  In this paper we present full-wave signal models for magnetic and electric
field measurements in magnetic resonance imaging (MRI). Our analysis is based
on a scattering formalism in which the presence of an object or body is taken
into account via an electric scattering source. We show that these signal
models can be evaluated, provided the Green's tensors of the background field
are known along with the dielectric parameters of the object and the
magnetization within the excited part of the object. Furthermore, explicit
signal expressions are derived in case of a small homogeneous ball that is
embedded in free space and for which the quasi-static Born approximation can be
applied. The conductivity and permittivity of the ball appear as explicit
parameters in the resulting signal models and allow us to study the sensitivity
of the measured signals with respect to these dielectric parameters. Moreover,
for free induction decay signals we show that under certain conditions it is
possible to retrieve the dielectric parameters of the ball from
noise-contaminated induction decay signals that are based on electric or
magnetic field measurements.
