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Updated: May 13, 2026

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Published on: May 1, 2018
Iterative separation of transmit and receive phase contributions and B1(+)-based estimation of the specific
Stefanie Buchenau1, Martin Haas, Daniel Nicolas Splitthoff
1Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany, stefanie.buchenau@uniklinik-freiburg.de.
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.
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