A coupler assembly (100; 200; 701; 801) for an intravascular catheter comprising: a coupler; an ultrasonic transducer array mechanically coupled to a distal end of the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000); first and second magnetic positioning sensors (101, 102; 201', 202'; 701', 702') coupled to the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000) at nonparallel orientations relative to one another, the first and second magnetic positioning sensors (101, 102; 201', 202'; 701', 702') configured and arranged to transmit an electrical signal indicative of the six degrees of freedom that the ultrasonic transducer array has within a controlled magnetic field; a pull-ring (714; 814) coupled to the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000) and one or more steering wires (715 1-4 ; 815 1-4 ), the pull-ring (714; 814) and one or more steering wires (715 1-4 ; 815 1-4 ) configured to facilitate steering the intravascular catheter via actuation of the one or more steering wires (715 1-4 ; 815 1-4 ), and a plurality of trenches (107; 201, 202; 301, 302; 401, 402; 501, 502; 601, 602; 1001, 1002) extending into an outer surface of the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000), the trenches (107; 201, 202; 301, 302; 401, 402; 501, 502; 601, 602; 1001, 1002) housing the magnetic positioning sensors and a thermistor , wherein electrical conductors from each of the magnetic sensors and thermistor are routed proximally along a pathway (103, 103'; 203; 303, 303'; 403; 503; 603; 703; 803; 903; 1003) cut into the outer surface of the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000).. a coupler; an ultrasonic transducer array mechanically coupled to a distal end of the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000); first and second magnetic positioning sensors (101, 102; 201', 202'; 701', 702') coupled to the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000) at nonparallel orientations relative to one another, the first and second magnetic positioning sensors (101, 102; 201', 202'; 701', 702') configured and arranged to transmit an electrical signal indicative of the six degrees of freedom that the ultrasonic transducer array has within a controlled magnetic field; a pull-ring (714; 814) coupled to the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000) and one or more steering wires (715 1-4 ; 815 1-4 ), the pull-ring (714; 814) and one or more steering wires (715 1-4 ; 815 1-4 ) configured to facilitate steering the intravascular catheter via actuation of the one or more steering wires (715 1-4 ; 815 1-4 ), and a plurality of trenches (107; 201, 202; 301, 302; 401, 402; 501, 502; 601, 602; 1001, 1002) extending into an outer surface of the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000), the trenches (107; 201, 202; 301, 302; 401, 402; 501, 502; 601, 602; 1001, 1002) housing the magnetic positioning sensors and a thermistor , wherein electrical conductors from each of the magnetic sensors and thermistor are routed proximally along a pathway (103, 103'; 203; 303, 303'; 403; 503; 603; 703; 803; 903; 1003) cut into the outer surface of the coupler (100'; 200'; 300; 400; 500; 600; 700; 800; 900; 1000).. <EOS>