The usage of ITK patented code

I am trying to build an old version of ITK to use the patented code in it.
I am building ITK-3.20 and I enabled the generation of the patented code but I still cannot use it.
So I have two questions here:
First: Any advice on how to use the patented code in a correct way ?
Second : How can I get the license of the patented ITK code ?

Any help is appreciated.
Thanks in advance.
Best Regards,

What does this mean?

Correct use of patented code is to pay licensing fee to the patent owner, then use it just like any other code.

As the classes generally don’t contain patent information, you will have to search on your own who the patent owner is, and whether that patent has expired. If it has expired, the code can be used freely.