3-D Microwave Scanner for Biomedical Applications: A Preliminary Prototype

This paper introduces the prototype of a scanning system operating in the microwave range 0.5–4 GHz with strong potential in biomedical applications such as breast cancer detection or to assess shape-discontuinity in bones. Based on the research outcomes in [1], a fully automated scanner was designed to reduce mechanical uncertainties and data acquisition time. Accurate positioning and synchronization with data acquisition enables a rigorous proofof-concept for the microwave imaging procedure.
The system can remotely control two printed antipodal Vivaldi antennas that scan a phantom across a set of positions arranged in cylindrical coordinates. For antenna miniaturization and improved coupling, the antennas, interface and phantom are immersed in a coupling medium that offers electric properties similar to adipose tissue. The antenna positioning, data acquisition and post-processing are automated. In the current version the reflection coefficients are measured by a Vector Network Analyzer (VNA). The integration of dedicated electronics attached to each antenna will replace the VNA to speed up data acquisition. Without any difficult a priori antenna
characterization, the system is capable of detecting distinctive dielectric contrast in the phantom enclosed regions. By processing measured reflection coefficients with an interferometric version of the Multiple Signal Classification (MUSIC) algorithm [1], the detection of inserted targets in three-dimensional reconstructions is successful. The achievable performance obtained by IMUSIC is then compared with two other methods in the literature: the non-coherent migration [2] which is a particular version of beamforming, and the standard wideband MUSIC technique [3].
From experimental results carried out on a multi-layer phantom made of glass and pork fat, a metallic bar of diameter equal to 8 mm was used as a target for a preliminary characterization of the scanning system.