Impact of advanced detector technology and iterative reconstruction on low-dose quantitative assessment of lung computed tomography density in a biological lung model.

PURPOSE: Quantitative computed tomography (QCT)-derived measures of lung density are valued methods for objectively characterizing lung parenchymal and peripheral airways disease and are being used in a growing number of lung disease focused trials. Detector and reconstruction improvements in CT technology have allowed for significant radiation dose reduction in image acquisition with comparable qualitative image quality. We report the impact of detector type and reconstruction type on QCT lung density measures in relation to decreasing dose indices. METHODS: Two sets of studies were completed in an in vivo pig model with a SOMATOM Definition Flash CT system: (a) prior to system upgrade with conventional detectors (UFC) and filtered back projection (FBP), and (b) post system upgrade with integrated electronic detectors (STELLAR) and iterative reconstruction (SAFIRE). CT data were acquired across estimated CT volume dose indices (CTDIvol ) ranging from 0.75 to 15 mGy at both inspiratory and expiratory breath holds. Semiautomated lung segmentations allowed calculation of histogram median, kurtosis, and 15th percentile. Percentage of voxels below -910 HU and -950 HU (inspiratory), and -856 HU (expiratory) were also examined. The changes in these QCT metrics from dose reduction (15 mGy down to 0.75 mGy) were calculated relative to paired reference values (15 mGy). Results were compared based on detector and reconstruction type. RESULTS: In this study, STELLAR detectors improved concordance with 15 mGy values down to 3 mGy for inspiratory scans and 6 mGy for expiratory scans. The addition of SAFIRE reconstruction in all acquired measurements resulted in minimal deviation from reference values at 0.75 mGy. CONCLUSION: The use of STELLAR integrated electronic detectors and SAFIRE iterative reconstruction may allow for comparable lung density measures with CT dose indices down to 0.75 mGy.

Sinogram Affirmed Iterative Reconstruction (SAFIRE) versus weighted filtered back projection (WFBP) effects on quantitative measure in the COPDGene 2 test object.

PURPOSE: Assessing pulmonary emphysema using Quantitative CT of the lung depends on accurate measures of CT density. Sinogram-Affirmed-Iterative-Reconstruction (SAFIRE) is a new approach for reconstructing CT data acquired at significantly lower doses. However, quantitative effects of this method remain unexplored. The authors investigated the effects on the median values of materials in the COPDGene2 test-object as a function of the reconstruction method [weighted filtered back projection (WFBP) versus SAFIRE], test-object size, dose, and material composition using a Siemens SOMATOM Definition FLASH CT scanner. METHODS: The COPDGene2 test-object contains eight materials; acrylic, water, four foams (20 lb, 12 lb, lung-equivalent, and 4 lb emphysema-equivalent), internal and external-air. The test-object was scanned with three different outer ring sizes, simulating three different body habitus. There is an average size (36 cm) Ring A, large size (40 cm) Ring B, and small size Ring C (30 cm). The CT protocol used 120 kVp, 0.5 s rotation, 1.0 pitch, and a 0.6 slice collimation with progressively decreasing x-ray exposure values, 11.94-0.74 mGy. With a thorax length of 30 cm, the corresponding effective doses would be 5.01-0.31 mSv. The effects of using SAFIRE versus WFBP were assessed using a two tailed t-test for each ring size, material, and dose. Multivariable linear regression was used to evaluate the relative effects of ring size, material composition, dose, and reconstruction method on the measured median value in HU. RESULTS: SAFIRE versus WFBP, at the largest ring size and two lowest doses there was a significant difference in median values of 4 lb-foam, p<0.01. Using the smallest ring size at the lowest dose level there was a significant difference in the median value of 4 lb-foam, but the effect size was small, 1 HU. There is a significant difference in median values of both internal and external air using both the small and medium size rings at the three lowest dose levels, p<0.05. There are significant differences noted at both high and low dose levels when using the large ring size in the median values of internal and external air when, p<0.05. These effects on 4 lb-foam, inside and outside air are shown to be in part due to truncation effects on the median value since the lowest HU value in the CT scale used is -1024 HU. Multivariable linear regression results demonstrated significant effects on the measured material median value and standard deviation due to ring size, material composition, dose level, and reconstruction method, p<0.05. CONCLUSIONS: The authors have shown that there is no significant effect on the median values obtained when using WFBP versus SAFIRE in materials with CT density between 120 and -856 HU using three different test-object sizes and CT doses that vary from 11.94 to 0.74 mGy. The authors have demonstrated there are significant effects on median values obtained when using WFBP versus SAFIRE in materials with CT density values between -937 and -1000 HU depending on the ring size and dose used. As expected, there is considerable reduction in image noise (lower standard deviation) using SAFIRE versus WFBP with all ring sizes, doses, and materials in the COPDGene2 test-object.

