Background: Determination of regional lung air volume has several clinical applications. This study investigates the\nuse of mid-tidal breathing CT scans to provide regional lung volume data.\nMethods: Low resolution CT scans of the thorax were obtained during tidal breathing in 11 healthy control male\nsubjects, each on two separate occasions. A 3D map of air volume was derived, and total lung volume calculated.\nThe regional distribution of air volume from centre to periphery of the lung was analysed using a radial transform\nand also using one dimensional profiles in three orthogonal directions.\nResults: The total air volumes for the right and left lungs were 1035 +/? 280 ml and 864 +/? 315 ml, respectively\n(mean and SD). The corresponding fractional air volume concentrations (FAVC) were 0.680 +/? 0.044 and\n0.658 +/? 0.062. All differences between the right and left lung were highly significant (p < 0.0001). The coefficients\nof variation of repeated measurement of right and left lung air volumes and FAVC were 6.5% and 6.9% and 2.5%\nand 3.6%, respectively. FAVC correlated significantly with lung space volume (r = 0.78) (p < 0.005). FAVC increased\nfrom the centre towards the periphery of the lung. Central to peripheral ratios were significantly higher for the\nright (0.100 +/? 0.007 SD) than the left (0.089 +/? 0.013 SD) (p < 0.0001).\nConclusion: A technique for measuring the distribution of air volume in the lung at mid-tidal breathing is described.\nMean values and reproducibility are described for healthy male control subjects. Fractional air volume concentration is\nshown to increase with lung size.
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