Figure 1.

a) The magnetic flux lines in and around an oblate ellipsoid of bulk magnetic susceptibility (BMS) χ_i in an external medium with susceptibility χ_e (> χ_i), and positioned in a horizontal applied magnetic field. The field inside the ellipsoid is uniform, but there is a BMS frequency shift (δ_χ) relative to that of the external medium. The BMS frequency shift when the ellipsoid normal is aligned with the magnetic field (top) is smaller than when it is perpendicular (bottom), and the perpendicular orientation occurs much more often in randomly oriented cells. Lorentz cavities are not illustrated. b) The resulting intracellular ¹H₂O resonance frequency spectral distribution for a large ensemble of randomly oriented ellipsoids is the powder pattern (“in”). External to the ellipsoid, the magnetic field is perturbed, creating extracellular field inhomogeneities. The extracellular spectral distribution (“out”) is also shown. For these cartoon spectra, there is no trans-cytolemmal water molecule exchange (k_io = 0). Lorentz cavity effects are implicit in the spectra (compare Sup. Figs. S1 and S5).