Serial high resolution CT in non-specific interstitial pneumonia: prognostic value of the initial pattern.

AIM: To assess the relationship between initial CT pattern and serial changes in CT findings and pulmonary function tests (PFTs) in patients with non-specific interstitial pneumonia (NSIP). MATERIALS AND METHODS: Serial high resolution (HR) CTs and PFTs were retrospectively analyzed in 38 cases of histologically proven NSIP, including 4 with cellular NSIP, 13 with mixed cellular and fibrotic NSIP, and 21 with fibrotic NSIP. The presence and extent of various CT findings were assessed. A fibrosis index (defined as the ratio of the extent of a reticular/honeycomb pattern to the overall extent of abnormal parenchyma) was derived. RESULTS: The predominant CT pattern was reticular/honeycomb in 27 (84%) cases and ground-glass/consolidation in 6 (16%) cases. Between scans, mean disease extent reduced by 5.2%. Disease extent reduced by >10% in 13 (34%) and increased by >10% in 6 (16%) patients. Histopathological subtype of NSIP did not correlate with individual CT pattern, predominant pattern, fibrosis index or serial change in disease extent on CT or PFTs. Response on follow-up CT was associated with fibrosis index, predominant pattern and extent of consolidation on initial CT. CONCLUSION: In NSIP disease, progression on CT correlates with the predominant CT pattern, fibrosis index, and extent of consolidation but not with histopathological subtype. An inflammatory (ground-glass/consolidation) predominant pattern is associated with better outcome in terms of disease extent on HRCT.

Interstitial pneumonia in progressive systemic sclerosis: serial high-resolution CT findings with functional correlation.

PURPOSE: The aim of our study was to assess the serial high-resolution CT findings and their correlation with the results of pulmonary function tests in patients with progressive systemic sclerosis (PSS) and interstitial pneumonia. METHOD: The study included 40 patients with symptoms or signs of PSS and interstitial pneumonia, who underwent serial high-resolution CT scans (mean follow-up period 39 months). Seventeen patients simultaneously had serial pulmonary function tests (mean follow-up period 40 months). On high-resolution CT, the pattern and extent of parenchymal abnormalities were retrospectively analyzed. Serial changes on high-resolution CT were correlated with the changes of pulmonary function tests. RESULTS: On initial CT, areas of ground-glass opacity (mean +/- SD extent 17.7 +/- 12.3% in all patients), irregular linear opacity (4.4 +/- 4.4% in 36 patients), small nodules (3.9 +/- 12.5% in 28), consolidation (1.9 +/- 4.2% in 13), and honeycombing (1.9 +/- 3.8% in 12) were seen. The total disease extent (p = 0.042) and extents of ground-glass opacity (18.9 +/- 15.5%; p = 0.04) and honeycombing (5.0 +/- 7.2%; p = 0.002) increased significantly on follow-up CT. Both forced vital capacity (from 2.4 +/- 0.4 to 2.0 +/- 0.4 L; p = 0.002) and forced expiratory volume in 1 s (from 2.0 +/- 0.4 to 1.6 +/- 0.3 L; p = 0.013) decreased significantly on follow-up examination. The increase in the extent of honeycombing on CT correlated significantly with the decrease in diffusing capacity for carbon monoxide (r = -0.411, p = 0.049). CONCLUSION: In patients with PSS and interstitial pneumonia, the overall extent of disease and extents of honeycombing and ground-glass opacity increase significantly on follow-up CT. Increase of honeycombing correlates well with decrease of diffusing capacity for carbon monoxide.

Hyperoxia-induced acute lung injury using a pig model: correlation between MR imaging and histologic results.

PURPOSE: To correlate MR imaging findings with pathology in experimental hyperoxia-induced acute lung injury, which has similar pathology to diffuse alveolar damage (DAD). MATERIALS AND METHODS: Seventeen Yorkshire pigs were studied. These animals were exposed to more than 80% oxygen for 24, 48, 72, and 96 hours in a sealed cage. The lungs were removed and inflated with air infused through the trachea, and then examined by both MRI and high-resolution CT (HRCT). T1-weighted spin-echo (T1WSE), T2-weighted fast (T2WFSE), and half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences were performed. RESULTS: Severity in MR findings and signal-to-noise ratios (SNR) on MR images were well correlated with pathological scores. CT values were also correlated well with pathologic scores. Abnormal SNR values were obtained from a pathological score of 5, whereas abnormal CT values were obtained from a pathological score of 15. Furthermore, significant differences in SNR were observed in each histopathological phase. CONCLUSION: SNRs on MR images were superior to CT values in detecting early pathologic changes in DAD. MR study also is potentially useful for evaluation of the histopathological phases in acute lung injury.

