Multidetector-row CT of the airways

Quantitative computed tomography analysis of the airways in patients with cystic fibrosis using automated software: correlation with spirometry in the evaluation of severity

Objective

To perform a quantitative analysis of the airways using automated software, in computed tomography images of patients with cystic fibrosis, correlating the results with spirometric findings.

Materials and Methods

Thirty-four patients with cystic fibrosis were studied-20 males and 14 females; mean age 18 ± 9 years-divided into two groups according to the spirometry findings: group I (n = 21), without severe airflow obstruction (forced expiratory volume in first second [FEV1] > 50% predicted), and group II (n = 13), with severe obstruction (FEV1 ≤ 50% predicted). The following tracheobronchial tree parameters were obtained automatically: bronchial diameter, area, thickness, and wall attenuation.

Results

On average, 52 bronchi per patient were studied. The number of bronchi analyzed was higher in group II. The correlation with spirometry findings, especially between the relative wall thickness of third to eighth bronchial generation and predicted FEV1, was better in group I.

Conclusion

Quantitative analysis of the airways by computed tomography can be useful for assessing disease severity in cystic fibrosis patients. In patients with severe airflow obstruction, the number of bronchi studied by the method is higher, indicating more bronchiectasis. In patients without severe obstruction, the relative bronchial wall thickness showed a good correlation with the predicted FEV1.

Airway wall thickness of allergic asthma caused by weed pollen or house dust mite assessed by computed tomography

PURPOSE

Little was known about Airway wall thickness of asthma patients with different allergen allergy. So we explored the possible difference of Airway wall thickness of asthma patients mono-sensitized to weed pollen or HDM using high-resolution computed tomography.

MATERIALS AND METHODS

85 severe asthma patients were divided into weed pollen group and HDM group according to relevant allergen. 20 healthy donors served as controls. Airway wall area, percentage wall area and luminal area at the trunk of the apical bronchus of the right upper lobe were quantified using HRCT and compared. The values of pulmonary function were assessed as well.

RESULTS

There were differences between HDM group and weed pollen group in WA/BSA,WA% and FEF25-75% pred, and no significant difference in FEV1%pred, FEV1/FVC and LA/BSA. In weed pollen group, WA/BSA was observed to correlate with the duration of rhinitis, whereas in HDM group, WA/BSA and LA/BSA was observed to correlate with the duration of asthma. In weed pollen group, FEV1/FVC showed a weak but significant negative correlation with WA%, but in HDM group FEV1/FVC showed a significant positive correlation with WA% and a statistical negative correlation with LA/BSA. FEV1/FVC and FEF25-75% pred were higher and WA/BSA and LA/BSA were lower in healthy control group than asthma group. FEV1%pred and WA% was no significant difference between asthma patients and healthy subjects.

CONCLUSION

There are differences between HDM mono-sensitized subjects and weed pollen mono-sensitized subjects, not only in airway wall thickness, but also small airway obstruction.

Computed tomographic imaging of the airways in COPD and asthma

Computed tomography (CT) is the modality of choice for imaging the airways. Volumetric data sets with isotropic spatial resolution based on multidetector thin-section CT with overlapping reconstruction should be used. Chronic obstructive pulmonary disease and asthma are the 2 most common disease entities that are defined by airflow obstruction. The morphologic correlates of airway changes are dilation of the lumen, thickening of the wall, visibility of small airways due to mucus or edema, air trapping, hypoxic vasoconstriction, and collapsibility. To assess air trapping, additional expiratory low-dose scans are recommended. In clinical routine, these findings are visually assessed and should be routinely reported. However, the interobserver variability is high, and there is a clear need for objective software-based measurements. The development of such tools is challenging, and they are just becoming available on a broader scale. Novel techniques based on dual-energy CT aim to measure iodine distribution maps to assess pulmonary perfusion as well as the distribution of inhaled xenon gas to assess the distribution and time course of pulmonary ventilation. However, these techniques are still being investigated in clinical studies. This review will provide an overview of CT for the diagnosis of chronic obstructive pulmonary disease and asthma, its role in phenotyping these diseases, and the measurement of disease severity and functional compromise.

