Hi,
The terminology in the literature is not always clear, which might cause the confusion between DWI and DTI.
By DWI, I would refer to any image/volume whose contrast is weighted by water diffusion. To get that, we apply a diffusion-sensitizing magnetic field gradient along a direction u and the image contrast is sensitive to water diffusion along u. So a DWI volume corresponds to a single diffusion-sensitizing direction.
The diffusion tensor is a *model* applied to a set of DWI volumes. I would call the maps obtained after applying this model (e.g. FA, MD, etc) as DTI images.
In FDT, the convention is to expect all the input DWI volumes, as merged into a single multi-volume (4D) file. So, the number of volumes of the input file corresponds to the number of diffusion-sensitising directions that have been applied during acquisition.
In your case, I suspect that what you call DTI images (data1) is the DWI volumes I describe above. I am not sure what data2 can be, you can have a look in fslview, it might be an FA or MD map that some scanners generate.
Hope this helps,
Stam
On 20 Oct 2011, at 15:44, Suchada Tantisatirapong wrote:
> Hi Yingying,
>
> Isn't scalar image, FA, MD and etc derived from DTI images which is obtained from different epi directions? Raw DTI images contain only single volume?
>
> Cheers
> Suchada
>
>
>
>
> ________________________________
> From: FSL - FMRIB's Software Library [[log in to unmask]] On Behalf Of Yingying Wang [[log in to unmask]]
> Sent: 20 October 2011 15:34
> To: [log in to unmask]
> Subject: Re: [FSL] Confusion between DTI and DWI data
>
> Hi Suchada,
>
> From your description, data1 should be your DWIs. data2 should be your DTI. You can probably see the difference between the images using fslview. DWI - diffusion weighted images: different volumes with different contrasts for white matter due to the anisotropic diffusion of water molecule in WM, while the diffusion of gray matter and CSF is roughly isotropic. Then, we can model the water diffusion using a simple ellipsoid model and get the DTI data which can be FA, MD, RD, AD. Those are the scalar images with one single volume not like DWI with different volumes representing different directions.
>
> Hope this is helpful to you.
> Cheers,
> Yingying
>
>>>> Suchada Tantisatirapong <[log in to unmask]> 10/20/2011 8:52 AM >>>
> Hi,
>
> I got the dicom images which are claimed to be DTI images. Those data have different file sizes, e.g. data1 contains 42 files and each file is about 1500 kB; data2 contains 55 files and each file is about 130 kB.
>
> After convert those file from dicom to nifty, I saw that the data1 has 42 volumes (bval and bvec is generated normally) while data2 has only 1 volume (no bvec and bval is generated). I guess the data2 is dwi images.
>
> Could you please tell me what is going on here??
> Thank you for your time
> Regards,
> Suchada
>
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