an intravascular filter is constructed to electrostatically capture and retain particles of a targeted type , even if those particles are physically small enough to slip through the filter in the absence of electrostatic attraction . specific types of targeted particles are thereby captured and retained with improved efficiency , while permitting free flow of non - targeted particles . this improvement permits intravascular filters to be constructed with low - resistance , widely spaced filter elements . accordingly , more targeted particles are captured , less thrombosis occurs , less pressure drop occurs across the filter , and perfusion or blood collection in downstream areas is maintained .