Is the VBR still a useful measure of changes in the cerebral ventricles?

Standard methods of ventricular measurement with computed tomography (CT) and magnetic resonance imaging (MRI) allow for as much as a 10-mm variation in the level of the "best" axial slice through the lateral ventricles. In a series of 10 patients who received MRI scans, the effect of 1-mm variations in slice center level on measured ventricle-brain ratio (VBR) was determined; even variations as small as 1 mm can result in a 10% change in VBR. The amount of within-subject variability in VBR that could result from this factor alone appears to be more than twice as large as that encountered with direct volume measurements, indicating that the latter measure would be at least twice as sensitive to real changes in ventricular size as the VBR.