RECENT TRENDS IN MEDICAL MICROWAVE RADIOMETRY

Microwave radiometry has been investigated for non-invasive measuremen t of temperature in human body. Recent trends are to explore the capab ility of retrieving a temperature profile or map from a set of brightn ess temperatures measured by a multifrequency radiometer operating in a 1-6 GHz range. The retrieval of temperature from the multifrequency measurement data is formulated as an inverse problem in which the numb er of independent measurement or data is limited (less than or equal t o 7) and the data suffer from considerably large random fluctuations; The standard deviation of the data fluctuation is given by the brightn ess temperature resolution of the instrument (0.04-0.1K). Solutions ar e prone to instabilities and large errors unless proper solution metho ds are used. Solution methods developed during the last few years are reviewed: singular system analysis, bio-heat transfer solution matched with radiometric data, and model-fitting combined with Monte Carlo te chnique. Typical results obtained by these methods are presented to in dicate a crosssection of the present-state-of-the-development in the f ield. This review concludes with discussions on the radiometric weight ing function which connects physical temperatures in object to the bri ghtness temperature. Three-dimensional weighting functions derived by the modal analysis and the FDTD method for a rectangular waveguide ant enna coupled to a four layered lossy medium are discussed. Development of temperature retrieval procedures incorporating the 3-D weighting f unctions is an important and challenging task for future work in this field.