title: From complex B(1) mapping to local SAR estimation for human brain MR imaging using multi-channel transceiver coil at 7T.
abstract: Elevated specific absorption rate (SAR) associated with increased main magnetic field strength remains a major safety concern in ultra-high-field (UHF) magnetic resonance imaging (MRI) applications. The calculation of local SAR requires the knowledge of the electric field induced by radio-frequency (RF) excitation, and the local electrical properties of tissues. Since electric field distribution cannot be directly mapped in conventional MR measurements, SAR estimation is usually performed using numerical model-based electromagnetic simulations which, however, are highly time consuming and cannot account for the specific anatomy and tissue properties of the subject undergoing a scan. In the present study, starting from the measurable RF magnetic fields (B1) in MRI, we conducted a series of mathematical deduction to estimate the local, voxel-wise and subject-specific SAR for each single coil element using a multi-channel transceiver array coil. We first evaluated the feasibility of this approach in numerical simulations including two different human head models. We further conducted experimental study in a physical phantom and in two human subjects at 7T using a multi-channel transceiver head coil. Accuracy of the results is discussed in the context of predicting local SAR in the human brain at UHF MRI using multi-channel RF transmission.
authors.forename: Xiaotong
authors.initials: X
authors.lastname: Zhang
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schmitter
authors.forename: Pierre-Francois
authors.initials: PF
authors.lastname: Van de Moortele
authors.forename: Jiaen
authors.initials: J
authors.lastname: Liu
authors.forename: Bin
authors.initials: B
authors.lastname: He
mesh_terms: D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000295:instrumentation* / Q000379:methods*; D003198:Computer Simulation; D006257:Head / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging; D012815:Signal Processing, Computer-Assisted; D014054:Tomography