Lung Attenuation Research Articles

Development and testing of image-processing methods for the quantitative assessment of airway hyperresponsiveness from high-resolution CT images.

Our goal was to develop a protocol and image-processing methods to quantitate both bronchial and lung attenuation changes in patients imaged with helical high-resolution CT (HRCT). Human subjects underwent helical HRCT at two suspended breath-hold conditions, functional residual capacity and residual volume, at baseline and following methacholine-induced bronchoprovocation. A semiautomated contouring program was used to define anatomically like bronchi and axial lung sections from the different physiologic sequences, from which automated measurements of area, shape, and attenuation were made. Because the gray level threshold for contouring directly affects the measured area of an anatomic structure, two types of evaluation studies were performed. These included in vivo measurements using baseline parameters of human subjects as the standard of reference and in vitro measurements of a CT phantom designed to simulate the air-soft tissue interfaces of bronchi. Phantom tests showed that the minimum difference between actual and measured areas of holes occurred at a threshold of -500 HU. The smallest diameter holes were most sensitive to changes in threshold value. However, although absolute area measurements of both simulated and human bronchi varied with threshold level, the percent changes in airway areas between baseline and bronchoprovocation sequences were relatively stable at any given threshold. These image-processing tools provide reproducible measurements of area as well as attenuation characteristics of pulmonary structures and may offer insights into the practical use of functional imaging in evaluating conditions of airflow obstruction.

Evaluation of in vivo total and regional air content and distribution in primate lungs with high-resolution CT.

The authors sought to determine whether gray-scale quantitative information from high-resolution computed tomography (CT) could reliably yield estimates of lung air content and help determine changes in air content with lung inflation and deflation. High-resolution CT images (n = 40) of lungs of two anesthetized monkeys were obtained after inflation with known air volumes. Percentage air content was calculated for each voxel, and lung volumes and patterns of air distribution were determined. When corrected for pressure and temperature, high-resolution CT-based volumes correlated closely with inflation volumes (r = .99; standard error = 3.4%). Patterns of regional change in air content demonstrated known patterns of ventilation. Although the high-spatial-frequency algorithm used in high-resolution CT enhances edges of structures and improves visualization of anatomic detail, gray-scale values from the same high-resolution CT data set remain a reliable index of regional lung attenuation.

Mosaic pattern of lung attenuation on CT scans: frequency among patients with pulmonary artery hypertension of different causes.

The purpose of this study was to determine the frequency with which a mosaic pattern of lung attenuation is seen on chest CT scans in patients with various causes of pulmonary artery hypertension (PAH). Chest CT scans of 64 patients with known PAH were reviewed to assess the patterns of lung attenuation. Patterns of lung attenuation were divided into three categories: class I, homogeneous lung parenchymal attenuation; class II, slightly heterogeneous lung attenuation that does not conform to the anatomic boundaries of the secondary pulmonary lobule; and class III (mosaic pattern), heterogeneous lung attenuation in geographic regions with well-defined borders corresponding to the anatomic units of single or multiple secondary pulmonary lobules. The patients medical histories were reviewed to determine the primary cause of PAH for each patient. Peak pulmonary artery pressure of the patients in our study averaged 74 mm Hg (range, 36-194 mm Hg). Twenty-one patients had PAH due to lung disease: 17 patients, due to cardiac disease; and 23 patients, due to vascular disease. Three other patients had PAH due to miscellaneous causes. Of the 23 patients with PAH due to vascular disease, 17 patients (74%) had a mosaic pattern of lung attenuation. Of the 21 patients with PAH due to lung disease, one patient (5%) had a mosaic pattern of lung attenuation. Among the 17 patients with PAH due to cardiac disease, two patients (12%) had a mosaic pattern of lung attenuation. A mosaic pattern of lung attenuation was seen significantly more often in patients with PAH due to vascular disease than in patients with PAH due to cardiac or lung disease. A mosaic pattern of lung attenuation can be seen on CT scans in patients with PAH due to vascular disease, cardiac disease, or lung disease. However, the mosaic pattern is seen significantly more often in patients with PAH due to vascular disease than in patients with PAH due to cardiac or lung disease.

