Imaging studies in emphysema

Abstract

Definitions of types of emphysema within the framework of chronic obstructive pulmonary disease are given. The classic findings on the chest radiograph are described, and the advances in sensitivity and specificity achieved with computed tomography (CT) scanning are noted. The "density mask" and the "percentile point" measurements rely on the densitometric property of X-rays, but the scan also shows the severity and distribution of low-attenuation regions that usually represent pathologic emphysema. The alteration of absolute density with changes in lung inflation, CT slice thickness, collimation, and reconstruction algorithm make comparison between CT scans and across studies more difficult. Nevertheless, quantitative CT has superseded subjective scoring of scan appearance by readers as a sensitive way to measure emphysema.

Figure 1.

Upper lobe 5-mm slice of lung showing centriacinar emphysema. (A) Conventional windowing. (B) Narrow windowing, with center adjusted upward to optimize appearance. The emphysematous spaces are much easier to recognize on this high contrast scan, although vessels are thickened.

Figure 1.

Upper lobe 5-mm slice of lung showing centriacinar emphysema. (A) Conventional windowing. (B) Narrow windowing, with center adjusted upward to optimize appearance. The emphysematous spaces are much easier to recognize on this high contrast scan, although vessels are thickened.

Figure 2.

Lower lobe showing pan lobular emphysema anteriorly, especially in the right middle lobe. (A) Collimation 7.5 mm. (B) Collimation 1.25 mm. Note the centriacinar emphysema posteriorly, seen much better on this high-resolution scan than in A.

Figure 2.

Lower lobe showing pan lobular emphysema anteriorly, especially in the right middle lobe. (A) Collimation 7.5 mm. (B) Collimation 1.25 mm. Note the centriacinar emphysema posteriorly, seen much better on this high-resolution scan than in A.

Figure 3.

Upper lobe (in a different case) showing upper lobe pan lobular emphysema. (A) A 7.5-mm thick slice showing unequivocal emphysema from the vascular pattern. (B) A high-resolution, 1.25-mm slice showing emphysema equally well.

Figure 3.

Upper lobe (in a different case) showing upper lobe pan lobular emphysema. (A) A 7.5-mm thick slice showing unequivocal emphysema from the vascular pattern. (B) A high-resolution, 1.25-mm slice showing emphysema equally well.

Figure 4.

Histogram of density of pixels or voxels in the whole lung in an emphysematous individual (same as Figure 2). The proportion of the area under the curve to the left of the vertical line at −950 Hounsfield units (HU) is a common measure of emphysema. (A) Inspiratory scan histogram made with standard algorithm, 7.5 mm collimation; 18.0% of pixels/voxels less than −950 HU. Total lung volume (at −600 HU threshhold) 5,875 mL; mean density −889 HU; SD 74.9 HU. (B) Expiratory scan showing only 5.7% of pixels/voxels less than −950 HU; volume of 4,115 mL; mean density −849 HU; SD 80.9 HU. (C) Inspiratory scan with edge-enhancing (bone) algorithm, also slightly thinner collimation (same raw data as A). The curve is broader and much less peaked, with 21.3% of pixels/voxels less than −950 HU in density. Total lung volume measured as 5,851 mL; mean density −888 HU; SD 80.8 HU. Compare the appearance of the curve with A. Note also the changed scale of the vertical axis.

Figure 4.

Histogram of density of pixels or voxels in the whole lung in an emphysematous individual (same as Figure 2). The proportion of the area under the curve to the left of the vertical line at −950 Hounsfield units (HU) is a common measure of emphysema. (A) Inspiratory scan histogram made with standard algorithm, 7.5 mm collimation; 18.0% of pixels/voxels less than −950 HU. Total lung volume (at −600 HU threshhold) 5,875 mL; mean density −889 HU; SD 74.9 HU. (B) Expiratory scan showing only 5.7% of pixels/voxels less than −950 HU; volume of 4,115 mL; mean density −849 HU; SD 80.9 HU. (C) Inspiratory scan with edge-enhancing (bone) algorithm, also slightly thinner collimation (same raw data as A). The curve is broader and much less peaked, with 21.3% of pixels/voxels less than −950 HU in density. Total lung volume measured as 5,851 mL; mean density −888 HU; SD 80.8 HU. Compare the appearance of the curve with A. Note also the changed scale of the vertical axis.

Figure 4.

Histogram of density of pixels or voxels in the whole lung in an emphysematous individual (same as Figure 2). The proportion of the area under the curve to the left of the vertical line at −950 Hounsfield units (HU) is a common measure of emphysema. (A) Inspiratory scan histogram made with standard algorithm, 7.5 mm collimation; 18.0% of pixels/voxels less than −950 HU. Total lung volume (at −600 HU threshhold) 5,875 mL; mean density −889 HU; SD 74.9 HU. (B) Expiratory scan showing only 5.7% of pixels/voxels less than −950 HU; volume of 4,115 mL; mean density −849 HU; SD 80.9 HU. (C) Inspiratory scan with edge-enhancing (bone) algorithm, also slightly thinner collimation (same raw data as A). The curve is broader and much less peaked, with 21.3% of pixels/voxels less than −950 HU in density. Total lung volume measured as 5,851 mL; mean density −888 HU; SD 80.8 HU. Compare the appearance of the curve with A. Note also the changed scale of the vertical axis.