Heat equation inversion framework for average SAR calculation from magnetic resonance thermal imaging.

Deposition of radiofrequency (RF) energy can be quantified via electric field or temperature change measurements. Magnetic resonance imaging has been used as a tool to measure three dimensional small temperature changes associated with RF radiation exposure. When duration of RF exposure is long, conversion from temperature change to specific absorption rate (SAR) is nontrivial due to prominent heat-diffusion and conduction effects. In this work, we demonstrated a method for calculation of SAR via an inversion of the heat equation including heat-diffusion and conduction effects. This method utilizes high-resolution three dimensional magnetic resonance temperature images and measured thermal properties of the phantom to achieve accurate calculation of SAR. Accuracy of the proposed method was analyzed with respect to operating frequency of a dipole antenna and parameters used in heat equation inversion. Bioelectromagnetics. 37:493-503, 2016. © 2016 Wiley Periodicals, Inc.

[1]  Kim Butts Pauly,et al.  MR thermometry , 2008, Journal of magnetic resonance imaging : JMRI.

[2]  D. Lesnic,et al.  Determination of a spacewise dependent heat source , 2007 .

[3]  A. Sherry,et al.  TmDOTA-: a sensitive probe for MR thermometry in vivo. , 2001, Journal of magnetic resonance.

[4]  Fritz Schick,et al.  Accuracy of real-time MR temperature mapping in the brain: a comparison of fast sequences. , 2010, Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics.

[5]  Emmanuel J. Candès,et al.  Robust uncertainty principles: exact signal reconstruction from highly incomplete frequency information , 2004, IEEE Transactions on Information Theory.

[6]  W F Pickard,et al.  On the assumption of negligible heat diffusion during the thermal measurement of a nonuniform specific absorption rate. , 1999, Radiation research.

[7]  Leeor Alon,et al.  A method for safety testing of radiofrequency/microwave‐emitting devices using MRI , 2015, Magnetic Resonance in Medicine.

[8]  John C Gore,et al.  Measurement of heat transfer coefficients by nuclear magnetic resonance. , 2008, Magnetic resonance imaging.

[9]  L. Moeller,et al.  NMR imaging of cell phone radiation absorption in brain tissue , 2012, Proceedings of the National Academy of Sciences.

[10]  国際非電離放射線防護委員会.  ICNIRP statement on the "Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz)". , 2009, Health physics.

[11]  John C. Gore,et al.  Measurement of specific heat and specific absorption rate by nuclear magnetic resonance , 2010 .

[12]  Michael Lustig,et al.  Reweighted ℓ1 referenceless PRF shift thermometry , 2010, Magnetic resonance in medicine.

[13]  John C Gore,et al.  Measurement of thermal diffusivity by magnetic resonance imaging. , 2006, Magnetic resonance imaging.

[14]  Jinbo Liu,et al.  Determination of a source term in a heat equation , 2010, Int. J. Comput. Math..

[15]  K. Kuroda,et al.  A precise and fast temperature mapping using water proton chemical shift , 1995, Magnetic resonance in medicine.

[16]  M. N. Özişik,et al.  Finite Difference Methods in Heat Transfer , 2017 .

[17]  Yoshinobu Okano,et al.  Comparison Measurement for Specific Absorption Rate With Physically Different Procedure , 2012, IEEE Transactions on Instrumentation and Measurement.

[18]  Paul Tseng.  Further Results on Stable Recovery of Sparse Overcomplete Representations in the Presence of Noise , 2009, IEEE Transactions on Information Theory.

[19]  K. Uğurbil,et al.  Temperature and SAR calculations for a human head within volume and surface coils at 64 and 300 MHz , 2004, Journal of magnetic resonance imaging : JMRI.

[20]  Bu S. Park,et al.  Real Time MR Thermometry Using Tm-DOTMA , 2015 .

[21]  Niels Kuster,et al.  Automated E-field scanning system for dosimetric assessments , 1996 .

[22]  James C. Lin,et al.  SAR and temperature: Simulations and comparison to regulatory limits for MRI , 2007, Journal of magnetic resonance imaging : JMRI.

[23]  R. de Seze,et al.  Biological effects of amplitude-modulated radiofrequency radiation. , 1998, Scandinavian journal of work, environment & health.

[24]  Jing Yuan,et al.  Towards fast and accurate temperature mapping with proton resonance frequency-based MR thermometry. , 2012, Quantitative imaging in medicine and surgery.

[25]  John C. Gore,et al.  Simultaneous measurements of thermal conductivity, thermal diffusivity and specific heat by nuclear magnetic resonance imaging , 2011 .

[26]  R. Mallozzi,et al.  Radiofrequency power deposition utilizing thermal imaging , 2004, Magnetic resonance in medicine.

[27]  Chu-Li Fu,et al.  A computational method for identifying a spacewise‐dependent heat source , 2010 .