Evaluation of the hot embossing technology for the fabrication of resonant circuits as instrument visualization method for interventional magnetic resonance imaging

Magnetic resonance imaging (MRI) possesses the advantages of an arbitrary slice positioning, the absence of ionizing radiation and a superior soft tissue contrast. On that account, it is a well-suited image guiding modality during minimally-invasive interventions. However, there is a lack of the visibility instruments such as polymer catheters. Therefor, resonant circuits enable a promising method for instrument visualization during interventional MRI. For that reason, this paper focuses on the fabrication of single loop coils onto a 2 mm polymer catheter using the foil-based hot embossing technology. Based on simulation for determining the achievable inductance and resistance, an embossing punch for planar substrates was designed. Embossing parameters for the specific polymer material were identified with the planar embossing process and adapted to the cylindrical shape of the catheter. The embossing results were evaluated according to self-defined criteria regarding embossing errors, geometrical changes and the adherence. The frequency tuning of the entire resonant circuit was verified by inductive coupling to a vector network analyzer. Thereby a quality factor of 29.4±3.6 could be measured. MRI visibility tests have been conducted inside the MAGNETOM Skyra 3T MRI scanner and demonstrated a proper functionality of the tuned resonant circuits. In summary, it can be stated that the foil-based hot embossing process is well-suited for manufacturing single loop coils onto polymer catheters. However, future investigations should target an implementation of the capacitance by using pre-structured foils.