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8.0‐Tesla human MR system: Temperature changes associated with radiofrequency‐induced heating of a head phantom
Author(s) -
Kangarlu Allahyar,
Shellock Frank G.,
Chakeres Donald W.
Publication year - 2003
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.10236
Subject(s) - imaging phantom , specific absorption rate , radio frequency , human head , materials science , dielectric heating , nuclear magnetic resonance , head (geology) , magnetic resonance imaging , absorption (acoustics) , biomedical engineering , nuclear medicine , physics , optics , medicine , optoelectronics , radiology , dielectric , antenna (radio) , computer science , telecommunications , geomorphology , geology , composite material
Purpose To investigate if the heat induced in biological tissues by typical radio frequency (RF) energy associated with an 8.0‐Tesla magnetic resonance (MR) system causes excessive temperature changes. Materials and Methods Fluoroptic thermometry was used to measure temperatures in multiple positions in a head phantom made of ground turkey breast. A series of experiments were conducted with measurements obtained at RF power levels ranging from a specific absorption rate (SAR) of up to 4.0 W/kg for 10 minutes. Results The highest temperature increases were up to 0.7°C. An inhomogeneous heating pattern was observed. In general, the deep regions within the phantom registered higher temperature increases compared to the peripheral sites. Conclusion The expectation of an inhomogeneous RF distribution in ultra high field systems (> 4 T) was confirmed. At a frequency of 340 MHz and in‐tissue RF wave length of about 10 cm, the RF inhomogeneity was measured to create higher temperatures in deeper regions of a human head phantom compared to peripheral tissues. Our results agree with the computational electromagnetic calculations for such frequencies. Importantly, these experiments indicated that there were no regions of heating that exceeded the current FDA guidelines. J. Magn. Reson. Imaging 2003;17:220–226. © 2003 Wiley‐Liss, Inc.