The 1991 International Conference on Information Processing in Medical Imaging (IPMI '91) is the twelfth in the series and was held in Wye College, part of the University of London. The purpose of IPMI is to provide a forum for the detailed examination of methodological issues in computing which are at the heart of advances in medical image formation, manipulation and interpretation. This volume presents the proceedings of IPMI '91. Full-length scientific papers describing the latest techniques and results are organized into the following nine sections: - Image formation and reconstruction - Incorporation of priors in tomographic reconstruction - Multi-modal registration - Segmentation: specific applications - Segmentation: multi-scale, surfaces and topology - Anatomical models and variability - Factor analysis - Rule based systems and learning - Image quality, display and interaction. The volume also includes a set of color plates and a subject index. The book provides an up- to-date account of current work in the expanding and fast-moving area of image processing and