1. Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.
2. Department of Biomedical Engineering, Hanyang University, Seoul 133-792, Korea.
3. Department of Neurology, College of Medicine, Ewha Womans University, Seoul 110-783, Korea.
4. Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.