Trajectory-specific motion-induced electromotive force assessment of pacemaker-carrying workers in MRI environments

Motion of individuals carrying active implantable medical devices (AIMDs), such as pacemakers (PMs) and implantable cardioverter defibrillators (ICDs), within the spatially varying static magnetic field in and around magnetic resonance imaging (MRI) systems can induce electromotive forces (EMFs) in conductive leads. This mechanism is not explicitly addressed in standard MRI safety assessments. This study presents a measurement-based computational framework to estimate motion-induced EMF under representative exposure conditions relevant to clinical practice.

Measured maps of the static magnetic field components (Bx, Bz) in the fringe region of 3 and 7 T MRI systems were interpolated on regular grids. Spatial gradients were derived and used to compute motion-induced EMF in an equivalent conductive loop representing a PM/ICD lead configuration. Three motion types were considered: linear motion along the scanner axis (z), linear motion transverse to the bore (x), and in-place rotation of the loop. EMF was calculated using Faraday's law, assuming a loop area of 0.0225 m², a reference linear velocity of 1 m/s, and an angular velocity of 1 rad/s. Spatial EMF distributions and time-dependent waveforms were obtained for each motion scenario.

Induced EMF varied significantly with motion direction and spatial location. For linear motion, the highest values were observed near the bore entrance, where strong spatial field variations occur. At 3 T, maximum EMF reached 160 mV (z-motion) and 114 mV (x-motion), while at 7 T the corresponding values were 81 and 104 mV for the analyzed trajectories. Rotational motion produced lower and more localized EMF values, with maxima of 30 mV (3 T) and 35 mV (7 T). Despite the higher nominal field strength, the 7 T system did not consistently yield higher EMF, reflecting differences in spatial field gradients.

Motion-induced EMF in MRI fringe fields depends on local spatial field gradients and motion characteristics rather than nominal field strength alone. The proposed measurement-based framework provides spatially resolved, scenario-specific estimates of EMF and can be applied to different MRI systems given appropriate field maps. This approach complements existing safety assessments by addressing motion-related exposure conditions not explicitly covered in standard evaluations.