  Waveguides have been successfully used to generate magnetic resonance images
at 7 T with whole-body systems. The bore limits the magnetic resonance signal
transmitted because its specific cut-off frequency is greater than the majority
of resonant frequencies. This restriction can be overcome by using a
parallel-plate waveguide whose cut-off frequency is zero for the transversal
electric modes and it can propagate any frequency. To investigate the potential
benefits for whole-body imaging at 3 T, we compare numerical simulations at 1.5
T, 3 T, 7 T, and 9 T via the propagation of the parallel-plate waveguide
principal mode filled with a cylindrical phantom and two surface coils. B1
mapping was computed to investigate the feasibility of this approach at 3T. The
point spread function method was used to measure the imager performance for the
traveling-wave magnetic resonance imaging experiment. Human leg images were
acquired to experimentally validate this approach. The principal mode shows
very little field magnitude variations along the propagation direction at 3 T
when compared to other higher resonant frequencies. The B1 mapping showed that
it is possible to conduct experiments using the traveling-wave approach at 128
MHz. The point spread function results showed a good scanner performance for
these type of experiments. Leg images were obtained with the whole-body
birdcage coil and the waveguide with two circular coils for comparison
purposes. The simulated and in vivo traveling-wave results correspond very well
for both magnetic field and specific absorption rate. A pretty similar
performance was observed for the traveling-wave approach and the conventional
one. We have demonstrated the feasibility of traveling-wave magnetic resonance
imaging at 3T for whole-body magnetic resonance systems, using a parallel-plate
waveguide with standard pulse sequences and only one coil array.
