Author: Clifford Eskey, Scott Gordon-Wylie, Scott Gordon-Wylie, Dhrubo Jyoti, Daniel Reeves, John B. Weaver 👨🔬
Affiliation: Flow Aluminum, Dartmouth College, Fred Hutch Cancer Center, University of Washington, Dartmouth-Health 🌍
Purpose: Mechanical thrombectomy (MT) is the preferred treatment for ischemic stroke from large vessel occlusion. The thrombus or clot is extracted from the vessel via a catheter using a stent retriever or simple suction. However, the thrombus can slip or fragment as it is moved through the vessel especially around curves. Real-time feedback about the position of the clot relative to the stent should enable the physician to adjust the speed and force used to pull the thrombus to minimize fragmentation and incomplete removal. We are exploring a system using: a) antibody-targeted magnetic nanoparticles (NPs) injected via a microcatheter to coat the clot, b) alternating magnetic fields to induce a magnetization, and c) a small coil attached to the catheter or stent to measure the magnetization. We are reporting on a method of estimating the distance that is independent of the orientation of the stent and pickup coil relative to the applied field and the thrombus so the method functions as the thrombus is pulled around curves in the vessel.
Methods: Simulations of the signal from NPs distributed on the thrombus from three orthogonally applied magnetic fields were made. An in vitro apparatus was built that applied fields and read out signals from a 1.5 mm pickup coil at variable distances and orientation angle from a sample of 100 nm iron oxide core/shell NPs.
Results: The sum of the simulated voltages induced in the pickup coil from three orthogonal alternating fields achieved localization to within 180 µm independent of orientation. Further precision was added via rotation-correction formulae. Experiments validated the simulations; we calculated a precision of 41 µm 1 mm from the pickup coil.
Conclusion: Magnetic nanoparticle sensing could provide a real-time method to identify thrombus slippage or fragmentation during extraction.