Yes, in fact, it does not work!
However, for me, it is strange that I have big differences between single shell and multi shell fits. I have area in CC and other WM locations where FA is very very low...
Maurizio
>Hi
>I am sorry I have no idea why that option sneaked into the released DTIFIT. It has not been implemented yet :)
>Cheers
>Saad
> On 9 Nov 2018, at 15:26, Maurizio Bergamino <[log in to unmask]> wrote:
>
> Hi Szabolcs,
> I have 98 directions + 10 B0.
> The b-values are: 500, 1000, 2000, 3000
> The voxel was in the CC. But I have big differences in other part of the brain.
>
> And... another question:
> I saw that in 'dtifit' there is the option: --kurtdir -> Output parallel/perpendicular kurtosis maps (for multi-shell data)
> Is it better than -kurt option?
> Maurizio
>
>
>
>
>> Hi Maurizio,
>
>> What are your b-values?
>> And also: where is this voxel? Which part of the brain?
>
>> Best,
>> Szabolcs
>
>>> On Wed, Nov 7, 2018 at 3:36 PM Maurizio Bergamino <[log in to unmask]> wrote:
>>> 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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