Pulmonary function tests and computed tomography lung attenuation in chronic obstructive pulmonary disease

In the August 2015 issue of Radiology, Paoletti et al. reported the results of a study showing lack of linear correlation between pulmonary function tests (PFT) and lung attenuation on computed tomography (CT) in 132 patients with chronic obstructive pulmonary disease (COPD) (1). PFT were assessed according to the recommended and standardized procedures and measurements (2-4). Lung attenuation was measured with CT densitometry which unfortunately is not a standardized procedure both on the side of acquisition technique and on the side of image processing and measurements (5). In particular CT densitometry implies scanning the patient lying supine while she/he maintains breath-hold at end inspiration or expiration. Variables on the acquisition side include the inspiratory or expiratory lung volumes reached by the patient, number and collimation of sections, radiation dose and scanner calibration. Variables on the image processing and measurements side include application of reconstruction filters, automatic or semiautomatic segmentation of the lungs, correction for lung volume, automatic creation of histograms of density distribution and choice of measurement parameters to describe lung structural or functional status. Currently the main indications of lung CT densitometry in COPD include differentiation of emphysema and chronic bronchitis components in the single patient (alone or in combination with airways measurements) (6), monitoring progression of smoke-related pulmonary emphysema (7) and to be used as surrogate marker in trials assessing replacement therapy in alfa1-deficiency emphysema (8).