title: Radiofrequency heating at 9.4T: in vivo temperature measurement results in swine.
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.
authors.affiliation: Center for Magnetic Resonance Research, Univesity of Minnesota, Minneapolis, Minnesota 55455, USA. dev@cmrr.umn.edu
authors.forename: Devashish
authors.initials: D
authors.lastname: Shrivastava
authors.forename: Timothy
authors.initials: T
authors.lastname: Hanson
authors.forename: Robert
authors.initials: R
authors.lastname: Schlentz
authors.forename: William
authors.initials: W
authors.lastname: Gallaghar
authors.forename: Carl
authors.initials: C
authors.lastname: Snyder
authors.forename: Lance
authors.initials: L
authors.lastname: Delabarre
authors.forename: Surya
authors.initials: S
authors.lastname: Prakash
authors.forename: Paul
authors.initials: P
authors.lastname: Iaizzo
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Vaughan
mesh_terms: D000818:Animals; D001831:Body Temperature; D001921:Brain; D006257:Head; D006358:Hot Temperature; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D011846:Radio Waves; D013552:Swine