Hi John and others,
I found the following information about the combined field. Is
there a script for generating a combined field that can be applied to
the imported images? This will save much time since the images will be
imported anyway during Dartel processing.
Thanks
Ze
-----Original Message-----
From: John Ashburner [mailto:[log in to unmask]]
Sent: Thursday, December 18, 2008 7:49 AM
To: Dana Perantie; [log in to unmask]
Subject: Re: [SPM] forward/backward flow, warp, map
> Thank you, John. I understand all but your last sentence. The u* can be
> applied to the DARTEL-imported images (Create Warped is applied to
> rc1*.nii), but the transform that was made by combining u* flow fields
> cannot be applied to the imported images? I would have guessed the other
> way around - that they could not be applied to the original-native-space
> images. Are the u* files flow fields between the imported images and the
> resulting template, or original-native-space and the resulting template?
The deformation fields are generated so that there is a mapping to the
images
prior to their being imported, rather than to the imported images. I figured
that this would be generally more useful. It is possible to achieve because
the imported images (and u_*.nii files) contain two different matrices in
their headers. One of them (the one used by Display and Check Reg) shows the
imported images in alignment with each other. The other one (not used by
Display and Check Reg) contains a mapping that relates the imported to the
original image.
> We made a script (attached) to convert the y* deformation field to
Jacobian
> determinant image that can be used to multiply/modulate. This was
based on
> snippets of HDW scripts as suggested in previous posts. Our next step is
> to make a script to do it in a batch: calculate the compositions y*,
> translate to Jacobians and modulate (for a list of subjects at multiple
> timepoints).
That's a good approach.
Best regards,
-John
>>>
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Ze Wang, Ph. D
Research Assistant Professor of Biomedical Engineering,
Department of Psychiatry,
School of Medicine,
University of Pennsylvania,
3900 Chestnut Street,
Philadelphia, PA 19104, USA
Tel: 215-222-3200 ext 123
Fax: 215-386-6770
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