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Measurement of Focal Ground-glass Opacity Diameters on CT Images

Posted Mar 31, 2012 Updated Apr 10, 2023
By Ryutaro Kakinuma MD , Kazuto Ashizawa MD , Keiko Kuriyama MD , Aya Fukushima MD , Hiroyuki Ishikawa MD , Hisashi Kamiya MD , Naoya Koizumi MD , Yuichiro Maruyama MD , Kazunori Minami MD , Norihisa Nitta MD , Seitaro Oda MD , Yasuji Oshiro MD , Masahiko Kusumoto MD , Sadayuki Murayama MD , Kiyoshi Murata MD , Yukio Muramatsu MD , Noriyuki Moriyama MD
8 min read

Purpose

To evaluate interobserver agreement in regard to measurements of focal ground-glass opacities (GGO) diameters on computed tomography (CT) images to identify increases in the size of GGOs.

Materials and Methods

Approval by the institutional review board and informed consent by the patients were obtained. Ten GGOs (mean size, 10.4 mm; range, 6.5–15 mm), one each in 10 patients (mean age, 65.9 years; range, 58–78 years), were used to make the diameter measurements. Eleven radiologists independently measured the diameters of the GGOs on a total of 40 thin-section CT images (the first [n = 10], the second [n = 10], and the third [n = 10] follow-up CT examinations and remeasurement of the first [n = 10] follow-up CT examinations) without comparing time-lapse CT images. Interobserver agreement was assessed by means of Bland-Altman plots.

Results

The smallest range of the 95% limits of interobserver agreement between the members of the 55 pairs of the 11 radiologists in regard to maximal diameter was −1.14 to 1.72 mm, and the largest range was −7.7 to 1.7 mm. The mean value of the lower limit of the 95% limits of agreement was −3.1 ± 1.4 mm, and the mean value of their upper limit was 2.5 ± 1.1 mm.

Conclusion

When measurements are made by any two radiologists, an increase in the length of the maximal diameter of more than 1.72 mm would be necessary in order to be able to state that the maximal diameter of a particular GGO had actually increased.

Since the advent of multislice computed tomography (CT) technologies and the widespread use of CT scanning of the chest for CT lung cancer screening as well as for clinical purposes, increasing numbers of focal ground-glass opacities (GGOs) are being detected . GGOs are defined as focal nodular areas of increased lung attenuation through which normal parenchymal structures such as airways, vessels, and interlobular septa can be seen . Most persistent GGOs are assumed to be pulmonary neoplasms . Although several computer-assisted volumetry studies of GGOs have been reported , measurement of GGO diameters on thin-section CT (TS-CT) images is a simple method of evaluating the size of GGOs in clinical practice. However, measurements of pulmonary nodules on TS-CT images have been found to vary with the radiologists . To our knowledge, no assessment of interobserver agreement in regard to diameter measurements of GGOs on TS-CT images and causes of its variability has ever been performed.

The purpose of this study was to evaluate interobserver agreement in regard to measurements of GGO diameters on TS-CT images as a means of identifying increases in the size of GGOs.

Materials and methods

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GGO Selection

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CT Scanning and Reconstruction Conditions

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Reading and Measurement Settings

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Statistical Analysis

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Results

Interobserver and Intraobserver Agreement in Regard to Diameter Measurements

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Table 1

Interobserver and Intraobserver Agreement in Regard to Diameter Measurements

Diameter 95% Limits of Agreement (mm) Lower Limit Upper Limit Groups Lower Limit to Upper Limit Minimum Maximum Mean SD Mean SD Maximal Interobserver −1.14 to 1.72 −7.7 to 1.7 −3.1 1.4 2.5 1.1 1, 2, 3, 4 Intraobserver −0.13 to 0.13 −3.3 to 2.5 −2.6 2.1 2.1 1.7 1, 4 Perpendicular Interobserver −2.14 to 0.84 −6.5 to 2.0 −3 1.2 2.3 0.9 1, 2, 3, 4 Intraobserver −0.34 to 0.32 −3.6 to 2.4 −2 0.9 2.1 1 1, 4

CT, computed tomography; SD, standard deviation.

