Measurements of intracranial pressure with an ultrasound signal processing system. Data from volunteers

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We investigated changes in thin layer thickness between the skull and the brain in association with changes in intracranial pressure (ICP) in human subjects using our ultrasound (UT) system. A thin-disc-type prototype probe (5 MHz) was attached to the supra-auricular areas of seven adult volunteers. ICP was varied by changing posture between the sitting and supine positions, and Valsalva's maneuver, or neck compression in the supine position. Our UT system was triggered at 200 msec after the peak time of R wave on the ECG. The interference echoes from the thin layer were clearly visualized utilizing our revised algorithm of FFT-Cepstrum analysis with the maximum entropy method. The thickness of the thin layer in the supine or sitting position decreased significantly during Valsalva's maneuver or neck compression in the supine position (Wilcoxon U test, p<0.05) . The thickness of the thin layer was quite similar to that of the dura mater. The reproducibility of the data was confirmed using theKolmogorov-Smirnov test. Our ultrasound system for ICP measurement appears to be useful for estimating changes in ICP levels of human subjects.