Effects of motion and retrospective motion correction on the visualization and quantification of perivascular spaces in ultrahigh resolution T2-weighted images at 7T.

Purpose Motion can strongly affect MRI image quality and derived imaging measures. We studied the effects of motion and retrospective motion correction (MC) on the visualization and quantitative measures of the perivascular space and penetrating vessel (PVSV) complex, an essential part of the glymphatic system, on high-resolution T2 -weighted MRI images at 7T. Methods MC was achieved by adjusting k-space data based on head positions measured using fat navigator images. PVSV visibility and quantitative measures including diameter, volume fraction (VF), count, and contrast were compared between images with and without MC. Results Without MC, VF, and count decreased significantly with increasing head rotation. MC improved PVSV visualization in all cases with severe motion artifacts. MC decreased diameter in white matter (WM) and increased VF, count, and contrast in basal ganglia and WM. The changes of VF, count, and contrast after MC strongly correlated with motion severity. MC eliminated the significant dependences of VF and count on rotation and reduced the inter-subject variations of VF and count. The effect sizes of age and breathing gas effects on VF and count, and contrast increased in most cases after MC, while those on diameter exhibited inconsistent behavior. Conclusions Motion affects PVSV quantification without MC. MC improves PVSV visibility and increases the statistical power of detecting physiological PVSV VF, count, and contrast changes but may have limited benefits for increasing the power for detecting diameter changes.