Exploring Microwave Bone Imaging: Preliminary Reconstructions of Realistic Calcaneus Phantoms in Experimental Settings for Bone Health Monitoring.

Microwave Imaging (MWI) is an emerging imaging technique that can potentially replace current clinical methods (i.e., Dual-energy X-ray absorptiometry (DXA), computerized tomography (CT)) involved in the identification of bone anomalies and in the diagnosis of conditions like osteoporosis and osteoarthritis. Experimental characterizations along with imaging tests are required to validate this technology. In this work, an experimental multi-layer calcaneus-shaped phantom has been employed, which has already been tested from a numerical point of view in our previous works, providing promising results. The tissue-mimicking materials (TMMs) involved in this study (i.e., skin, cortical bone and trabecular bone phantoms) have been characterized and their dielectric properties are reported at 3 GHz. The multi-layer conformal phantom, composed of the three above-mentioned tissue-like mixtures, was then arranged within the imaging setup. A total of nine microstrip antennas were placed in contact with the phantom. The imaging system is equipped with a 2-port Vector Network Analyzer (VNA). Following the same procedure as in previous numerical investigations, a Distorted Born Iterative Method (DBIM) combined with an Iterative Method with Adaptive Thresholding for Compressed Sensing (IMATCS) was employed to reconstruct the collected signals at 3.3 GHz. The Normalized Root Mean Square Error (NRMSE) was calculated as a metric to evaluate the performance of 2D reconstructions. The findings of this preliminary investigation suggest that the proposed phantom is suitable for representing the corresponding human tissues and that the employed method can properly reconstruct the considered scenario.