Reference standard and statistical model for intersite and temporal comparisons of CT attenuation in a multicenter quantitative lung study.

PURPOSE: The purpose of this study was to detect and analyze anomalies between a large number of computed tomography (CT) scanners, tracked over time, utilized to collect human pulmonary CT data for a national multicenter study: chronic obstructive pulmonary disease genetic epidemiology study (COPDGene). METHODS: A custom designed CT reference standard "Test Object" has been developed to evaluate the relevant differences in CT attenuation between CT scanners in COPDGene. The materials used in the Test Object to assess CT scanner accuracy and precision included lung equivalent foam (-856 HU), internal air (-1000 HU), water (0 HU), and acrylic (120 HU). Nineteen examples of the Test Object were manufactured. Initially, all Test Objects were scanned on the same CT scanner before the Test Objects were sent to the 20 specific sites and 42 individual CT scanners that were used in the study. The Test Objects were scanned over 17 months while the COPDGene study continued to recruit subjects. A mixed linear effect statistical analysis of the CT scans on the 19 Test Objects was performed. The statistical model reflected influence of reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency on CT attenuation. RESULTS: Depending on the Test Object material, there were significant differences between reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency. The two Test Object materials of most interest were lung equivalent foam and internal air. With lung equivalent foam, there were significant (p < 0.05) differences between the Siemens B31 (-856.6, ±0.82; mean ± SE) and the GE Standard (-856.6 ± 0.83) reconstruction kernel relative to the Siemens B35 reference standard (-852.5 ± 1.4). Comparing lung equivalent foam attenuation there were also significant differences between CT scanner models (p < 0.01), tube current (p < 0.005), and in temporal consistency (p < 0.005) at individual sites. However, there were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. For internal air, significant (p < 0.005) differences were found between all reconstruction kernels (Siemens B31, GE Standard, and Phillips B) compared to the reference standard. There were significant differences between CT models (p < 0.005), and tube current (p < 0.005). There were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. Differences, across scanners, between external air and internal air measures in this simple (relative to the in vivo lung) test object varied by as much as 15 HU. CONCLUSIONS: The authors conclude that the Test Object designed for this study was able to detect significant effects regarding individual CT scanners that altered the CT attenuation measurements relevant to the study that are used to determine lung density. Through an understanding of individual scanners, the Test Object analysis can be used to detect anomalies in an individual CT scanner and to statistically model out scanner differences and individual scanner changes over time in a large multicenter trial.

Report of a workshop: quantitative computed tomography scanning in longitudinal studies of emphysema.

It has been reported that quantitative computed tomography (CT) scanning of the lungs showed decreased progression of emphysema in a randomised clinical trial in patients with severe alpha1-antitrypsin (alpha1-AT) deficiency receiving monthly intravenous augmentation therapy with human alpha1-AT. Comparable results were not obtained using rate of decline of forced expiratory volume in one second. Accordingly, the Alpha-1 Foundation convened a workshop to explore the feasibility of using quantitative CT data as a primary outcome variable in trials of drugs for treating alpha1-AT deficiency. This report reviews the following: the principles for the use of modern CT scanners for quantifying emphysema; the methods and data on validation by comparison with measurements of severity of emphysema in inflation-fixed specimens of lungs; and the possibility of decreasing radiation dosage from CT to make it safe and ethically possible to use CT in longitudinal studies. The workshop concluded that it is feasible, safe and ethically possible to use computed tomography in longitudinal studies of emphysema. It recommended that the primary end-point should be a significant shift in the 15th percentile of lung density.

