Assessment of Intracranial Pressure via Ocular Hemodynamics Using Transocular Ultrasound Localization Microscopy

Knowledge of intracranial pressure (ICP) is essential for making decisions of surgical interventions for hydrocephalus patients. Direct invasive ICP measurements are risky. Hence, we explore noninvasive methods, where ICP is inferred from ocular hemodynamics. Ultrafast ultrasound localization microscopy (450 fps) is used for tracking microbubbles in the ocular vasculature of hydrocephalic infant pig models. Data processing involves SVD filtering to remove tissue signals, spatio-temporal band-pass filtering in the frequency domain for noise removal, and application of blind deconvolution to localize the bubble center. A Kalman filter along with several criteria are utilized for bubble tracking, which in turn define the location of blood vessels and the flow velocity in them. Data are acquired in 8 parallel horizontal planes to address potential effects of eye motion, and three of them, which contain similar vasculature, are used for analysis. Results of five pigs indicate that both retinal microcirculation and retrobulbar vascular flow decrease with increasing ICP. Accounting for pulse pressure, the correlation coefficients are 0.91 and 0.80, respectively. Such high correlation between ICP and quasi-3D imaging of ocular hemodynamics could have significant clinical implications.