Print

Print


DTIFIT does not impose that the fitted tensor is positive definite, so you may have negative eigenvalues (i.e. negative Ls, which can produce FA>1). 
Since you only have 6 data points to calculate your tensor, your chances of getting negative tensors are higher, esp if SNR is low..


Saad.


On 11 Mar 2009, at 15:40, Mi Jung Kim wrote:

Yes, I can see V1 and FA. But when I check the values with fslstats they seemed to be odd to me. Because FA has max of 1, but it was more than 1 something like that. Here is my question. I do not think that lamdas can have negative values, but fslstats shows them in negative min as well. Why is that?

Thanks,

Mi Jng


On Wed, Mar 11, 2009 at 8:22 AM, Saad Jbabdi <[log in to unmask]> wrote:
They look all right to me.
Why are you saying they are not right? 
Did you have a look at FA and V1 in fslview?

Saad.

On 11 Mar 2009, at 15:18, Mi Jung Kim wrote:

Hi,

These are my outputs from dtifit.
I did a carriage return in bvals.
Are they right? They do not seem to be right values to me.
Any thought?

Sincerely,

Mi Jung
computer-four:~/data macadmin$ fslstats dti_FA.nii.gz -R
0.000000 1.224744
computer-four:~/data macadmin$ fslstats dti_V1.nii.gz -R
-0.999986 0.999999
computer-four:~/data macadmin$ fslstats dti_L1.nii.gz -R
-0.000893 0.003149
computer-four:~/data macadmin$ fslstats dti_L2.nii.gz -R
-0.001136 0.002519
computer-four:~/data macadmin$ fslstats dti_L3.nii.gz -R
-0.002149 0.002262
computer-four:~/data macadmin$ fslstats dti_V2.nii.gz -R
-0.999982 0.999999
computer-four:~/data macadmin$ fslstats dti_V3.nii.gz -R
-0.999986 1.000000
computer-four:~/data macadmin$ fslstats dti_MD.nii.gz -R
-0.001113 0.002447
computer-four:~/data macadmin$ fslstats dti_S0.nii.gz -R
0.000000 16406.000000

On Wed, Mar 11, 2009 at 8:01 AM, Mark Jenkinson <[log in to unmask]> wrote:
Hi,

Just add a blank line at the end with a text editor.

All the best,
       Mark



On 11 Mar 2009, at 14:49, Mi Jung Kim wrote:

Hi Sadd,

How can I add a carriage return?

Thanks,

Mi Jung

On Wed, Mar 11, 2009 at 1:54 AM, Saad Jbabdi <[log in to unmask]> wrote:
Yes, it sounds like you have a version which still had the bvals bug.
Just add a carriage return at the end of your bvals file and that should solve the problem.

Saad.

On 10 Mar 2009, at 18:00, Mi Jung Kim wrote:

Hi,

I am using FSL4.0 on Mac.

Thanks,

Mi Jung

On Tue, Mar 10, 2009 at 10:19 AM, Saad Jbabdi <[log in to unmask]> wrote:
I suspect this is because you need to add a carriage return at the end of your bvals file (which version of FSL are you using?)

Saad.


On 10 Mar 2009, at 16:29, Mi Jung Kim wrote:

Hi,

I have been working capillary phantom for muscle DTI.

I just was able to run all procedures, but after dtifit, outputs are
blank..Do you have any thought on that?

One more question right now is that since I am dealing with phantom data, do
I still go though all steps before probtrack?


Thanks,

Mi Jung


Saad Jbabdi
Oxford University FMRIB Centre

JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545  (fax 717)
www.fmrib.ox.ac.uk/~saad


Saad Jbabdi
Oxford University FMRIB Centre

JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545  (fax 717)
www.fmrib.ox.ac.uk/~saad









Saad Jbabdi
Oxford University FMRIB Centre

JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545  (fax 717)








Saad Jbabdi
Oxford University FMRIB Centre

JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545  (fax 717)