Author: Scott Gordon-Wylie, Scott Gordon-Wylie, Dhrubo Jyoti, John B. Weaver, Terrence Welch 👨🔬
Affiliation: Flow Aluminum, Dartmouth College, Dartmouth-Health 🌍
Purpose: Identifying vulnerable plaques is critical to preventing stroke and myocardial infarction. There are two components contributing to the risk of rupture: the mechanical integrity of the plaque and the external forces on the plaque. There has been real progress on understanding the mechanical integrity but there has been little progress on understanding the forces on the plaque from blood flow. Computational methods have proven to be challenging and Doppler ultrasound has had limited impact at least partly because it is measuring bulk properties. We are developing nanoparticle methods of measuring the microscopic velocity gradients within the flow.
Methods: Nanoparticle methods measure the effects of the microenvironment surrounding the nanoparticle. Magnetic nanoparticles (MNPs) can be detected deep in tissue because the magnetic fields used to manipulate the NPs and the resulting magnetizations penetrate tissue with essentially no loss. So we are exploring the impact of fluid flow on MNPs in an alternating magnetic field. Glass tubes with MNPs were inserted in the spectrometer and a peristaltic pump was used to generate controlled flow of a solution containing 100nm diameter MNPs. The MNP spectrometer generates an alternating magnetic field that induces a magnetization in the MNPs that is measured by a pickup coil. The third and fifth harmonics of the applied field were measured.
Results: Both the average phase and the size of the magnetization are monotonically related to the mean velocity gradient of the fluid in the tube for all velocities and tube sizes. The shape changed less dramatically and less consistently.
Conclusion: The dimensionless mean velocity gradient is the natural parameter to describe the flow effects on MNPs. The results suggest that the MNP measurements can be used to estimate the spatial average of the microscopic velocity gradients in the flow.