Thanks, Matt - I appreciate that!

________________________________________
Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von Matt Glasser [[log in to unmask]]
Gesendet: Mittwoch, 26. Januar 2011 17:16
An: [log in to unmask]
Betreff: Re: [FSL] AW: [FSL] AW: [FSL] AW: [FSL] DWI scanning

Well, that isn't an even comparison, because 40 directions twice will be
better SNR than 60 directions once, and you would get better distortion
correction.  If it were phase up phase down 30 directions vs 1 phase of 60
directions and a field map, it would be balanced as far as SNR.  Typically,
one wants to increase the number of directions rather than increasing the
averages, but in your dilemma below, I would go for the second option
because you are getting an extra 20 scans.

Peace,

Matt.

-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Andreas Bartsch
Sent: Wednesday, January 26, 2011 9:59 AM
To: [log in to unmask]
Subject: [FSL] AW: [FSL] AW: [FSL] AW: [FSL] DWI scanning

Hi,

I guess even in that case the fieldmaps may be fair enough.

One more question: If you have the choice between a 60 dir acquisition with
a fieldmap and a 40 dir blip-up/blip-down acquisition, what would you
choose?

Thanks,
Andreas

________________________________________
Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von Matt
Glasser [[log in to unmask]]
Gesendet: Mittwoch, 26. Januar 2011 16:26
An: [log in to unmask]
Betreff: Re: [FSL] AW: [FSL] AW: [FSL] DWI scanning

I thought they were taking the patient out, but if they aren't doing
anything that changes the shim/then I agree no additional field maps are
needed.

Peace,

Matt.

-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Andreas Bartsch
Sent: Wednesday, January 26, 2011 5:21 AM
To: [log in to unmask]
Subject: [FSL] AW: [FSL] AW: [FSL] DWI scanning

Yep, you are right: we would just cocentenate, eddy correct and register to
the field map...
I guess I was not fully alert.
Cheers-
Andreas
________________________________________
Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von
Derek Jones [[log in to unmask]]
Gesendet: Mittwoch, 26. Januar 2011 11:31
An: [log in to unmask]
Betreff: Re: [FSL] AW: [FSL] DWI scanning

Hi Guys

I'm probably being a bit slow - but why do you think you need a new field
map each time?

For clarification...is the participant lying in the scanner in one session -
and the only thing that is changing is the directions of the encoding
vectors, between sessions (bandwidth etc. all remain the same)?

Thanks in advance
Derek