Quantitative videobronchoscopy: a new technique to assess airway caliber.

Abstract

Quantitative assessment of airway caliber is generally confined to indirect physiologic methods or to radiographic techniques. Fiberoptic bronchoscopy provides a direct view of airways, permitting quantification of airway caliber by image analysis. We investigated the characteristics of a bronchoscopic imaging system, determined its limitations in quantification and the corrections necessary for accurate assessment of image dimension, validated the methodology with airway models, and applied the technique to airways in vivo. The system comprised a bronchoscope, videocamera, videocassette recorder (VCR), computer with a frame grabber, and image-analysis program. Image quantification was affected by two sources of distortion: (1) Distance distortion: a loss of image resolution with increasing distance between the object and bronchoscope, requiring determination of the operational distance range. (2) Radial distortion: a progressive reduction in image size from the center to the periphery of the bronchoscopic field of view (FOV), requiring correction of airway dimension according to airway size and location in FOV. Validation of the methodology with different sized airway models indicated an underestimation of measured diameters, which normalized with distortion correction. We provide an example of quantitative videobronchoscopy with measurements of in vivo airway narrowing due to vagal stimulation in the anesthetized dog. Measurements of airway narrowing made with videobronchoscopy were also compared with those made with high-resolution computer-assisted tomography (HRCT) which suggested that the two technologies provide unique but complementary perspectives on airway dimensions. We conclude that videobronchoscopy and image analysis provide a novel and accurate method for the quantification of airway caliber.

Measuring Central Airway Obstruction: What Do Bronchoscopists Do?

“…Methods that quantify CAO without ionizing radiation have relied primarily upon bronchoscopic image processing (4,5). Majid and colleagues (6) demonstrated favorable inter-and intraobserver reliability using bronchoscopy to measure anteriorposterior airway luminal dimensions in patients with dynamic airway collapse.…”

“…Murgu and Colt (7) have been proponents of morphometric bronchoscopy, which uses image software processing techniques that enable analysis of still digital images to measure airway lumen caliber. Studies in normal patients and patients with tracheobronchomalacia and benign strictures have demonstrated that morphometric bronchoscopy reliably measured airway caliber, had high intraand interobserver agreement, and correlated well with measurements performed by CT (4,8,9). However, this method has disadvantages in terms of providing real-time measurements, and has not been widely adopted (10).…”

A new method to perform quantitative measurement of bronchoscopic images

“…In contrast, bronchoscopy is a relatively inexpensive and routine procedure that allows direct, real-time imaging of the bronchial lumen. Quantification of bronchoscopic images would provide a useful alternative to tantalum bronchography or HRCT for measuring the responsiveness of individual airways in vivo [13].…”

“…This form of distortion has been termed "barrel distortion" [14,15]. Bronchoscopic distortion is radial, increasing with displacement from the centre of the FOV in a nonlinear manner [13,[15][16][17][18]. Bronchoscopic distortion also alters the apparent shape of objects, making straight lines appear curved and compressing objects radially so that a circle will appear elliptical near the periphery of the field.…”

“…Bronchoscopic distortion also alters the apparent shape of objects, making straight lines appear curved and compressing objects radially so that a circle will appear elliptical near the periphery of the field. The extent of distortion depends on how close the object is located to or extends to the edge of the field [13]. Without correction, only small objects near the centre can be measured accurately [13,15,19,20].…”