Hi Torsten,
see below.
On 24 Mar 2009, at 20:36, Torsten Ruest wrote:
> Hi there,
>
> I have a supposedly trivial question about the S0 image that is the
> output
> of the DTI reconstruction. Since the fed into dtifit b0 image does
> not have
> exactly 0 diffusion weighting, I suppose the routine extrapolates to
> get the
> interception with the signal axis, which then is truly 0 diffusion
> weighting, is this the case?
yes, we fit a straight line to the log of the signal.
so when you have at least two non-equal b-values, S0 will be the zero-
crossing.
> Another question regarding the S0 image is the comparability of one
> S0 image
> to another. I have been pointed to a possible problem when visually
> comparing 2 individual S0 images. I have been told that they might not
> necessarily be comparable, as the magnet gain settings (it's a
> preclinical
> MRI) may have changed, and therefore the inherent contrast (when eg.
> loaded
> into MRIcro with identical brightness/contrast settings) may not be
> the
> same. Can anyone give me advice on that?
i think you are right. S0 will be dependent on the gain, which makes
it difficult to compare in absolute values, or even in terms of
contrast, across different sessions.
Cheers,
Saad.
>
>
> Thank you very much in advance for any comments.
>
> Cheers,
>
> T
> .
>
Saad Jbabdi
Oxford University FMRIB Centre
JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545 (fax 717)
www.fmrib.ox.ac.uk/~saad
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