Pulmonary involvement in mixed connective tissue disease: high-resolution CT findings in 41 patients.

The objective of this study was to describe the pulmonary abnormalities on high-resolution computed tomography (CT) in patients with mixed connective tissue disease (MCTD). The study included 41 patients who met the diagnostic criteria for MCTD and showed abnormal findings on high-resolution CT. The presence, extent, and distribution of various high-resolution CT findings were evaluated. The predominant abnormalities included areas of ground-glass attenuation (n = 41), subpleural micronodules (n = 40), and nonseptal linear opacities (n = 32). Other common findings included peripheral predominance (n = 40), lower lobe predominance (n = 39), intralobular reticular opacities (n = 25), architectural distortion (n = 20), and traction bronchiectasis (n = 18). Less common findings included honeycombing, ill-defined centrilobular nodules, airspace consolidation, interlobular septal thickening, thickening of bronchovascular bundles, bronchial wall thickening, bronchiectasis, and emphysema. Pulmonary involvement of MCTD is characterized by the presence of ground-glass attenuation, nonseptal linear opacities, and peripheral and lower lobe predominance. Ill-defined centrilobular opacities were uncommonly seen.

Acute respiratory distress syndrome and acute interstitial pneumonia: comparison of thin-section CT findings.

PURPOSE: The purpose of this work was to compare the thin-section CT findings of acute respiratory distress syndrome (ARDS) with those of acute interstitial pneumonia (AIP). METHOD: The thin-section CT scans from 25 patients with ARDS and 25 with AIP were independently assessed by two observers without knowledge of clinical and pathologic data. The presence, extent, and distribution of various CT findings were independently analyzed. RESULTS: Honeycombing was seen more frequently in lobes of patients with AIP (26%) than in lobes with ARDS (8%) (p < 0.001). Compared with patients with ARDS, a greater number of patients with AIP had a predominantly lower lung zone distribution (p < 0.05) and a symmetric distribution (p < 0.05) of the parenchymal abnormalities. CONCLUSION: Patients with AIP have a greater prevalence of honeycombing and are more likely to have a symmetric bilateral distribution and a lower lung zone predominance than patients with ARDS. However, significant overlap exists among the CT findings.

Expression of matrix metalloproteinases in pigs with hyperoxia-induced acute lung injury.

The aim of this study was to determine the role of matrix metalloproteinases (MMPs) in the pathogenesis of acute lung injury induced by hyperoxia. Twenty-three pigs were exposed in sealed cages to >80% oxygen (for 24-120 h) or room air. Correlation between MMP-2/MMP-9 activity, measured by gelatin zymography in bronchoalveolar lavage fluid (BALF), and the histological findings and pathological parameters were examined in detail. Sources of these MMPs in the hyperoxic lung were analysed by immunohistochemistry. The histological progression of acute lung injury in this model ranged from the early exudative to the early proliferative phase of diffuse alveolar damage (DAD). MMP-2 and -9 activities were elevated under prolonged hyperoxic exposure. MMP-9 activity correlated significantly with the oxygen tension in arterial blood/inspiratory oxygen fraction, the lung wet-to-dry weight ratio, and the number of neutrophils in BALF, whereas MMP-2 activity did not correlate at all with these factors. MMP-9 activity correlated more closely with the pathological findings of DAD than did MMP-2 activity. Strong MMP-9 expression was observed in neutrophils, alveolar macrophages as well as alveolar lining epithelial cells. These results suggest that matrix metalloproteinase. which may derive from neutrophils recruited into airspaces, plays an important role in the pathogenesis of hyperoxic diffuse alveolar damage

Can acute interstitial pneumonia be differentiated from bronchiolitis obliterans organizing pneumonia by high-resolution CT?

