Abstract: An aspiration thrombectomy system is described with an aspiration catheter assembly having fittings interfaced with conduit and a pump. The aspiration catheter assembly can include a guide catheter and an aspiration catheter. The aspiration catheter can be introduced with a proximal end of a tubular element placed within the guide catheter to form a suction lumen extending through the aspiration catheter and a portion of the guide catheter. A connection section forming an effective seal between the aspiration catheter and the inner wall of the guide catheter can be fixed or extendable through actuation or release of a self-extending structure. The aspiration catheter can be positioned into an artery with a distal opening positioned proximal to a clot. The fittings can include a filter for removing thrombus from the aspiration flow. The fittings and/or the tubing adjacent the pump can include a flow meter for measuring flow to the pump.