Exploring intra- and inter-reader variability in uni-dimensional, bi-dimensional, and volumetric measurements of solid tumors on CT scans reconstructed at different slice intervals

Abstract

Objective: Understanding magnitudes of variability when measuring tumor size may be valuable in improving detection of tumor change and thus evaluating tumor response to therapy in clinical trials and care. Our study explored intra- and inter-reader variability of tumor uni-dimensional (1D), bi-dimensional (2D), and volumetric (VOL) measurements using manual and computer-aided methods (CAM) on CT scans reconstructed at different slice intervals.

Materials and methods: Raw CT data from 30 patients enrolled in oncology clinical trials was reconstructed at 5, 2.5, and 1.25 mm slice intervals. 118 lesions in the lungs, liver, and lymph nodes were analyzed. For each lesion, two independent radiologists manually and, separately, using computer software, measured the maximum diameter (1D), maximum perpendicular diameter, and volume (CAM only). One of them blindly repeated the measurements. Intra- and inter-reader variability for the manual method and CAM were analyzed using linear mixed-effects models and Bland-Altman method.

Results: For the three slice intervals, the maximum coefficients of variation for manual intra-/inter-reader variability were 6.9%/9.0% (1D) and 12.3%/18.0% (2D), and for CAM were 5.4%/9.3% (1D), 11.3%/18.8% (2D) and 9.3%/18.0% (VOL). Maximal 95% reference ranges for the percentage difference in intra-reader measurements for manual 1D and 2D, and CAM VOL were (-15.5%, 25.8%), (-27.1%, 51.6%), and (-22.3%, 33.6%), respectively.

Conclusions: Variability in measuring the diameter and volume of solid tumors, manually and by CAM, is affected by CT slice interval. The 2.5mm slice interval provides the least measurement variability. Among the three techniques, 2D has the greatest measurement variability compared to 1D and 3D.

Fig. 1

Effects of slice thickness on the lesion appearance and measurement. From left to right, a liver lesion depicted on 1.25 mm, 2.5 mm and 5 mm slice thickness images (a). Overlays of the greatest diameter (Uni) line and the greatest perpendicular diameter (Perp) line of the lesion that were drawn by two independent radiologists (blinded to the slice interval information) on the three slice thickness images (b and c). Corresponding Uni, Perp and Bi (product of Uni and Perp) measurements of the lesion (d).

Fig. 2

Bland–Altman plots: manual (a) intra- and (b) inter-reader agreement for 1D and 2D measurements. The solid line shows the mean percentage difference in measurements and the dashed lines show the 95% reference range. Note: measurements within the 95% reference range can be considered as intrinsic measurement errors (or variations) that are associated with the given measurement tools and imaging techniques. Therefore, a narrower reference range indicates a lower measurement error/variation.

Fig. 3

Bland–Altman plots: CAM (a) intra- and (b) inter-reader agreement for VOL measurements. The solid line shows the mean percentage difference in measurements and the dashed lines show the 95% reference range. Abbreviations: CAM, computer-aided method; VOL, volumetric.