Array design and development for steerable robotic guidewire
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Olomodosi, Adeoye Oluwatunmise
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Abstract
Approximately 4 million people with peripheral artery disease (PAD) present with critical limb ischemia each year, posing significant health risks including limb loss, exacerbating other comorbidities, and increasing risk of mortality. Urgent revascularization procedures are required for 1-2 patients per 10000 per year, however, navigating through occlusions in affected arteries, especially chronic total occlusions (CTOs), can be challenging, with failure rates up to 20% or greater depending on navigator’s experience. Minimally-invasive (i.e. endovascular) revascularization is preferable due to decreased recovery time and increased risk of complications associated with open surgery. However, 40% of people with PAD also have chronic total occlusions (CTOs), resulting in >20% of revascularization procedures failing when CTOs are present. A steerable robotic guidewire with integrated forward-viewing imaging capabilities would allow the guidewire to navigate through tortuous vasculature and facilitate crossing CTOs in revascularization procedures that currently fail due to inability to route the guidewire. The robotic steering capabilities of the guidewire can be leveraged for 3D synthetic aperture imaging with a simplified, low element count, forward-viewing 2D array on the tip of the mechanically-steered guidewire. Images can then be formed using a hybrid beamforming approach, with focal delays calculated for each element on the tip of the guidewire and for each physical location to which the robotically-steered guidewire is steered. Unlike synthetic aperture imaging with a steerable guidewire having only a single element transducer, an array with even a small number of elements can allow estimation of blood flow and physiological motion in vivo. A miniature, low element count 2D array transducer with 9 total elements (3 × 3) having total dimensions of 1.5 mm × 1.5 mm was designed to operate at 17 MHz. A proof-of-concept 2D array transducer was fabricated and characterized acoustically. The developed array was then used to image a wire target, a peripheral stent, and an ex vivo porcine iliac artery. Images were formed using the described synthetic aperture beamforming strategy. Acoustic characterization showed a mean resonance frequency of 17.6 MHz and a -6 dB bandwidth of 35%. Lateral and axial resolution were 0.271 mm and 0.122 mm, respectively, and an increase in SNR of 4.8 dB was observed for the 2D array relative to the single element case. The first 2D array imaging system utilizing both mechanical and electronic steering for guidewire-based imaging was developed and demonstrated. A 2D array imaging system operating on the tip of the mechanically-steered guidewire provides improved frame rate and increases field of view relative to a single element transducer.
To facilitate crossing CTOs, we propose a flexible, robotically steerable guidewire with an ultrasound transducer at the tip for procedural guidance. A miniature 2D array imaging transducer was developed and characterized for this application. The presented studies demonstrate i.) the fabrication of the aforementioned mechanically-steered 2D array transducer, ii.) image formation approach for the mechanically-steered system, iii.) the imaging experiments to demonstrate imaging performance in phantoms, and iv.) opportunities for future research and development. Results of this study suggest that this device could image occluded vascular regions to allow interventionalists to advance the guidewire beyond CTOs, which could improve procedural outcomes for PAD patients. Facilitating safer navigation through chronic total occlusions could ultimately reduce procedural risk and improve overall patient outcomes following peripheral endovascular revascularization.
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2024-07-25
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