These are the specific classes that started me on this quest:
for reader_class in vtk.vtkBMPReader, vtk.vtkJPEGReader, vtk.vtkPNGReader, vtk.vtkTIFFReader, vtk.vtkPNMReader:
reader = reader_class()
reader.SetFileName(file_name)
reader.Update()
It appears that David Gobbi’s DICOM reader already handles Unicode properly, as including ‘vtkDICOMReader’ in the above list simply complains appropriately about invalid file contents and lists out the name as expected in the error message.