Ferrimagnetic Particles in the Lung Part 1: The Magnetizing Process

The magnetization process of ferrimagnetic particles in the lung takes place when an external magnetic field is applied to the lung; the particles both become magnetized and rotate toward alignment with the applied field. The purpose here is to consolidate previous and new measurements of this process, for Fe3O4 particles in the human lung, and to interpret the measurements. The particular quantity measured was Bn, the remanent magnetic field at the chest produced by the particles after removal of the applied field. Bn was measured as a function of three variables. The first two are the strength and duration of the applied field, yielding the remanent magnetization curve and the viscosity curve respectively; these were measured both for particles initially unmagnetized and initialiy magnetized. The curves are qualitatively explained by a simple physics model consisting of single-domain and multidomain particles; these reside in a viscous fluid and experience physiological impulses (relaxation) which oppose the alignment during magnetization. The third variable is the state of breathing; Bn was measured when normal breathing was switched to exhale-and-hold during either magnetization or measurement. The effects on Bn of this switch are explained by considering the alveolar walls; forced exhalation is assumed to "crumple" the walls, thereby realigning the particles contained in the alveoli.