An automatic procedure to estimate the dielectric properties of human tissues at microwave band based on water and solid content

In this work, we propose a heuristic methodology using hydration models as a base to realize an automatic and non-invasive procedure to estimate an ad hoc map of the complex dielectric permittivity of a generic human tissue. The frequency range of microwaves was considered based on the tissue’s solid and water content, where the water characteristic was modelled in four hydration pools (Cameron I.L. et al., 2011; Tannino M. et al, 2023). We propose this heuristic method to obtain an ad hoc dielectric mapping of human tissues in vivo, with a standard magnetic resonance imaging (MRI) scanner for medical imaging used to quantify the water (free and bound), the lipid content, and the solid content. The homogenization theory was adopted in the study because, in the considered frequency range, the protein sizes were constantly shorter than λmin ~ 5 × 10−3 m. This method can be particularly useful in medical applications where the exact knowledge of the patient’s anatomy and the related electromagnetic properties would be of great benefit to the success of the treatment. Our methodology was validated by evaluating the dielectric spectrum of a 7.69 mM lysozyme aqueous solution (Cametti C. et al., 2011) and the permittivity and conductivity of tendon/collagen human tissue in the frequency range from 0.1 to 10 GHz. Then, using the collagen/tendon-optimized Debye parameters and Maxwell Garnett mixture formulas (Garnett J.C.M., 1906), we evaluate the complex permittivity of human tissues. Comparing our results to a gold standard (Gabriel S. et al., 1996), it was found that the estimated permittivity and conductivity showed a 13.2% Root Mean Square Relative Error % on average.