The algorithm in the book is intended to assist in finding probable diagnoses based on recognition of patterns. At the highest levels of the algorithm, the patterns are grouped under respectively high or low attenuation as follows: nodules, ground-glass, reticular pattern, consolidation (high attenuation), and cystic pattern, mosaic perfusion (low attenuation). At bottom levels of the algorithm some of the patterns are divided into sub-groups. Finally, at the lowest level of the algorithm a number of differential diagnoses are listed for each pattern/sub-pattern. Note that some of diagnosis may also be secondary manifestations of rheumatoid systemic diseases or part of a drug reaction.