[Mristudio-users] CC in elderly patients
Dafna Ben Bashat
dafnab at tasmc.health.gov.il
Sat Mar 13 16:42:19 EST 2010
Dear Susumu,
I would like to thank you and all other, for the detailed answers.
The interpretation of the data is indeed problematic, since in some
patients we get the CC in the u shape and in other we don't. It seems
that the comparison of the mean values of FA, MD and eigen values of the
CC, is wrong. In addition, the parameter of the size of the CC obtained
from the number of fibers in the reconstructed fiber is also unreliable.
We found it to be highly dependent on the one who make the tractography,
while the mean of the other parameters are much more repeatable.
Thanks again
Dafna
Thank you very much for the detailed explanation
Dafna Ben Bashat Ph.D.
Senior Physicist, In charge of MR systems
The Wohl institute for Advanced Imaging
Brain Imaging Center
Tel Aviv Sourasky Medical Center
Phone: 972-3-6973953 (o) Fax: 972-3-6973080
972-52-4262515 (m) Mail: dafnab at tasmc.health.gov.il
________________________________
From: mristudio-users-bounces at mristudio.org
[mailto:mristudio-users-bounces at mristudio.org] On Behalf Of susumu mori
Sent: Thursday, March 11, 2010 11:49 PM
To: DTI Studio, ROI Editor, Landmarker Questions/Support
Subject: Re: [Mristudio-users] CC in elderly patients
No I don't. My research is application-driven and I haven't requested by
any application to resolve fibers within a pixel to answer an important
clinical question.
Most of application research is talking about inter-pixel or
pixel-cluster anatomical information (e.g. what is the size of a
structure) but not intra-pixel information (e.g. how much water
population is going up-down and how much in right-left).
On Thu, Mar 11, 2010 at 3:45 PM, Jun Yi Wang <junyiwang2002 at yahoo.com>
wrote:
Hi Susumu,
Just realized that I have a question to ask: are you working on a way to
handle the crossing fiber issue such as the two-tensor streamline
tractography proposed by Qazi et al. (2009), NeuroImage 47:T98-106?
Jun Yi
________________________________
From: Jun Yi Wang <junyiwang2002 at yahoo.com>
To: "DTI Studio, ROI Editor, Landmarker Questions/Support"
<mristudio-users at mristudio.org>
Sent: Thu, March 11, 2010 12:34:50 PM
Subject: Re: [Mristudio-users] CC in elderly patients
Hi Susumu,
Thank you very much for the detailed explanation! It is very useful. I
have the same impression of the difficulty of defining a gold standard
for tractography after I read the paper by Dauguet et al. (2007):
Comparison of fiber tracts derived from in-vivo DTI tractography with 3D
histological neural tract tracer reconstruction in a macaque brain.
Jun Yi
________________________________
From: susumu mori <susumu at mri.jhu.edu>
To: "DTI Studio, ROI Editor, Landmarker Questions/Support"
<mristudio-users at mristudio.org>; Xin Li <xli16 at jhmi.edu>
Sent: Thu, March 11, 2010 12:01:50 PM
Subject: Re: [Mristudio-users] CC in elderly patients
Hi all,
We have noticed the same phenomena and also got several inquiries from
outside. Here is my understanding;
1) For young subjects, the shape of the CC has a clean U shape in
coronal sections. If you do fiber tracking, you usually can reconstruct
the U-shape trajectory, which makes some anatomical sense.
2) For the population with enlarged ventricles, such as elderly, AD, and
stroke patients, the trajectory of the CC becomes more like a "W" shape
with a sharp turn where the CC merges to the corona radiata. I believe
that this is the primary reason that most streamlines end up in going
downward toward the internal capsule, which doesn't make much anatomical
sense.
3) Think about the 90 degree rotated "T" shape and the vertical line is
the corona radiata and the horizontal line is the CC. If the horizontal
line merges at the right angle, the probability of the tracking to go
upward and downward is 50/50. If the horizontal line is slightly tiled
upward, the CC tracking merges to the vertical line (corona radiata) and
continues to travel upward. It's as simple as this. Once we get a vector
(or tensor) field and ask a computer to reconstruct a path, the computer
doesn't know the anatomy. All it knows is just a bunch of vectors. One
may think that probabilistic tracking can deal with it but the
connectivity strength could be influenced by the merging angle too.
4) This exemplifies what tractography is. It is just a region growing
(or pixel-connection) tool based on pixel-by-pixel information, no
matter which algorithm we use. It is just a feature extraction tool
from MRI that observes water molecules. Some results look right and some
results do not.
