> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On
Behalf
> Of Mark Jenkinson
> Sent: 25 April 2004 23:07
> To: [log in to unmask]
> Subject: Re: [FSL] Fugue and Prelude applied on Siemens 3T Allegra
>
> As for gradient-echo vs spin-echo, at the moment we only recommend
> using spin-echo because the field maps are then undistorted and do
> not suffer from signal loss.
It is not true to say that spin-echo images are undistorted. Assuming
the same sequence parameters (except of course replacing the spin-echo
with a gradient-echo), spin-echo and gradient-echo images should have
the same distortions. The gradient-echo image would have signal losses
due to phase dispersion over the voxel, whereas the integrated intensity
of a spin-echo image should be independent of background gradients. In
other words, integrated over the whole image, a gradient-echo would give
reduced intensity, but a spin-echo image should give a constant
intensity, but with increased or decreased signal in some voxels.
Dave
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