Elsevier

Academic Radiology

Volume 14, Issue 4, April 2007, Pages 476-485
Academic Radiology

Original investigation
The Effect of Lung Volume on Nodule Size on CT1

https://doi.org/10.1016/j.acra.2007.01.008Get rights and content

Rationale and Objectives

We sought to determine how measures of nodule diameter and volume on computed tomography (CT) vary with changes in inspiratory level.

Materials and Methods

CT scans were performed with inspiration suspended at total lung capacity (TLC) and then at residual volume (RV) in 41 subjects, in whom 75 indeterminate lung nodules were detected. A fully automated contouring program was used to segment the lungs; followed by segmentation of all nodules and the corresponding lobe using semiautomated contouring in both TLC and RV scans. The percent changes in lung and lobar volumes between TLC and RV were correlated with percent changes in nodule diameters and volumes.

Results

Both nodule diameter and volume varied nonuniformly from TLC to RV—some nodules decreased in size, while others increased. There was a 16.8% mean change in absolute volume across all nodules. Stratified by size, the mean value of the absolute percent volume changes for nodules ≥5 mm and <5 mm were not significantly different (P = .26). Stratified by maximum attenuation, the mean value of the absolute percent volume changes between the TLC and RV series for noncalcified (17.7%, SD = 13.1) and completely calcified nodules (8.6% SD = 5.7) were significantly different (P < .05).

Conclusion

Significant differences in nodule size were measured between TLC and RV scans. This has important implications for standardizing acquisition protocols in any setting where size and, more important, size change are being used for purposes of lung cancer staging, nodule characterization, or treatment response assessment.

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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    1

    This work was funded by UCLA SPORE in Lung Cancer grant 5P50CA090388.

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