Methods of operating an interrogation system that has a plurality of patches attached to a host structure. Each patch is capable of generating a diagnostic wave and/or developing a sensor signal in response to the diagnostic wave. In each method, a Euclidean undirected graph is generated by forming a plurality of paths; wherein each path connects two of the patches and the length of the path is shorter than a preset limit. Then, a directed graph or network is generated by assigning a propagation direction of the diagnostic wave to each path. Structural condition index (SCI) values are measured by use of the directed graph and, based on the SCI values, the host structure is scanned for anomalies. The directed graph is reconfigured to determine the shape and location of the anomalies.