High-resolution CT features of severe asthma and bronchiolitis obliterans.

AIM: To evaluate the high-resolution CT findings of severe asthma (SA) and bronchiolitis obliterans (BO) and determine whether any reliable discriminating HRCT features exist. MATERIALS AND METHODS: HRCT examinations of the chest of 30 patients with SA and 14 patients with BO were analysed. Images were scored for the presence and extent of 21 CT findings. RESULTS: The most consistent HRCT features in SA were bronchial wall thickening in 30 (100%), expiratory air trapping in 19 of 22 examinations with expiratory images (87%), inspiratory decreased attenuation in 18 (60%), and bronchial luminal narrowing in 12 (40%). The most consistent HRCT features in BO were expiratory air trapping in 10 of 10 examinations with expiratory images (100%), bronchial wall thickening in 13 (93%), inspiratory decreased attenuation in 11 (79%), ground glass opacity in seven (50%), and mosaic pattern of attenuation in seven (50%). Decreased attenuation was more extensive in BO than in SA on both inspiratory and expiratory images. The mosaic pattern of attenuation was present in seven (50%) BO patients but in only one (3%) SA patients (P=0.0006). CONCLUSIONS: Mosaic pattern of attenuation, when present, is highly suggestive of BO, but SA and BO may be indistinguishable.

Obliterative bronchiolitis: varying presentations and clinicopathological correlation.

In obliterative bronchiolitis, inflammation and fibrosis lead to narrowing or occlusion of bronchiolar lumina. To determine how bronchiolar structural alterations relate to lung physiology, 19 patients with a pathological diagnosis of obliterative bronchiolitis were studied. The bronchiolar inflammatory and fibrotic features were correlated to the clinical presentation, and lung function tests. Eleven patients demonstrated airflow limitation, one had a restrictive pattern and one had a mixed pattern, two had isolated gas trapping, but four had normal spirometry. Mild-to-moderate bronchiolar inflammation was invariably present. It involved 60% of bronchioles subepithelially and 54% in the adventitia. Subepithelial fibrosis was observed in 15 patients and adventitial in 12. Adventitial bronchiolar inflammation correlated with forced expiratory volume in one second and forced vital capacity and inversely correlated with residual volume. Subepithelial fibrosis inversely correlated with subepithelial and adventitial inflammation. High-resolution computed tomography in 10 patients revealed inspiratory (five out of 10) and expiratory air trapping (five out of five), ground glass opacities (seven out of 10), bronchial wall thickening (five out of 10), bronchiectasis (two out of 10) and centrilobular nodules (two out of 10). The present study suggests that inflammation and fibrosis occurs in bronchioles at different time points in the disease process, or that there is no transition between these types of pathology in the same patient. No correlation was observed between the degree of bronchiolar fibrosis and the degree of airflow limitation.

CT findings in 14 patients with Mycobacterium chelonae pulmonary infection.

OBJECTIVE: The purpose of this report is to describe helical and high-resolution CT findings in 14 patients with pulmonary infection caused by Mycobacterium chelonae, a nontuberculous mycobacterial species that has become increasingly recognized as a rare but significant cause of chronic lung infection in immunocompetent patients. CONCLUSION: Bronchiectasis, nodules, and consolidation are the most common CT features of M. chelonae pulmonary infection. Cavities are less common. These CT findings resemble those reported for Mycobacterium avium complex. In this study, M. chelonae pulmonary infection occurred exclusively in middle-aged and older women.

Distribution and severity of bronchiectasis in allergic bronchopulmonary aspergillosis (ABPA).

