TY - JOUR
T1 - From Complex B1 Mapping to Local SAR Estimation for Human Brain MR Imaging Using Multi-Channel Transceiver Coil at 7T
AU - Zhang, Xiaotong
AU - Schmitter, Sebastian
AU - Van De Moortele, Pierre Francois
AU - Liu, Jiaen
AU - He, Bin
PY - 2013
Y1 - 2013
N2 - 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.
AB - 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.
KW - B-mapping
KW - Electrical properties tomography (EPT)
KW - magnetic resonance imaging (MRI)
KW - parallel transmission
KW - specific absorption rate (SAR)
KW - ultra-high-field (UHF)
UR - http://www.scopus.com/inward/record.url?scp=84878613294&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84878613294&partnerID=8YFLogxK
U2 - 10.1109/TMI.2013.2251653
DO - 10.1109/TMI.2013.2251653
M3 - Article
C2 - 23508259
AN - SCOPUS:84878613294
SN - 0278-0062
VL - 32
SP - 1058
EP - 1067
JO - IEEE Transactions on Medical Imaging
JF - IEEE Transactions on Medical Imaging
IS - 6
M1 - 6477144
ER -