RESUMO
Superparamagnetic iron oxide nanoparticles (SPIOs) are used as tracers in Magnetic Particle Imaging (MPI). It is crucial to understand the magnetic properties of SPIOs for optimizing MPI imaging contrast, resolution, and sensitivity. Brownian and Néel relaxation theory developed in the early 1950s posits that relaxation times can vary with particle size, shell thickness, medium viscosity, and the applied field strength. Magnetic relaxation can soon provide a unique imaging capability, the ability to distinguish bound from unbound MPI tracers in vivo. Yet experimental validation of these theories has not been completed. In this paper, a novel method of pulsed magnetic field relaxometry is used to directly probe the relaxation behavior of superparamagnetic magnetite nanoparticles over a spectrum of magnetic field amplitudes, providing the first experimental validation of theoretical relaxation models. It is also shown that closed-form approximations generated in the early 1970s accurately match both data and numerical Fokker Planck computational models, which are computationally burdensome. This means researchers can trust these approximations for future modeling. All the findings can be translated to sinusoidal excitations used in conventional MPI scanning trajectories.
RESUMO
The Center for Bioengineering Innovation and Design (CBID) at Johns Hopkins University (JHU) has established a comprehensive approach to addressing global health challenges. Central to CBID's modality on global health is a strategy that integrates education, research, and collaboration. Through its graduate program, CBID trains the next generation of health care innovators to address the specific needs of low- and middle-income countries (LMICs). Graduate student teams at CBID begin their year with a focus on a health care thematic area associated with a target country.