The purpose of this paper was to quantitate the distribution and severity of computed tomography (CT) and radiographic findings in patients with allergic bronchopulmonary aspergillosis (ABPA), probable ABPA, and asthmatic controls. Chest radiographs and high-resolution CT images were evaluated in 19 patients with documented ABPA and 18 asthmatic controls. Ten patients with probable ABPA were also evaluated. On CT examination 17 patients (89%) with ABPA had central cystic or varicoid bronchiectasis in at least one lobe. One patient had no evidence for bronchiectasis. Three asthmatic patients (17%) had findings of cylindrical bronchiectasis. All 10 patients with probable ABPA had evidence of bronchiectasis on high-resolution CT (HRCT). The majority of patients with ABPA have diffuse disease at the time of diagnosis, manifested by central cystic and/or varicoid bronchiectasis in four or five lobes. Evaluation with HRCT can facilitate a diagnosis of ABPA and probable ABPA, allowing for earlier treatment which may prevent progression to fibrosis.

Pediatric diffuse lung disease: diagnosis and classification using high-resolution CT.

OBJECTIVE: Our purpose was to categorize high-resolution CT findings in children with diffuse lung disease and to evaluate the accuracy of diagnoses made using CT. MATERIALS AND METHODS: The chest radiographs and high-resolution CT scans of 20 children (1-16 years old; median, 9 years old) with biopsy-proven chronic diffuse lung diseases were reviewed separately by two independent chest radiologists. Thirteen types of diffuse lung disease were included in the study. Radiographic and CT features were noted, and three choices of diagnosis were recorded, with the confidence level. RESULTS: Diagnoses were made with a high degree of confidence (definite or probable) in 25 of 40 interpretations of CT scans, compared with only five of 40 interpretations of chest radiographs (p < .001). Fourteen (56%) of the 25 confident first-choice diagnoses on CT scans were correct, compared with two (40%) of the five interpretations on chest radiographs. Diseases were classified as belonging to one of five distinct groups on the basis of dominant CT features. Airway disease (n = 5) (bronchiolitis obliterans or bronchocentric granulomatosis) showed geographic hyperlucency on CT. Septal disease (n = 4) (lymphangiomatosis, hemangiomatosis, or microlithiasis) showed septal thickening. Infiltrative lung disease (n = 7) (desquamative interstitial pneumonitis, hypersensitivity pneumonitis, or lymphoid interstitial pneumonitis) showed ground-glass opacity. Air-space disease (n = 3) (aspiration, vasculitis, or bronchiolitis obliterans organizing pneumonia) showed lung consolidation. Langerhans' histiocytosis (n = 1) showed cysts and nodules. Surprisingly little overlap was seen among these groups. CONCLUSION: CT increases the level of diagnostic confidence for pediatric infiltrative lung disease, improves diagnostic accuracy, and provides a useful classification system.

Observer variation and relationship of computed tomography to severity of beryllium disease.

Although high resolution computed tomography (HRCT) is commonly used to assess interstitial lung disease (ILD), relatively little is known about interrater reliability and construct validity of HRCT-reported nodules, ground-glass opacity, or other typical findings. We determined the interobserver and intraobserver variability of HRCT findings and correlated HRCT abnormalities with physiologic measures in 57 patients with chronic beryllium disease (CBD). Reliability of HRCT scan measurements were assessed using weighted kappa (K(W)) and intraclass correlation coefficients. We correlated HRCT with spirometry, body plethysmographic lung volumes, diffusing capacity for carbon monoxide (DL(CO)), maximal exercise testing with measurement of arterial blood gases, and bronchoalveolar lavage (BAL). Interobserver agreement for three of the HRCT abnormalities found in CBD was moderate: the K(W) for nodules, septal lines, and ground-glass attenuation were 0.53, 0.44, and 0.53, respectively. Agreement was poor for bronchial wall thickening (K(W) = 0.15). HRCT scores correlated significantly with DL(CO), gas exchange at rest and at maximal exercise, and lung volume. This study demonstrates that HRCT has good interrater reliability and correlates with indices of the severity of granulomatous lung diseases such as CBD.

