Reproducibility of Lung and Lobar Volume Measurements Using Computed Tomography

Rationale and Objectives

Lung and lobar volume measurements from computed tomographic (CT) imaging are being used in clinical trials to assess new minimally invasive emphysema treatments aiming to reduce lung volumes. Establishing the reproducibility of lung volume measurements is important if they are to be accepted as treatment planning and outcome variables. The aims of this study were to (1) investigate the correlation between lung volumes assessed on CT imaging and on pulmonary function testing (PFT), (2) compare the two methods’ reproducibility, and (3) assess the reproducibility of CT lobar volumes.

Materials and Methods

CT imaging and body plethysmography were performed at baseline and after a 9-month interval in multicenter emphysema treatment trials. Lung volumes were measured at total lung capacity (TLC) and at residual volume (RV). Lobar volumes were measured on CT imaging using a semiautomated technique. The correlations between CT and PFT volumes were computed for 486 subjects at baseline. Reproducibility was assessed in terms of the intraclass correlation coefficient (ICC) for 126 subjects from the control group at TLC and 120 subjects at RV.

Results

Correlations between CT and PFT lung volumes were 0.86 at TLC and 0.67 at RV. At TLC, the ICCs were 0.943 for CT imaging and 0.814 for PFT. At RV, the ICCs were 0.886 for CT imaging and 0.683 for PFT. CT lobar volumes showed good reproducibility (all P values < .05).

Conclusion

CT lung and lobar volume measurements could be captured in a multicenter trial setting with high reproducibility and were highly correlated with those obtained on PFT. CT imaging showed significantly better reproducibility than PFT between interval lung volume measurements, offering the potential for designing emphysema treatment trials involving fewer subjects.

Lung volume and density measurements from computed tomographic (CT) imaging play a prominent role in the diagnosis of emphysema . Traditionally, forced expiratory volume in 1 second has been used to measure the progression of emphysema, but destructive changes in lung parenchyma often precede decreases in forced expiratory volume by several years . The quantitative assessment of the lungs using CT imaging provides important complementary information to the results of pulmonary function testing (PFT) because it allows the assessment of single and lobar lung volumes . This ability for the regional measurement of volumes is important in volume reduction treatments for emphysema .

CT lung volumes are playing a key role in clinical trials of new minimally invasive therapies aimed at the reduction of lung volume . These treatments involve placing a one-way valve in the lobar or segmental airway to prevent air from entering these portions of the lung while still allowing air to exit. Reduction in the volume of the treated lobe measured using CT imaging is used to assess atelectasis resulting from the treatment. Therefore, establishing the reproducibility of lung volume measurements is important if they are to be accepted as treatment planning and outcome variables in these trials. In this paper, we report on the reproducibility of CT lung and lobar volume measurements in two parallel multicenter clinical trials. We compared the reproducibility of CT lung volumes against those from PFT.

Materials and methods

Subject Recruitment

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Lung Volume Measurements From Body Plethysmography

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Lung Volume Measurement From CT Imaging

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Statistical Analysis

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Results

Baseline Characteristics

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Table 1

Subject Baseline Characteristics

Variable Absolute (Mean ± SD) Range Age (y) 63 ± 7 41–76 PFT TLC (L) 7.62 ± 1.48 3.4–12.14 PFT RV (L) 4.83 ± 1.21 0.86–9.22 CT TLC (L) 6.99 ± 1.38 3.98–10.45 CT RV (L) 5.12 ± 1.26 2.29–8.99 Voxels below −910 HU (%) 56.53 ± 10.30 30.45–81.27

CT, computed tomographic; HU, Hounsfield units; PFT, pulmonary function testing; RV, residual volume; SD, standard deviation; TLC, total lung capacity.

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Lung Volume Correlations

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Lung Volume Reproducibility

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Table 2

Summary of the Reproducibility Statistics on Baseline and Follow-Up Lung Volumes From the Control Group From CT Imaging and PFT

CT PFT Parameter Baseline Follow-Up_P_ Difference_r_ ICC Baseline Follow-Up_P_ Difference_r_ ICC TLC volume (L) of control group ( n = 126) 6.93 ± 1.36 6.87 ± 1.42 .18 −0.056 ± 0.467 0.94 ( P < .001) 0.94 7.68 ± 1.50 7.53 ± 1.49 .07 −0.149 ± 0.903 0.82 ( P < .001) 0.81 RV volume (L) of control group ( n = 120) 5.17 ± 1.27 5.16 ± 1.29 .75 −0.018 ± 0.61 0.89 ( P < .001) 0.89 4.90 ± 1.25 4.74 ± 1.25 .0656 −0.17 ± 0.99 0.69 ( P < .001) 0.68

CT, computed tomographic; ICC, intraclass correlation coefficient; PFT, pulmonary function testing; RV, residual volume; TLC, total lung capacity.

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Table 3

Number of Subjects Required to Detect Differences Between Two Visits in TLC Lung Volumes From Two Visits in a Prospective Study with 80% Power at a 5% α Level

Difference in TLC Lung Volume (L) Number of Subjects Required Using CT Imaging Number of Subjects Required Using PFT 0.1 174 641 0.2 45 162 0.3 22 74 0.4 13 42 0.5 9 28

CT, computed tomographic; PFT, pulmonary function testing; TLC, total lung capacity.

Table 4

Study Power When Detecting a Difference in TLC Lung Volume of 0.3 L Between Two Visits for Given Sample Sizes at a 5% α Level

Sample Size Study Power Using CT Lung Volumes Study Power Using PFT Lung Volumes 30 0.9250 0.4206 40 0.9773 0.5356 50 0.9937 0.6342 60 0.9983 0.7161 70 0.9996 0.7825 80 0.9999 0.8353

CT, computed tomographic; PFT, pulmonary function testing.

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Table 5

ICCs Between Lobar Lung Volumes Computed From Two CT Scans at TLC for the RUL, RML, RLL, LUL, and LLL

Lobe Assessed at TLC ICC 95% CI RUL 0.959 0.945–0.973 RML 0.873 0.831–0.914 RLL 0.930 0.907–0.954 LUL 0.970 0.959–0.980 LLL 0.945 0.927–0.964

CI, confidence interval; ICC, intraclass correlation coefficient; LLL, left lower lobe; LUL, left upper lobe; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe; TLC, total lung capacity.

Table 6

ICCs Between Lobar Lung Volumes Computed From Two CT Scans at RV for the RUL, RML, RLL, LUL, and LLL

Lobe Assessed at RV ICC 95% CI RUL 0.906 0.874–0.938 RML 0.845 0.794–0.897 RLL 0.913 0.884–0.943 LUL 0.913 0.884–0.943 LLL 0.931 0.908–0.955

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Discussion

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Conclusion

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References

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Reproducibility of Lung and Lobar Volume Measurements Using Computed Tomography

Rationale and Objectives

Materials and Methods

Results

Conclusion

Materials and methods

Subject Recruitment

Lung Volume Measurements From Body Plethysmography

Lung Volume Measurement From CT Imaging

Statistical Analysis

Results

Baseline Characteristics

Lung Volume Correlations

Lung Volume Reproducibility

Discussion

Conclusion

References

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