Using pulsed or continuous-wave sources, broadband electromagnetic energy generally in the 10 MHz to 300 GHz range is applied through one or a plurality of near-field antennas such as coaxial probe tips. The electromagnetic energy reflected from the surface or transmitted through the near surface of the object (e.g. surface of skin or other tissue or cells) is detected, and the ratio of the test measurement to that from normal tissue is recorded and presented to determine the degree of dielectric contrast, hence inhomogeneity. This degree of contrast is used both on its own and in conjunction with simultaneously acquired optical images to map the boundary of an organ inhomogeneity such as a tumor. The bundle of antennas may be scanned over a surface of the object on a pixel-by-pixel basis to determine the spectra of the sample on a pixel-by-pixel basis, allowing a two dimensional display of the absorption spectra to be provided.