Longitudinal Investigation of Brain Blood Flow Changes in Neurosurgical Patients

Inclusion criteria Patients: * Male and Female subjects \>18 years of age * Written informed consent after participants' information. Foreign speaking patients should be accompanied by a person with sufficient German language proficiency to act as a translator * Neurosurgical diseases with the potential to alter blood flow to the brain: * Cerebrovascular disease * Brain tumors * Normal Pressure Hydrocephalus Healthy subjects: * Male and Female subjects \>18 years of age * Written Informed Consent by the participant after information about the project. Foreign speaking healthy subjects should be accompanied by a person with sufficient German language proficiency to act as a translator Exclusion criteria: Patients: * Unwilling or unable to co-operate with breathing maneuvers * Respiratory or cardiac limitations to breathing through a mask * Medical contra-indications to limited hypercapnia (high CO2 - 50 mmHg) or hypocapnia (low CO2 - 30 mmHg) (i.e., known increased intracerebral pressure, metabolic acidosis or alkalosis) * Standard contraindications for MRI scanning * Verbal confirmed pregnancy * Known multiple intracranial diseases * Presence of intracranial hemorrhage within the last 3 months * Symptomatic increased intracranial pressure Healthy subjects: * Unwilling or unable to co-operate with breathing maneuvers * Respiratory or cardiac limitations to breathing through a mask * Medical contra-indications to limited hypercapnia (high CO2 - 50 mmHg) or hypocapnia (low CO2 - 30 mmHg) (i.e., known increased intracerebral pressure, metabolic acidosis or alkalosis) * Standard contraindications for MRI scanning * Verbal confirmed pregnancy * Anamnesticly a history of neurological disease or current neurological deficits.