The optimal slice to quantify the volumes of subcutaneous adipose tissue and skeletal muscle on chest computed tomography as imaging marker for body composition estimation

BACKGROUND/OBJECTIVES: This study aims to identify the optimal anatomical site that best predicts the total thoracic subcutaneous adipose tissue (SAT) and skeletal muscle (SM) volumes on chest computed tomography (CT), and to evaluate the relationships between SAT and SM areas at optimal slice and lung function. SUBJECTS/METHODS: Healthy participants and chronic obstructive pulmonary disease (COPD) patients undergoing chest CT between January 2022 and April 2023 were retrospectively included. On chest CT, cross-sectional areas of SAT and SM at 14 specific anatomical levels, and thoracic SAT and SM volumes were measured using 3D Slicer software. Correlations were calculated by Spearman's correlation coefficients. RESULTS: About 58 healthy participants and 68 COPD patients were included. In healthy participants, the T4 SAT area correlated most strongly with thoracic SAT volume (r = 0.888, P < 0.01), and the aortic arch SM area with SM volume (r = 0.941, P < 0.01). The combined Spearman's correlation coefficients reached their highest sum (1.816) at the aortic arch level. In COPD patients, correlations were identified between SAT area at the aortic arch slice with forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC) (r = 0.472, P < 0.001), while SM area with both FEV1(r = 0.431, P < 0.001) and FVC (r = 0.522, P < 0.001). CONCLUSION: Considering measurement simplicity and accuracy, the aortic arch slice was identified as the optimal single slice for predicting total thoracic SAT and SM volumes. Additionally, the clinical significance of SAT and SM area at this slice was verified with lung function in COPD patients. Key messages What is already known on this topic: Specific abdominal slices have been shown to estimate abdominal volumes accurately, while the optimal slice to predict thoracic volumes is uncertain. What this study adds: To identify the optimal slice for simultaneously predicting both thoracic SAT and SM volumes. How this study might affect research, practice or policy: The optimal slice in the chest for measurement is crucial for advancing research on thoracic SAT and SM.