Quantitative CT predicts the severity of physiologic dysfunction in patients with lymphangioleiomyomatosis.

PURPOSE: To assess quantitative high-resolution CT (quantitative CT) as a diagnostic and prognostic tool in pulmonary lymphangioleiomyomatosis. METHODS: Spirometry, lung volumes, diffusing capacity, exercise physiology, and expiratory high-resolution CT (HRCT) examinations were performed on a cohort of ten patients with the diagnosis of lymphangioleiomyomatosis (LAM) referred to a tertiary care center. HRCT examinations were also done on ten normal control subjects. A thresholding technique was used to quantitatively assess the amount of abnormal cystic parenchyma present on each of the two images obtained for each subject with LAM and for each normal control subject. This numeric index of cystic parenchyma, the quantitative CT index, was then examined (1) as a diagnostic measure to distinguish the subjects with LAM from the normal control subjects and (2) as a prognostic measure to assess disease severity in the subjects with LAM. Linear regression of the quantitative CT index against physiologic indexes of pulmonary function and exercise performance was analyzed to determine the relationship between this radiologic assessment of disease severity and functional impairment. RESULTS: The quantitative CT index was significantly greater for the LAM patients, 37.2 +/- 6.9 (SEM), compared with the control group, 0.8 +/- 0.2 (p = 0.0001). Linear regression analysis demonstrated significant linear correlation between the quantitative CT index and measures of airflow (FEV1, r = -0.90, p = 0.0005), air trapping (residual volume, r = 0.70, p = 0.02), diffusing capacity (diffusing capacity for carbon monoxide, r = -0.76, p = 0.01), gas exchange (alveolar to arterial oxygen gradient) at rest, r = 0.69, p = 0.007, and at maximum exercise, r = 0.79, p = 0.007) and exercise performance (maximum workload, r = -0.84, p = 0.002), and oxygen utilization (oxygen utilization at maximum exercise, r = -0.76, p = 0.01). CONCLUSION: Quantitative CT techniques can distinguish subjects with LAM from normal controls. Further, the quantitative CT index correlates well with physiologic measurements of airflow, lung volumes, diffusing capacity, and exercise performance and, thus, may provide a useful measure of disease severity.

How common are renal angiomyolipomas in patients with pulmonary lymphangiomyomatosis?

Pulmonary lymphangiomyomatosis has been associated with renal angiomyolipoma in case reports, but the prevalence of this association has not been well documented. The objective of this study was to determine the frequency of renal angiomyolipoma in a series of subjects with pulmonary lymphangiomyomatosis. Eighteen consecutive patients with pulmonary lymphangiomyomatosis were seen at a single institution between 1989 and 1994. Of these, one patient was excluded because she did not have an abdominal computed tomographic (CT) scan. We found eight out of 17 (47%) patients with pulmonary lymphangiomyomatosis to have renal angiomyolipomas. These were found either at surgery or on abdominal CT scanning. Thus, renal angiomyolipomas occur commonly in association with pulmonary lymphangiomyomatosis. Consequently, the early detection of renal angiomyolipoma by abdominal CT may be important, because lesions with dimensions larger than 4 cm may present an increased risk for complications related to tumor growth or hemorrhage. Serial follow-up by ultrasonography or CT scanning is important in identifying and monitoring high-risk patients. Prophylactic treatment (partial or total nephrectomy) may be considered for patients with tumors that show significant growth or other complications, such as hemorrhage.

Can CT distinguish hypersensitivity pneumonitis from idiopathic pulmonary fibrosis?