PURPOSE: In the early stages, clinical and chest radiographic findings of acute interstitial pneumonia (AIP) are often similar to those of bronchiolitis obliterans organizing pneumonia (BOOP). However, patients with AIP have a poor prognosis, while those with BOOP can achieve a complete recovery after corticosteroid therapy. The objective of this study was to identify differences in high-resolution CT (HRCT) findings between the two diseases. METHODS: The study included 27 patients with AIP and 14 with BOOP who were histologically diagnosed [open-lung biopsy (n=7), autopsy (n=17), transbronchial lung biopsy (n=17)]. The frequency and distribution of various HRCT findings for each disease were retrospectively evaluated. RESULTS: Traction bronchiectasis, interlobular septal thickening, and intralobular reticular opacities were significantly more prevalent in AIP (92.6%, 85.2%, and 59.3%, respectively) than in BOOP (42.9%, 35.7%, and 14.3%, respectively) (p<0.01). Parenchymal nodules and peripheral distribution were more prevalent in BOOP (28.6% and 57.1%, respectively) than in AIP (7.4% and 14.8%, respectively) (p<0.01). Areas with ground-glass attenuation, air-space consolidation, and architectural distortion were common in both AIP and BOOP. CONCLUSION: For a differential diagnosis of AIP and BOOP, special attention should be given to the following HRCT findings: traction bronchiectasis, interlobular septal thickening, intralobular reticular opacities, parenchymal nodules, pleural effusion, and peripheral zone predominance.

Lymphocytic interstitial pneumonia: follow-up CT findings in 14 patients.

The aim of the present study was to assess the evolution of various computed tomographic (CT) findings of lymphocytic interstitial pneumonia (LIP) with determination of potentially reversible or irreversible features. The study included 14 patients with biopsy-proved LIP who had serial thin-section CT examination 4 to 82 months (median 13 months) apart. Initial and follow-up CT scans were evaluated independently and then directly compared with each other by two observers. The main parenchymal abnormalities on the initial CT scan consisted of ground-glass attenuation (n = 14), thickening of interlobular septa (n = 13), centrilobular nodules (n = 12), cystic airspaces (n = 10), and airspace consolidation (n = 4). On follow-up CT, nine patients improved, one showed no change, and four showed increased extent of disease. With the exception of cysts, the parenchymal opacities were reversible. On follow-up CT, new cysts were seen in three patients; these developed mainly in areas with centrilobular nodules on initial CT. Honeycombing was seen on follow-up CT in four patients; in three patients it developed in areas of airspace consolidation and in one patient it developed in an area with ground-glass attenuation on initial CT. The majority of patients with LIP improved on follow-up. However, airspace consolidation may progress to honeycombing and centrilobular nodules may precede cystic formation.

Hyperoxia-induced diffuse alveolar damage in pigs: correlation between thin-section CT and histopathologic findings.

PURPOSE: To determine whether lung abnormalities at thin-section computed tomography (CT) in experimental hyperoxic lung injury correlate with the pathologic phases of diffuse alveolar damage (DAD). MATERIALS AND METHODS: Eighteen juvenile pigs were exposed to more than 80% oxygen-for 24, 48, 72, 96, or 120 hours-or room air in sealed cages. Their removed lungs were inflated with air infused through the trachea and examined with thin-section CT. Two independent observers, without knowledge of the exposure times, compared 63 areas selected on the CT scans with the corresponding pathologic and histologic findings, which were evaluated independently by two pathologists. RESULTS: CT findings correlated well with histologic findings (rho = 0.86, P <.001), which corresponded to the pathologic phases of DAD. All areas of normal CT attenuation, eight of nine spared regions within areas of opacity, and two of 15 areas of ground-glass opacity corresponded to the early exudative pathologic phase of DAD. All areas that showed traction bronchiolectasis at CT corresponded to the early proliferative pathologic phase. There was good observer agreement regarding the interpretation of CT findings (kappa statistic, >0.60) and histologic results (>/=0.70). CONCLUSION: Thin-section CT findings reflect the pathologic phases of DAD, although the early exudative phase cannot be specifically depicted by thin-section CT. Traction bronchiolectasis on a CT scan suggests progression to the proliferative phase.

Near drowning: thin-section CT findings in six patients.

