  Type U radio bursts are impulsive coherent radio emissions produced by the
Sun that indicate the presence of subrelativistic electron beams propagating
along magnetic loops in the solar corona. In this work, we present the analysis
of a type U radio burst that was exceptionally imaged on 2011 March 22 by the
Nan\c{c}ay Radioheliograph (NRH) at three different frequencies (298.7, 327.0,
and 360.8 MHz). Using a novel modelling approach, we show for the first time
that the use of high-resolution radio heliograph images of type U radio bursts
can be sufficient to both accurately reconstruct the 3D morphology of coronal
loops (without recurring to triangulation techniques) and to fully constrain
their physical parameters. At the same time, we can obtain unique information
on the dynamics of the accelerated electron beams, which provides important
clues as to the plasma mechanisms involved in their acceleration and as to why
type U radio bursts are not observed as frequently as type III radio bursts. We
finally present plausible explanations for a problematic aspect related to the
apparent lack of association between the modeled loop as inferred from radio
images and the extreme-ultraviolet (EUV) structures observed from space in the
same coronal region
