Hi Tim
Thanks a lot for your advise
Regards
Juergen
On 2.6.2008 13:50 Uhr, "Tim Behrens" <[log in to unmask]> wrote:
> If the algorithm converges appropriately there is no penalty in
> increasing the maximum number of fibres to estimate.
> However, the bigger this number, the more difficult it is to get
> convergence - you would have to do various comparisons of results
> with (very) different burnin periods to convince yourself.
>
> If you have 15 gradient directions only however, you should certainly
> stick to 1 orientation. 2 fibre populations require 9 parameters to
> estimate - with 15 datapoints only, you will not find sufficient
> evidence for the extra parameters.
>
> Cheers
>
> T
>
>
>
>
> On 2 Jun 2008, at 12:42, Juergen Haenggi wrote:
>
>> Dear FSL experts
>>
>> In bedpostx we can select the number of fibres modelled per voxel.
>> Because
>> our DTI data were acquired with only 15 different diffusion
>> directions. This
>> is in contrast to the 60 directions used in the Behrens et al.,
>> NeuroImage,
>> 34, 144-155, 2007 paper, where two fibres per voxel were modelled.
>>
>> Should we modelled only one fibre per voxel in bedpostx because
>> there are
>> only 15 different diffusion directions? Does results could be
>> biased when
>> modelling tot many (e.g. three) fibres per voxel?
>>
>> Thanks in advance
>> Best regards
>> Juergen
>>
>> -----------------------------------------------------------
>> Juergen Haenggi
>> Ph.D. (Dr. des.)
>> Division of 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)
>> [log in to unmask] (email)
>> http://www.psychologie.uzh.ch/neuropsy/ (website)
>> http://www.juergenhaenggi.ch (private website)
>> -----------------------------------------------------------
>>
-----------------------------------------------------------
Juergen Haenggi
Ph.D. (Dr. des.)
Division of 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)
[log in to unmask] (email)
http://www.psychologie.uzh.ch/neuropsy/ (website)
http://www.juergenhaenggi.ch (private website)
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