Airway dimensions measured from micro computed tomography (CT) and high resolution CT

¹ Woolcock Institute of Medical Research, Sydney 2050, Australia.; Cooperative Research Centre (CRC) for Asthma, Sydney 2050, Australia.; and University of Sydney, Sydney 2006, Australia.
² Key Centre for Microscopy and Microanalysis, the University of Sydney 2006, Australia.
³ Woolcock Institute of Medical Research, Sydney 2050, Australia.; and Dept of Radiology, Royal Prince Alfred Hospital, Camperdown 2050, Australia.
⁴ Woolcock Institute of Medical Research, Sydney 2050, Australia.; Cooperative Research Centre (CRC) for Asthma, Sydney 2050, Australia.; University of Sydney, Sydney 2006, Australia.; and Dept of Respiratory Medicine, Royal North Shore Hospital, St. Leonards 2065, Australia.

^* To whom correspondence should be addressed. E-mail: ggk{at}woolcock.org.au.

	Abstract

Volume averaging results in over- and underestimation of airway dimensions measured from High-resolution CT (HRCT). We calibrated computerized measurements of airway dimensions from HRCT against a novel 3-dimensional micro-CT standard, which has a fifty-fold greater resolution, as well as with traditional morphometry.

Inflation-fixed porcine lung cubes were scanned by HRCT and micro-CT. 59 lumen area (Ai), 30 wall area (Aaw) and 11 lumen volume (Vi) measurements were made. Ai 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 Ai, Aaw and Vi HRCT measurements were determined.

We found a systematic, size-dependent under-estimation of Ai and overestimation of Aaw from HRCT measurements which we used to calibrate our HRCT measurement algorithm. The 95% limits of agreement of subsequent measurements were ±3.2 mm² for Ai, ±4.3 mm² for Aaw, and ±11.2 mm³ for Vi with no systematic error. Morphometric measurements agreed with micro-CT (±2.5 mm²) without systematic error.

Micro-CT image data from inflation fixed airways can be used as calibration standards for three-dimensional Vi measurements for HRCT, while morphometry is acceptable for two-dimensional measurements. This image dataset could be used to validate other developmental 3-dimensional segmentation algorithms.

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