Airway Remodelling in Asthma and COPD: Findings, Similarities, and Differences Using Quantitative CT

Airway remodelling is a well-established feature in asthma and chronic obstructive lung disease (COPD), secondary to chronic airway inflammation. The structural changes found on pathological examination of remodelled airway wall have been shown to display similarities but also differences. Computed tomography (CT) is today a remarkable tool to assess airway wall morphology in vivo since submillimetric acquisitions over the whole lung volume could be obtained allowing 3D evaluation. Recently, CT-derived indices extracted from CT images have been described and are thought to assess airway remodelling. This may help understand the complex mechanism underlying the remodelling process, which is still not fully understood. This paper summarizes the various methods described to quantify airway remodelling in asthma and COPD using CT, and similarities and differences between both diseases will be emphasized.

Modern imaging of the tracheo-bronchial tree

Recent state-of-the-art computed tomography and improved three-dimensional (3-D) postprocessing techniques have revolutionized the capability of visualizing airway pathology, offering physicians an advanced view of pathology and allowing for appropriate management planning. This article is a comprehensive review of trachea and main bronchi imaging, with emphasis on the dynamic airway anatomy, and a discussion of a wide variety of diseases including, but not limited to, congenital large airway abnormalities, tracheobronchial stenoses, benign and malignant neoplasms and tracheobronchomalacia. The importance of multiplanar reconstruction, 3-D reconstruction and incorporation of dynamic imaging for non-invasive evaluation of the large airways is stressed.

Imaging-bronchoscopic correlations for interventional pulmonology

The improvements to patient care that can be achieved by combining advanced imaging techniques and bronchoscopy are considerable. In this regard, CT imaging often plays an indispensable role in both the selection of appropriate candidates tor therapy as well as the choice of optimal interventional techniques. However, it is apparent that alternate methods for evaluating the airways and lung including ultrasound and electromagnetic navigation will likely play an increasingly important diagnostic role, necessitating a thorough understanding of their advantages and limitations. Disease-specific applications for which imaging technologies, including CT and VB, are either currently routinely used or show the greatest promise are for suspected or diagnosed lung cancers, central and peripheral, and emphysema. It may be anticipated that with growing experience, the potential for additional indications of these remarkable technologies are likely to increase in the near future.

Development and validation of automated 2D-3D bronchial airway matching to track changes in regional bronchial morphology using serial low-dose chest CT scans in children with chronic lung disease

To address potential concern for cumulative radiation exposure with serial spiral chest computed tomography (CT) scans in children with chronic lung disease, we developed an approach to match bronchial airways on low-dose spiral and low-dose high-resolution CT (HRCT) chest images to allow serial comparisons. An automated algorithm matches the position and orientation of bronchial airways obtained from HRCT slices with those in the spiral CT scan. To validate this algorithm, we compared manual matching vs automatic matching of bronchial airways in three pediatric patients. The mean absolute percentage difference between the manually matched spiral CT airway and the index HRCT airways were 9.4 ± 8.5% for the internal diameter measurements, 6.0 ± 4.1% for the outer diameter measurements, and 10.1 ± 9.3% for the wall thickness measurements. The mean absolute percentage difference between the automatically matched spiral CT airway measurements and index HRCT airway measurements were 9.2 ± 8.6% for the inner diameter, 5.8 ± 4.5% for the outer diameter, and 9.9 ± 9.5% for the wall thickness. The overall difference between manual and automated methods was 2.1 ± 1.2%, which was significantly less than the interuser variability of 5.1 ± 4.6% (p<0.05). Tests of equivalence had p<0.05, demonstrating no significant difference between the two methods. The time required for matching was significantly reduced in the automated method (p<0.01) and was as accurate as manual matching, allowing efficient comparison of airways obtained on low-dose spiral CT imaging with low-dose HRCT scans.

Imaging-bronchoscopic correlations for interventional pulmonology

The development and rapid advancement of both bronchoscopic, CT and ultrasound imaging technology has had considerable impact on the management of a wide variety of pulmonary diseases. The synergy between these newer imaging modalities and advanced interventional endoscopic procedures has led to a revolution in diagnostic and therapeutic options in patients with both central and peripheral airway disease. Given the broad clinical implications of these technological advances, only the most important areas of interventional pulmonology in which imaging has had a major impact will be selectively reviewed to highlight fundamental principles.

