[1] Department of Radiology, Institute of Clinical Medicine, University of Tsukuba, Tsukuba-shi
[2] R and D Center, Hitachi Medical Corporation, Chiba
[3] Department of Neurosurgery, Institute of Clinical Medicine, University of Tsukuba, Ibaraki
[4] Department of Neurosurgery, Hata General Hospital, Ibaraki
[5] Division of Radiation Medicine, Natl. Inst. of Radiological Sciences, Chiba 263, Inage-ku
[6] Department of Radiology, Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki 305