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
>
> ########################################################################
>
> To unsubscribe from the FSL list, click the following link:
> https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=FSL&A=1
########################################################################
To unsubscribe from the FSL list, click the following link:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=FSL&A=1
########################################################################
To unsubscribe from the FSL list, click the following link:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=FSL&A=1
########################################################################
To unsubscribe from the FSL list, click the following link:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=FSL&A=1
|