Assessment of factors affecting MRI measurement of intracranial volume changes and elastance index

Non-invasive measurement of cerebral hydrodynamic parameters may be of great use in the study and treatment of conditions involving abnormal intracranial pressure (ICP). ICP can be assessed indirectly in humans by calculation of intracranial volume changes and elastance using MRI. These two hydrodynamic parameters are derived from mathematical analysis of the relationships between blood flow to and from the brain, CSF flow and heart rate. This paper examines the variability in these three critical subject specific parameters. Three healthy adult males had measurements of blood and CSF flow to and from the brain made on three occasions. Inter-individual variation in vasculature and intra-individual variation in heart rates led to modest repeatability (defined as standard deviation divided by the mean) of intracranial volume change and elastance index in two subjects and poor repeatability in the third. Particular care is required in the selection of image planes and the blood vessels to include, and the analysis is very sensitive to differences in heart-rate. Because of these difficulties, caution is required in the interpretation of results obtained from a single examination. Techniques and methods that may reduce the variability in the derived hydrodynamic parameters are discussed.