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

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Abstract
To develop a noninvasive method for intracranial elastance and intracranial pressure (ICP) measurement. 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. 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 (R:(2) = 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. 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.