In this paper we propose a qualitative spatial relation called "arrangement" which serves to identify medical images obtained from similar tomographic sections. "Arrangement" describes the sequence in which neighbors of each part are situated around it in the image. "Arrangement" is closely related to the Voronoi diagram of the parts. Based on the Voronoi diagram a metric for comparing "arrangements" is proposed. The metric enables robust use of "arrangement" in reMworld situations. The mechanism for comparing tomographic sections is useful in medical image databases.