Patients with emphysema: quantitative CT analysis before and after lung volume reduction surgery. Work in progress.

To quantitatively assess the morphologic changes in the lungs after lung volume reduction surgery and determine whether changes at quantitative computed tomography (CT) reflect changes in lung function. In 10 patients, chest CT images were obtained at full inspiration and expiration before and after surgery. A semiautomated segmentation method was developed to isolate the lung regions and calculate the lung volumes and frequency distribution of attenuation values. The changes in lung volume and attenuation after surgery were compared with clinical findings, and an exploratory evaluation of outcome predictors was conducted. Semiautomated segmentation and quantitative analysis compared favorably with manual techniques, and there was good correlation between the emphysema indexes and percentage predicted forced expiratory volume in 1 second, forced expiratory volume in 1 second/forced vital capacity, and diffusing capacity. The emphysema index decreased from 60% to 38% at inspiration and from 60% to 27% at expiration after surgery. The average CT lung volume decreased from 7.5 to 5.6 L at inspiration (25%) and from 6.4 to 3.8 L (41%) at expiration after surgery and correlated well with measurements at plethysmography. Substantial decreases in the lung volumes and emphysema index, increased airflow, possible reexpansion of some remaining lung, and the relation between preoperative quantitative CT indexes and clinical outcome suggest a multifactorial mechanism for improvement seen after surgery.

Airway obstruction in asthmatic and healthy individuals: inspiratory and expiratory thin-section CT findings.

To determine differences in computed tomographic (CT) findings in asthmatic and healthy individuals and to correlate the findings with severity of airway obstruction. Thirty-nine asthmatic patients and 14 healthy subjects were prospectively evaluated with thin-section CT. Inspiratory CT scans were subjectively evaluated for presence of bronchial wall thickening, bronchial dilatation, and mosaic lung attenuation; expiratory scans were subjectively evaluated for presence of air trapping. Objective measurement of bronchoarterial-diameter ratio was performed on inspiratory scans. CT findings were compared with pulmonary function test results. Bronchial wall thickening, severe air trapping, and reduced bronchoarterial-diameter ratio were observed more commonly in asthmatic patients than in healthy subjects. Bronchial wall thickening was more prevalent among patients with severe airflow obstruction (10 of 12 readings [83%]) than in patients with normal airflow (15 of 40 readings [38%]) or mild obstruction (nine of 26 readings [35%]). Other subjectively determined CT findings did not correlate with pulmonary function test results. The mean bronchoarterial-diameter ratios +/- 1 standard deviation were 0.65 +/- 0.16 in healthy subjects and 0.60 +/- 0.16, 0.60 +/- 0.18, and 0.48 +/- 0.11 in patients with normal airflow and mild and severe obstruction, respectively. Thin-section CT is of limited value in distinguishing asthmatic patients with normal airflow or mild airflow obstruction from healthy subjects.

Serial computed tomographic evaluation in desquamative interstitial pneumonia.

BACKGROUND: Desquamative interstitial pneumonia (DIP) may represent the early stage and usual interstitial pneumonia (UIP) the late stage of the same disease. The purpose of this study was to evaluate...

Regional ventilation-perfusion mismatch in interstitial pneumonia. Correlation between scintigraphy and CT.

Interstitial pneumonia is one of the many causes of a scintigraphic ventilation-perfusion (V/Q) mismatch. To evaluate the morphologic features of V/Q mismatched areas in patients with interstitial pneumonia, we correlated the findings on lung scintigraphy using Kr-81m and Tc-99m MAA with CT scan findings. Of 41 patients, 20 (49%) had a high V/Q mismatched areas. All of these areas corresponded to cystic air spaces shown on CT, and most of the showed a honeycomb pattern. Ventilation-perfusion matched defects were seen in 23 patients (56%). The matched defects corresponded to cystic air spaces (honeycomb or bullous changes) or lung attenuation changes of varying degrees on CT. Cystic air spaces with high V/Q mismatch are considered to be normally ventilated. To distinguish mismatched areas of interstitial pneumonia from areas of pulmonary embolism, it may be necessary to compare scintigraphic findings with CT.

