Quantitative analysis of intracranial compliance using MRI

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To assess a state and dynamics of the intracranial system noninvasively, intracranial compliance was measured with magnetic resonance imaging (MRI).The intracranial compliance (ICC) index was obtained from the ratio of the maximum intracranial volume loading change to the maximum pressure gradient change during the cardiac cycle, which were calculated from the net transcranial blood and cerebrospinal fluid (CSF) flow measured with phase-contrast (PC) cine MRI. ICC indices were determined in patients with normal pressure hydrocephalus (NPH), brain atrophy or asymptomatic ventricular dilation (VD), and in healthy volunteers. Concurrently, a time constant of the integral of the CSF wave response function, which represents the intracranial mechanical property was determined with PC cine MRI. The changes in ICE indices were also analyzed after intravenous injection of acetazolamide, i.e., hemodynamics independent. These values were then compared with the volume-pressure response (VPR) as a invasive compliance measurement during the shunt operations.The ICC index in the NPH group was significantly lower than in the control or VD group, but no difference was found between the control and VD groups. There was no significant change in the ICC index after acetazolamide injection. There were significant correlations between the ICC index and the time constant. A negative correlation was noted between the ICC index and the VPR.Compliance analysis with ICC index measured by PC cine MRI makes it possible to obtain noninvasively a more detailed intracranial state and dynamics in the NPH and to assist in diagnosis of the NPH.