Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2008 Jan;59(1):73-8.
doi: 10.1002/mrm.21425.

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

Devashish Shrivastava  1 , Timothy Hanson, Robert Schlentz, William Gallaghar, Carl Snyder, Lance Delabarre, Surya Prakash, Paul Iaizzo, J Thomas Vaughan
Affiliations

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

Devashish Shrivastava et al. Magn Reson Med. 2008 Jan.

Abstract

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.

PubMed Disclaimer

Figures

FIG. 1
FIG. 1
Normalized temperature change vs. normalized RF heating duration at the depth of 10 mm for Location 1 with corresponding average parametric curve and 95% CI curves.
FIG. 2
FIG. 2
Normalized temperature change vs. normalized RF heating duration at the depth of 10 mm for Location 2 with corresponding average parametric curve and 95% CI curves.
FIG. 3
FIG. 3
Normalized temperature change vs. normalized RF heating duration at the head-skin with corresponding average parametric curve and 95% CI curves.
FIG. 4
FIG. 4
Normalized rectal temperature change vs. normalized RF heating duration with corresponding average parametric curve and 95% CI curves.
FIG. 5
FIG. 5
Average normalized parametric curves for the brain, rectum, and head-skin.
FIG. 6
FIG. 6
Temperatures in the brain and head-skin of an anesthetized, unheated animal.
FIG. 7
FIG. 7
Temperatures in the brain, rectum, and head-skin of an anesthetized, heated animal.
See this image and copyright information in PMC

References

    1. Vaughan JT, Garwood M, Collins CM, Liu W, DelaBarre L, Adriany G, Andersen P, Merkle H, Goebel R, Smith MB, Ugurbil K. 7T vs. 4T: RF power, homogeneity, and signal-to-noise comparison in head images. Magn Reson Med. 2001;46:24 –30. - PubMed
    1. Roschmann P. Radiofrequency penetration and absorption in the human body: limitations to high-field whole-body nuclear magnetic resonance imaging. Med Phys. 1987;14:922–931. - PubMed
    1. Jin J, Chen J. On the SAR and field inhomogeneity of birdcage coils loaded with the human head. Magn Reson Med. 1997;38:953–963. - PubMed
    1. Chen J, Feng Z, Jin JM. Numerical simulation of SAR and B1-field inhomogeneity of shielded RF coils loaded with the human head. IEEE Trans Biomed Eng. 1998;45:650 – 659. - PubMed
    1. Gandhi OP, Chen XB. Specific absorption rates and induced current densities for an anatomy-based model of the human for exposure to time-varying magnetic fields of MRI. Magn Reson Med. 1999;41:816 –823. - PubMed

Publication types