1. Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.
2. Department of Biomedical Engineering, College of Medicine, Cheju National University, Jeju-si 690-716, Korea.
3. Medical Physics Department, GSST & Division of Medical Imaging, Medical School, King's College London, University of London, UK.