illuminating the host medium at a plurality of different positions with frequency-swept modulated signals;

detecting signals following propagation through the host medium and the abnormality within the host medium;

creating a shadow image based upon the detected signals in which the abnormality is depicted as a suspicious region;

illuminating at least that portion of the host medium that contains the suspicious region with frequency-swept modulated signals, following creation of the shadow image, wherein the signals are frequency-swept modulated across a larger range of frequencies during the illumination of the suspicious region than during the initial illumination of the host medium;

detecting the frequency-swept modulated signals following propagation through at least that portion of the host medium that contains the suspicious region; and

characterizing the abnormality based upon the detected frequency-swept modulated signals.