Technical aspects of ultrasound imaging guidewires

In many interventional catheterization laboratories around the world the use of intravascular ultrasound (IVUS) has become a routine addition to the catheter-based interventional procedures. IVUS catheters, for coronary use, typically of a size around 3 French, provide images that assist in diagnosing the coronary obstructive disease, choosing the most appropriate recanalization method, monitoring the recanalization process and evaluating the end result. The downside of the use of IVUS, apart from additional cost to the procedure, is the additional exchange of catheters during the procedure. Several designs of hybrid catheters have been proposed, combining IVUS imaging with a therapeutic de-obstruction method in one catheter. A more modular approach is to equip the guidewire with imaging capability. Such a guidewire would provide an image of the stenotic region as well as guide the recanalization catheter to its location. It will, however, require further miniaturization of the ultrasound imaging technology, which already is scaled down considerably to enable coronary imaging. In addition, the ultrasound imaging guidewire (UIG) would have to possess specific qualities in bending and torque to act as a true guidewire. A first step to modularity is the separately used 'imaging core', which is advanced into the guidewire lumen of a therapeutic catheter, but cannot guide this catheter to the desired location. The combination of both imaging and mechanical requirements would yield a true UIG, but constitutes major technical challenges.