Automated pattern analysis of growing rat lung

This study discusses the use of automatic image analysis equipment in quantifying the structural changes during growth of rat pulmonary parenchyma. At birth the latter consists of primary septa delineating a coarse structure of alveolar sacs which are then subdivided into alveoli by outgrowth of secondary septa from day 4 onwards. This process is followed by internal restructuring of the septa in the third week which further increases the surface area by formation of small irregularities. A partial quantification of these processes was obtained by measuring the full set of parameters available with the Quantimet 720 using light microscopy on rat lung sections at the ages of 4, 10 and 21 days. This yielded basic data, e.g. volume and surface densities of air space and tissue. Using closure and opening as preprocessing operations made it possible to split up such parameters into contributions from different ranges of detail resolution. The mass of eighty-four variables obtained could be reduced to six independent factors by Factor Analysis techniques. Interpretation through their correlation with the original variables yielded septal surface, septal volume, minor and major axes of the large air spaces, and surface detail as important structural descriptors explaining 70% of total variance. The remainder is attributed to between-field variations.