IVUS of micromotors for cardiovascular imaging

Intravascular ultrasound is the new gold standard for detection of coronary artery disease. It is an adjunctive diagnostic procedure in cardiac catheterization laboratories. Currently, mechanical single elements or electronic multi-element catheter-based imaging systems are available with significant drawbacks either due to the long catheter drive shaft with an external motor or the multi-element methodological problems of the technology. In order to overcome the limitations of mechanical single element catheters, a micromotor was mounted in the distal part of a scanning compartment in front of a rotating mirror which reflected the ultrasound beam of a 30 MHz transducer. The rotation was between 3000 and 20000 rev/min, the position accuracy was +/-10 degrees, the torque force 1-3 mu Nm, the power dissipation 10-50 mW, the diameter 1 mm, the length 2 mm. Cross-sectional images (360 degrees) are provided. The catheter is connected to a console generating the transmission pulse, amplification of the echo signals and the envelope detection of the ultrasound. The unit is interfaced with a control unit which provides the isolated motor currents with isolated power for the electronics and synchronization signals. For the first time the micromotor tip catheter was used in a 64-year-old patient for imaging the iliac artery in full length. The wall structure, the vessel lumen and even adjacent structures like the iliac vein could be visualized with changes during respiration. Signs of arteriosclerosis were seen by the plaque formation which was located eccentrically. The resolution was as high as with conventional mechanical catheters. Most importantly, no non-uniform rotation artefacts occurred. A micromotor system can be successfully used for replacing the motor drive shaft of catheters which are used for intracoronary and intravascular ultrasound and eliminate nonuniform rotational artefacts due to friction and multiple vessel angulations.