Pulmonary venoocclusive disease: CT findings in eight patients.

The objective of the study was to describe the CT findings of pulmonary venoocclusive disease. Eight patients with CT scans of the thorax and a diagnosis of pulmonary venoocclusive disease were identified from three institutions. The six males and two females had a mean age of 32 years old (range, 5-58 years old). All scans were evaluated with consensus reading by two chest radiologists. Lung parenchyma were assessed for the type and distribution of disease. Bronchi, pleura, hila, mediastina, and chest walls were evaluated for abnormalities. Pathologic specimens from five patients were reviewed and specifically correlated with the radiologic findings. Seven of the eight patients had interlobular septal thickening. All eight patients had regions of ground-glass opacity. Four of the eight patients had a mosaic pattern of lung attenuation. No enlarged hilar or mediastinal nodes were revealed. Five patients had bilateral pleural effusions. The most common CT findings in these eight patients with pulmonary venoocclusive disease were smooth interlobular septal thickening, diffuse multifocal regions of ground-glass opacity, pleural effusions, enlarged central pulmonary arteries, and pulmonary veins of normal caliber. Four patients had a mosaic pattern of lung attenuation on the CT scans. These findings are highly suggestive of pulmonary venoocclusive disease and may be helpful in difficult cases. Definitive diagnosis requires lung biopsy.

Thin-section CT findings of the lungs: experimentally induced bronchial and pulmonary artery obstruction in pigs.

The purpose of this study was to investigate whether a mosaic pattern of lung attenuation, or lobular low attenuation, is revealed on CT imaging after induction of bronchial and pulmonary artery obstruction in pigs. Eight anesthetized and ventilated pigs, four for bronchial obstruction and four for pulmonary artery obstruction, were examined with thin-section CT. Bronchial obstruction was induced at the subsegmental level using 2- to 3-mm radiopaque silicon spheres at 14 sites. Pulmonary artery obstruction was induced at 11 sites by dislodging 2- to 3-mm silicon spheres at the level of the superior vena cava. CT scans were obtained at end expiration immediately after the obstruction in all pigs (n = 8) and after 1 day (n = 3), 3 days (n = 5), 7 days (n = 4), 14 days (n = 4), and 28 days (n = 3). Of the 14 sites of bronchial obstruction, six sites (43%) on the immediate scans showed a lobular distribution of low attenuation distal to the spheres, which changed to atelectasis, consolidation, or normal on follow-up CT. Of the four sites that did not show changes in lung attenuation on immediate CT scans, two sites showed lobular low attenuation after 1 day. The mean attenuation value +/- SD for the lobular low attenuation was -737 H +/- 122 and that of the adjacent lung was -522 H +/- 53 (p = .0077). None of the pulmonary artery obstruction sites showed visible change in lung attenuation, and mean attenuation values for obstructed sites and unobstructed sites did not show significant differences when scanned as many as 28 days after the immediate scans. Lobular low attenuation on thin-section CT was induced by bronchial obstruction, but we found no change in lung attenuation due to obstruction of the pulmonary arteries as many as 28 days after the immediate scans.

Spirometrically controlled quantitative CT for assessing diffuse parenchymal lung disease.

