Hi
Disentangling macro from micro changes of DTI metrics in cortical grey matter is hard, because of partial volume.
You will find, e.g., a systematic increase in MD with GM atrophy.
Have a look at this paper which suggests a way around:
Neuroimage. 2012 Jan 16;59(2):1394-403. Epub 2011 Sep 5.
How and how not to correct for CSF-contamination in diffusion MRI.
Metzler-Baddeley C, O'Sullivan MJ, Bells S, Pasternak O, Jones DK.
Cheers
Saad
On 23 Mar 2012, at 18:27, Rajagopalan, Venkateswaran wrote:
> Hi Matt,
>
> I want to evaluate whether the regions seen with GM atrophy (by VBM) also show reduction in DTI metrics in my patient population. I would like to see whether DTI (to my understanding reflects microscopic changes) changes agree with GM changes (which I believe reflects macroscopic changes). In order to study this I am not sure which DTI measure to use because to my understanding FA is more appropriate to study WM instead of GM, similarly radial diffusivity as it reflects more of myelin changes whereas I can use MD and axial diffusivity (which I believe reflects more of changes in axonal membrane, microfilaments and microtubules similalrly I beleive that axial diffisivity in GM will be reflective of damages to membrane). Please correct me whereever I am wrong and suggest what will be appropriate DTI measure to use.
>
> Thanks
> Venkat
>
> ________________________________
>
> From: FSL - FMRIB's Software Library on behalf of Matt Glasser
> Sent: Fri 3/23/2012 12:30 PM
> To: [log in to unmask]
> Subject: Re: [FSL] Gray Matter DTI
>
>
>
> What is your hypothesis?
>
> Peace,
>
> Matt.
>
> -----Original Message-----
> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
> Of Rajagopalan, Venkateswaran
> Sent: Friday, March 23, 2012 11:26 AM
> To: [log in to unmask]
> Subject: Re: [FSL] Gray Matter DTI
>
> Thanks Saad, could you tell me whether axial diffusivity be an appropriate
> measure to study changes in GM or what measures of DTI will be more
> appropriate to study GM changes.
>
> Thanks a lot
>
> Venkat
>
> ________________________________
>
> From: FSL - FMRIB's Software Library on behalf of Saad Jbabdi
> Sent: Fri 3/23/2012 8:52 AM
> To: [log in to unmask]
> Subject: Re: [FSL] Gray Matter DTI
>
>
> Hi
>
>
>
>
>
> Dear All,
>
> I am interested in studying DTI changes (MD, I am wondering whether
> it will appropriate to study axial diffusivity also in the sense for
> instance FA is more for WM than GM) in gray matter between control and our
> patient population. I am wondering what is way to segment white matter (WM)
> from gray matter (GM).
>
>
> You can use FAST on a T1-weighted image and map back onto DTI space using
> FLIRT.
>
>
>
>
> I am also interested in extracting different lobes of the brain to
> study GM changes in each lobe. Basically based on our VBM results where I
> see GM volume changes I would like to study whether DTI measure MD changes
> in frontal, temporal, occipital and parietal lobes. If so, is there a way I
> can use the atlases to separate out different lobes of the brain.
>
>
>
> You can use the MNI structural atlas in fslview.
>
> Saad
>
>
>
>
> Thanks
> Venkat
>
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> Saad Jbabdi
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>
> JR Hospital, Headington, OX3 9DU, UK
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> Please consider the environment before printing this e-mail
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> Visit us online at http://www.clevelandclinic.org <http://www.clevelandclinic.org/> for
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> Confidentiality Note: This message is intended for use
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> Please consider the environment before printing this e-mail
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> Cleveland Clinic is ranked one of the top hospitals
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> Confidentiality Note: This message is intended for use
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--
Saad Jbabdi
University of Oxford, FMRIB Centre
JR Hospital, Headington, OX3 9DU, UK
(+44)1865-222466 (fax 717)
www.fmrib.ox.ac.uk/~saad
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