OBJECTIVE: The clinical management of patients with idiopathic pulmonary fibrosis differs markedly from that of patients with hypersensitivity pneumonitis. However, the two diseases often cannot be differentiated on clinical grounds. The purpose of this study was to establish whether CT can be used to make the distinction. MATERIALS AND METHODS: Thirty-six patients with idiopathic pulmonary fibrosis and 27 patients with hypersensitivity pneumonitis were studied. All diagnoses were confirmed or supported by open lung biopsy. Three of the patients with idiopathic pulmonary fibrosis had desquamative interstitial pneumonia, and the remainder had usual interstitial pneumonia. In 19 of the 27 patients with hypersensitivity pneumonitis, the disease was chronic (symptoms lasting more than 1 year), while eight had acute or subacute symptoms. Two radiologists, who had not previously seen any of the cases and were blinded to the diagnosis, reviewed the CT images by consensus. The extent and distribution of CT features (including ground-glass attenuation, honeycombing, and micronodules) were recorded. In each case, a CT diagnosis was made, and the level of diagnostic confidence was recorded. RESULTS: A CT diagnosis was made with a high level of confidence in 39 (62%) of 63 patients. In these patients, the CT diagnosis was correct in 35 cases (90%): 23 of 26 patients with a CT diagnosis of idiopathic pulmonary fibrosis and 12 of 13 patients with a CT diagnosis of hypersensitivity pneumonitis. In the three patients with desquamative interstitial pneumonia, the CT diagnoses were probable hypersensitivity pneumonitis in two cases and definite hypersensitivity pneumonitis in one case. Of the 19 patients with chronic hypersensitivity pneumonitis, only seven had a definite diagnosis of hypersensitivity pneumonitis based on CT findings; three had a definite diagnosis of idiopathic pulmonary fibrosis. The patients with idiopathic pulmonary fibrosis and usual interstitial pneumonia were more likely to have honeycombing and peripheral or lower lung zone predominance of disease, and less likely to have micronodules, than were patients with chronic hypersensitivity pneumonitis. The patients with idiopathic pulmonary fibrosis and desquamative interstitial pneumonia had widespread ground-glass opacity indistinguishable from some cases of acute or subacute hypersensitivity pneumonitis. CONCLUSION: Our results show that CT can be used to distinguish idiopathic pulmonary fibrosis from hypersensitivity pneumonitis in most but not all cases. Desquamative interstitial pneumonia cannot reliably be distinguished from acute or subacute hypersensitivity pneumonitis. Chronic hypersensitivity pneumonitis may have findings identical to those of usual interstitial pneumonia. Lung biopsy should still be considered the gold standard for diagnosis of interstitial lung disease.

Quantitative chest computed tomography as a means of predicting exercise performance in severe emphysema.

RATIONALE AND OBJECTIVES: We assessed the value of quantitative high-resolution computed tomography (CT) as a diagnostic and prognostic tool in smoking-related emphysema. METHODS: We performed an inception cohort study of 14 patients referred with emphysema. The diagnosis of emphysema was based on a compatible history, physical examination, chest radiograph, CT scan of the lung, and pulmonary physiologic evaluation. RESULTS: As a group, those who underwent exercise testing were hyperinflated (percentage predicted total lung capacity +/- standard error of the mean = 133 +/- 9%), and there was evidence of air trapping (percentage predicted respiratory volume = 318 +/- 31%) and airflow limitation (forced expiratory volume in 1 sec [FEV1] = 40 +/- 7%). The exercise performance of the group was severely limited (maximum achievable workload = 43 +/- 6%) and was characterized by prominent ventilatory, gas exchange, and pulmonary vascular abnormalities. The quantitative CT index was markedly elevated in all patients (76 +/- 9; n = 14; normal < 4). There were correlations between this quantitative CT index and measures of airflow limitation (FEV1 r2 = .34, p = 09; FEV1/forced vital capacity r2 = .46, p = .04) and between maximum workload achieved (r2 = .93, p = .0001) and maximum oxygen utilization (r2 = .83, p = .0007). CONCLUSION: Quantitative chest CT assessment of disease severity is correlated with the degree of airflow limitation and exercise impairment in pulmonary emphysema.

Lipoid pneumonia: CT findings.

