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Airway dimensions measured from micro-computed tomography and high-resolution computed tomography

¹ The Woolcock Institute of Medical Research, and ² The Cooperative Research Centre for Asthma, and ³ University of Sydney, and ⁴ The Key Centre for Microscopy and Microanalysis, University of Sydney, Sydney, and ⁵ Dept of Radiology, Royal Prince Alfred Hospital, Camperdown, and ⁶ Dept of Respiratory Medicine, Royal North Shore Hospital, St. Leonards, Australia.

CORRESPONDENCE: G. G. King, The Woolcock Institute of Medical Research, University of Sydney, Sydney 2006, Australia. Fax: 61 299066391. E-mail: ggk{at}woolcock.org.au

Keywords: Computer-assisted image processing, imaging, phantoms, validation studies

Received: February 3, 2005
Accepted June 30, 2006

Volume averaging results in both over- and underestimation of airway dimensions when they are measured by high-resolution computed tomography (HRCT). The current authors calibrated computerised measurements of airway dimensions from HRCT against a novel three-dimensional micro-computed tomography (CT) standard, which has a 50-fold greater resolution, as well as against traditional morphometry.

Inflation-fixed porcine lung cubes were scanned by HRCT and micro-CT. A total of 59 lumen area (A_i), 30 wall area (A_aw) and 11 lumen volume (V_i) measurements were made. A_i was measured from the cut surface of 11 airways by morphometry. Airways in scanned images were matched using branching points. After calibration, the errors of A_i, A_aw and V_i HRCT measurements were determined.

The current authors found a systematic, size-dependent underestimation of A_i and overestimation of A_aw from HRCT measurements. This was used to calibrate an HRCT measurement algorithm. The 95% limits of agreement of subsequent measurements were ±3.2 mm² for A_i, ±4.3 mm² for A_aw, and ±11.2 mm³ for V_i with no systematic error. Morphometric measurements agreed with micro-CT (±2.5 mm²) without systematic error.

In conclusion, micro-computed tomography image data from inflation-fixed airways can be used as calibration standards for three-dimensional lumen volume measurements from high-resolution computed tomography, while morphometry is acceptable for two-dimensional measurements. The image dataset could be used to validate other developmental three-dimensional segmentation algorithms.

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