Dear SPM team,
Although there are a number of similar studies in literature, I have
downloaded synthetic T1-weighted MR volumes from Brainweb to investigate the
accuracy of SPM2-bias field estimation. The volumes had different Gaussian
noise but the same level of intensity non-uniformity.
After masking non-cortex tissues, I applied the following 2 lines of Matlab
code on every volume (volumes that have different level of noise but same
amount of bias):
======
EstimatedBiasField = spm_bias_estimate(maskedVOLUME, [1024 1 35]);
correctedVOLUME = spm_bias_apply(maskedVOLUME, EstimatedBiasField);
======
Then, I compared "correctedVOLUME.dat" with the ground truth bias field
supplied by Brainweb. The aforementioned Gaussian noise levels were 0%, 1%,
3%, 5% and 7%, and interestingly the lowest accuracy (far lowest) is
obtained at zero Gaussian noise.
I know that applying default parameters for the "spm_bias_estimate" may be
one of the causes, but do you have another guess for this outcome ?
Best Regards,
- Taha
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