A microcatheter for insertion within a vessel comprising: a first, inner, tube sized and shaped for surrounding at least a portion of guidewire and having a first flange at a distal side thereof; a second, outer, tube at least partially disposed around said inner tube, said outer tube being slidingly associated with said inner tube and having a second flange at a distal side thereof, such that axial displacement of inner said tube relative to said outer tube increases or decreases the distance between said first and second flanges (306, 320); a deployment element comprising a helix, and disposed along the outer surface of said inner tube, and around at least a portion of an exterior of a distal end of the microcatheter between said first flange and said second flange and including edges for positioning against said flanges, wherein said deployment element is not secured to said inner tube; said deployment element being configured for repeated and reversible expansion and collapsing radially, increase in radial dimension of said deployment element due to reduction in axial length of said deployment element, said reduction in axial length due to reducing an axial distance between said first and said second flanges (306, 320), said microcatheter being arranged to allow forward pushing of said guidewire while said deployment element is expanded; and said expanded deployment element contacts the wall of said vessel so that at least part of said inner tube and said portion of the distal end of the microcatheter are radially positioned approximately in the middle of said vessel and wherein said deployment element has a cross sectional area in said expanded state that is small enough so as not to block more than 50% of blood flow in said vessel. a first, inner, tube sized and shaped for surrounding at least a portion of guidewire and having a first flange at a distal side thereof; a second, outer, tube at least partially disposed around said inner tube, said outer tube being slidingly associated with said inner tube and having a second flange at a distal side thereof, such that axial displacement of inner said tube relative to said outer tube increases or decreases the distance between said first and second flanges (306, 320); a deployment element comprising a helix, and disposed along the outer surface of said inner tube, and around at least a portion of an exterior of a distal end of the microcatheter between said first flange and said second flange and including edges for positioning against said flanges, wherein said deployment element is not secured to said inner tube; said deployment element being configured for repeated and reversible expansion and collapsing radially, increase in radial dimension of said deployment element due to reduction in axial length of said deployment element, said reduction in axial length due to reducing an axial distance between said first and said second flanges (306, 320), said microcatheter being arranged to allow forward pushing of said guidewire while said deployment element is expanded; and said expanded deployment element contacts the wall of said vessel so that at least part of said inner tube and said portion of the distal end of the microcatheter are radially positioned approximately in the middle of said vessel and wherein said deployment element has a cross sectional area in said expanded state that is small enough so as not to block more than 50% of blood flow in said vessel.