Posture-dependent cerebrospinal fluid flow measurement in the optic nerve subarachnoid space using multi-delay 2D interslice saturation MRI.

Recent studies have indicated that CSF dynamics within the optic nerve subarachnoid space (ONSAS) may play an important role in the progression of optic diseases. Yet, as common optical tests are limited to the ocular structures and cannot probe beyond the optic nerve head, direct evaluation of CSF dynamics in ONSAS remains challenging due to limited imaging methods. In this study, we propose a non-invasive MRI method, inversion-recovery alternate ascending/descending directional navigation (IR-ALADDIN), that utilizes interslice saturation and variable delay times (TD) to enable quantification of extremely slow CSF flow in ONSAS. Simulations and flow phantom experiments were performed with various flow velocities to characterize the IR-ALADDIN signal. Then, a human study was conducted using multi-TD IR-ALADDIN to measure net/pulsatile CSF movements in ONSAS, under normal supine and head-down tilt (HDT) conditions. Our results demonstrate that human IR-ALADDIN signals were statistically significantly negative across all TD values, indicating posterior-to-anterior net CSF flow in the ONSAS, with an estimated velocity of ∼0.5-0.8 mm/s. The absolute values of IR-ALADDIN indicated existence of CSF pulsatile movements. Under the HDT condition, net CSF flow increased, while pulsatile CSF movements decreased (p < 0.01). Overall, we measured net/pulsatile CSF movements in the human ONSAS for the first time with flow direction and velocity consistent with previous predictions. This technique holds potential for identifying new biomarkers in patients with optic nerve-related diseases.