Assessment of lung attenuation by CT reflects changes in the air-to-tissue ratio of the lung. We have analyzed the interdependence of intrathoracic gas volume, lung morphology, and functional disorder by high resolution CT (HRCT) to assess quantitative disease threshold in obstructive and restrictive diffuse lung disease. Pulmonary HRCT was performed on 24 healthy volunteers, 11 patients with chronic obstructive pulmonary disease (COPD), and 16 patients with idiopathic lung fibrosis (IPF). HRCT measurement was standardized by taking three scans at the carina +/- 5 cm and by defining inspiration levels by percent vital capacity (VC) via spirometrically gating to the scanner. The mean lung density at 50% VC (DL50) for healthy subjects was -819 +/- 3.8 (mean +/- SEM) HU. In contrast, COPD DL50 was lower, averaging -861 +/- 6.4 HU, and the IPF DL50 was considerably higher (-731 +/- 17.7 HU), both significantly different (p < 0.001) compared with the control group. The accuracy of quantitative HRCT at different inspiration levels was evaluated by scanning the basal layer at 20, 50, and 80% VC. The control values were -747 +/- 5.6, -816 +/- 3.6, and -855 +/- 3.0 HU, respectively, which were significantly higher (p < 0.001) than those seen in COPD patients at 20 and 50% VC. Again, the IPF patients exhibited increased lung density (p < 0.001) at all inspiratory levels. Discrimination power was best among all cohorts at 20 and 50% VC. Position-dependent artifacts on lung density were quantified by the anteroposterior density gradient (APG). Irrespective of the underlying disease, APG at 50 and 80% VC was similar, but was up to twofold higher at 20% VC, indicating that quantitative estimates near RV may misrepresent mean lung density. Our data indicate that quantitative HRCT measurements should be performed not near full inspiration or expiration, but at an intermediate degree of lung inflation, e.g., 50% VC, for reasons of accuracy, intra- and intersubjective comparability, and feasibility. We conclude quantitative HRCT to be a sensitive tool for the evaluation of diffuse parenchymal lung disease.

CT mosaic pattern of lung attenuation: distinguishing different causes.

Areas of variable lung attenuation in a lobular or multilobular distribution are occasionally seen on CT or high-resolution CT scans of the lungs [1], although never as a normal finding. This mosaic pattern of lung attenuation presents a challenge to the radiologist when deciding which are the abnormal regions of lung--those of low attenuation, those of high attenuation, or both. We have observed three categories of disease known to cause a CT mosaic pattern of lung attenuation: small-airway disease, vascular lung disease, and infiltrative disease. Diseases from each of these categories can cause similar patterns of mosaic lung attenuation on CT scans. However, it is sometimes possible to distinguish among these categories by using additional CT findings. We illustrate the known causes of a CT mosaic pattern of lung attenuation and highlight distinguishing features.

CT Mosaic Pattern of Lung Attenuation

Areas of variable lung attenuation forming a "mosaic pattern" are occasionally seen on computed tomography (CT) or high-resolution CT (HRCT) images of the lungs. This CT mosaic pattern of lung attenuation is a nonspecific finding that can reflect the presence of vascular disease, airway abnormalities, or ground-glass interstitial or air-space infiltrates. However, it is often possible to distinguish among these categories. In small airways disease and pulmonary vascular disease, the pulmonary vessels within the lucent regions of lung are small relative to the vessels in the more opaque lung. In infiltrative diseases, the vessels are more uniform in size throughout the different regions of lung attenuation. The distinction of small airways disease from primary vascular disease requires the use of paired inspiratory/expiratory CT scans. The terms "mosaic perfusion" or "mosaic oligemia" have also been used to describe this heterogeneous pattern of lung attenuation. We believe that the term "mosaic pattern of lung attenuation" is preferable when describing areas of variable lung attenuation because the term "mosaic perfusion" implies pulmonary vascular pathology.

Administration of large doses of vitamin C does not decrease oxidant-induced lung lipid peroxidation caused by bacterial-independent acute peritonitis.

