step size of "0"

[Jason]

Dear Frank,

We have been tracking some cerebellar peduncle fibers using DTI reconstruction and a step size of "0". The guide states that using "0" means DSI studio will randomly choose a step size value between .1 and 1. However, we get the same exact results every time we run the tracking (even after several weeks) which suggests that a step size is not being chosen 'randomly'. We have tried plugging in different values for the step size, but cannot recreate what is happening when it is set to "0". 

Do you have any more details on what exactly DSI studio is choosing for a step size if the input is "0"?

thanks!

Jason

[Fang-Cheng Yeh]

Hi Jason,

The random here is "deterministically-random", which means the
random sequence will be identical everytime you initiate fiber
tracking. To allow for the random sequence to change randomly, you may
enable "Randomize seeding" and you will see the result varies time to
time.

Best regards,
Frank

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[jason.n...@gmail.com]

Hi Frank,

Is there any advantage to using a deterministically-random step size sequence? Any disadvantage? What is the difference between a deterministically random step size and say, a step size of 1mm (half of the voxel size which is usually recommended). 

Thanks!

[Fang-Cheng Yeh]

It will make sure that the results of repeat analysis are consistent.

A random step size will have a different step size for each track, and the purpose is to capture a variety of structural geometry. 

There is no absolute advantage or disadvantage, and the choice depends on your application.

Best regards,

Frank

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[jason.n...@gmail.com]

Thank you Frank!