embodiment of fig1 and can be u shaped with an opening between the legs of the u201c u u201d dimensioned to frictionally clamp onto the outer wall of the catheter 110 that is the coupler can be in the form of a u shaped clip with the radius of the u smaller than that of the outer wall of the catheter so it flexes outwardly when placed over the strain relief of the catheter and then is frictionally retained on the catheter in another embodiment a second connector half is placed opposite the connector to form a 360 degree clip or clamp surrounding the outer wall of the catheter to retain the connector coupler on the catheter 110 other methods of attachment are also contemplated such as magnetic attachments a cable 134 is connected to the coupler at one end 135 and connected at the opposing end 136 to density reader 140 as shown the coupler 130 is attached to the region of catheter 110 just distal of hub 122 although other locations are also contemplated the density sensor 126 is positioned at the distal portion 114 of the catheter 110 at the distalmost tip 115 and is electrically coupled to cable 134 via a pair of wires not shown extending from the sensor 126 to the coupler 130 and or cable 134 the wires can be embedded in a wall of the catheter 110 or alternatively extend through a lumen in the catheter 110 the sensor 126 in the illustrated embodiment is at the distalmost tip but alternatively could be spaced from the distalmost end so the catheter tip can extend past the clot during use while the.