OBJECTIVE: To assess the CT findings of lipoid pneumonia. METHODS: Chest radiography and CT performed in six patients with proven lipoid pneumonia were reviewed by two observers. Diagnosis was confirmed by biopsy (five cases) or bronchoalveolar lavage (one case). The clinical history of taking oily substance could be obtained retrospectively in all patients. RESULTS: Chest radiography showed bilateral air space consolidation in three cases, irregular mass-like lesions in two, and a reticulonodular pattern in one case. Computed tomography demonstrated diffuse parenchymal consolidation in three cases, localized areas of consolidation in two, and subpleural pulmonary fibrosis in one case. In two cases, fat with localized areas of consolidation could be seen on CT. In three cases with diffuse consolidation the attenuation was decreased but higher than that of subcutaneous fat. In one case with subpleural fibrosis no areas of low attenuation could be seen on CT. CONCLUSION: We conclude that in patients with lipoid pneumonia CT may demonstrate areas with low attenuation diagnostic of fat or areas with nonspecific low attenuation or soft tissue density.

Automated discrimination and quantification of idiopathic pulmonary fibrosis from normal lung parenchyma using generalized fractal dimensions in high-resolution computed tomography images.

RATIONALE AND OBJECTIVES: We computed generalized fractal dimensions for high-resolution computed tomography (HRCT) images to investigate their value in the discrimination and quantification of idiopathic pulmonary fibrosis (IPF) from normal lung parenchyma. METHODS: A probability distribution that was based on the pixel value in each image was used to compute capacity, information, and higher fractal dimensions for a series of 52 HRCT slices obtained from four patients. Qualitative classification of normal, mild, moderate, and severe IPF cases was achieved by computing the following parameter: DD = D0 - 2D1 + D2, where D0, D1, and D2 represents the capacity, information, and pair correlation dimensions, respectively. A multiple linear regression analysis using morphometric quantification for the set of 52 slices was tested for all possible combinations of the parameters D0, D1, D2, and D3. The generalizability of the model was tested by predicting the extent of IPF for each patient from a regression model computed with the remaining slices in the database. RESULTS: The best regression results were obtained using the independent parameters D1 and D2 to quantify the extent of diseased lung parenchyma. The technique was tested with 48 slices from 12 new patients. The results indicated that the extent of IPF could be predicted within the confidence limits given by the regression analysis. CONCLUSION: The extent of IPF can be predicted well within the 90% confidence interval given by the model. The width of the confidence interval decreases as the number of slices used in the linear regression model increases. This operator-independent quantitative technique may be useful in the follow-up of patients with IPF.

Radiologic findings of adult primary immunodeficiency disorders. Contribution of CT.

STUDY OBJECTIVE: We wished to review the chest radiographic and computed tomographic (CT) findings in adults with primary immunodeficiency disorders, and to evaluate the influence of CT on the treatment of these patients. DESIGN: Retrospective blinded review of radiographs, CT scans, and clinical data. SETTING: National referral center for immunodeficiency disorders. PATIENTS: Forty-six chest radiographs and 22 CT examinations of subjects with primary immunodeficiency disorders were independently scored. Nineteen of the subjects who had CT scans had B-cell deficiency, while 3 had T-cell deficiency. RESULTS: CT-detected bronchiectasis in 15 of 19 subjects with B-cell deficiency, compared with 7 cases detected on chest radiograph. Unsuspected upper lobe bronchiectasis was found on CT in 15 cases. Other CT findings in this group included small nodules in seven subjects, interstitial lines in four, air trapping in seven, ground glass or parenchymal consolidation in nine, evidence of small airways disease in nine, and mucus plugs in four. Two of the three subjects with T-cell disorders showed cavitation and two had unsuspected reactive mediastinal adenopathy. Clinical management appeared to be altered in five subjects with B-cell deficiency by CT findings of severe focal or diffuse bronchiectasis or small airways disease. Additionally, CT localized the bleeding site in three subjects with hemoptysis. CONCLUSIONS: CT is valuable for detection of bronchiectasis in subjects with B-cell immunodeficiency and may alter treatment of these patients.

