Thin-Film Detector System for Internal Magnetic Resonance Imaging

A detector for in vivo internal magnetic resonance imaging (MRI) is demonstrated based on a thin-film RF resonator and a thin-film cable. Each component is constructed on a flexible sheet and mounted on the outside of a catheter, leaving its internal lumens free for clinical use. Space constraints require the sheet to be extremely thin (< 100 μm). Cable formats are compared, and thin-film cables with ≈ 50 Ω impedance at low frequency are formed as a microstrip with a periodically patterned ground, using copper conductors on polyimide substrates. Resonant detectors are also formed on polyimide from multi-turn electroplated copper coils and integrated parallel plate capacitors, which use the substrate as an interlayer dielectric. Methods are developed for obtaining capacitor values for matching and tuning, and compensating for loading. The detector and cable are linked to form a two-metre-long printed detection system and 1H MRI is demonstrated at 1.5 T using in vitro liver tissue.