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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