A diffusion-weighted
(DW) imaging method was developed to mitigate off-resonance-induced distortion
and signal loss, which are problematic for body applications. A 2D RF pulse is
used in place of the conventional spectral-spatial excitation used for DW spin
echo echo-planar imaging. In the presence of off-resonance, a narrow band of
frequencies is excited due to the different bandwidths between excitation and
refocusing pulses. By progressively shifting the center frequency, the whole
range of off-resonance can be excited and a composite image, corrected for
off-resonance-induced distortion, can be reconstructed by estimating the field
map from the spectral information.
