Rationale and Objectives
The purpose of this study was to evaluate the effect of various tube currents on the accuracy of volumetric measurements of ground-glass opacity (GGO) nodules using a chest phantom.
Materials and Methods
A chest phantom containing 13 artificial GGO nodules with known volumes was scanned using a 64-slice computed tomographic scanner at different tube currents (30, 60, 90, 120, 150, 180, and 210 mA). Volumetric measurements were performed using software. The relative percentage error and the absolute percentage error between the volume measures on computed tomography and the reference-standard volumes were calculated. Correlations between the mean absolute percentage error and the mean attenuation of nodules and between the ratio of solid component and the mean attenuation of nodules were analyzed.
Results
The relative percentage errors showed that there was substantial underestimation of nodule volumes at 30, 60, and 90 mA and substantial overestimation of volumes at 120, 150, 180, and 210 mA, but there was no statistically significant difference in absolute percentage errors ( P = .876). Pearson’s correlation coefficient of the mean absolute percentage errors of nodules on volumetric measurement versus the mean attenuation value of nodules showed a negative correlation, and the ratio of solid component to whole nodule versus the mean attenuation of nodules showed a positive correlation.
Conclusion
Volume measurement is a promising method for the quantification of GGO nodule volume. It is important to know that different tube currents can affect the accuracy of volumetric measurements.
Since the introduction of low-dose computed tomography for lung cancer screening, an increasing number of nodules with ground-glass opacity (GGO) have been detected . GGO is a nonspecific finding that may be caused by various disorders, including inflammatory disease, fibrosis, and neoplastic disease . Henschke et al reported that GGO nodules have a higher malignancy rate than solid nodules. In addition, the relationship between the proportion of ground-glass component in pulmonary adenocarcinoma and histologic features has recently been determined . In some reports , patients with ground-glass components of <50% had worse prognoses than those with ground-glass components of >50%. Therefore, quantitative analysis of GGO nodules is useful for both preoperative diagnosis and treatment planning.
Various methods for the measurement of ground-glass component have been reported. In many studies , the proportion of ground-glass component was semiquantified by visual estimation of the area in the lung window setting. In another report , both the diameter of nodules with ground-glass components and the central solid portions were measured instead of area. However, a limitation of current studies includes a lack of objectivity, and reproducibility in quantifying GGO nodules is highly dependent on the quality of computed tomographic (CT) images and on observers’ levels of experience. To reduce interobserver variability in the evaluation of GGO nodules and to allow for more accurate assessments, observer-independent analysis and objective measurement are necessary.
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Materials and methods
Phantom
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Determination of Reference-Standard GGO Nodule Volume
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CT Imaging
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Nodule Volume Measurement on CT Images
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Data and Statistical Analysis
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Results
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Table 1
Mean APE and Mean RPE of Volume Measurements at Various Tube Currents
Tube Current (mA) Mean V m (mm 3 ) Pearson’s Correlation Coefficient ( P ) Mean APE (%) ∗ Mean RPE (%) 30 683.85 ± 109.20 0.811 (.001) 7.64 ± 6.71 −5.63 ± 8.60 60 679.69 ± 100.41 0.833 (.000) 7.85 ± 5.40 −6.07 ± 7.49 90 683.54 ± 91.02 0.759 (.003) 7.62 ± 6.24 −5.50 ± 8.31 120 740.46 ± 101.59 0.805 (.001) 6.23 ± 5.35 2.32 ± 8.05 150 744.08 ± 97.21 0.786 (.001) 6.31 ± 5.82 3.06 ± 8.18 180 756.23 ± 89.73 0.801 (.001) 7.64 ± 4.37 4.71 ± 7.63 210 746.46 ± 97.73 0.809 (.001) 6.31 ± 5.27 3.05 ± 7.79 Mean V rs 724.62 ± 94.38
APE, absolute percentage error; RPE, relative percentage error; V m , volume of nodule measured on computed tomography; V rs , reference-standard nodule volume.
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Table 2
Correlations Between the Mean Attenuation of Nodule and the Ratio of Solid Component and the APE
Tube Current (mA) Pearson’s Correlation Coefficient 30 60 90 120 150 180 210P % solid and MHU 0.901 0.938 0.942 0.945 0.914 0.928 0.941 .000 APE and MHU −0.832 −0.821 −0.844 −0.855 −0.850 −0.839 −0.853 .000
APE, absolute percentage error; MHU, mean attenuation value of nodule; % solid, ratio of solid component to whole nodule.
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Discussion
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