PURPOSE: The purpose of this study was to assess the thin-section CT findings of near drowning in six patients. METHOD: Thin-section (1 mm collimation) CT scans of six patients who experienced near drowning were retrospectively analyzed. The CT scans were performed 0-5 days (median 1 day) after near drowning. RESULTS: Thin-section CT findings included bilateral patchy or diffuse areas of ground-glass attenuation (n = 6) with geographic pattern (n = 3) and fine intralobular reticular opacities ("crazy-paving" appearance) (n = 3), ill-defined centrilobular nodules (n = 4), and air-space consolidation (n = 1). Distribution of ground-glass attenuation was predominantly central (n = 4) or diffuse (n = 2). Interstitial pulmonary emphysema and pneumomediastinum were present in two patients. CONCLUSION: The thin-section CT findings of near drowning consist of ground-glass opacities with or without associated reticular opacities and centrilobular nodules.

Eosinophilic lung diseases: diagnostic accuracy of thin-section CT in 111 patients.

PURPOSE: To determine whether various eosinophilic lung diseases can be differentiated by means of thin-section computed tomography (CT). MATERIALS AND METHODS: Thin-section CT scans in 111 patients with eosinophilic lung diseases-40 with chronic eosinophilic pneumonia, 16 with Churg-Strauss syndrome, 16 with allergic bronchopulmonary aspergillosis (ABPA), 13 with acute eosinophilic pneumonia, 12 with simple pulmonary eosinophilia, 11 with drug-induced eosinophilic pneumonia, and three with hypereosinophilic syndrome-were assessed independently by two observers. The observers recorded the abnormalities, diagnosis, and degree of confidence in the diagnosis. RESULTS: The two observers made a correct first-choice diagnosis on average in 61% of readings. The correct diagnosis was made in 78% of cases of chronic eosinophilic pneumonia; 81%, acute eosinophilic pneumonia; 44%, Churg-Strauss syndrome; 84%, ABPA; 17%, simple pulmonary eosinophilia; 27%, drug-induced eosinophilic pneumonia; and 33%, hypereosinophilic syndrome. The two observers made a correct diagnosis with a high degree of confidence in 36% of readings. There was moderate agreement between the observers for the correct diagnosis (kappa, 0.47) and for the correct diagnosis with a high degree of confidence (kappa, 0.59). CONCLUSION: Although eosinophilic lung diseases often can be differentiated by means of thin-section CT, correlation between CT findings and careful clinical evaluation are required for a definitive diagnosis.

Acute parenchymal lung disease in immunocompetent patients: diagnostic accuracy of high-resolution CT.

OBJECTIVE: The purpose of this study was to determine whether acute parenchymal lung diseases can be differentiated on the basis of the pattern and distribution of abnormalities revealed on high-resolution CT. MATERIALS AND METHODS: High-resolution CT scans of 90 patients with acute parenchymal lung diseases (19 with bacterial pneumonia, 13 with mycoplasmal pneumonia, 21 with acute interstitial pneumonia, 18 with hypersensitivity pneumonitis, 10 with acute eosinophilic pneumonia, and nine with pulmonary hemorrhage) were independently assessed by two observers who had no knowledge of clinical or pathologic data. The observers recorded abnormalities, their first-choice diagnosis, and their degree of confidence in their first-choice diagnosis. RESULTS: The two observers made a correct first-choice diagnosis in an average of 55 (61%) of 90 cases. Correct first-choice diagnosis was made in 50% of cases of bacterial pneumonia, 62% of mycoplasmal pneumonia, 90% of acute interstitial pneumonia, 72% of hypersensitivity pneumonitis, 30% of acute eosinophilic pneumonia, and 28% of pulmonary hemorrhage. CT findings allowed distinction between infectious and noninfectious causes in 81 (90%) of 90 cases. CONCLUSION: High-resolution CT is helpful in the differential diagnosis of infectious from noninfectious acute parenchymal lung disease. However, high-resolution CT is of limited value in making a specific diagnosis.

Acute and subacute non-infectious lung diseases: usefulness of HRCT for evaluation of activity especially in follow-up.