Quantitative computed tomography detects air trapping due to asthma.

OBJECTIVE: The purpose of this study was to prospectively see if quantitative computed tomography (QCT) could separate asthmatic patients from normal control subjects. The QCT results were also correlated with the pulmonary function tests (PFT) that were done on both the asthmatic patients and control subjects. SUBJECTS AND METHODS: Eighteen adult nonsmoking asthmatics and 22 adult control subjects were entered into the study. Quantitative CT was performed at the level of the transverse aorta and just above the diaphragm at both end inspiration and end expiration in all patients and control subjects: 10-mm and 1.5-mm collimation using a high spatial frequency algorithm was used to obtain the QCT examinations. The percent of pixels below -900 Hounsfeld units, pixel index, in each of the QCT axial images of the lungs was calculated for each asthmatic and control subject in the study. Pulmonary function testing was performed on both the asthmatics and control subjects and included determination of FEV1, FVC, FRC, RV, and TLC. Unpaired Student's t test analysis of the QCT data was done to statistically compare the asthmatics with the control subjects. Linear regression analysis was done to compare the QCT results with PFT data on the asthmatics and control subjects. RESULTS: When scans were performed at end expiration, at a level immediately superior to the diaphragm, the mean pixel index was significantly higher in asthmatic subjects compared with normal individuals on both CT (mean for normal subjects 0.16 vs 4.45 for asthmatics, p < 0.004) and high-resolution CT (HRCT) images (mean for normal subjects 1.04 vs 10.03 in asthmatics, p < 0.0001) indicating more areas of low attenuation in asthmatics. The CT and HRCT images from the lower lung zones that were performed at end expiration provided the best separation between the groups. The pixel index on expiration correlated with the degree of air trapping and airflow limitation in the asthmatic group based on FEV1, FRC, RV, and to a lesser extent, FVC. CONCLUSION: Expiratory QCT is a useful method to assess air trapping in asthmatic patients. The percent of abnormal lung in asthmatics as determined by QCT has a significant correlation with the PFTs that reflect air trapping in asthmatic patients. Quantitative CT may be helpful in assessing degrees of air trapping present in other diseases affecting the airways.

Proliferative and constrictive bronchiolitis: classification and radiologic features.

The small airways of the lung consist of the terminal bronchioles, respiratory bronchioles, and alveolar ducts. A recently introduced pathologic classification system divides bronchiolitis into proliferative and constrictive types. The histologic classification of small-airways disease into proliferative and constrictive bronchiolitis frequently correlates with the radiographic appearances. Proliferative bronchiolitis is characterized by air-space opacification, whereas constrictive bronchiolitis tends to be associated with lobular areas of decreased attenuation and airway dilatation. The purpose of this essay is to illustrate the radiographic and CT features of these two varieties of bronchiolitis.

Beryllium disease: assessment with CT.

PURPOSE: To describe the thin-section computed tomographic (CT) features of beryllium disease and compare the sensitivities of thin-section CT and chest radiography. MATERIALS AND METHODS: In 28 patients with biopsy-proved beryllium disease and 12 healthy control subjects, radiographs were scored with an international classification system. Thin-section CT scans were scored for 11 parenchymal, airway, pleural, and mediastinal findings. RESULTS: Thin-section CT revealed at least one abnormality in 25 patients (89%); chest radiography, in 15 patients (54%). After the finding of bronchial wall thickening attributable to tobacco smoking was excluded, CT scans in 21 (75%) of 28 patients were abnormal because of beryllium disease. The most common CT abnormalities were parenchymal nodules (n = 16) and septal lines (n = 14). With use of CT, abnormalities were detected in 10 (77%) of 13 patients with normal radiographs. CONCLUSION: Thin-section CT was more sensitive than chest radiography in detection of beryllium disease, but the diagnosis was missed in up to 25% of cases with histologic proof.