An intrabody device, comprising: a liquid medical substance comprising a sclerosing agent for ablating a target vein; an intrabody device tip comprising: an administration channel forming an administration duct having a plurality of outlets substantially perpendicular to a main axis of said administration channel for releasing said liquid medical substance; an extraction channel encircling the administration channel, the lumen between the extraction channel and the administration channel forming a withdrawing duct having at least one inlet for withdrawing at least some of a residue of said released liquid medical substance; an additional withdrawing duct in the administration channel, the additional withdrawing duct having an inlet; an ejection force source connected to said administration duct and configured for applying an ejection force for conducing said liquid medical substance via said plurality of one outlets for administering said liquid medical substance at an ejection pressure, quantity and direction; and a suction force source connected to said withdrawing duct and to the additional withdrawing duct for applying a suction force for withdrawing said at least a residue of said liquid medical substance in a suction pressure, quantity and direction via the additional withdrawing duct from a distal end of the intrabody device tip and via a lumen between the extraction channel and the administration channel; wherein the plurality of outlets (2 15) are positioned between the at least one inlet of the extraction channel and the inlet of the additional withdrawing duct along the main axis, with the plurality of outlets positioned distally from the at least one inlet of the extraction channel; wherein a relation between said ejection and suction pressure, quantity and direction limits the extent of said liquid medical substance within a venous lumen to a predefined space. a liquid medical substance comprising a sclerosing agent for ablating a target vein; an intrabody device tip comprising: an administration channel forming an administration duct having a plurality of outlets substantially perpendicular to a main axis of said administration channel for releasing said liquid medical substance; an extraction channel encircling the administration channel, the lumen between the extraction channel and the administration channel forming a withdrawing duct having at least one inlet for withdrawing at least some of a residue of said released liquid medical substance; an additional withdrawing duct in the administration channel, the additional withdrawing duct having an inlet; an administration channel forming an administration duct having a plurality of outlets substantially perpendicular to a main axis of said administration channel for releasing said liquid medical substance; an extraction channel encircling the administration channel, the lumen between the extraction channel and the administration channel forming a withdrawing duct having at least one inlet for withdrawing at least some of a residue of said released liquid medical substance; an additional withdrawing duct in the administration channel, the additional withdrawing duct having an inlet; an ejection force source connected to said administration duct and configured for applying an ejection force for conducing said liquid medical substance via said plurality of one outlets for administering said liquid medical substance at an ejection pressure, quantity and direction; and a suction force source connected to said withdrawing duct and to the additional withdrawing duct for applying a suction force for withdrawing said at least a residue of said liquid medical substance in a suction pressure, quantity and direction via the additional withdrawing duct from a distal end of the intrabody device tip and via a lumen between the extraction channel and the administration channel; wherein the plurality of outlets (2 15) are positioned between the at least one inlet of the extraction channel and the inlet of the additional withdrawing duct along the main axis, with the plurality of outlets positioned distally from the at least one inlet of the extraction channel; wherein a relation between said ejection and suction pressure, quantity and direction limits the extent of said liquid medical substance within a venous lumen to a predefined space.