PURPOSE: The purpose of this study was to survey the usefulness of high-resolution CT (HRCT) for the evaluation of activity in acute and subacute non-infectious diffuse infiltrative lung diseases before and after corticosteroid treatment. PATIENTS AND METHODS: Sequential HRCT images and chest radiographs obtained before and after treatment were retrospectively evaluated in 33 patients with acute or subacute noninfectious diffuse infiltrative lung diseases. All these patients were histologically confirmed to have pulmonary Inflammation and to have responded to treatment with corticosteroid. Radiographic and CT scores were correlated with the degree of dyspnea and the results of arterial blood gas analysis using Spearman's rank-correlation coefficient. RESULTS: On follow-up HRCT, the profusion score of areas with increased attenuation was significantly correlated with arterial oxygen tension (PaO2) (p=.003, r=-.53) and the alveolar-arterial oxygen tension difference (AaDO2) (p=.001, r=.57). No other correlation was found after treatment. Nodular and linear opacities were more commonly seen on follow-up chest radiographs and HRCT images than on initial ones. CONCLUSION: HRCT is useful for the evaluation of disease activity in acute and subacute noninfectious infiltrative lung diseases before and after treatment if paying special attention to the profusion of ground-glass attenuation. Even if pretreatment HRCT has not been performed, posttreatment HRCT should be examined.

Lymphocytic interstitial pneumonia: thin-section CT findings in 22 patients.

PURPOSE: To assess the thin-section computed tomographic (CT) findings of lymphocytic interstitial pneumonia. MATERIALS AND METHODS: The study included 22 patients (five men, 17 women; age range, 24-83 years; mean age, 50 years) with biopsy-proved lymphocytic interstitial pneumonia. The CT scans were obtained by using 1-3-mm collimation and reconstructed by using a high-spatial-frequency algorithm. RESULTS: The predominant abnormalities consisted of areas of ground-glass attenuation and poorly defined centrilobular nodules present in all 22 patients and subpleural small nodules seen in 19 patients. Other common findings included thickening of bronchovascular bundles (n - 19), interlobular septal thickening (n = 18), cystic airspaces (n = 15), and lymph node enlargement (n = 15). Less common findings included large nodules, emphysema, airspace consolidation, bronchiectasis, architectural distortion, honeycombing, and pleural thickening. CONCLUSION: Lymphocytic interstitial pneumonia is characterized by the presence of ground-glass attenuation, poorly defined centrilobular nodules, and thickening of the interstitium along the lymphatic vessels. Lymph node enlargement is more common than previously recognized; it was seen in 68% of patients.

Differential diagnosis of lymphocytic interstitial pneumonia and malignant lymphoma on high-resolution CT.

OBJECTIVE: Lymphoproliferative disorders span a spectrum from inflammatory lesions to malignant neoplasms. The purpose of this study was to compare high-resolution CT findings of lymphocytic interstitial pneumonia with those of malignant lymphoma of the chest. MATERIALS AND METHODS: The study included 17 patients with lymphocytic interstitial pneumonia and 44 patients with malignant lymphoma (35 with non-Hodgkin's lymphoma and nine with Hodgkin's disease). Without knowledge of the pathologic diagnosis, two chest radiologists evaluated the frequency and distribution of high-resolution CT findings in both groups of patients. RESULTS: Cysts were more common in patients with lymphocytic interstitial pneumonia (14/17, 82%) than in patients with malignant lymphoma (1/44, 2%) (p < .0001). Air-space consolidation was more commonly seen in patients with malignant lymphoma (29/44, 66%) than in patients with lymphocytic interstitial pneumonia (3/17, 18%) (p < .001). Large nodules (11-30 mm in diameter) were more common in patients with malignant lymphoma (41%) than in patients with lymphocytic interstitial pneumonia (6%). Pleural effusions (25%) were seen only in patients with malignant lymphoma. We found no statistically significant difference in the distribution of lung lesions between patients with lymphocytic interstitial pneumonia and patients with malignant lymphoma. CONCLUSION: On high-resolution CT, cysts are characteristic in patients with lymphocytic interstitial pneumonia, whereas consolidation, large nodules, and pleural effusions are characteristic in patients with malignant lymphoma. These findings on high-resolution CT help differentiate lymphocytic interstitial pneumonia from malignant lymphoma.

The subtypes of localized bronchioloalveolar carcinoma: CT-pathologic correlation in 18 cases.

OBJECTIVE: The purpose of this study was to correlate thin-section CT findings with histologic findings for the three histopathologic subtypes of localized bronchioloalveolar carcinoma. CONCLUSION: Thin-section CT can be used to predict the histologic subtype of bronchioloalveolar carcinoma.

