Evaluation of radiofrequency safety by high temperature resolution MR thermometry using a paramagnetic lanthanide complex.
PURPOSE
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.


CONCLUSION
A novel method with high temperature sensitivity is proposed as a tool to evaluate radiofrequency safety in MRI.
['Dharmadhikari|Shalmali|S|http://orcid.org/0000-0001-6225-2172', 'James|Judy R|JR|', 'Nyenhuis|John|J|', 'Bansal|Navin|N|']
D002138:Calibration D002151:Calorimetry D003198:Computer Simulation D004867:Equipment Design D006801:Humans D006979:Hyperthermia, Induced D007091:Image Processing, Computer-Assisted D021621:Imaging, Three-Dimensional D028581:Lanthanoid Series Elements D008279:Magnetic Resonance Imaging D010080:Oxazoles D011744:Pyrimidinones D011846:Radio Waves D013696:Temperature D013817:Thermography
MR thermometry paramagnetic lanthanide complex specific absorption rate (SAR) RF heating