Hi Megan,
dtifit uses the tensor model. When you log-transform the data, this
turns up to be a simple linear model which is solved using least
squares.
(note that this is the same as maximum likelihood if you assume that
the noise is gaussian).
If you have FSL4.1.3 or above, you should have access to the --sse
option, which tells dtifit to output the sum of squares error.
Cheers,
Saad.
On 13 May 2009, at 17:01, Megan Twiss wrote:
> Hello,
> I've been using your DTIfit for some DTI analyses. I am wondering
> what
> sort of algorithm is employed to estimate the parameters? Are you
> using
> a maximum likelihood method or least squares etc? I need to know as
> it's been
> shown that some methods are better than others.
>
> Also, what sort of diffusion model is assumed? Finally, is there a
> way to extract chi-
> squared values or some sort of measure of the goodness of the fit?
>
> Thank-you,
> Megan Twiss
>
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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