Friday, 7 may 2010

Devashish Shrivastava¹, Timothy Hanson, Jeramy Kulesa, Jinfeng Tian², Gregor Adriany, John Thomas Vaughan

¹CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States; ²Univeristy of Minnesota, Minneapolis, MN, United States

In vivo radio-frequency (RF) heating was measured due to a 7T head coil in four anesthetized porcine models (N = 4). Temperatures were measured using fluoroptic probes in the scalp; 5 mm, 10 mm, 15 mm, and 20 mm in the brain; and rectum. Continuous wave, 296 MHz, RF power was delivered for ~3 hours using the head coil. The whole head average SAR was maintained close to 3 W/kg. Systemic, uniform heating up to ~1.85 °C was produced. No RF heating induced adverse thermo-physiologic temperature response was detected as measured by the difference in post-RF and pre-RF temperature slopes.

11:42 780. An Automated Method for Subject Specific Global SAR Prediction in Parallel Transmission

Leeor Alon^1,2, Cem Murat Deniz^1,2, Riccardo Lattanzi¹, Graham Wiggins¹, Ryan Brown¹, Daniel K. Sodickson^1,2, Yudong Zhu<sup>1

1</sup>Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, NYU School of Medicine, New York, NY, United States; ²Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, United States

Current SAR measurement schemes are missing the capability to track and manage SAR under in-vivo conditions. Existing hardware schemes monitor forward and reflective power in real time only, but offer no prediction capability and tend to considerably overestimate SAR by assuming complete constructive interference of electric fields. In this study, we present, and demonstrate in vivo, a rapid and simple calibration method for the accurate prediction of subject specific global power deposition on an 8-channel transmit 7T MR system. This global SAR prediction capability is scalable to parallel transmit systems with any number of transmit channels.

11:54 781. Real Time RF Monitoring in a 7T Parallel Transmit System

Borjan Aleksandar Gagoski¹, Rene Gumbrecht^1,2, Michael Hamm³, Kawin Setsompop^4,5, Boris Keil^4,5, Joonsung Lee¹, Khaldoun Makhoul^4,5, Azma Mareyam⁴, Kyoko Fujimoto⁴, Thomas Witzel^4,6, Ulrich Fontius⁷, Josef Pfeuffer³, Elfar Adalsteinsson^1,6, Lawrence L. Wald<sup>4,6

1</sup>Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States; ²Department of Physics, Friedrich-Alexander-University Erlangen, Erlangen, Germany; ³Siemens Healthcare, Charlestown, MA; ⁴A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States; ⁵Harvard Medical School, Boston, MA, United States; ⁶Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States; ⁷Siemens Healthcare, Erlangen, Germany

Current challenges to high-field applications of parallel RF transmission (pTx) in vivo include the monitoring and management of local SAR. We developed and tested real-time RF monitoring system for MAGNETOM 7T (Siemens Healthcare, Erlangen, Germany) with an 8-channel prototype pTx system that limits local SAR based on numerical simulation of E fields and power deposition in a segmented head model, and tracks and compares RF waveforms on each channel to the expected digital pulse waveform and shuts down the scan in the event of a mismatch due to spurious sources of pTx RF errors.

12:06 782. Effects of a High Static Magnetic Field on (Higher) Cognitive Functions