I wrote a new DICOM reader for VTK (it’s called vtkDICOMReader, instead of vtkDICOMImageReader) that is able to read compressed DICOM files and decompress them in memory with GDCM. So if you are able to rebuild Activiz from source, then you can enable the new DICOM reader as part of your build:
VTK_MODULE_ENABLE_VTK_vtkDICOM=WANT
After configuring, it is also necessary to turn on GDCM, otherwise image decompression will not work:
USE_GDCM=ON