CT lung density is usually measured for detecting and quantifying a pulmonary emphysema (COPD, includes two main conditions—emphysema and chronic obstructive bronchitis).
Acctually, it gives a good reflection of the degree of hyperinflation, or enlargement of distal airways.
The parenchimal scarring at the base of the lung is most likely a result of a previous, resolved inflammatory process, such as a pneumonia.