Probabilistic analysis of the specific absorption rate intersubject variability safety factor in parallel transmission MRI.
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.



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.



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.



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.
CEA, DRF, I2BM, NeuroSpin, Unirs, Gif sur Yvette, France.
Morgane
M
Le Garrec
CEA, DRF, I2BM, NeuroSpin, Unirs, Gif sur Yvette, France.
Vincent
V
Gras
CEA, DRF, I2BM, NeuroSpin, Unirs, Gif sur Yvette, France.
Marie-France
MF
Hang
CEA, DRF, Irfu, SACM, Unirs, Gif sur Yvette, France.
Guillaume
G
Ferrand
CEA, DRF, Irfu, SACM, Unirs, Gif sur Yvette, France.
Michel
M
Luong
CEA, DRF, I2BM, NeuroSpin, Unirs, Gif sur Yvette, France.
Nicolas
N
Boulant
D065966:Absorption, Physicochemical; D003198:Computer Simulation; D005260:Female; D020342:Finite Element Analysis; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015233:Models, Statistical
intersubject variability; parallel transmission; specific absorption rate