ABSTRACT
This chapter explores both analytical and numerical methods to study the radiofrequency (RF) field in biological objects related to magnetic resonance imaging applications. The analytical method is for simple models, which is used to validate numerical methods. The numerical methods include the finite difference, finite element, finite-difference time-domain, and moment methods. The method of moments (MoM) is one of the popular methods for the computation of electromagnetic fields in arbitrarily-shaped, inhomogeneous dielectric bodies. The chapter explains the finite-difference time-domain (FDTD) algorithm to analyze the specific absorption rate and field inside the human head generated by a shielded, quadrature birdcage coil. An integro-differential equation is first formulated in terms of volumetric equivalent current that accounts for the effect of the permittivity and conductivity of an inhomogeneous body. The electric currents in the birdcage coil are calculated using the MoM described in the preceding chapter and are used as the excitation in the FDTD calculations.
