Premium
Radiofrequency heating at 9.4T: In vivo temperature measurement results in swine
Author(s) -
Shrivastava Devashish,
Hanson Timothy,
Schlentz Robert,
Gallaghar William,
Snyder Carl,
DelaBarre Lance,
Prakash Surya,
Iaizzo Paul,
Vaughan J. Thomas
Publication year - 2008
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21425
Subject(s) - specific absorption rate , rectal temperature , in vivo , nuclear magnetic resonance , skin temperature , radiofrequency coil , materials science , nuclear medicine , dielectric heating , chemistry , biomedical engineering , electromagnetic coil , physics , medicine , optoelectronics , anesthesia , biology , telecommunications , microbiology and biotechnology , quantum mechanics , computer science , antenna (radio) , dielectric
In vivo temperatures were correlated to the whole head average specific absorption rate (SAR avg ) at 9.4T using 12 anesthetized swine (mean animal weight = 52 kg, standard deviation = 6.7 kg). Correlating the temperatures and SAR avg is necessary to ensure safe levels of human heating during ultra‐high field MR exams. The temperatures were measured at three depths inside the brain, in the rectum, and at the head‐skin of swine. A 400 MHz, continuous wave RF power was deposited to the head using a volume coil. The SAR avg values were varied between 2.7–5.8 W/kg. The RF power exposure durations were varied between 1.4–3.7 hr. To differentiate the temperature response caused by the RF from that of the anesthesia, the temperatures were recorded in four unheated swine. To study the effect of the spatial distribution of the RF and tissue properties, the temperature probes were placed at two brain locations ( n = 4 swine for each location). Results showed that the in vivo brain temperatures correlated to the SAR avg in a geometry‐dependent manner. Additionally, 1) the skin temperature change was not the maximum temperature change; 2) the RF heating caused an inhomogeneous brain temperature distribution; and 3) the maximum temperature occurred inside the brain. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.