[Mristudio-users] tractography of CST

[susumu mori]

Hi Kevin;

1) What we call, "CST" is actually the mixture of the CST and
cortico-pontine-cerebellar pathways.
2) once the CST tract leaches pons, the CST branches to the real CST that
penetrate the pons toward the spinal cord and the cortico-pontine-cerebellar
pathways.
3) The latter pathways outnumber the real CST by far.
4) Of course, DTI, which is pixel-by-pixel imaging, can not distingish these
two pathways when they bifurcate at the pons.
5) Anatomically, the best ROI positoins for the CST would be one at the
motor cortex and the other at the medula or spinal cord, which can eliminate
all cortico-pontine-cerebellar pathways effectively.
6) However, if you use this combination (similar to what you did: use NOT to
remove that latter pathways), the tractography results become unstable
because so many exit to the cerebellum (which is anatomically correct) and
subtle differences in pixel locations and partial voluming could afect the
outcome.
7) That is the reason we reconstructed only up to the cerebral peduncle,
avoiding the complex pons area.
8) Some more elaborated tractography methods, either deterministic
approaches with some kinds of regularization or probabilistic methods may
provide more stable results, less affected by a small number of pixels that
would wobble due to mixed fibers, but what these provide is mathematically
more stable solution, not necessarily anatomically more correct solution.
Nonetheless, they could be usefull tools as long as you know the nature of
the tool well.

If your finiding, the CST is located too lateral, is a reproducible finding
among different subjects, you may want to check your DTI processing
pipeline.

One of the most common mistakes is how oblique angles are handled. GE,
Philips (non-overplus), and Siemens (the latest version VB15?) do not
require any procedure to incorporate the oblique information, but Philips
(overplus) and Siemens (previous version) require recalculation of gradient
table based on the oblique angles. If you are using DICOM or Mosaic, this
can be easily done by check a box beneath the gradient table window.

Susumu


On Wed, Jul 1, 2009 at 9:23 AM, Kevin Spitler <kevinspitler at ucla.edu> wrote:

> Hello,
>
> I am trying to trace the corticospinal tract using DTI Studio and the
> tractography algorithm proposed by Wakana et al 2007 NeuroImage.
> After making the 2 ROIs at the cerebral peduncle and then at the
> precentral gryus, I find the majority of remaining fibers enter the
> cerebellum.  After removing these with the "NOT" ROIs, I find the
> remaining fibers are very lateral in the cerebral peduncle which is
> not the typical position of the corticospinal tract.  Is there a
> mistake I am making or is there another algorithm for ROI placement
> that may be better in my situation?
> Thank you for your help
>
> Best,
> Kevin
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