OBJECT: The specific absorption rate (SAR) can be determined from radiofrequency transmit fields measured via magnetic resonance imaging. MATERIALS AND METHODS: The proposed method estimates the SAR solely from the complex transmit field (B1(+)) by taking into account the particular properties of the electromagnetic field generated by an 8-channel transmit array. It is further based on an iterative consistency check between the measured B1(+) magnitude and an appropriate field estimate fulfilling Maxwell's equations. For testing the method, simulations and phantom experiments were performed for a multi-transmit array at 3T using a cylindrical phantom. RESULTS: The method's robustness with respect to the assumptions made about electric tissue properties as well as its stability under different initial conditions regarding the signal phase was shown. A high sensitivity to signal noise was found. Robust reconstruction results were achieved including information from more than two transmit elements. The validity of the experimental results was confirmed by a qualitative comparison to simulated electromagnetic fields. CONCLUSIONS: The method allows the determination of the SAR as well as the transmit phase of the individual channels of a multi-transmit array. With additional B0 inhomogeneity measurements, a reconstruction of the receive phase is feasible independent of the receive coil type in use.
OBJECT: The specific absorption rate (SAR) can be determined from radiofrequency transmit fields measured via magnetic resonance imaging. MATERIALS AND METHODS: The proposed method estimates the SAR solely from the complex transmit field (B1(+)) by taking into account the particular properties of the electromagnetic field generated by an 8-channel transmit array. It is further based on an iterative consistency check between the measured B1(+) magnitude and an appropriate field estimate fulfilling Maxwell's equations. For testing the method, simulations and phantom experiments were performed for a multi-transmit array at 3T using a cylindrical phantom. RESULTS: The method's robustness with respect to the assumptions made about electric tissue properties as well as its stability under different initial conditions regarding the signal phase was shown. A high sensitivity to signal noise was found. Robust reconstruction results were achieved including information from more than two transmit elements. The validity of the experimental results was confirmed by a qualitative comparison to simulated electromagnetic fields. CONCLUSIONS: The method allows the determination of the SAR as well as the transmit phase of the individual channels of a multi-transmit array. With additional B0 inhomogeneity measurements, a reconstruction of the receive phase is feasible independent of the receive coil type in use.
Authors: Ulrich Katscher; Tobias Voigt; Christian Findeklee; Peter Vernickel; Kay Nehrke; Olaf Dössel Journal: IEEE Trans Med Imaging Date: 2009-04-14 Impact factor: 10.048
Authors: Janot P Tokaya; Alexander J E Raaijmakers; Peter R Luijten; Cornelis A T van den Berg Journal: Magn Reson Med Date: 2018-04-24 Impact factor: 4.668
Authors: Janot P Tokaya; Alexander J E Raaijmakers; Peter R Luijten; Alessandro Sbrizzi; Cornelis A T van den Berg Journal: Magn Reson Med Date: 2019-10-21 Impact factor: 4.668