MR safety and in vivo thermal characterization of an RF coil at 9.4T

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

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Correlating In vivo temperatures to the radio-frequency (RF) coil induced total RF power is necessary to ensure human safety in an ultra high field magnetic resonance (MR) application. Thus to ensure human safety in an ultra high field MR head imaging experiment, temperatures were measured as a function of time in the brain and surrounding cutaneous layer of twelve human sized, anesthetized swine (mean animal weight=52kg, SD=±6.7kg). In vivo temperatures were correlated to the RF power by developing coil and geometry specific normalized temperatures such that the RF coil induced cranial temperature change could be obtained during an MR exam by measuring only the whole head average specific absorption rate (ASAR) and the duration of the RF deposition. Thus, the feasibility of the thermal characterization of an RF volume head coil was shown. More specifically, a continuous wave (CW) RF was deposited in porcine cranium using a four loop RF head coil at 400 MHz (proton larmor frequency at 9.4T). Temperatures were recorded continuously using an inline probe placed at a predetermined location of 15mm inside the brain and a separate probe in the cutaneous layer. To differentiate the temperature response caused by the RF from that of anesthesia, the temperatures were recorded in four unheated, anesthetized swine for the complete duration of experiments (∼8hours). To study the effect of the spatial distribution of the RF as well as the tissue thermal/electrical properties and blood perfusion, the inline temperature probe was placed at two locations (N = 4 for each location). Results showed that the thermal characterization of an RF coil was possible such that the normalized temperature maps when multiplied by the ASAR and the RF heating time would predict In vivo temperature change during heating. Further, it was shown that at 9.4 T 1) the RF heating caused an inhomogeneous normalized temperature distribution in the brain; and 2) the skin temperature change was an unreliable parameter to assess In vivo temperature change.

Original languageEnglish (US)
Title of host publicationProceedings of the ASME Summer Bioengineering Conference 2007, SBC 2007
PublisherAmerican Society of Mechanical Engineers(ASME)
Pages699-700
Number of pages2
ISBN (Print)0791847985, 9780791847985
DOIs
StatePublished - 2007
Event2007 ASME Summer Bioengineering Conference, SBC 2007 - Keystone, CO, United States
Duration: Jun 20 2007Jun 24 2007

Publication series

NameProceedings of the ASME Summer Bioengineering Conference 2007, SBC 2007

Other

Other2007 ASME Summer Bioengineering Conference, SBC 2007
CountryUnited States
CityKeystone, CO
Period6/20/076/24/07

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