This paper presents some preliminary results obtained by using a Newton-Kantoro- vitch iterative scheme for retrieving the complex permittivity profile in biological targets via active microwave imaging. On the contrary to classical diffraction tomography, this technique provides quantitative imaging of the dielectric properties. This technique has been used for the reconstruction of the complex permittivity of a simulated human cross-section and has been compared to the results obtained by means of classical diffraction tomography. Furthermore, the ability to detect thermal gradients has been assessed by considering Emulated hot spots.