Quantifying the effect of slice thickness, intravenous contrast and tube current on muscle segmentation: Implications for body composition analysis.

Objectives: To quantify the effect of IV contrast, tube current and slice thickness on skeletal muscle cross-sectional area (CSA) and density (SMD) on routine CT.

Methods: CSA and SMD were computed on 216 axial CT images obtained at the L3 level in 72 patients with variations in IV contrast, slice thickness and tube current. Intra-patient mean difference (MD), 95 % CI and limits of agreement were calculated using the Bland-Altman approach. Inter- and intra-analyst agreement was evaluated.

Results: IV contrast significantly increased CSA by 1.88 % (MD 2.33 cm; 95 % CI 1.76-2.89) and SMD by 5.99 % (p<0.0001). Five mm slice thickness significantly increased mean CSA by 1.11 % compared to 2 mm images (1.32 cm; 0.78-1.85) and significantly decreased SMD by 11.64 % (p<0.0001). Low tube current significantly decreased mean CSA by 4.79 % (6.44 cm; 3.78-9.10) and significantly increased SMD by 46.46 % (p<0.0001). Inter- and intra-analyst agreement was excellent.

Conclusions: IV contrast, slice thickness and tube current significantly affect CSA and SMD. Investigators designing and analysing clinical trials using CT for body composition analysis should report CT acquisition parameters and consider the effect of slice thickness, IV contrast and tube current on myometric data.

Key Points: • Intravenous contrast, slice thickness and tube current significantly affect myometric data. • Image acquisition parameter variations may obscure intrapatient muscle differences on serial measurements. • Investigators using CT for body composition analysis should report CT acquisition parameters.