title: Evaluation of radiofrequency safety by high temperature resolution MR thermometry using a paramagnetic lanthanide complex.
abstract: OBJECTIVE
  The current practice of calculating the specific absorption rate (SAR) relies on local temperature measurements made using temperature probes. For an accurate SAR measurement, a temperature imaging method that provides high temperature sensitivity is desirable, because acceptable levels of SAR produce small temperature changes. MR thermometry using paramagnetic lanthanide complexes can be used to obtain absolute temperature measurements with sub-degree temperature and sub-millimeter spatial resolution. The aim of this study was to develop and evaluate a high temperature resolution MR technique to determine SAR.
  
  
  METHODS
  MR thermometry using a paramagnetic lanthanide complex thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene phosphonate) (TmDOTP(5-)), which has an almost 10(2) times stronger chemical shift temperature dependence than water, was used to develop a novel method for SAR measurement. Three-dimensional temperature and SAR images were calculated using MR images acquired with a conventional gradient recalled echo sequence and SAR-intensive T1ρ sequence. Effects of the presence of conducting wire and increasing T1ρ spin-lock pulse duration were also examined.
  
  
  RESULTS
  SAR distribution could be visualized clearly and surges associated with conducting wires and increasing pulse duration were identified clearly in the computed high spatial resolution SAR images.
  
  
  CONCLUSIONS
  A novel method with high temperature sensitivity is proposed as a tool to evaluate radiofrequency safety in MRI.
authors.affiliation: School of Health Sciences, Purdue University, West Lafayette, Indiana, USA.|Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Shalmali
authors.identifier: http://orcid.org/0000-0001-6225-2172
authors.initials: S
authors.lastname: Dharmadhikari
authors.affiliation: Department of Radiology, Mayo Clinic, Scottsdale, Arizona, USA.
authors.forename: Judy R
authors.initials: JR
authors.lastname: James
authors.affiliation: Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, USA.
authors.forename: John
authors.initials: J
authors.lastname: Nyenhuis
authors.affiliation: Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Navin
authors.initials: N
authors.lastname: Bansal
mesh_terms: D002138:Calibration; D002151:Calorimetry / Q000379:methods; D003198:Computer Simulation; D004867:Equipment Design; D006801:Humans; D006979:Hyperthermia, Induced; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008279:Magnetic Resonance Imaging; D010080:Oxazoles / Q000737:chemistry; D011744:Pyrimidinones / Q000737:chemistry; D011846:Radio Waves; D013696:Temperature; D013817:Thermography / Q000379:methods
chemical_list: D028581:Lanthanoid Series Elements; D010080:Oxazoles; D011744:Pyrimidinones; C063359:2,3-dihydro-5H-oxazolo(3,2-a)thieno(3,2-d)pyrimidin-5-one
keywords: MR thermometry; RF heating; paramagnetic lanthanide complex; specific absorption rate (SAR)