Original investigationThe Effect of Lung Volume on Nodule Size on CT1
Section snippets
Nodule Database
Image datasets were selected from participants in an ongoing emphysema-related clinical trial in which CT scans were first acquired at total lung capacity (TLC) and then at residual volume (RV) in the same setting; no participants were recruited exclusively for this study. This convenience sample was chosen because it provided two image series obtained in the same setting, at different levels of suspended respiration. Between March 2004 and October 2005, 41 participants with one or more nodules
Results
Among 41 participants, 75 nodules were identified, ranging in diameter from 3.2 to 22.4 mm (median 7.6 mm) at TLC and 3.4 to 22.5 mm (median 7.6 mm) at RV. Nodule volumes ranged from 30 to 2638 mm3 (median 165 mm3) at TLC and 25 to 2300 mm3 (median 156 mm3) at RV (Table 1). Nodules were of variable attenuations corresponding to: soft tissue (GG, solid, or mixed attenuation; n = 51), partially calcified (n = 16), and completely calcified (n = 8). Of the 67 nodules ≥5 mm, 45 were of soft tissue
Discussion
In clinical practice, chest CT scans are routinely performed at suspended maximal inspiration, although expiratory breathholds are considered more reproducible (16). However, inspiratory volumes provide greater contrast between focal opacities and aerated lung, thus ensuring optimal delineation of pathology. Our results support the premise that the state of lung inflation influences the measure of nodule size. In our dataset of 75 nodules, we found that nodule size, measured by greatest axial
Conclusion
Significant differences in nodule volume were found between TLC and RV scans. Nodule size varied nonuniformly relative to lung volumes. This suggests that differences in breathhold between serial CT exams can affect the reproducibility of nodule size measurement and that significant attention must be paid to specifying and reproducing the level of suspended breathhold used to acquire CT scans in which change analysis is anticipated for clinical decision-making.
Acknowledgments
We thank Brandon Bigby, BA, and Erin Angel, BS, for providing editorial assistance and Yang Wang, MS, and Sumit Shah, PhD, for their assistance with figure procurement.
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This work was funded by UCLA SPORE in Lung Cancer grant 5P50CA090388.