Velocity Filtering with a Median Filter Better Preserves Small Vessels for Ultrasound Localization Microscopy

Recently, velocity filters have been proposed for ultrasound localization microscopy to ensure a good localization for increased microbubble concentrations by separating microbubbles into different bands by flow velocity and direction before the localization. However, testing these filters on B-mode data of curved and short microvessels and of low frame rates typical for commercial US devices, we observed the disappearance of short vessels and the prolongation of vessels. Therefore, we tested with simulations the use of a median filter instead of the recently proposed Gaussian filter since the median filter is known to preserve edges while removing noise. We show that the median filter performs slightly better regarding the standard metrics like the sensitivity or the mean squared error. Furthermore, it generally provides a better reconstruction of short and curved vessels.