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

To develop an analytical model of the RF-shielding of laser-cut venous stents for different orientations and stent geometries.

Laser-cut venous stents are modeled as a grid composed of circular and rectangular loops. As these loops are orthogonal they shield different components of the transmit RF field. The shielding is calculated using Faraday's induction law, taking into account the self-inductance and mutual coupling of circular and rectangular loops, and Biot-Savart's law. The shielding of 95 stent-mimicking models was calculated, and numerical simulations and measurements were performed at both 1.5 and 3T for validation.

The shielding of circular and rectangular loops differed by less than 3.3% and 10% between calculations, simulations, and measurements. The overall stent length had negligible impact on the shielding (< 8%). The combined shielding of both loop types showed deviations of less than 10% compared to stent models with varying cell sizes. Orienting the stents at an oblique angle other than 0° or 90° to B₀, the model-predicted shielding values deviated by less than 14%/10% from the measured values at 1.5 T/3 T.

The model allows for the calculation of the B₁ shielding of laser-cut venous stents depending on their geometry and orientation relative to B₀. Thus, it may help to adapt imaging parameters such as the flip angle to optimize monitoring of stent patency.