123 - Developing 3D Intravascular Ultrasound Guidance for Recanalization of Central Venous Occlusions

Purpose: Central venous occlusions (CVOs) are a common long-term complication of central venous catheter placement in a broad patient population including those receiving hemodialysis {1}, parenteral nutrition {2}, chemotherapy {3}, or repeat drug infusions for sickle cell disease {4}.  Sharp recanalization of CVOs is technically challenging due to increased fibrosis and tortuosity of collateral vasculature, with severe complications including vessel perforation, pericardial tamponade, and hemothorax. To mitigate these risks, we developed a 3-D, forward-viewing ultrasound device compatible with a 9 French sheath that will allow interventionalists to directly visualize the occlusion and surrounding environment.

Materials and Methods:

The device was designed based on clinical parameters and further optimized by simulations using Field II and 1D Krimholtz- Leedom-Matthaei (KLM) modeling (PiezoCAD). We designed a ring-shaped ultrasound array with a frequency around 20 MHz to allow for greater penetration into surrounding tissue and visualization of deeper layers compared to existing IVUS technology. The device was then fabricated by building a cylindrical acoustic stack and laser-micromachining to separate each individual transducer element while maintaining a continuous matching layer for grounding. The layers in the fabricated acoustic stack were 0.065 mm E-solder 3022 matching layer, 0.07 mm PZT, and 1.0 mm E-solder 3022 backing. Lastly, the device was coated with a 0.002 mm parylene matching layer, which also protects the device from the environment.



Results:

After fabrication, the electrical behavior of each transducer element was characterized with a calibrated impedance analyzer (Keysight E4990A). Element yield was 75.7% (44/58) elements. The device then underwent acoustic testing with a point target in water, which showed clear visualization of the point target (the tip of a 75 μm wire) at a scale of -6dB. Pulse-echo testing of an element on this point target yielded a center frequency of 17.1 MHz and -6dB fractional bandwidth of 42.9%. Next, an 8 mm diameter stent was imaged using synthetic aperture. The stent was placed in water and successfully visualized from the top, through a depth of 18 mm.



Conclusion:

We successfully designed and fabricated a 3 mm, 17 MHz forward-viewing IVUS array that can be integrated on the tip of a catheter for use in high-risk CVO revascularization procedures. This device serves as a proof of concept for a novel fabrication method that is adaptable to different catheter sizes and shapes, allowing application to multiple clinical needs.