Hi Carlos,
I'm not sure this is going to work. The contents of the u_*.nii files
encode stuff that is totally different from anything that FSL uses.
In FNIRT, deformations are constructed by adding a displacement field
to an identity transform. This is sometimes known as a small
deformation approximation. I would guess that vecreg requires such a
displacement field.
For Dartel, deformations are constructed by repeatedly composing
identical very small deformations together. The small deformations
are generated from the velocity field stored in u_*.nii.
Virtually everyone who has done some image registration will know that
deformation fields should be combined by composing them together,
rather than adding displacement fields. It is easy to demonstrate
that adding displacements gives the wrong answer. It is a bit like
computing x*y using (x-1)+(y-1)+1. If x and y are very close to 1,
then it is a reasonable approximation, but if they are further away,
then the approximation is not so good (2*2 = 3). What is much less
widely appreciated is that larger deformations should really be
constructed by composing a series of smaller deformations together.
In turn, the approach used by Dartel is an approximation to a yet more
correct way of doing stuff (as in the more recent Geodesic Shooting
toolbox, which appeared in a later update of SPM8).
All the best,
-John
On 30 April 2012 13:09, CARLES M. FALCON FALCON <[log in to unmask]> wrote:
> Dear spmers,
> I am trying to apply DARTEL flow fields (u_rc1...) to V1maps by means of FSL's 'vecreg -w' and I am getting a message error about there should be three components in the warp file. As u_rc1 maps have three components, I think the problem should be the format compatibility. MRICROn detects 3 components but fslview just one.
> Does anybody know how to make DARTEL u_rc1 maps compatible with FSL?
> Thank you very much
>
> Carles Falcon
> Medical Imaging Platform-IDIBAPS
> GIB-UB, CIBER-BBN
>
>
> Aquest correu electrònic i els annexos poden contenir informació confidencial o protegida legalment i està adreçat exclusivament a la persona o entitat destinatària. Si no sou el destinatari final o la persona encarregada de rebre’l, no esteu autoritzat a llegir-lo, retenir-lo, modificar-lo, distribuir-lo, copiar-lo ni a revelar-ne el contingut. Si heu rebut aquest correu electrònic per error, us preguem que n’informeu al remitent i que elimineu del sistema el missatge i el material annex que pugui contenir. Gràcies per la vostra col·laboració.
>
> Este correo electrónico y sus anexos pueden contener información confidencial o legalmente protegida y está exclusivamente dirigido a la persona o entidad destinataria. Si usted no es el destinatario final o la persona encargada de recibirlo, no está autorizado a leerlo, retenerlo, modificarlo, distribuirlo, copiarlo ni a revelar su contenido. Si ha recibido este mensaje electrónico por error, le rogamos que informe al remitente y elimine del sistema el mensaje y el material anexo que pueda contener. Gracias por su colaboración.
>
> This email message and any documents attached to it may contain confidential or legally protected material and are intended solely for the use of the individual or organization to whom they are addressed. We remind you that if you are not the intended recipient of this email message or the person responsible for processing it, then you are not authorized to read, save, modify, send, copy or disclose any of its contents. If you have received this email message by mistake, we kindly ask you to inform the sender of this and to eliminate both the message and any attachments it carries from your account. Thank you for your collaboration.
|