1. Magnetic Resonance and Image Analysis Research Centre, University of Liverpool, Liverpool, U.K.
2. Department of Mathematics, Statistics and Computation, Faculty of Sciences, University of Cantabria, Santander, Spain
3. Department of Radiology, University of Wales NHS Health Care Trust, Cardiff, U.K.
4. Department of Diagnostic Radiology, University of Stanford, California, U.S.A.
5. Biomedical Imaging Resource, Department of Physiology and Biophysics, Mayo Foundation, Rochester, Minnesota, U.S.A.