High-resolution computed tomography evaluation of airway distensibility in asthmatic and healthy subjects

PURPOSE

Airway-wall remodelling may result in reduced airway distensibility in bronchial asthma. This study evaluated the baseline airway calibre and distensibility in asthmatic patients by means of high-resolution computed tomography (HRCT).

MATERIALS AND METHODS

We studied seven patients (two men, age range 36-69 years) with chronic asthma [forced expiratory volume in the first second (FEV(1)) range: 30%-87% of predicted; FEV1/forced vital capacity (FVC) range 48%-75% of predicted) under stable clinical conditions and six healthy control subjects (three men, age range 29-50 years). In all subjects, HRCT scanning, at suspended end-expiratory volume, was performed at rest and during ventilation with 6 and 12 cmH(2)O by nasal insufflation with continuous positive airway pressure (nCPAP), both at baseline and after inhalation of 200 mug oxitropium bromide metered dose inhaler (MDI). External and lumen diameter (mm) of the right apical upper lobe bronchus were measured in all HRCT scans.

RESULTS

In asthmatics, 12 cmH(2)O insufflation significantly changed baseline lumen (3.3+/-0.7 mm vs. 3.8+/-0.6 mm; p<0.01) and external diameter (6.2+/-0.9 mm vs. 6.7+/-0.8 mm; p<0.05), whereas in healthy controls, both 6 and 12 cmH(2)O insufflation significantly changed baseline lumen diameter (4.0+/-1.6 mm vs. 4.8+/-1.6 mm and 4.7+/-1.7 mm; p<0.01). In asthmatic patients, oxitropium bromide inhalation significantly changed baseline lumen diameter (3.3+/-0.7 mm vs. 4.4+/-0.6 mm; p<0.05), whereas the application of 6 or 12 cmH(2)O insufflation did not modify any bronchial diameters. In healthy controls, oxitropium bromide inhalation significantly changed baseline lumen diameter (4.0+/-.6 mm vs. 5+/-1.5 mm; p<0.05). The application of 12 cmH(2)O but not of 6 cmH(2)O induced a significant change in lumen diameter (5.0+/-1.5 mm vs. 6,0+/-1.6 mm; p<0.05).

CONCLUSIONS

Our results show that airway distensibility in asthmatic patients, as assessed by HRCT, can differ compared with that of healthy controls. HRCT can provide useful information on airway distensibility.

Fully automated system for three-dimensional bronchial morphology analysis using volumetric multidetector computed tomography of the chest

Recent advancements in computed tomography (CT) have enabled quantitative assessment of severity and progression of large airway damage in chronic pulmonary disease. The advent of fast multidetector computed tomography scanning has allowed the acquisition of rapid, low-dose 3D volumetric pulmonary scans that depict the bronchial tree in great detail. Volumetric CT allows quantitative indices of bronchial airway morphology to be calculated, including airway diameters, wall thicknesses, wall area, airway segment lengths, airway taper indices, and airway branching patterns. However, the complexity and size of the bronchial tree render manual measurement methods impractical and inaccurate. We have developed an integrated software package utilizing a new measurement algorithm termed mirror-image Gaussian fit that enables the user to perform automated bronchial segmentation, measurement, and database archiving of the bronchial morphology in high resolution and volumetric CT scans and also allows 3D localization, visualization, and registration.

Pulmonary airways: 3-D reconstruction from multislice CT and clinical investigation

In the framework of computer-aided diagnosis, this paper proposes a novel functionality for the computerized tomography (CT)-based investigation of the pulmonary airways. It relies on an energy-based three-dimensional (3-D) reconstruction of the bronchial tree from multislice CT acquisitions, up to the sixth- to seventh-order subdivisions. Global and local analysis of the reconstructed airways is possible by means of specific visualization modalities, respectively, the CT bronchography and the virtual bronchoscopy. The originality of the 3-D reconstruction approach consists in combining axial and radial propagation potentials to control the growth of a subset of low-order airways extracted from the CT volume by means of a robust mathematical morphology operator-the selective marking and depth constrained (SMDC) connection cost. The proposed approach proved to be robust with respect to a large spectrum of airway pathologies, including even severe stenosis (bronchial lumen obstruction/collapse). Validated by expert radiologists, examples of airway 3-D reconstructions are presented and discussed for both normal and pathological cases. They highlight the interest in considering CT bronchography and virtual bronchoscopy as complementary tools for clinical diagnosis and follow-up of airway diseases.