Repeatability and reproducibility of CT small lung nodule measurements in vivo using volumetric measurements

Objective: To evaluate interobserver and the three contemporaneous scans variability of lung nodule volume measurements using GE advanced lung analysis(ALA) software. Methods: Fifty-two nodules, less than 20 mm in diameter, in 20 patients were scanned with 2 mm collimation using Highspeed NX/i (time 1= T1). During the same session, two additional scans, using identical technique, were obtained through each nodule (T2, T3). Three observers working independently then acquired volumetric measurements using ALA. Qualitative nodule characterization was also performed. The Bland-Altman method of Medcalc software for assessing measurement agreement was used to calculate the 95% limits for agreement for nodule volumes at T1, T2 and T3. Results: Automated nodule segmentation was successful in 396 (84.6%) of 468 measurements. Forty-four nodules were available for final evaluation. Thirty-two nodules had well-defined edges, and 12 had irregular or spiculated margins. Thirty-one were freestanding, 9 were juxtapleural, and 4 were juxtavascular in location. The average nodule volume was 501.9 mm3 (range, 17 ∼ 2496.4 mm3). The mean interobserver variability (repeatability) was-0.006% (SD=0.73%), and the SD of the mean for the three contemporaneous scans(reproducibility) was 7.06% (95% confidence limits, -14.1% ∼ 13.6%). Conclusion: Volumetric measurements show minimal interobserver variability (-0.0006%) but an interscan SEM of 7.06% (confidence limits, -14.1% ∼ 13.6%). Repeatability and reproducibility of volumetric measurements are better than those of linear measurements reported in the literature. (authors)