Figure 1: Calculation of the mean linear intercept (). A transparent sheet with 10 equally distributed horizontal lines is laid over the printed digitized image of an H&E-stained section. A transparent sheet with 11 equally distributed vertical lines is used thereafter (not shown). For each line, the intercepts with the tissue structures are counted. is calculated as the ratio between the product of the number of times the traverses are placed on the lung and the length of the traverses, and the sum of all the intercepts.