Radioisotope cisternography images from a 36-year-old man at 1, 3, 5 and 24 h after RI injection. Two regions of interest (ROI) were analyzed one covering the entire CSF space (dotted line) and the other the whole CSF space plus the urinary bladder (solid line). Quantitative analysis of RI cisternography was performed at 1, 3, 5 and 24 h after RI injection. RI residual activity at n hours after RI injection was calculated as follows: (RI activity in ROI of whole CSF space at n hours after injection/RI activity in ROI from head to urinary bladder at 1 h after injection) × 100. This patient showed late bladder filling at 5 h. L: left side.