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MR-Intracranial Pressure (ICP): A Method to Measure Intracranial Elastance and Pressure Noninvasively by Means of MR Imaging: Baboon and Human Study¹

¹ From the Departments of Radiology (N.J.A., S.H.L.), Bioengineering (N.J.A., S.H.L.), and Mechanical Engineering (F.L.), University of Illinois at Chicago, 1740 W Taylor, Chicago, IL 60612; the Department of Neurosurgery, Rush-Presbyterian-St Luke’s Medical Center, Chicago, Ill (P.B.R.); and the Department of Neurosurgery, Cook County Hospital, Chicago, Ill (T.L.). From the 1999 RSNA scientific assembly. Received February 25, 2000; revision requested April 3; revision received May 3; accepted May 5. N.J.A. and F.L. supported in part by National Institutes of Health grant RR14242-01. N.J.A. supported in part by a seed grant from the Department of Radiology at the University of Illinois at Chicago. Address correspondence to N.J.A. (e-mail: alperin@uic.edu).

PURPOSE: To develop a noninvasive method for intracranial elastance and intracranial pressure (ICP) measurement.

MATERIALS AND METHODS: Intracranial volume and pressure changes were calculated from magnetic resonance (MR) imaging measurements of cerebrospinal fluid (CSF) and blood flow. The volume change was calculated from the net transcranial CSF and blood volumetric flow rates. The change in pressure was derived from the change in the CSF pressure gradient calculated from CSF velocity. An elastance index was derived from the ratio of pressure to volume change. The reproducibility of the elastance index measurement was established from four to five measurements in five healthy volunteers. The elastance index was measured and compared with invasive ICP measurements in five patients with an intraventricular catheter at MR imaging. False-positive and false-negative rates were established by using 25 measurements in eight healthy volunteers and six in four patients with chronically elevated ICP.

RESULTS: The mean of the fractional SD of the elastance index in humans was 19.6%. The elastance index in the five patients with intraventricular catheters correlated well with the invasively measured ICP (R² = 0.965; P < .005). MR imaging–derived ICPs in the eight healthy volunteers were 4.2–12.4 mm Hg, all within normal range. Measurements in three of the four patients with chronically elevated ICP were 20.5–34.0 mm Hg, substantially higher than the normal limit.

CONCLUSION: MR imaging–derived elastance index correlates with ICP over a wide range of ICP values. The sensitivity of the technique allows differentiation between normal and elevated ICP.

Index terms: Animals • Brain, volume, 10.368, 10.436, 10.82 • Cerebrospinal fluid, flow dynamics, 10.368, 10.436, 10.82 • Cerebrospinal fluid, MR, 10.12144 • Magnetic resonance (MR), experimental studies, 10.12144 • Magnetic resonance (MR), phase imaging, 10.12144 • Magnetic resonance (MR), volume measurement, 10.12144

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