title: Specific absorption rate benefits of including measured electric field interactions in parallel excitation pulse design.
abstract: Specific absorption rate management and excitation fidelity are key aspects of radiofrequency pulse design for parallel transmission at ultra-high magnetic field strength. The design of radiofrequency pulses for multiple channels is often based on the solution of regularized least-squares optimization problems for which a regularization term is typically selected to control the integrated or peak pulse waveform amplitude. Unlike single-channel transmission, the specific absorption rate of parallel transmission is significantly influenced by interferences between the electric fields associated with the individual transmission elements, which a conventional regularization term does not take into account. This work explores the effects upon specific absorption rate of incorporating experimentally measurable electric field interactions into parallel transmission pulse design. Results of numerical simulations and phantom experiments show that the global specific absorption rate during parallel transmission decreases when electric field interactions are incorporated into pulse design optimization. The results also show that knowledge of electric field interactions enables robust prediction of the net power delivered to the sample or subject by parallel radiofrequency pulses before they are played out on a scanner.
authors.affiliation: Center for Biomedical Imaging, Department of Radiology, New York University, School of Medicine, New York, New York, USA. cemmurat.deniz@nyumc.org
authors.forename: Cem Murat
authors.initials: CM
authors.lastname: Deniz
authors.forename: Leeor
authors.initials: L
authors.lastname: Alon
authors.forename: Ryan
authors.initials: R
authors.lastname: Brown
authors.forename: Daniel K
authors.initials: DK
authors.lastname: Sodickson
authors.forename: Yudong
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D000042:Absorption; D000465:Algorithms; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D051598:Whole Body Imaging / Q000379:methods*