Acute zymosan-induced peritonitis in rats produces lung inflammation and lipid peroxidation. The effect of this process on plasma and lung tissue ascorbic acid was determined, as was the effect of infusing 150 mg/kg of ascorbic acid immediately after zymosan on the degree of lung insult. Ascorbic acid levels were significantly decreased in plasma and lung tissue at 24 h after zymosan, and lung tissue conjugated diene and neutrophil content was also significantly increased. Vitamin C infusion increased postzymosan plasma levels by 50% over normal control levels. However, lung tissue ascorbic acid was still decreased, and no decrease in the lung injury process was noted. Added ascorbic acid also did not prevent a decrease in plasma vitamin E with the peritonitis. We conclude that the amount of ascorbic acid given in this study did not diminish the lung oxidant inflammatory changes. An insufficient dose or inadequate time for plasma ascorbic acid to equilibrate with the lung cytosol are possible explanations for the lack of attenuation of lung oxidant stress.

HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF OBSTRUCTIVE LUNG DISEASE

High-resolution CT (HRCT) scanning and dynamic CT techniques have significantly improved our ability to image morphologic abnormalities associated with chronic airflow obstruction. Abnormalities visible on HRCT include emphysema, lung cysts, and large airways abnormalities, such as bronchiectasis, which are accurately assessed using this technique. Also visible are small airways abnormalities, such as bronchiolar dilation and filling of bronchioles with mucus or fluid. Perfusion abnormalities resulting from abnormal lung ventilation result in regional differences in lung attenuation, so-called mosaic perfusion. Expiratory HRCT scans or dynamic scans during expiration can show areas of air trapping.

Dynamic Quantitative Computed Tomography

Nine patients were examined using dynamic electron beam computed tomography to assess the utility of this technique in detecting airway obstruction and air trapping, and to compare this technique with pulmonary physiologic testing. Dynamic computed tomography (C-100 Ultrafast CT scanner, Imatron, Inc., South San Francisco, CA) was performed, with a series of ten, 100-msec images obtained in a 6-second period during forced inhalation and exhalation. Time-attenuation curves were calculated from the observed changes in lung attenuation. Estimates of the percentage of each lung that showed air trapping were made at each level scanned, using a 5-point scale. Specific correlations were made for pulmonary function test results and air-trapping score. In all nine patients, dynamic computed tomography demonstrated one or more sites that failed to show a normal increase in lung attenuation during forced exhalation. Four of these 9 patients showed a paradoxical decrease in lung attenuation during exhalation in at least one region of the lung. Extent of air-trapping correlated well with forced expiratory volume in one second (r = -.92). Based on this small sample, the authors believe that this technique will prove sensitive for detecting abnormalities of ventilation and may be a useful adjunct to conventional diagnostic procedures in the management of disorders of airway obstruction.

An emission-based technique for obtaining attenuation correction data for myocardial SPECT studies.

In this paper, a technique is described for obtaining the information needed to perform attenuation correction in the thorax entirely from an emission study. This technique is based on the observation that the variation in soft tissue and lung attenuation coefficients is small among individuals. Thus only the outer contours of the body and lungs need be determined for obtaining the attenuation map. The contours are determined by using 99Tcm-macroaggregated albumin (MAA) to locate the lungs and an external source wrapped about the chest to locate the body boundary. Simulation studies were performed to investigate how errors in the presumed tissue attenuation coefficients affect the accuracy of the correction. Body and lung attenuation coefficients were varied from 20% less to 20% more than the coefficients used in the corrections. Over this range, there was less than a 15% alteration in the relative distribution of counts in the left ventricle. To test clinical feasibility, seven patients referred for clinical myocardial perfusion studies were scanned before and after the placement of the body source and the administration of 99Tcm-MAA. Reconstructed images from these studies showed clear demarcation of all body and lung boundaries. The presence of 99Tcm-MAA in the lungs had no significant effect on the clinical interpretation of the single photon emission computed tomographic (SPECT) studies. It is concluded that this technique is feasible for clinical application and that it offers important advantages over other current methods.

Dynamic pulmonary CT: findings in healthy adult men.

