Asymmetry in the tracts

[Arian Klows]

Hi,

I was tracking the SLF branches and I observed significant symmetry in some patients. Is it normal or did I do something wrong?

Screenshots are attached which has the details of the parameters I used for tracking. I would appreciate if you could shed some light on this.

SLF-I

SLF-II

  

SLF-III

[Frank Yeh]

What are your slice thickness and in-plane resolution?

Fiber tracking won't work the best with non-isotropic resolution.

The low b-value setting (b=1000) with 64 directions may not be enough to map some difficult tracts.

The results may be due to acquisition limitations.

Frank

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[Arian Klows]

Slice thickness is 2 mm 

in-plane resolution is 1.98 mm

 b-val = 1000 s/mm2 with 64 directions.

Is that inadequate for tracking SLFs?

Do you have any alternative suggestions to track these tracts?

[Frank Yeh]

The low b-value could be a problem here. 

It seems that some tracts prematurely terminated at regions where there are crossing fibers.

Increasing the b-value to 1,500 or more would help a lot.

Frank

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[Arian Klows]

Thank you for your suggestion. These datasets were downloaded from PPMI site and I can't modify anything.

As I mentioned earlier, these problems were noticed only in a few subjects. 

So would it be okay to discard those subjects and continue analysis with subjects that showed SLF in both hemispheres?

[Frank Yeh]

It may not be good to drop them because these subjects may have smaller bundles that caused challenges in mapping.

Dropping them creates a bias.

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[Arian Klows]

Aw! That's a bummer. It would be ideal to drop the tractography in these data then.

Thank you letting me know. It saved my time and really appreciate it.