Group 1: 10 thin-section CT images from the first follow-up CT examination.

Group 2: 10 thin-section CT images from the second follow-up CT examination.

Group 3: 10 thin-section CT images from the third follow-up CT examination.

Group 4: the same 10 thin-section CT images as in Group 1.

Figure 1, Bland-Altman plots. Bland-Altman plot of the maximal diameters of 10 ground-glass opacities measured by observer D and observer K in each of 4 groups (total of 40 measurements each). SD: standard deviation.

Figure 2, Summary of Bland-Altman plots of differences in the 1.96 SD of diameters measured by members of 55 pairs of 11 radiologists. The horizontal axis indicates the means in each Bland-Altman plot for any two observers. The vertical axis indicates the 95% limits of agreement of differences in maximal diameter in each Bland-Altman plot for any two observers. The two black dots (•) marked with an asterisk that are located slightly to the right of the vertical axis, one above and the other below the horizontal axis, indicate the smallest range of the 95% limits of agreement (see also Fig 1 ). The gray dots (○) marked by the symbol “¶” located at the left end of each curve indicate the largest range of the 95% limits of agreement. SD: standard deviation.

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Interobserver and Intraobserver Percentage Agreement in Regard to Slice Selection

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Figure 3, Intraobserver variation in selection of the computed tomography (CT) slice on which the observers thought the area of the ground glass opacities appeared to be maximal. These four thin-section CT images are sequential craniad ( left ) to caudad ( right ) images acquired at 1-mm intervals. The numbers in the first row represent the numbers of observers who selected each CT slice during the first reading of the thin-section CT images from the first follow-up CT examination (Group 1). The numbers in the second row represent the numbers of observers who selected each CT slice during the second reading of the thin-section CT images from the first follow-up CT examination (Group 4). The alphabets within the parentheses indicate the respective observers. At the second reading, only four (Drs. D, E, G, and H) of the 11 observers selected the same CT slice as that selected at the first reading, while the others selected CT slices that were different from the CT slices selected at the first reading.

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Distances between Click Points for the Maximal Diameter Measurements

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Table 2

Distances between Click Points for Diameter Measurements Measured by Members of 55 Pairs of 11 Radiologists

Group n Mean (mm) Minimum (mm) Maximum (mm) SD (mm) 1 10 2.8 0 14.2 2.8 2 10 2.6 0 12.6 2.6 3 10 2.2 0 13 2.4 4 10 2.7 0 15.8 2.5 Overall 40 2.6 0 15.8 2.6

SD, standard deviation.

Figure 4, Results of measurement of the maximal diameter of a ground-glass opacity (GGO). The three thin-section computed tomography (CT) images ( a , b , and c ) are sequential craniad (a) to caudad (c) images acquired at 1-mm intervals (20× magnified images). Each pair of arrowheads ( the same color arrowheads ) indicates the start or end point of a particular maximal diameter of the GGO measured by each observer. The three thin-section CT images ( d , e , and f ) are sequential craniad (d) to caudad (f) images acquired at 1-mm intervals (20× magnified images). Each black line indicates the maximal diameter measured by each observer. The size of the scale on the right of each CT image is 2 mm.

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Differences in Angles of the Maximal Diameters

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Table 3

Differences in Angles between Maximal Diameters Measured by Members of 55 Pairs of 11 Radiologists

Group n Mean (degree) Minimum (degree) Maximum (degree) SD (degree) 1 10 25 0 89 25 2 10 22 0 89 24 3 10 16 0 89 19 4 10 24 0 89 22 Overall 40 22 0 89 23

SD, standard deviation.

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Figure 5, A non-zoomed original computed tomography image (a craniad image of Fig 4 ) with a ground-glass opacity marked with an asterisk.

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Discussion

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Assessment of the Cause of the Variability

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Comparison with Two-dimensional CT Measurements of Solid Nodules

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Other Parameters Available to Assess the Growth of GGOs

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Limitations of This Study

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Conclusion

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Acknowledgments

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Academic Radiology, Volume 19, Issue 4
Journals General Radiology
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