Quantitative MRI for Rapid and User-Independent Monitoring of Intracranial CSF Volume in Hydrocephalus

Abstract

Background and purpose: Quantitative MR imaging allows segmentation of different tissue types and automatic calculation of intracranial volume, CSF volume, and brain parenchymal fraction. Brain parenchymal fraction is calculated as (intracranial volume - CSF volume) / intracranial volume. The purpose of this study was to evaluate whether the automatic calculation of intracranial CSF volume or brain parenchymal fraction could be used as an objective method to monitor volume changes in the ventricles.

Materials and methods: A lumbar puncture with drainage of 40 mL of CSF was performed in 23 patients under evaluation for idiopathic normal pressure hydrocephalus. Quantitative MR imaging was performed twice within 1 hour before the lumbar puncture and was repeated 30 minutes, 4 hours, and 24 hours afterward. For each time point, the volume of the lateral ventricles was manually segmented and total intracranial CSF volume and brain parenchymal fraction were automatically calculated by using Synthetic MR postprocessing.

Results: At 30 minutes after the lumbar puncture, the volume of the lateral ventricles decreased by 5.6 ± 1.9 mL (P < .0001) and the total intracranial CSF volume decreased by 11.3 ± 5.6 mL (P < .001), while brain parenchymal fraction increased by 0.78% ± 0.41% (P < .001). Differences were significant for manual segmentation and brain parenchymal fraction even at 4 hours and 24 hours after the lumbar tap. There was a significant association using a linear mixed model between change in manually segmented ventricular volume and change in brain parenchymal fraction and total CSF volume, (P < .0001).

Conclusions: Brain parenchymal fraction is provided rapidly and fully automatically with Synthetic MRI and can be used to monitor ventricular volume changes. The method may be useful for objective clinical monitoring of hydrocephalus.

© 2016 by American Journal of Neuroradiology.

Figures

Fig 1.

A, Fully automatic calculation of total intracranial CSF by using SyMRI. The green line is an intracranial mask used to automatically calculate the intracranial volume (the line was originally red but was colored green in external graphics-editing software to increase clarity). B, Manual segmentation of the lateral ventricles by using SyMRI.

Fig 2.

Baseline brain parenchymal fraction for all subjects as a function of age.

Fig 3.

A, The mean difference in manually segmented lateral ventricular volume with respect to the baseline value (solid line) and the mean difference in automatically calculated total CSF volume with respect to the baseline value (dotted line) plotted at the 5 different time points. B, The mean difference of brain parenchymal fraction with respect to the baseline value at the same time points. Time point 1 and 2 are baseline investigations and the lumbar puncture with CSF removal was performed right after time point 2. The error bars indicate 1 SD.

Fig 4.

A, Correlation plot between the difference in ventricular volume and the difference in total CSF volume for all subjects at all time points. The line indicates a slope of 1.67 and intercept of 0.37. B, Correlation plot between the difference in ventricular volume and the difference in brain parenchymal fraction for all subjects at all time points. The line indicates a slope of −0.104 and an intercept of 0.008.