An inverse methodology for high frequency RF head coil design with preemphasized B1 field in MRI

An inverse methodology to assist in the design of radio-frequency (RF) head coils for high field MRI application is described in this work. Free space time-harmonic electromagnetic Green´s functions and preemphasized B₁ field are used to calculate the current density on the coil cylinder. With B₁ field preemphasized and lowered in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the EM field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T is calculated using inverse methodology with preemphasized B₁ fields. FDTD is employed to calculate B₁ field and signal intensity inside a homogenous cylindrical phantom and human head. A comparison with conventional RF birdcage coil is reported here and demonstrated that inverse-method designed coil with preemphasized B₁ field can help in decreasing the notorious bright region caused by EM field/tissue interactions in the human head images at 4 T.