Ultrasonic Tracking of a Rapid-Exchange Microcatheter with Simultaneous Pressure Sensing for Cardiovascular Interventions

Ultrasound imaging is widely used for guiding minimally invasive cardiovascular procedures such as structural heart repair and renal denervation. Visualization of medical devices such as catheters is critically important and it remains challenging in many clinical contexts. When 2D ultrasound imaging is used, the catheter can readily stray from the imaging plane; with 3D imaging, there can be a loss of visibility at steep angles of insonification. When the catheter tip is not accurately identified, there can be damage to critical structures and procedural inefficiencies. In this paper, we present a tracking system to directly visualize a custom fiber optic ultrasound sensor integrated into a rapid-exchange microcatheter, in the coordinate system of an external ultrasound imaging probe. Pairs of co-registered images were acquired in rapid succession: a tracking image obtained from the ultrasonic sensor signals that were time-synchronized to the ultrasound imaging probe transmissions, and a conventional B-mode ultrasound image. The custom fiber-optic sensor comprised a free-standing membrane originally developed for blood pressure sensing, which was optically interrogated with a wavelength-tunable laser for ultrasound reception. The measured axial and lateral tracking accuracies in water were both within the range of 0.2 to 1 mm. To obtain a preliminary indication of the clinical potential of this ultrasonic tracking system, the microcatheter was delivered over a guidewire into the femoral and renal arteries in an in vivo porcine model and intravascular blood pressure waveforms were obtained concurrently. The results demonstrate that ultrasonic catheter tracking using optically-interrogated fiber optic blood pressure sensors is viable, and that it could be useful to guide minimally invasive cardiovascular procedures by providing accurate, real-time position measurements.