RF-Shielding of Laser-Cut Venous Stents: Calculations, Simulations, and Experiments.

Area of Science:

• Biomedical Engineering
• Medical Imaging Physics
• Materials Science

Background:

• Laser-cut venous stents are crucial medical devices, but their impact on Magnetic Resonance Imaging (MRI) signal is not fully understood.
• Accurate prediction of radiofrequency (RF) shielding by these stents is necessary for safe and effective MRI monitoring.
• Existing models may not fully capture the complex interactions between stent geometry and RF fields.

Purpose of the Study:

• To develop and validate an analytical model for calculating the RF shielding properties of laser-cut venous stents.
• To investigate the influence of stent geometry (circular and rectangular loops) and orientation relative to the main magnetic field (B₀) on shielding.
• To provide a tool for optimizing MRI parameters for enhanced visualization of stented venous segments.

Main Methods:

• Modeled laser-cut venous stents as grids of orthogonal circular and rectangular loops.
• Calculated RF shielding using Faraday's induction law, incorporating self-inductance and mutual coupling.
• Validated the model through numerical simulations and experimental measurements at 1.5T and 3T across 95 stent configurations.

Main Results:

• The model demonstrated high accuracy, with calculated shielding values showing <3.3% and <10% deviation from simulations and measurements for individual loop types.
• Stent length had a minimal effect (<8%) on overall shielding.
• Model predictions for combined loop shielding and oblique orientations showed deviations <10% and <14%/10% (at 1.5T/3T) compared to measurements.

Conclusions:

• The developed analytical model accurately predicts the B₁ shielding of laser-cut venous stents.
• The model's dependence on stent geometry and orientation allows for tailored predictions.
• This tool can assist in adapting MRI parameters, like flip angle, to improve the monitoring of stent patency.