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Fig. 2 | BMC Pulmonary Medicine

Fig. 2

From: Fractal analysis of low attenuation clusters on computed tomography in chronic obstructive pulmonary disease

Fig. 2

Comparisons of new fractal dimensions to the conventional fractal dimension. a The relationship between the CT-derived total lung volume (CT-TLV) and physiologically-measured total lung capacity (TLC). Blue dots indicate cases with better-quality scans defined as those with ratios of CT-TLV to TLC (the proxy for inspiration) > 0.8 and < 1.2. b Correlation between D based on thresholds of − 950 HU (D950) and the 15th, 25th, and 35th percentiles of a CT density histogram (D’15, D’25, and D’35) are shown. Rall and Rsub indicate coefficient correlations for the analyses of all scans (n = 170) and the better-quality scans (n = 144), respectively; ** p < 0.01. c and (d) show examples of 2 cases, both of which had similar D950 but different D’25 values. Large (> 500 mm3, pink) and moderate (> 50 and < 499 mm3, yellow) low attenuation clusters are expressed as spheres with volumes equivalent to that of actual clusters. Small (< 50 mm3, blue) clusters are shown only in the coronal CT images. When using a fixed threshold of − 950 HU, both cases showed 2 large clusters and many small clusters similarly. In contrast, when using a threshold of the 25th percentile of the CT value histogram, case 2 (d) showed several (4 or more) relatively larger clusters and other small clusters, whereas case 1 (c) still showed 2 larger clusters and many small clusters

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