Hi,
It is not a question of which is better - it is a question of whether
one is
appropriate or not appropriate. For within-subject scans, there can
only
be 6 dof movement and so if there are no distortions, 6 dof is the
*correct*
dof and 12 dof is *not* as it allows too much freedom - scaling the A-P
axis for instance. However, if you are doing registration between a
subject
and an affinely-derived template such as the MNI152, then 12 dof is the
appropriate choice (or even higher dof, non-linear registrations).
The question of why your images have not registered well is unlikely to
be a problem of dof, if is more likely to be due to image artifacts or
other causes if it is within-subject.
Feel free to upload your images to our upload site (see previous list
emails).
All the best,
Mark
On 17 Dec 2007, at 16:20, WangPing wrote:
> Dear Mark:
>
> Thanks for your email. So I have a question regarding Flirt, do
> you think the affine (12 paramters modal) is better than 6dof method?
> In my case, sometimes I found the tissue not registered well ---
> the structures are not aligned well. I may find some images show
> you later.
> Thanks again,
> Ping
>
> > Date: Mon, 17 Dec 2007 10:07:03 +0000
> > From: [log in to unmask]
> > Subject: Re: [FSL] non-linear registration
> > To: [log in to unmask]
> >
> > Just to add to this:
> > If you are trying to get registrations within-subject then you
> > probably don't want to use
> > non-linear registration unless you are expecting substantial
> > distortions. For the
> > within-subject case, 6 dof should be the *correct* degrees-of-
> freedom
> > to use, which
> > can be done with flirt.
> >
> > Can you describe more fully in what way that are "not good".
> > Note that you can only successfully register images that show the
> > same structures
> > (albeit with different contrasts). So registering a CBF map (or ADC)
> > could be
> > problematic. It is more usual to use an image that is already
> > aligned (an example
> > functional or the b=0 weighting diffusion image) for the
> > registrations and then
> > transform these other images using the spatial transformation found
> > by the
> > previous registration.
> >
> > I hope this is helpful.
> > All the best,
> > Mark
> >
> >
> >
> > On 17 Dec 2007, at 09:56, Steve Smith wrote:
> >
> > > Hi - FSL 4.0 includes the IRTK nonlinear registration tool; see
> the
> > > TBSS scripts for example usage. However you're on your own wrt
> > > getting this to work on multimodal data, as we've not had much
> > > experience on this with IRTK.
> > >
> > > The next release of FSL will include FNIRT, a generic nonlinear
> > > registration tool which seems to work really well.
> > >
> > > Cheers.
> > >
> > >
> > >
> > >
> > > On 14 Dec 2007, at 19:05, Ping Wang wrote:
> > >
> > >> Dear FSL users:
> > >>
> > >> I have data in this situation: each subject has images from
> > >> different modalities: T1,T2, ADC, CBF. Now I only consider one
> > >> subject, I want to register all other modilitiy images to T2
> > >> image. I know Flirt only do linear registration, I tested the
> > >> results by Flirt, some are not good. Should I use non-linear
> > >> registration? I am wondering which tool in FSL can do non-linear
> > >> registration? tbss?
> > >>
> > >> Thanks, Ping
> > >>
> > >> Windows Live Writer,支持离线撰写博客内容,随时随地想写就写。
> 立即
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> > >
> > >
> > >
> ----------------------------------------------------------------------
> > > -----
> > > Stephen M. Smith, Professor of Biomedical Engineering
> > > Associate Director, Oxford University FMRIB Centre
> > >
> > > FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
> > > +44 (0) 1865 222726 (fax 222717)
> > > [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
> > >
> ----------------------------------------------------------------------
> > > -----
> > >
>
>
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