Hi Saad,
Thank you for the explanation.
Now, everything is clearer for me!
Maurizio
>Hi Maurizio
>The kurtosis model essentially interpolates your diffusivities (slope of log(signal) vs bvalue) to their value at b=0. This interpolation assumes that >the log(signal) vs bvalue curve is a quadratic with a curvature that is controlled by an extra ‘kurtosis’ parameter.
>In DTIFIT the --kurt option assumes a single kurtosis along all directions (as opposed to, e.g. a kurtosis tensor). However, it turns out this model >underestimates the ‘interpolated’ parallel diffusivity, which explains the lower FA value. One simple alternative is to have a parallel and a >perpendicular kurtosis (so two extra parameters compared to a standard tensor model) but this is not available in the released version of DTIFIT.
>I hope this clarifies the issue.
>Best wishes
>Saad
>> On 3 Nov 2018, at 16:21, Maurizio Bergamino <[log in to unmask]> wrote:
>>
>> Thanks Manuel,
>> It is the same thing that I understood.
>> But I did not expect to have big differences when I fitted the same DTI data by using two different procedures, with --kurt and without --kurt.
>> FA difference between, for example, 0.72 and 0.42 in the same voxel, is big.
>>
>> Maurizio
>>
>>
>>
>>> Hi Maurizio,
>>>
>>> If I understand correctly, when you activate the --kurt option, you are fitting the kurtosis model, that is more suitable for multishell data. The >>problem is if you want to compare with other FA values from literature, then probably you'd like to split the data and just use dtifit to one shell >>without the --kurt flag. I hope this helps.
>>>
>>> Best regards,
>>>
>>> Manuel
>>>
>
>>>> Hello,
>>>> It is the first time that I use a DTI multishell acquisition. My question is related to dtifit.
>>>> When I use dtifit, do I have to use the option --kurt to fit my data?
>>>> Because, I used dtifit with and without that option, and I had big differences in FA maps.
>>>> For example, in the same voxel, I had FA=0.72 (without --kurt) and FA=0.42 (with --kurt).
>
>>>> Thanks,
>>>> Maurizio
>
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