Performance Evaluation of Various Antenna Configurations for Microwave Thermography During Superficial Hyperthermia

Abstract

Microwave thermography is currently under investigation for its potential in non-invasive monitoring and control of tissue temperature during superficial microwave hyperthermia treatments. In this effort, six antennas were tested for their suitability as radiometric probes in terms of penetration depth, signal-to-noise ratio, and the sensitivity and accuracy of measured temperature signals over the frequency range from 1.2-3.5 GHz. Due to the intended integration of this radiometry technique with large area multi-aperture heat applicators such as Dual Concentric Conductor (DCC) arrays, the size of each receive antenna was limited to 4 cm. The performance of logarithmic and Archimedean spiral microstrip structures was compared to dielectric loaded waveguide antennas. Results showed adequate signal-to-noise ratio for all antennas at frequencies above 2.5 GHz and for all antennas except the electrically small waveguides over the entire frequency range. Overall, the signal sensitivity from 1 to 3 GHz was approximately 2-3 times higher for the three broadband spirals than the waveguides or DCC apertures, and similar at the upper part of the band. Under clinically relevant conditions of probing the tissue load through a 5 mm water bolus maintained at constant 40° C, the spiral antennas all produced comparable accuracy of temperature measurements on the order of 0.15-0.2° C for a uniform temperature load.