3-T MRI in vitro characterisation of a SPION-polymer balloon catheter: a proof-of-concept study.

OBJECTIVE: Magnetic resonance imaging (MRI)-guided endovascular interventions represent a radiation-free alternative to x-ray fluoroscopy but remain limited by the lack of compatible and visible instruments. This study aimed to characterise a balloon catheter with polymer-embedded superparamagnetic iron oxide nanoparticles (SPIONs) as a passive MR-visible marker. MATERIALS AND METHODS: The SPION balloons consisted of a polymer with integrated iron oxide particles. A custom-built phantom study was conducted on a clinical 3-T MRI scanner using a balanced steady-state free precession sequence. Parameters influencing the balloons' imaging properties were evaluated: SPION content (5 weight percent (wt%), 20 wt% and 30 wt%), flip angle (10° to 60°), the balloons' spatial orientation relative to the main magnetic field B0, the inflation state and phase-encoding direction across different spatial orientations. The SPION-induced susceptibility artefacts were quantified from segmentations independently performed by two board-certified radiologists. RESULTS: All SPION-polymer balloons were discernible at 3-T MRI across all tested SPION concentrations. No linear correlation was observed between SPION concentration and artefact dimension, with the intermediate concentration of 20 wt% yielding the smallest artefact size. The balloons' artefact dimensions increased with higher angulations relative to B0. Balloons were visualised in the inflated and deflated configurations. The flip angle had a limited impact on artefact dimensions, while higher flip angles resulted in increased SNR. The influence of phase-encoding direction was generally minor with a single exception (90° coronal plane, AP to RL). CONCLUSION: The SPION-polymer balloons were effectively visualised at 3-T MRI irrespective of orientation and inflation. This in vitro study outlines a proof-of-concept supporting future clinical use of polymer-integrated SPIONs for passive device visualisation in interventional MRI. RELEVANCE STATEMENT: SPION-polymer balloons can be visualised in 3-T MRI, providing a foundation for future MRI-visible interventional instrument designs. KEY POINTS: Visualisation properties of a SPION-polymer balloon catheter were systematically assessed at 3-T MRI to overcome the shortage of MRI-visible instruments. SPION-polymer balloons were effectively visualised across different spatial orientations in the inflated and deflated state. Polymer-integrated SPIONs demonstrate potential as passive instrument markers for MRI-guided interventions.