Effect of contrast phase upon quantitative analysis of skeletal muscle and adipose tissue by computed tomography

Objective Significant variability exists in the contrast phases applied during computed tomography (CT) studies when assessing morphometric measurements of muscle area (CT-assessed sarcopenia), density (CT-assessed myosteatosis), and visceral adipose tissue area (CT-assessed visceral obesity). This study explored the impact of contrast phase timing on changes in morphometric measurements of body composition. Research Methods & Procedures This single-center retrospective cohort study included 459 patients undergoing a multiphase CT scan. Morphometric measurements were obtained at the third lumbar vertebra level. Patients were classified as sarcopenic, myosteatotic, or visceral obese using pre-defined cutoff values. The intra-class correlation coefficient was used to assess correlations across different enhancement phases, and Cohen's κ measured the inter-enhancement agreement for sarcopenia, myosteatosis, and visceral obesity. Results Significant differences were observed in mean visceral adipose tissue area, muscle density, and muscle area (p<0.001). The intra-class correlation coefficient between unenhanced and arterial phases was 0.987 (95% confidence interval [CI], 0.759-0.996) for adipose tissue, 0.995 (95% CI, 0.989-0.997) for muscle area, and 0.850 (95% CI, 0.000-0.956) for muscle density. However, when morphometric measurements were categorized using predefined cutoffs, the κ agreement was considerably lower, particularly for CT-assessed myosteatosis, ranging from 0.635 (unenhanced to arterial) to 0.331 (unenhanced to late venous phase). Conclusion Different CT contrast phases induce small, but clinically significant, alterations in the measurements of muscle area, density, and visceral fat. Such minor changes can result in misclassification issues when fixed cutoff values are used to diagnose myosteatosis with computed tomography. This underscores the importance of reporting absolute values and the specific contrast phase used in future studies.