1. We retrospectively identified 648 patients who fulfilled each diagnosis criteria specific to each entity (Table 1) (7, 10-18) and with predominant centrilobular nodules or preferentiallycentrilobular disease, who had undergone chest HRCT scans between January 1996 and December 2005 at 3 institutions. Thirty-one HTLV-1 (Human T-cell lymphotropic virus type 1) carriers, 3 withMycoplasma pneumoniae pneumonia, 8 with Mycobacterium tuberculosis (Tb), 7 with Mycobacterium avium-intracellulare complex (MAC), 2 with diffuse panbronchiolitis (DPB), 2 with follicularbronchiolitis (FB), and 9 with alveolar hemorrhage were excluded because of poor image quality caused by motion artifacts, inadequate window level settings, or for which hard copies of the CT filmhad been destroyed. Moreover, 10 HTLV-1 carriers, 8 with Mycoplasma pneumoniae pneumonia, 5 with DPB, 5 with DAB, and 5 with alveolar hemorrhage, who were diagnosed with concurrent infectiousdiseases by serological tests and clinical findings, were excluded. 2. Thus, the study group comprised 553 patients (298 men; 255 women; age range, 15-86 years; mean, 56) with centrilobular diseaseswere retrospectively reviewed. Patients included 243 HTLV-1 carriers, 52 with Mycoplasma pneumoniae pneumonia, 52 Tb, 37 MAC, 33 Mycobacterium Kansasii, 9 allergic bronchopulmonary aspergillosis(ABPA), 12 DPB, 7 FB, 13 diffuse aspiration bronchiolitis (DAB), 15 subacute hypersensitivity pneumonitis (HP), 4 metastatic calcification, 68 alveolar hemorrhage, and 8 respiratorybronchiolitis-associated interstitial lung disease (RB-ILD). 3. Among the patients with diffuse pulmonary hemorrhage, underlying diseases included MPA (n = 48), CSS (n = 12), and SLE (n = 8), and allthese patients also fulfilled the diagnostic criteria for each entity (19-21). 4. Technetium-99m methylene diphosphonate (Tc-99m MDP) scintigraphy was performed in all patients with metastaticcalcification. If patients whose histories were suggestive of metastatic calcification did not undergo Tc-99m MDP scintigraphy, they were excluded from our study. 5.Moreover, patients withsarcoidosis were excluded because HRCT findings in these patients consisted of perilymphatic nodules (ie. peribronchial/perivascular axial interstitial and subpleural/fissural nodules). As well,patients with miliary tuberculosis or lung metastases were excluded because these can manifest as CT findings including randomly distributed nodules. Patients with Langerhans cell granulomatosis orpneumoconiosis were also excluded. None of theses previous entities present with an HRCT pattern of primary centrilobular disease. 6.CT examinations were performed with a Hi-Speed Advantage scanner(General Electric Medical Systems, Milwaukee, WI), Hi-Speed LX/i Advantage scanner (General Electric Medical Systems) or an X-press unit (Toshiba, Tokyo, Japan). High-resolution CT was performed with1-mm collimation at 10-mm intervals. Images were obtained at the lung (width, 1,500 HU; level, -700 HU) and mediastinal (width, 400 HU; level, 20-40 HU) window settings. 7. Two chest radiologists(F.O., Y.A., with 18 and 10, respectively, years of experience in chest CT image interpretation), who were aware of the underlying diagnoses, retrospectively and independently interpreted the CTscans using hard copy images. Conclusions were reached by consensus. 8. CT images were assessed for the following radiologic patterns: GGA, consolidation, centrilobular nodules, bronchial wallthickening, interlobular septal thickening, crazy paving appearance, bronchiectasis, enlarged hilar/mediastinal lymph node(s) (>1 cm in diameter of the short axis), and pleural effusion. Areas ofGGA were defined as hazy increases in attenuation without obscuration of vascular markings. Areas of consolidation were defined as areas of increased attenuation causing obscuration of normal lungmarkings. Centrilobular nodules were defined as nodules present around the peripheral pulmonary arterial branches or 3-5 mm away from the pleura, interlobular septa or pulmonary veins. Moreover,centrilobular nodules were divided into 2 patterns: centrilobular nodules with tree-in-bud appearance, and ill-defined centrilobular nodules of GGA without tree-in-bud appearance. Tree-in-budappearance was characterized by well-defined centrilobular nodules of soft tissue attenuation connected to linear and branching opacities thus resembling a tree-in-bud. 9. The distribution of theparenchymal disease was noted. In addition, zonal predominance was classified as upper, lower or random. 10. Comparison with Pathology: CT-pathologic comparisons for 141 patients were performed usingactual specimens by a pathologist and 2 chest radiologists, by surgical biopsies in 3, transbronchial lung biopsies (TBLB) in 109, and both TBLB and surgical specimens in 29 patients. Surgical lungbiopsies and TBLB corresponding to abnormal regions observed on chest CT scans were performed within 2 and within 22 days after CT, respectively.