The authors examined 10 healthy male subjects with dynamic computed tomography to determine normal dynamic and expiratory findings. In both the supine and prone positions, the average increase in lung attenuation during exhalation was found to be significantly greater in dependent lung regions than in nondependent lung regions. In each of the lung zones studied, there was a significant correlation between the decrease in cross-sectional lung area during exhalation and the increase in lung attenuation. At the lung bases, a greater increase in lung attenuation was noted during exhalation for a given change in cross-sectional lung area than in the upper lungs. All 10 subjects showed a distinct lobar attenuation gradient in the supine position. In general, lung attenuation increased homogeneously during exhalation, but four of the 10 subjects showed regions of inhomogeneity in lung attenuation during rapid exhalation indicative of air trapping, despite normal results on pulmonary function tests.

Dynamic Imaging of Lung Morphology With Ultrafast High-Resolution Computed Tomography

To aid in the diagnosis of lung diseases associated with airway obstruction and air-trapping, we use dynamic ultrafast high-resolution computed tomography (DUHRCT). We obtain a rapid series of ultrafast HRCT scans during a forced inspiratory and expiratory maneuver to demonstrate dynamic lung attenuation changes. Alteration in lung morphology can be seen coincident with changes in lung attenuation during different phases of the respiratory cycle. Lung attenuation changes can be evaluated qualitatively or quantitatively by using time-attenuation curves measured for specific regions of lung. In a normal population, we noted that the lingula is a common site of unsuspected and asymptomatic air-trapping. In subjects with airway obstruction, and in those with cystic lung disease, air-trapping is readily detected, even at the secondary pulmonary lobule level. In some of those cases with air-trapping, a paradoxical decrease in lung attenuation was noted during forced exhalation. Recent development of spiral CT scanners may allow more common usage of a similar dynamic technique. Simple paired inspiratory and expiratory scans, obtained during suspended respiration at the same level, may be sufficient for the detection of air-trapping in many patients.

Diffuse panbronchiolitis: correlation of high-resolution CT and pathologic findings.

Diffuse panbronchiolitis (DPB) is characterized by chronic airflow limitation and airway inflammation with bronchiolar lesions. Chest radiographs of patients with DPB usually show small nodular shadows throughout both lungs. The authors investigated the nature and pathogenesis of the radiologic features of DPB by correlating high-resolution computed tomographic (HRCT) findings with histopathologic features. The HRCT images of nine patients with DPB were compared with the observations made with inflated lung specimens. The HRCT findings of DPB included centrilobularly distributed, small rounded areas of attenuation; branched linear areas of attenuation, contiguous with the small rounded areas; dilated airways with thick walls, also common outside secondary pulmonary lobules; and decreased lung attenuation in peripheral areas due to air trapping caused by bronchiolar narrowing in the subpleural zones. The authors believe that HRCT best demonstrates this characteristic location of small rounded areas of attenuation associated with dilated airways.

Usual interstitial pneumonia: histologic correlation with high-resolution CT.

The authors reviewed 46 cases of idiopathic pulmonary fibrosis with usual interstitial pneumonia (UIP), correlating findings on high-resolution computed tomographic (HRCT) scans with findings in specimens obtained at open lung biopsy and autopsy. The following HRCT findings were observed: (a) an accumulation of small cystic spaces with thick walls, (b) air bronchiolograms within areas of intense lung attenuation, (c) rugged pleural surfaces, (d) irregularly thickened pulmonary vessels, (e) bronchial wall thickening, and (f) slightly increased lung attenuation. Macroscopic honeycombing correlating with small cystic spaces was demonstrated at HRCT and pathologic examination. Air bronchiolograms in the areas of intense lung attenuation (ie, microscopic honeycombing) corresponded to dilated bronchioles (greater than 1 mm in diameter) with fibrosis. Irregularly thickened vessels and bronchial walls and irregular pleural surfaces were the result of fibrosis in the periphery of the secondary pulmonary lobules. Areas of slightly increased lung attenuation seen on the HRCT scans correlated with patchy alveolar septal fibrosis or inflammation. The authors conclude that microscopic honeycombing and a perilobular distribution in UIP may be clearly identified with HRCT.