Radiofrequency heating at 9.4T: In vivo temperature measurement results in swine

Devashish Shrivastava, Timothy Hanson, Robert Schlentz, William Gallaghar, Carl Snyder, Lance DelaBarre, Surya Prakash, Paul Iaizzo, J. Thomas Vaughan

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

In vivo temperatures were correlated to the whole head average specific absorption rate (SARavg) at 9.4T using 12 anesthetized swine (mean animal weight = 52 kg, standard deviation = 6.7 kg). Correlating the temperatures and SARavg 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 SARavg 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 SARavg 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.

Original languageEnglish (US)
Pages (from-to)73-78
Number of pages6
JournalMagnetic resonance in medicine
Volume59
Issue number1
DOIs
StatePublished - Jan 2008

Keywords

  • Bioheat thermal model
  • High field MRI
  • RF heating
  • RF safety

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