Re: [Teem-users] DWI volume to DTI volume

[Gordon K. <gk...@bw...>]

hi-

this page documents how to use Nrrd to describe a DWI volume:

http://wiki.na-mic.org/Wiki/index.php/NAMIC_Wiki:DTI:Nrrd_format

and then this page shows how to use "tend" for tensor estimation (via  
"tend estim")

http://wiki.na-mic.org/Wiki/index.php/NAMIC_Wiki:DTI:TeemExamples

Fractional anisotropy (FA) is *defined* by Basser in terms of a  
diffusion tensor, not it terms of any DWIs.  On the other hand, the  
measurement of anisotropy directly from DWIs is an interesting  
question, and it is the topic of some ongoing research; google for  
"HARDI anisotropy" for some examples.

What is lost is going from DWIs to a single tensor model is also a  
research topic, because it is known that a single tensor is sometimes  
a poor model of the DWI data.  Google for "HARDI diffusion model" for  
some examples.  So in going to a single tensor model, you lose  
information about the diffusion profile that is not captured by the  
single tensor model, but none of that information is relevant for  
measuring FA (or its gradients).

Gordon


On Apr 18, 2007, at 8:21 AM, James Bigler wrote:

> Fangxiang,
>
> I'm forwarding your question to the main teem-users list, because I
> don't know enough about tensors to answer your question.
>
> James
>
> Fangxiang Jiao wrote:
>> Hi,
>>
>> For the DWI volume, how to calculate the Fractional Anisotropy and  
>> the
>> Gradient of Fractional Anisotropy using teem?
>>
>> My understanding is changing the DWI volume to DTI volume  
>> using     tend
>> estim  , and then using    Vprobe  to detect
>>
>> the FA of the tensor volume. But, we will lose some signals by  
>> changing
>> DWI to DTI volume. My questions is do we have
>>
>> more direct method to calculate the FA and Gradient-FA of DWI volume?
>>
>> Thanks,
>>
>> Fangxiang
>
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