Asymmetry in the tracts

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Arian Klows

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Sep 13, 2021, 2:34:29 PM9/13/21
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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-Iimage (4).png

SLF-II
image (3).png  

SLF-III

image (5).png

Frank Yeh

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Sep 13, 2021, 11:28:47 PM9/13/21
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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

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Sep 14, 2021, 11:17:40 AM9/14/21
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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

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Sep 14, 2021, 11:29:32 AM9/14/21
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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

Arian Klows

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Sep 14, 2021, 11:44:44 AM9/14/21
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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

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Sep 14, 2021, 11:47:43 AM9/14/21
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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.

Arian Klows

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Sep 14, 2021, 12:03:32 PM9/14/21
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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.

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