[Mrtrix-discussion] questions about streamtrack command

[Curci Marina Carmela]

Good morning,

I have just started to use MRtrix to do probabilistic tractography and I have some questions to solve, especially about the streamtrack command.
My region of interest is a mask image, in which the values of the voxel are 1 o 0. So voxel with intensiy equal to 1 could be seed point.

How the command streamtrack choose the seed point? 
Morever, while the command is running, I notice that there are generated streamlines but only some of them are selected, and the number of selected streamlines corresponds to the value given at the -number parameter.
Which is the criterium by which streamlines are selected?
Is there an option to set the number of generated streamlines instead of the number of selected ones?
I've tried to run the command without any options but the numbers of generated tracks and selected ones do not match.

My aim is to have a certain number N of tracks beginning from each seed point (voxel with intensity equal to 1) of the mask. 

Thank you for your helpfulness,
Marina