Microwave thermography--characteristics of waveguide applicators and signatures of thermal structures.

In this paper, we study the problem of the interpretation of the signals provided by microwave thermography, which allows the detection of the thermal gradients in living tissues. These signals correspond to the thermal noise measured by a radiometer when the probe scans the surface of the tissues (passive process). We describe how these signals can be computed by means of a new method based on the antenna reciprocity principle. This process requires a knowledge of the electrical field distribution in the lossy medium when the applicator is radiating a microwave signal (active process). Examples of computations of the thermal signals and experimental verifications are presented. Then, we introduce a new concept of 'thermal signature' and show how it is possible to reach a quantitative interpretation of the thermal signals such as those obtained in clinical investigations (thermal pattern recognition).