imaging modality. In this study, the effect of local perturbations in the magnetic field caused by the magnetization of medical devices was examined using finite element analysis modeling. As an example, the influence of the geometric and material characteristics of a transurethral high-intensity ultrasound applicator on temperature measurements using proton resonance frequency (PRF)-shift thermometry was investigated.
  
  
  METHODS
  The effect of local perturbations in the magnetic field, caused by the magnetization of medical device components, was examined using finite element analysis modeling. The thermometry artifact generated by a transurethral ultrasound applicator was simulated, and these results were validated against analytic models and scans of an applicator in a phantom. Several parameters were then varied to identify which most strongly impacted the level of simulated thermometry artifact, which varies as the applicator moves over the course of an ablative high-intensity ultrasound treatment.
  
  
  RESULTS
  Key design parameters identified as having a strong influence on the magnitude of thermometry artifact included the susceptibility of materials and their volume. The location of components was also important, particularly when positioned to maximize symmetry of the device. Finally, the location of component edges and the inclination of the device relative to the magnetic field were also found to be important factors.
  
  
  CONCLUSIONS
  Previous design strategies to minimize thermometry artifact were validated, and novel design strategies were identified that substantially reduce PRF-shift thermometry artifacts for a variety of device orientations. These new strategies are being incorporated into the next generation of applicators. The general strategy described in this study can be applied to the design of other interventional devices intended for use with MRI.
authors.affiliation: Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390.
authors.forename: Ken
authors.initials: K
authors.lastname: Tatebe
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Ramsay
authors.affiliation: Philips Healthcare, 281 Hillmount Road, Markham, Ontario L6C 2S3, Canada.
authors.forename: Charles
authors.initials: C
authors.lastname: Mougenot
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Kazem
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada.
authors.forename: Hamed
authors.initials: H
authors.lastname: Peikari
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada and Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, Ontario M5G2M9, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Bronskill
authors.affiliation: Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390; Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390; Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada; and Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, Ontario M5G2M9, Canada.
authors.forename: Rajiv
authors.initials: R
authors.lastname: Chopra
mesh_terms: D016477:Artifacts; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D062125:Thermometry / Q000295:instrumentation*