• Tamer S Ibrahim and Lin Tang.
• Department of Radiology, University of Pittsburgh, B800 Presbyterian University Hospital, 200 Lothrop Street, Pittsburgh, PA 15213, USA. tsi2@pitt.edu
• J Magn Reson Imaging. 2007 Jun 1; 25 (6): 1235-47.

PurposeTo study the dependence of radiofrequency (RF) power deposition on B(0) field strength for different loads and excitation mechanisms.Material And MethodsStudies were performed utilizing a finite difference time domain (FDTD) model that treats the transmit array and the load as a single system. Since it was possible to achieve homogenous excitations across the human head model by varying the amplitudes/phases of the voltages driving the transmit array, studies of the RF power/B(0) field strength (frequency) dependence were achievable under well-defined/fixed/homogenous RF excitation.ResultsAnalysis illustrating the regime in which the RF power is dependent on the square of the operating frequency is presented. Detailed studies focusing on the RF power requirements as a function of number of excitation ports, driving mechanism, and orientations/positioning within the load are presented.ConclusionWith variable phase/amplitude excitation, as a function of frequency, the peak-then-decrease relation observed in the upper axial slices of brain with quadrature excitation becomes more evident in the lower slices as well. Additionally, homogeneity optimization targeted at minimizing the ratio of maximum/minimum B(1) (+) field intensity within the region of interest, typically results in increased RF power requirements (standard deviation was not considered in this study). Increasing the number of excitation ports, however, can result in significant RF power reduction.(c) 2007 Wiley-Liss, Inc.

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