On Fri, 29 Jan 1999, Sergio Carvalho wrote:
> Hi,
>
> Yes, I am using SPECT. I have not seen an option for non-linear
> normalization. How do I turn it off? Why would it absorb large differences
> to the template?
>
> Thank you,
>
Hi Sergio,
You may have to edit a file called spm_defaults.m in your spm directory.
It is clear on inspecting this where the option to turn off non-linear
basis functions is. You should easily be able to tell from the output file
called spm.ps, produced immediately after normalisation, which
normalisation options have been applied. You should see the transformation
parameters for the linear components and underneath it will state whether
non-linear components have been applied.
The reason this occurs I am not sure, but if you read the literature,
non-linear Basis functions are principally aimed at improving the
normalisation of hi-resolution images like MRI. What I have seen in SPECT
is very simliar to what you describe - the hole beomes very distorted in
shape or disappears completely. Bear in mind that these basis functions
are trying to fit, at the default setting, (4,5,4) components in the
x,y,z planes. These functions very closely resemble those derived in
Fourier analysis and are sinusoidal in appearance.
I hope you find this useful
Regards - Mike
--
_____________________________________________________________________
Mike Glabus PhD, Principal Physicist
MRC Brain Metabolism Unit Tel Intl: 44-(0)131 537 6818/6282
Royal Edinburgh Hospital FAX Intl: 44-(0)131 537 6110
Morningside Park Pager : 5236, via 0131 537 6000
Edinburgh, EH10 5HF, SCOTLAND
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