An analysis algorithm for measuring airway lumen and wall areas from high-resolution computed tomographic data

High-resolution computed tomography (HRCT) has been used to examine airway narrowing. We developed an automated computed tomographic image analysis al gorithm (computed tomographic airway morphometry; CTAM) to measure airway l umen area (Ai), airway wall area (Awa), and airway angle of orientation. Tu bes of varying size were embedded in Styrofoam and then scanned at angles b etween 0 degrees and 50 degrees to assess the accuracy of measurements made with CTAM. Two excised pig lungs were fixed in inflation, sectioned, and s canned. Ai and Awa were measured planimetrically from the cut surfaces to o ptimize CTAM measurement parameters, In CTAM, Ai was defined according to a n airway-size-dependent threshold value, and total Awa was determined throu gh a score-guided erosion method. Results were compared with measurements m ade through a previously validated method (manual method). CTAM provided ac curate measurements of the tubes' Ai values at all angles; Awa was overstim ated in direct relation to airway size. The manual method underestimated Ai and overestimated Awa in a manner directly related to airway size as well as to airway angle of orientation. In the excised lung, the mean errors of Ai and Awa measurements made with CTAM were 0.52 +/- 0.24 mm(2) and 0.17 +/ - 0.32 mm(2) (mean +/- SEM), respectively. Ai errors with the manual method were similar, but Awa was overestimated to a greater degree (6.3 +/- 0.38 mm(2); p < 0.01) and the error was proportional to Awa (r = 0.64; p < 0.01) . CTAM allows accurate measurements of airway dimensions and angle of orien tation.