The operational relevance of this gap according to the NASA Human Research Roadmap is that elevated ICP and likely associated vision disturbances due to microgravity exposure are serious health risks for astronauts. Furthermore, this is an even greater concern for potential longer duration missions such as to the moon or Mars where decreased vision may impact mission performance and may even require early mission termination. Permanent visual losses may result in lifetime disability issues. Almost certainly, during long-term flights, as the hydrostatic pressure gradients due to gravity are abolished with resultant large cephalad fluid shifts, an intracranial adaptive response occurs. Thus direct measurements of cerebral fluid shifts and cerebral hemodynamics as proposed in this study will allow us to more fully characterize the intracranial compartment guiding the development of preventive measures, such as specific pharmacological countermeasures, to combat the development and sequelae of increased ICP during future missions.

In order to fully characterize intracranial adaptation to long-term microgravity, we will use magnetic resonance imaging (MRI) which is the terrestrial gold standard. MRI allows direct visualization and functional characterization of the intracranial contents. Indeed, MR imaging is the clinical standard of care in evaluating patients with idiopathic intracranial hypertension. We will use a suite of advanced MRI sequences to: (1.) characterize weightlessness-induced intracranial compartmental fluid volume changes at the macroscopic (brain, CSF, orbit), microscopic (brain tissue water) and vascular (arterial and venous) levels following adaptation to long-term spaceflight and (2.) assess for potential resultant hemodynamic changes (cerebral perfusion) in the brain. This proposal represents the most relevant and advanced suit of MRI techniques for the characterization of intracranial compartmental fluid and hemodynamic changes induced by long-term microgravity. The specific sequences will be carried out by the recognized experts in each area and in most cases, the developer of the specific technique.

It is imperative to obtain this data in order to have an understanding of what is happening to the brain and orbits while living and working in microgravity. We are only now realizing the consequences of this lack of knowledge. This data will serve as the basis for the development of fundamental theories describing intracranial adaptation to microgravity. It may help establish a risk stratification strategy based on intracranial anatomy, dural venous sinus and jugular vessel outflow, cranial compliance, and cerebral vascular autoregulation. Importantly, it will serve as a basis for interpretation of in-flight data collected via other techniques such as ultrasound, the primary in-flight imaging modality.

New project for FY2013 in November 2012.