Motion-induced fields near an idealized actively shielded MRI magnet: a reproducible reduced-order framework for scaling and sensitivity from 1.5 to 7 T.

purposeTo present a transparent reduced-order electromagnetic framework for examining how an explicitly specified magnet geometry, movement trajectory, and body-conversion model affect movement-induced field estimates near MRI systems. The framework distinguishes dependencies imposed by the equations from spatial and sensitivity results computed from the field map.

methodsAn idealized actively shielded magnet was represented by primary and opposing coaxial solenoids. A 7-T reference system was calibrated at two axial points; 1.5 T and 3 T cases were then generated by matched-geometry ampere-turn scaling as a controlled thought experiment. Movement-induced dB/dt was calculated from the directional derivative v·∇|B|. The primary whole-trunk screening estimate used an ellipsoidal conversion coefficient of 0.16 V m

resultsAlong the specified axial path, the peak dB/dt at 1.5 m s

conclusionThis reproducible reduced-order framework quantifies how active-shield geometry, movement direction, and body-conversion assumptions shape motion-induced field estimates near an idealized MRI magnet. The calculations expose substantial sensitivity to the body model, shield geometry, and trajectory, providing a transparent basis for education, model verification, and the design of scanner-specific dosimetric studies. Translation to regulatory compliance or operational guidance requires measured or vendor-provided fringe-field maps, anatomically resolved dosimetry, waveform analysis, and local safety procedures.