Abstract
Patients with retained epicardial pacing leads following cardiac surgery are restricted MRI access due to risks of static-field translational forces and torques, despite frequent diagnostic need for MRI in this patient population. This thesis developed and clinically tested three custom non-magnetic fixtures to quantify these interactions at micro-Newton scales: a PVC platform for magnetic field characterization, a pendulum for displacement force, and a strain-gauge sensor and fixture for torque.
Each fixture was validated in a controlled laboratory environment using an air-core solenoid and Helmholtz/neodymium fields (≤180 G), then tested on a 3 T Siemens Magnetom™ scanner at CHI Health CUMC–Bergan Mercy. Laboratory field mapping confirmed the expected field spatial decay, establishing the |B∇B| product needed for force predictions. Trial pendulum measurements of a ferromagnetic object yielded χm/ρ = (2.01 ± 0.05) × 10 3 m3/kg (tan α = 0.002–0.012), validating the linear model before clinical deployment. Torque sensor calibration produced consistent linear voltage-to-force slopes across all orientations (τmin = 1.24 × 10 5N· m), and laboratory measurements confirmed τ ∝ B2 dependence (k = 379 ± 9 N/m, 2.3%).
Clinical field mapping yielded |B∇B| between 12.68 and 22.95 T2/m at the bore entrance. Translational-force ratios (FR = tan α) remained below the ASTM F2052-15 threshold of 1.0 for all tested materials. The Medtronic STREAMLINE 6492 unipolar epicardial lead reached the highest deflection (α = 9.5 , FR = 0.166), substantially higher than titanium references (FR = 0.006) yet well within the safety criterion. Extrapolation yielded allowable gradients of 107 T/m at 1.5 T and 54 T/mat 3.0 T for the unipolar lead, both far exceeding the scanner’s physical maximum (≤ 19 T/m). Clinical torque runs at B ≈ 1.5 T produced no measurable deflection, requiring further investigation.
The results indicate that micro-Newton-scale magnetic-field mechanical effects on the tested epicardial lead can be measured under 3 T conditions. Though the findings are limited to a single configuration and do not support general safety conclusions, it established a methodology that can be extended to evaluate a broader range of leaddesigns and conditions.