An exploratory in vitro investigation to assess the potential of Time Inversion Spatial Labeling as a tool to quantify Lagrangian drift in the spinal canal.*

The pulsating motion of the cerebrospinal fluid in the spinal canal includes a mean Lagrangian drift, a reflection of the cumulative submillimeter net displacement experienced by the fluid particles during each motion cycle. The noninvasive quantification of this bulk motion in in vivo studies is difficult, because its associated velocities (~ cm/min) are much smaller than those of the predominant oscillatory motion (~ cm/s), making methods such as phase contrast (PC) MRI inadequate for this purpose. We hypothesize that methods based on Time Inversion Spatial Labeling, such as time-spatial labeling inversion pulse (T-SLIP), can be better suited to characterize the mean Lagrangian motion, thereby motivating the present in vitro exploratory investigation. Our study combines (PC) MRI  and T-SLIP flow measurements in a simplified phantom model representing the compliant spinal canal with theoretical predictions based on asymptotic expansions for small stroke lengths. The preliminary results obtained at different spinal levels and relevant physiological conditions show the potential of T-SLIP as a non-invasive method to quantify mean Lagrangian motion in the spinal canal.