Just in case you're about to get offended by Steve's joke, it seems to
be related to the date on the calendar...
--
There are plenty of threads on the list on MD negative (and FA>1).
In summary, DTIFIT doesn't impose that the tensor is positive, which
may not be the case in noisy voxels.
The unit of MD is the inverse of the unit you consider for your
bvalues (e.g. b=1000s/mm^2 --> MD will be in mm^2/s)
Cheers,
Saad.
On 1 Apr 2009, at 12:22, Jürgen Hänggi wrote:
> Hi Steve
>
> Thanks a lot for the info
>
> Regards
> Jürgen
>
>
> On [DATE], "Steve Smith" <[ADDRESS]> wrote:
>
>> I think this is due to afferent, as opposed to efferent, neural
>> connections.
>> Cheers, Steve.
>>
>>
>>
>> On 1 Apr 2009, at 11:20, Jürgen Hänggi wrote:
>>
>>> Dear FSL experts
>>>
>>> We computed the mean diffusivity across the brain in order to use
>>> this
>>> measure as a covariate and noticed that there are also negative MD
>>> values.
>>>
>>> Why are there negative values in the MD maps and what does these
>>> negative
>>> values mean?
>>>
>>> The unit of the MD maps is mm2/s, isn't it?
>>>
>>> Thanks in advance
>>> Regards
>>> Jürgen
>>>
>>> ----------------------------------------------------------------------------
>>> Juergen Haenggi
>>> Ph.D. (Dr. des.)
>>> Division Neuropsychology
>>> Institute of Psychology
>>> University of Zurich
>>> Binzmuehlestrasse 14, PO Box 25
>>> 8050 Zurich, Switzerland
>>> 0041 44 635 73 97 (phone office)
>>> 0041 76 445 86 84 (phone mobile)
>>> 0041 44 635 74 09 (fax office)
>>> BIN 4.D.04 (office room number)
>>> j.haenggi[at]psychologie.uzh.ch (email)
>>> http://www.psychologie.uzh.ch/neuropsy/ (website)
>>> http://www.juergenhaenggi.ch (private website)
>>>
>>> This e-mail (and any attachment/s) contains confidential and/or
>>> privileged
>>> information. If you are not the intended recipient (or have received
>>> this
>>> e-mail in error) please notify the sender immediately and destroy
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>>
>>
>> ---------------------------------------------------------------------------
>> Stephen M. Smith, Professor of Biomedical Engineering
>> Associate Director, Oxford University FMRIB Centre
>>
>> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>> +44 (0) 1865 222726 (fax 222717)
>> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
>> ---------------------------------------------------------------------------
>
>
> ----------------------------------------------------------------------------
> Juergen Haenggi
> Ph.D. (Dr. des.)
> Division Neuropsychology
> Institute of Psychology
> University of Zurich
> Binzmuehlestrasse 14, PO Box 25
> 8050 Zurich, Switzerland
> 0041 44 635 73 97 (phone office)
> 0041 76 445 86 84 (phone mobile)
> 0041 44 635 74 09 (fax office)
> BIN 4.D.04 (office room number)
> j.haenggi[at]psychologie.uzh.ch (email)
> http://www.psychologie.uzh.ch/neuropsy/ (website)
> http://www.juergenhaenggi.ch (private website)
>
> This e-mail (and any attachment/s) contains confidential and/or
> privileged
> information. If you are not the intended recipient (or have received
> this
> e-mail in error) please notify the sender immediately and destroy this
> e-mail. Any unauthorised copying, disclosure or distribution of the
> material in this e-mail is strictly forbidden.
> ----------------------------------------------------------------------------
>
Saad Jbabdi
Oxford University FMRIB Centre
JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545 (fax 717)
www.fmrib.ox.ac.uk/~saad
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