Validation of Non-Invasive Intracranial Pressure (ICP) Monitoring Device

This study is designed to validate intracranial pressure measurements obtained with a novel, self-calibrating, non-invasive, intracranial pressure measuring (ICP) device based on trans-cranial Doppler technology. The ophthalmic artery is utilized as a natural ICP sensor. Up to 80 subjects will be recruited in 4 centers to achieve a power of 90% and a p\<0.05 compared to the values obtained from (a) patients in an ICU whose meet standard clinical indications for ICP measurement and whose ICP is measured using gold-standard implanted intracranial instrumentation and in (b) ambulatory subjects who meet clinical indications for lumbar puncture. At least two comparative readings, separated by an hour or more, will be obtained from each subject.