[Mristudio-users] CC in elderly patients

Thu Mar 11 16:48:32 EST 2010

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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>
>
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