Sorry for the delay, but I've just got back from vacation.
I don't know specifically about implementing sequences on specific
hardware - hopefully someone out there has done this with a Siemens
Allegra and can contact you. If someone there can pulse program then
it is pretty easy - you just need a normal spin-echo scan and then
where the 180 degree pulse is shifted away from t=TE/2 by an amount
we call the asym time. Note that the echo time, TE, is kept the same
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. If you do use a gradient-echo sequence
then these have to be accounted for, and at present that is not easy
with the software we have. However, if the expected distortions and
signal loss in the gradient-echo field maps are small, then you can
treat it like a spin-echo acquisition. Otherwise, you'll need to
your field map to begin with and then follow the sequence for
undistorting the EPI, but this is not an optimal way of doing it.
All the best,
On Friday, April 9, 2004, at 02:52 pm, Michael Benharrosh wrote:
> Dear FSL staff/users ,
> As a general question, I would like to know if any of you have
> been successful in applying
> Fugue and Prelude on EPI's generated by a Siemens 3T Allegra scanner.
> More specific questions, I would like to know if it is possible
> to use theses
> programs using field maps generated with gradient-echo pulse sequence ?
> Does one exactly knows which type of spin-echo pulse sequence do we
> need for this specific platform so I can ask provide more details to
> our physicist
> about it, in the case we really need to use this sequence.
> Thank you for your help,