Loss of anteroposterior intralobar attenuation gradient of the lung: Correlation with pulmonary function

Since the initial description of an intralobar attenuation gradient by Webb et al, it has been suggested that departure from the intralobar attenuation gradient could indicate early lung diseases. However, its significance has not been determined in detail. We aimed to quantify the anteroposterior intralobar attenuation gradient on volumetric end-inspiratory and end-expiratory high-resolution computed tomography (CT) in patients with emphysema and to correlate the gradient values with pulmonary function.

The study population consisted of 21 consecutive patients with emphysema evaluated with volumetric expiratory high-resolution CT and 6 patients with normal high-resolution CT findings. The anteroposterior intralobar attenuation gradient values were quantified on end-inspiratory and end-expiratory sagittal reformations using a lung analysis software program and were correlated with pulmonary function tests results.

The intralobar attenuation gradient values in patients with forced expiratory volume in 1 second (FEV1) < or =70% were significantly smaller compared with those in patients with FEV1 >70% in bilateral lower lobes at end-expiration (P = .0061, P = .047, respectively, unpaired t-test). The FEV1 values in patients with attenuation gradient values < or =0.02 were significantly lower than in those with attenuation gradient values >0.02 (right lower lobe: P = .024; left lower lobe: P = .0034; chi-squared test). The intralobar attenuation gradient values in bilateral lower lobes at end-expiration were significantly correlated with FEV1 and FEV1/forced vital capacity (right: P = .031, P = .039, respectively; left: P = .036, P = .030, respectively, Pearson correlation).

The quantitative measurement of the anteroposterior intralobar attenuation gradient values of the lung showed that these gradients at end-expiration in both lower lobes correlate with obstructive physiology.