Phantom-based evaluation of time-SLIP MRI for measuring spinal-canal Lagrangian drift

Abstract The pulsatile motion of cerebrospinal fluid (CSF) in the spinal canal includes a mean Lagrangian drift, representing the cumulative net displacement experienced by the fluid over each oscillatory cycle. Quantifying this motion in vivo is challenging because the associated velocities ( $$\\sim $$ cm min $$\\vphantom{0}^{-1})$$ are much smaller than those of the dominant oscillatory flow ( $$\\sim $$ cm s $$\\vphantom{0}^{-1}$$ ), limiting the applicability of conventional phase-contrast (PC) MRI. Here we assess the suitability of Time-Spatial Labeling Inversion Pulse MRI (Time-SLIP) for characterizing this motion using in vitro experiments in a spinal-canal phantom. The phantom consists of a flexible tube with a rigid insert forming an eccentric annular canal representative of the spinal subarachnoid space, driven by a 1 Hz sinusoidal flow mimicking cardiac-induced CSF pulsations. Oscillatory velocities were measured with PC-MRI, while net fluid displacement over successive cycles was quantified using Time-SLIP and compared with numerical simulations. The measurements reveal spatially varying Lagrangian drift directed caudally in narrow regions and cranially in wider regions of the annulus, with magnitude scaling with the square of the local stroke volume. These results demonstrate that Time-SLIP can quantify mean Lagrangian motion associated with pulsatile CSF flow.