A New RF Radiometer for Absolute Noninvasive Temperature Sensing in Biomedical Applications

Temperature sensing using microwave radiometry has proven value for non-invasively measuring the absolute temperature of tissues inside the human body. However, current clinical radiometers operate in GHz or infrared frequency ranges; this limits their depth of penetration since the human body is not "transparent" at these frequencies. To address this problem, we have designed and built an advanced, near-field radiometer operating at VHF frequencies (64MHz) with a ~100 KHz bandwidth. In the core of the radiometer lie an embedded impedance analyzer and an automatic antenna matching network; they compensate in-real time for any load variation that may occur due to near-field antenna coupling and movements of the human body. The radiometer has performed accurate temperature measurements to within plusmn0.1degC, over a tested physiological range of 28-40degC in saline phantoms whose electric properties match those of human tissue. The current method has the potential of being integrated on magnetic resonance imaging (MRI) modalities.