CT vs MRI reading

Is there any difference between read DICOM CT data or DICOM MRI data ? I have written code that read DICOM data and represent it as vtkVolume. I used DICOM VTK library for that (https://github.com/dgobbi/vtk-dicom) (BTW, excellent library), and goes well, and volume look well. But if I load a MRI dicom data, volume looks unclear somehow … and I wonder what could be the difference ? From your experience, is there any difference between how to read a CT or a MRI ? Because I don’t see another approach to build a volume from input data …