Numerical simulation of SAR and B1-field inhomogeneity of shielded RF coils loaded with the human head.

The finite-difference time-domain (FDTD) method is combined with the method of moments (MoM) to compute the electromagnetic fields of shielded radio-frequency (RF) coils loaded with an anatomically accurate model of a human head for high-frequency magnetic resonance imaging (MRI) applications. The combined method can predict both the specific energy absorption rate (SAR) and the magnetic field (known as the B1 field) excited by any RF coils. Results for SAR and B1 field distribution, excited by shielded and end-capped birdcage coils, are calculated at 64, 128, 171, and 256 MHz. The results show that the value of SAR increases when the frequency of the B1 field increases and the B1 field exhibits a strong inhomogeneity at high frequencies.