Perilobular pulmonary opacities: high-resolution CT findings and pathologic correlation.

This pictorial essay illustrates the high-resolution CT and histologic findings of various disease processes that involve the perilobular interstitium.

Acute interstitial pneumonia: thin-section CT findings in 36 patients.

PURPOSE: To characterize the computed tomographic (CT) findings of acute interstitial pneumonia and to correlate the pattern and the extent of abnormalities with the time between symptom onset and CT. MATERIALS AND METHODS: The study included 36 patients (20 men, 16 women; age range, 22-83 years; mean age, 61 years) with histopathologically proved acute interstitial pneumonia who were identified retrospectively. The time between symptom onset and CT was 2-90 days (mean, 22 days; median, 17 days). The presence, extent, and distribution of various CT findings were evaluated. Disease duration and extent of each finding were compared by using the Spearman rank correlation coefficient. RESULTS: Areas with ground-glass attenuation, traction bronchiectasis, and architectural distortion were present in all 36 patients. Airspace consolidation was present in 33 patients (92%). The extent of areas of ground-glass attenuation (r = 0.45, P < .01) and the extent of traction bronchiectasis (r = 0.35, P < .05) correlated with disease duration. No other significant correlation was found between the CT findings and disease duration. CONCLUSION: A combination of ground-glass attenuation, airspace consolidation, traction bronchiectasis, and architectural distortion is seen in the majority of patients with acute interstitial pneumonia. The extent of ground-glass attenuation and traction bronchiectasis increases with disease duration.

Comparison of high resolution CT findings of sarcoidosis, lymphoma, and lymphangitic carcinoma: is there any difference of involved interstitium?

PURPOSE: The purpose of this study was to determine distinguishing features of three diseases that are distributed along the lymphatics. METHOD: CT scans of 40 patients with lymphangitic carcinomatosis, 41 with sarcoidosis, and 44 with malignant lymphoma were retrospectively reviewed. We evaluated the degree of involvement of the interlobular septa, bronchovascular structures, subpleural interstitium, and other CT findings. RESULTS: The number of thickened interlobular septa and the extent of involvement of the subpleural interstitium in lymphangitic carcinomatosis were higher than those in sarcoidosis and malignant lymphoma (p<0.0001). Nodules of >1 cm in diameter were more often seen in malignant lymphoma (41.0%) than in the other two diseases (p < 0.001). Bilateral distribution was more common in sarcoidosis (100%) than in the others (p<0.001). CONCLUSION: The major difference among lymphangitic carcinomatosis, sarcoidosis, and malignant lymphoma is the greater involvement of the interlobular septa and subpleural interstitium in lymphangitic carcinomatosis than in either sarcoidosis or malignant lymphoma.

Idiopathic interstitial pneumonias: diagnostic accuracy of thin-section CT in 129 patients.

PURPOSE: To determine whether idiopathic interstitial pneumonias can be differentiated on the basis of the pattern and distribution of abnormalities at thin-section computed tomography (CT). MATERIALS AND METHODS: Thin-section CT scans in 129 patients with histologically proved idiopathic interstitial pneumonia (35 with usual interstitial pneumonia [UIP], 24 with bronchiolitis obliterans organizing pneumonia [BOOP], 23 with desquamative interstitial pneumonia [DIP], 20 with acute interstitial pneumonia [AIP], and 27 with nonspecific interstitial pneumonia and fibrosis [NIPF]) were independently assessed by two observers without knowledge of clinical or histologic data. The observers recorded the abnormalities, diagnosis, and degree of confidence in their diagnosis. Differential diagnosis was limited to the five types of idiopathic interstitial pneumonia. RESULTS: The two observers made a correct diagnosis, on average, in 74 (57%) cases. On average, the correct diagnosis was made in 25 (71%) cases of UIP, 19 (79%) of BOOP, 14.5 (63%) of DIP, 13 (65%) of AIP, and 2.5 (9%) of NIPF. The two observers made a correct diagnosis with a high degree of confidence in 50 (39%) readings. There was moderate agreement between the observers for the correct diagnosis (k = 0.55) and for the correct diagnosis with a high degree of confidence (k = 0.65). CONCLUSION: Except for NIPF, the various subtypes of idiopathic interstitial pneumonias often have a characteristic appearance that allows differentiation at thin-section CT.