Free-Space Time-Domain Approach for Dielectric Imaging of Biological Tissues

Quantitative microwave imaging (MWI) has been an ongo-ing challenge in the scientific community due to the difficulties associated with the dielectric constant computation for biological tissues in a real scenario. This work explores a novel methodology for in-vivo, dielectric imaging of biological tissues by estimating their dielectric properties in a practical scenario using the free-space measurement setup. The proposed scheme utilizes a Vivaldi antenna, working in the range of 1-10 GHz, to measure the reflection coefficient of the material under test (MUT) in the free space with metallic reflectors as references. The relative shift in the time-domain associated with various samples is then used to estimate the dielectric constant of the MUT. The applicability of the proposed scheme is first demonstrated using the simulation-based models for various standard samples. For biomedical applications, subcutaneous fat tissue is used as an MUT, and the water content is varied to emulate various abnormal conditions. Finally, the proposed scheme is experimentally validated by employing wood as a biological phantom, and the measurements are carried out by varying the water content in the reference sample. It is observed that the dielectric constant of samples can be computed quite accurately (with an error margin of <7%). This indicates the competence of the proposed scheme for utilization in in-body dielectric imaging.