Abstract
BackgroundQuantitative computed tomography (CT) analysis has been proposed as a means of objectively assessing fibrotic interstitial pneumonia (IP) including idiopathic pulmonary fibrosis (IPF). We investigated whether percentages of high-attenuation areas (HAA%) and cystic areas (CA%) quantified from CT images were useful as indices of fibrotic IP.MethodsCT images of 74 patients with fibrotic idiopathic interstitial pneumonias (IPF, 36; non-specific interstitial pneumonia, 9; unclassifiable idiopathic interstitial pneumonia, 29) were analyzed via in-house computer software, which automatically calculated HAA%, CA%, mean lung density (MLD), standard deviation of lung density (SD-LD), kurtosis, and skewness from CT attenuation histograms. These indices were compared in each instance with physiologic measures, visual fibrosis score, clinical diagnosis, radiologic CT pattern, and prognosis.ResultsHAA% correlated significantly with physiologic measures and visual fibrosis score to a moderate extent (%forced vital capacity, rs = −0.59; % carbon monoxide diffusion capacity, rs = −0.43; fibrosis score, rs = 0.23). Densitometric parameters (MLD, SD-LD, kurtosis, and skewness) correlated significantly with physiologic measures and fibrosis score (|rs| = 0.28-0.59). CA% showed no association with pulmonary functions but differed significantly between IPF and other interstitial pneumonias (IPs) (1.50 ± 2.41 % vs. 0.41 ± 0.80 %; P < 0.01) and between the definite usual interstitial pneumonia (UIP) pattern and other patterns (1.48 ± 2.38 % vs. 0.55 ± 1.19 %; P < 0.01). On univariate analysis, HAA%, MLD, SD-LD, kurtosis, skewness, fibrosis score, and definite UIP pattern all correlated with survival, with kurtosis alone identified as a significant predictor of mortality on multivariate analysis (hazard ratio = 0.67; 95 % CI, 0.44-0.96; P = 0.03).ConclusionCA% and HAA% are novel quantitative CT indices with differing properties in fibrotic IP evaluations. HAA% largely reflects physiologic impairments, whereas CA% corresponds with diagnosis and HRCT pattern. Of the CT indices examined, kurtosis constituted the strongest predictor of mortality.
Highlights
Quantitative computed tomography (CT) analysis has been proposed as a means of objectively assessing fibrotic interstitial pneumonia (IP) including idiopathic pulmonary fibrosis (IPF)
Densitometric parameters derived from CT attenuation histograms have served as indices in earlier studies [1,2,3,4,5,6], corresponding with histopathologic diagnosis [3], physiologic impairment [1, 2, 4, 6], and healthrelated quality of life [4] in fibrotic interstitial lung diseases (ILDs), and with survival in idiopathic pulmonary fibrosis (IPF) [5]
IPF and non-specific interstitial pneumonia (NSIP) were diagnosed according to the 2002 American Thoracic Society (ATS)/European Respiratory Society (ERS) Idiopathic interstitial pneumonia (IIP) statement [9], and high-resolution computed tomography (HRCT) patterns were classified based on the 2011 American Thoracic Society (ATS)/European Respiratory Society (ERS)/Japanese Respiratory Society (JRS)/Latin American Thoracic Association (LATA) IPF guidelines [7]
Summary
Quantitative computed tomography (CT) analysis has been proposed as a means of objectively assessing fibrotic interstitial pneumonia (IP) including idiopathic pulmonary fibrosis (IPF). Quantitative high-resolution computed tomography (HRCT) analysis of the lung has been proposed as an objective and non-invasive means of assessing parenchymal lesions in fibrotic interstitial lung diseases (ILDs) [1,2,3,4,5]. Densitometric parameters (such as mean lung density [MLD], standard deviation of lung density [SD-LD], kurtosis, and skewness) derived from CT attenuation histograms have served as indices in earlier studies [1,2,3,4,5,6], corresponding with histopathologic diagnosis [3], physiologic impairment [1, 2, 4, 6], and healthrelated quality of life [4] in fibrotic ILDs, and with survival in idiopathic pulmonary fibrosis (IPF) [5]. It was our view that HAA% and CA% might serve as quantitative CT indices of fibrotic ILDs
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