Quantitative cisternography.

By quantitative cisternography using a stationary detector system with correction for tissue background, an exponential elimination of 131I-HSA from the basal cisterns was demonstrated, allowing calculation of a biologic half time (BHT) of the clearance curve of a satisfactory level of reproducibility. 'Normal' range of BHT was calculated. Demented patients had significantly longer BHT. In 4 patients with normal pressure hydrocephalus prolonged BHT turned normal after shunting, paralleled by marked clinical improvement, in contrast to previous findings in 4 patients with presenile dementia. The method is now being modified employing 111In-DTPA and a computer assisted gamma camera for regional dynamic analysis.