Thin-film micro-coil detectors: Application in MR-thermometry

• Design, fabrication and integration of thin-film disposable micro-coils with ablation catheters for MR-thermometry are described.
• Integrated capacitors allow for tuning and matching by means of mechanical trimming.
• Improvement in the temperature accuracy and SNR by 1.5–10 times compared to the best locally available array coil was demonstrated in-vitro.
• Resolution of 1 mm can be maintained during motion by using short acquisition time sequences.
• The temperature noise does not exceed 1 °C during motion.

Thin-film micro-coils are integrated with commercially available ablation catheters, for MR-thermometry during laser interstitial thermal therapies (LITTs). The coils are formed on a flexible polyimide substrate and consist of a two-turn electroplated copper inductor and integrated parallel plate capacitors for tuning and matching. Their performance was assessed during Nd:YAG laser ablations in a static phantom study carried out in a 3 T clinical scanner. Further moving phantom studies were performed to calculate errors due to motion. The temperature accuracy is improved by 1.5–10 times in a radius matching the dimensions of the lesions typically treated. Resolution of 1 mm can be maintained during motion by using short acquisition time sequences while the SNR remains sufficient for accurate MR-thermometry. The temperature error on a moving un-heated phantom under respiratory gating does not exceed 1 °C. This demonstration suggests a possible improvement of the overall control of MR-guided LITTs by local temperature monitoring.