Metrizamide washout as a measure of CSF bulk flow

Metrizamide was injected into the ventricular system of three adults and five children with indwelling ventricular catheters and subcutaneous CSF reservoirs. A first-order rate constant, k, for metrizamide washout from one lateral ventricle was determined with reference to ventricular metrizamide concentration on serial (up to six) postinjection CT scans. Lateral ventricular volume, Vv, was estimated after metrizamide injection by a planimetric method and by partial volume analysis, an interactive computerized technique. The rate of lateral ventricular CSF formation, If, was calculated as k X Vv and ranged from 0.0622 to 0.103 ml/min. Precise measurements of lateral ventricular CSF bulk flow depend upon adequate mixing of the injected contrast material with ventricular CSF and accurate measurements of lateral ventricular volume.