I am using this filter in an external CTK-based project. To get this filter work, I needed to include the following line to the header:

itkB0ImageExtractionToSeparateImageFilter.h
#include <itkVectorImage.h>

In addition to the extracted B0 images, also the indices of the B0 images are needed for my work, therefore a method is added which provides the requested indices. Following lines are added to the header:

std::vector<int> m_B0Indices;
std::vector<int> GetB0Indices()
{
  return m_B0Indices;
}

In the .txx file following line was added:

m_B0Indices = indices;

The filter still works within the DWI Preprocessing view as expected (tested). Please test it yourself :-).

Branch is pushed to remote repo.