[MINC-users] nu_correct error

[minc-users@bic.mni.mcgill.ca]

Hello,

I have encountered the following error while running nu_correct:

inputCompactField(): Incorrect number of coefficients
Failure reading field file:
XXXXXXXXXXXX.imp
nu_evaluate: crashed while running evaluate_field (termination status=256)
nu_correct: crashed while running nu_evaluate (termination status=256)
nu_correct failed on XXXXXXXXXX.mnc.gz

Examination of the .imp file shows that it has 90 lines instead of the 
usual 110 lines.  Therefore it may be that nu_evaluate expects a greater 
number of field coefficients.  As a test I manually add 20 coefficients to 
the .imp file and then nu_evaluate works fine.

What could be causing this error in the automated processing?  Does 
nu_evaluate expect a different number of field coefficients than is 
provided by nu_estimate?  nu_correct has worked fine on our other scans 
so this seems to be an uncommon type of failure.

PS it would be very enlightening also to know what the parameters, matrix, 
and coefficients in the .imp file mean.  Somehow they must represent the 
non-uniformity field - but what would the mathematical formulation be?

Thanks in advance,


Ernest Lo
NeuroRX Research
Montreal, Canada