5) Then many people ask, "how do we know the validity". Here we (both
who ask the question and who is asked the question) have to think very
hard. To show the validity, we need to compare our observation (in this
case tractography result) and gold standard (real anatomy). Then what do
we really mean by "real anatomy" or "real connectivity"? What is
connectivity anyway? First of all many of the macroscopic anatomical
definition such as "superior longitudinal fasciculs" and "corona
radiata" are defined by human eyes based on anatomical features, which
doesn't have a clear definition and boundary. It's like a cloud.
Everybody can see it at the core but at the boundary, we don't know how
to define. Then how about the microscopic anatomical definition? Yes, we
have a very clear definition, which is axonal connection. However, we
know that one neuron communicate with multiple neurons through a
branching axon. We have 100 billion neurons. Even if one neuron
communicate with one neuron, this is a 100 billion x 100 billion
question. For MRI, even if you do 1,000-orientation Q-ball imaging, we
are talking about merely few GB of data. With a tensor fitting, what we
have is 20 MB. On top of it, we are measuring water properties. So, we
can understand that we are on a very shaky ground when we talk about
"validation" because we can't even define what is the gold standard we
are shooting for and our data is so small compared to what we are
interested in.
6) Then next question is, "why do we do tractography". Here, we should
go back and think why we do MRI first of all and what is the real power
of it. The real power is that we can examine the entire brain within 30
min non-invasively and quantitatively. This is something no other
modality, certainly histology, can't do. By performing a feature
extraction such as tractography, we can quickly and quantitatively
assess the anatomical status.
7) As long as we apply the same data acquisition method and the same
analysis method, the results itself is always correct. There is nothing
wrong with the results whatever they are. In this example, in some
population, the CC goes downward while it goes upward in the normal
subjects. The tractography sensitively detected some differences between
the two population.
8) If we make mistake in this situation, that is when we interpret the
data. For example, if we interpret the data like, "in young brains, the
CC goes up and in aged brain the CC goes down because the connectivity
changed", now such a statement becomes the subject of "right or wrong".
9) So, it is very important to evaluate why you got different results
between two groups. The real reason could be something not the
measurement was intended. For the case of the CC trajectory, the real
reason could be "enlarged ventricles" and the DTI + tractography could
be just an expensive and indirect way to show it.
10) This is a very typical issue in MRI, not just DTI. When we observe
cortical thinning in T1, it may be just a change in contrast due to
myelination status or other things. What we really observe is the
thinning of T1-indicated-cortical-compartment and the direct translation
into the real cortical thickness is sometimes dangerous or even
erroneous. As long as we are dealing with 10 MB of water information,
biological or cellular interpretation always requires caution.
11) Fiber reconstruction is a high-level image analysis tool, which is
sensitive to so many anatomical factors including both micro and
macroscopic factors. The microscopic factors are myelination, axonal
loss, cellular loss, edema, etc that would affect the FA and anatomy.
The microscopic factors are multiple compartments (e.g. crossing fibers)
within the 2 mm pixel. So, in general, the interpretation would be
difficult. It is a good tool to survey the overall white matter anatomy
but you need to exercise the caution when you interpret it.
I guess what I mentioned above contains a lot of my personal opinions
and please take it as just one of the opinions, but hope it helps to
understand the issue of the downard CC projection.
Susumu
On Thu, Mar 11, 2010 at 11:52 AM, Jun Yi Wang <junyiwang2002 at yahoo.com>
wrote:
Hi Dafna,
I only have a few subjects in 80s, but I have subjects from 16-65 years
old. I do see a substantial decrease of the amount of corpus callosum
fibers projecting towards the cortex as we age. Some fibers still
project to the cortex although a lot of them project downwards instead.
I don't know whether this is caused by aging or DTI artifacts such as
the termination of line propagation because of the lower FA or the
crossing fiber issue.
Jun Yi Wang
Postdoctoral Research Scholar
Fragile X Research and Treatment Center
UC Davis M.I.N.D. Institute
530.747.3808 (Lab)
________________________________
From: Dafna Ben Bashat <dafnab at tasmc.health.gov.il>
To: mristudio-users at mristudio.org
Sent: Thu, March 11, 2010 3:19:20 AM
Subject: [Mristudio-users] CC in elderly patients
Hi all,
We are currently working on data from elderly stroke/TIA patients.
In many of the TIA patients, who have good DTI data, for some reason the
CC does not built well, we can't see the fan.
This is not due to incorrect directions (the CST is built OK).
ROI measurements give reasonable values. We even changed the flip-angel
for the FACT, and got the same results.
Any suggestions? Is it a known phenomenon in elderly / stroke / TIA
patients?
Thank you in advance.
Dafna
Dafna Ben Bashat Ph.D.
Senior Physicist, In charge of MR systems
The Wohl institute for Advanced Imaging
Brain Imaging Center
Tel Aviv Sourasky Medical Center
Phone: 972-3-6973953 (o) Fax: 972-3-6973080
972-52-4262515 (m) Mail: dafnab at tasmc.health.gov.il
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