Anthropomorphic Calcaneus Phantom for Microwave Bone Imaging Applications

Recent studies have found a significant dielectric contrast between healthy and osteoporotic human trabecular bones. This dielectric contrast can be exploited by microwave imaging for monitoring human bone health. The tissue-mimicking phantoms play a vital role in preclinical testing of the microwave imaging system. This paper presents anatomically realistic multi-layered 3D-printed and carbon black-based human calcaneus structure. The liquid and solid based tissue-mimicking mixtures are also proposed to mimic the dielectric properties of skin, muscle, cortical bone, and trabecular bone. The liquid tissue-mimicking mixtures are composed of Triton X-100, water, and salt, whereas the solid tissue-mimicking mixtures are composed of carbon black, graphite, polyurethane, and isopropanol. The dielectric properties of the tissue-mimicking mixtures were measured using an open-ended coaxial probe measurement technique across 0.5–8.5 GHz. The average percentage difference between the relative permittivity and conductivity of reference data and proposed liquid tissue-mimicking mixtures was found to be 7.8% and 9.6% for skin, 0.38% and 14% for muscle, 9.6% and 5% for cortical bone, and 3.4% and 2.4% for trabecular bone, respectively, across 0.5–8.5 GHz. For solid tissue-mimicking mixtures, this difference was found to be 3.93% and 0.64% for skin, 6.13% and 9.21% for cortical bone, and 10.66% and 41.82% for trabecular bone, respectively for relative permittivity and conductivity. The proposed tissue-mimicking mixtures along with 3D-printed structures can be used as a valuable test platform for microwave bone imaging system development.