[Mrtrix-discussion] Number of tracks

[Luis Morís]

Hi again,

Thanks for your quick answer René.

My data is 31 directions  with b=1000. The point is that no matter how
much fibers I put in the -number parameter, it always finds enough
fibers even a couple millions fibres. Previously I was working with
Medinria and I had around 30000 fibres because seeding was dependant
on resolution, one seed per voxel.

My parameters are FA cutoff 0.3 and initcutoff 0.6 min and max length
10 and 200 mm respectively, at the moment I'm doing a whole brain
seeding. My problem is how to set this number of tracks. If I use a
-number of let's say a hundred thousand, will I have a nice
distribution of tracks that will be representantive of the brain's
track population?


Thanks in advance,

Luis.

On Wed, May 11, 2011 at 4:18 PM, René Besseling
<r.m.h.besseling at gmail.com> wrote:
> Hi Luis,
>
> Just type streamtrack -h; the tracks that are selected are those of
> sufficient length (-minlength option) and sufficiently high FA or FOD
> amplitude (-cutoff value). Note that the -maxnum option sets the
> maximum allowed number of trials. If your data is of low quality, the
> number of tracks generated can be lower than what you set by -number
> if not enough valid tracks can be constructed within -maxnum trials.
> Furthermore, tractography start points (seed points) are selected at
> random within the ROI you specify using -seed, so if you use the same
> streamtrack command twice, the result will be different (due to
> different random seed points). Information about a streamtrack result
> can be obtained by typing track_info your_file_name.tck
>
> Best regards,
>
> René
>
> On Wed, May 11, 2011 at 3:54 PM, Luis Morís
> <luis.moris.fernandez at gmail.com> wrote:
>> Hello everyone,
>>
>> I write because I have started to use mrtrix, and I've found a doubt.
>> To be able to do tractography you have to use the parameter -number
>> that will set the exact amount of tracks that will be calculated.
>>
>> My doubt is how does the program decide which tracks to include or
>> not. If I set it to 1000 and I run it again with 1000000. What
>> difference do I find between the two set of tracks? Is it purely
>> random, depends on the length, the FA...
>>
>> Thanks a lot in advance,
>>
>> Luis.
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>