Hi
After running tbss_2_reg I get several log files in /FA/tbss_logs saying, e.g.:
"Warning, Jacobian not within prescribed range. Prescription is 0.01 -- 100 and obtained range is -8.68585 -- 24.7955"
etc.
Some logs have one such message, others have several (e.g. 4).
I see in a message from October 2008 that Jesper Andersson spoke of altering the lambda in fnirt (quoted below). So presumably I need to do some corrections and re-run this step?
1. Do I need to change 'lambda' somehow for this tbss_2_reg set of error messages, and if so, how would I do that?
Or is there some other way to deal with this issue?
2. Depending on the answer to (1), do I need to set something to account for the specific range of values that appear in the error logs?
Cheers
James
Jesper Andersson:
> Warning, Jacobian not within prescribed range. Prescription is 0.01 -- 100
> and
> obtained range is -0.00444645 -- 3.01544
"After each iteration fnirt attempts to make sure that the Jacobians
(stretches and compressions) are within a pre-determined range. You have
used the default range, which basically just assures that the field is
invertible. When doing that fnirt runs a fixed number of iterations, and
if it hasn't succeeded after those iterations it prints the error message
above.
For the next release I'll change that so that one can set the number of
iterations (to make sure it "always" succeeds). For the time being I would
recommend that you slightly increase the amount of regularisation that you
are using. I.e. in your config file you increase the values for lambda.
If you are using the T1_2_MNI152_2mm file you might e.g. change lamda to
--lambda=400,200,150,75,60,45
and I would expect the problem to go away"
|