Detection of cardiac-induced motion in murine cerebrospinal fluid space captured in vivo with synchrotron radiation-based microtomography

Transport of immune cells, nutrients and waste products via the cerebrospinal fluid (CSF) has been implicated in the development of neurological disorders. Using time-resolved in vivo microtomography, we investigated pulsatile motion of CSF spaces in the mouse brain as a potential driver of CSF flow. Here we present a method for detecting motion captured in murine brain images acquired in vivo at the European Synchrotron Radiation Facility. Anesthetized mice were placed in a heated holder that was designed to minimize head motion and maintain physiological body temperature. Contrast agent was infused into the ventricle to improve visibility of the CSF spaces. Projections were retrospectively sorted based on the ECG recording. Cardiac phase images were reconstructed in 10ms intervals from the ECG peak and automatically analyzed for decorrelation. Motion was automatically quantified by non-rigid registration. Regions with high intensity structures, large motion magnitudes, large improvements in image similarity due to registration, or at the contrast-enhanced ventricles were visually inspected for structures with motion artifacts prior to registration. We detected mainly motion in the nasopharynx, skin, ear channels, and bones in the range of 2.3 to 14.8µm magnitude. Small motion artifacts were detectable only for high-contrast structures. No misalignments were visible for the contrast-enhanced ventricles at a voxel resolution of 6.30 to 6.45µm. In the future, dedicated active gating to ensure regular sampling and local scans with improved spatial resolution will be used to investigate the limits to the detection of in vivo ventricular motion in mice.