Microwave radiometric thermometry and its potential applicability to ablative therapy

Introduction: Current techniques for estimating catheter tip temperature in ablative therapy for cardiac arrhythmias rely on thermocouples or thermistors attached to or embedded in the tip electrode. These methods may reflect the electrode temperature rather than the tissue temperature during electrode cooling so that the highest temperature away from the ablation site may go undetected. A microwave radiometer is capable of detecting microwave radiation as a result of molecular motion. In this study, we evaluated microwave radiometric thermometry as a new technique to monitor temperature away from the electrode tip during ablative therapy utilizing a saline model. Methods and Results: A microwave radiometer antenna and fluoroptic thermometer were inserted in a test tube with circulating room temperature saline kept constant at 23.5°C while the surrounding saline bath was heated from 37°C to 70°C. For every degree rise in the warm saline bath placed either 5 mm or 8 mm from the radiometer antenna, the radiometer temperature changed 0.26°C and 0.14°C respectively while the fluoroptic temperature probe remained constant at 23.5°C. The radiometer temperature was highly correlated with the warm saline bath temperature (R² = 0.997 for warm saline 5 mm from the antenna, R² = 0.991 for warm saline 8 mm from the antenna). Conclusions: Microwave radiometry can estimate distant temperatures by detecting microwave electromagnetic radiation. The sensitivity of the microwave radiometer is also distance-dependent. The microwave radiometer thus serves as a promising instrument for monitoring temperatures at depth away from the catheter-electrode tip in ablative therapy for cardiac arrhythmias.