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Probabilistic analysis of the specific absorption rate intersubject variability safety factor in parallel transmission MRI
Author(s) -
Garrec Morgane,
Gras Vincent,
Hang MarieFrance,
Ferrand Guillaume,
Luong Michel,
Boulant Nicolas
Publication year - 2017
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26468
Subject(s) - specific absorption rate , monte carlo method , probabilistic logic , population , magnetic resonance imaging , computer science , statistics , mathematics , algorithm , physics , telecommunications , radiology , medicine , environmental health , antenna (radio)
Purpose Specific absorption rate (SAR) calculations in parallel transmission are commonly performed by using electromagnetic simulations on generic models. In this study, we propose a probabilistic analysis to study the safety factor employed to account for SAR intersubject variability versus risk relationship in head imaging at 7T. Methods Thirty‐three finite‐element electromagnetic simulations were conducted to sample the four‐dimensional parameter space consisting of the head length, head breadth, and shifts in Z and Y random variables. Based on the SAR matrices for each configuration, a multivariate second‐order polynomial of the SAR versus the different parameters was reconstructed for different types of radiofrequency pulses. A Monte Carlo calculation was then performed to compute the probability of occurrence of a given SAR value. Results By testing a large number of radiofrequency excitation pulses, the SAR calculated for the average model amplified by a safety margin of 1.5 was found to return a probability of less than 1% to be exceeded across the adult Caucasian population given the investigated parameters. Conclusion The proposed method to study SAR intersubject variability uses a reasonable number of electromagnetic simulations. Look‐ahead SAR safety margins can be deduced based on risk/benefit ratio assessments. Magn Reson Med 78:1217–1223, 2017. © 2016 International Society for Magnetic Resonance in Medicine.