Figure 5.
Magnetic fields vary as a function of both spatial position and conductivity value. (A) Ratio of the eddy current-induced magnetic fields to the fields without material along the z-axis of the cylinder phantom. The ratio is greatest in the center of the phantom. (B, C) Overall field variations as a function of ϕ at z = 4.5 cm and r = 6 cm, as indicated on the phantom schematic. The variations are distinct when the amplitude of the overall magnetic field is very small in (B) (corresponding to σp = 1000 S/m and t = 0.13 microseconds), but they become blurred, and a smaller fraction of the overall field grows in magnitude in (C) (corresponding to σp = 1000 S/m and t = 1.35 microseconds. When the overall field is 1 μT in (C), the variation between regions of 4 S/m is about 1 nT.