[Insight-users] MRI Bias Field correction

[Jisung Kim]

Hi.

--- Ricardo Ferrari <ferrari@ucalgary.ca> wrote:
> 
> Hi all,
> 
> I am trying to use the MRIBiasFieldCorrection
> algorithm. Although I've 
> gotten the examples running properly, I have a
> couple of doubts that I 
> would like to ask:
> 
> What does the mean-class and sigma-class mean ?  Are
> they the mean and 
> std of the grey level values for each tissue classes
> ? If so, is there 

Yes.

> any way to compute this automatically by using ITK ?
> 
> I really appreciate if someone could help me on
> this.
> 

the simple answer is no. One alternative is:
1) find a small region that includes all the tissue
classes and isn't affected much by the bias. 
2) use the intensity value of each class in that
region as the class mean.

For the standard deviations, you may find reasonable
values for different modality in literatures. However,
you have to adjust the standard deviation to get
better results. For this purpose, use the
ExneryPlotter utility. This utility creates a table of
enery values and intensity values. Using math tools
such as Matlab or GNU R, you can plot the table and
see the energy function graph. Usually, the graph has
as many valleys as the number of the tissue classes.
To make the enery function distiguish different tissue
classes. it is recommended that the ridges between
class means bigger than 0.5.

All this information is already in the article that is
reffered by the example web page of this example. 

Thanks,
 
> Thank you very much,
> 
> Ricardo
> 
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>
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=====
Jisung Kim
bahrahm@yahoo.com
106 Mason Farm Rd.
129 Radiology Research Lab., CB# 7515
Univ. of North Carolina at Chapel Hill
Chapel Hill, NC 27599-7515

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