A Transmission Line Matrix Model for Shielding Effects in Stents

In an attempt to determine the RF shielding artifacts produced by conducting stents during MRI scanning of patients, a Transmission Line Matrix (TLM) model was developed based on the symmetrical condensed node. This approach allows considerable flexibility including freedom from stability issues and the ability to reconstruct digital signals in the time or frequency domain. To validate the results of the model, simplified phantom stents were built, embedded in a gelatinous substance, scanned and the MR data compared directly with the TLM data. The ultimate purpose of the model is enhancement of MR data in stents by compensation of the artifacts with numerically generated data. By subtraction of the shielding artifacts, the MR image can be substantially enhanced. The results obtained from the TLM model compare very well with those obtained with MRI and are within the experimental error expected from MR data. Subtraction of the TLM data from experimental MR data shows significant enhancement in the contrast within the stent.