Xin Chen1, Michael Steckner1
1Toshiba Medical Research
Institute USA, Inc.,
While SAR is crucial for the RF safety control of an MR scan, B1rms (root mean square of the total B1 field ) serves as a supplemental safety metric. For example, B1rms is useful for defining the MR conditional labeling of implants. An unloaded quadrature driven (QD) birdcage coil generates nearly perfect B1 with circular polarization: B1+ (the tipping component) is homogeneous and B1- (the component rotating counter to the spin precession) is zero and thus |B1-|<<|B1+| is usually assumed. Loading the coil distorts the B1 field, causing B1+ and B1- components. While only B1+ is useful for MRI purposes, both components contribute to RF power deposition. In this work we use FDTD (Finite Difference Time Domain) numerical simulations to demonstrate that B1- should not be ignored in loaded coils at either 1.5T or 3T.