To assess the capability of the density histogram of high-resolution CT (HRCT) in differentiating nonspecific interstitial pneumonia (NSIP) from usual interstitial pneumonia (UIP) without definite honeycombing.
Twenty-eight NSIP and 32 UIP patients without definite honeycombing on CT were included in this study. We evaluated a CT image at the level of 1 cm above the diaphragm. The pixels of the lung parenchyma were classified into 4 ranges. The fractions of each range of corresponding density were calculated. The skewness (the degree of asymmetry of a distribution) and kurtosis (how sharply peaked a histogram is) were obtained from the density histogram. The mean value and the mode value of the lung attenuation were also measured.
The fraction of the range of ground-glass opacity and reticular opacity was greater in NSIP patients (32%, 12%) than in UIP patients (23%, 8%) (P < 0.001). UIP had a larger fraction of the range of normal lung. The density histogram was less skewed (P = 0.01) and had a wider peak (P = 0.02) in NSIP (skewness = 1.2879 ± 0.5672, kurtosis = 1.2115 ± 1.9470) than in UIP (skewness = 1.6426 ± 0.4664, kurtosis = 2.3880 ± 1.8183).
The density histogram reflected the differences in the CT features between NSIP and UIP. Therefore, a density histogram may be helpful for differentiating NSIP from UIP without definite honeycombing.
From the *Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea; †Division of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea; ‡Department of Laboratory Medicine and Pathology, Mayo Clinic, Scottsdale, Arizona and §Kyoto University Hospital, Laboratory and Anatomic Pathology, Kyoto, Japan.
Received for publication November 1, 2004; accepted March 21, 2005.
This work was supported by a grant of the Korean Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (0412-CR03-0704-0001).
Reprints: Jin Seong Lee, Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Pungnapdong, Songpagu, Seoul, 138-736, Republic of Korea (e-mail: firstname.lastname@example.org).