A reliable and robust method for the upper thigh muscle quantification on computed tomography: toward a quantitative biomarker for sarcopenia

BACKGROUND: We aimed to evaluate the feasibility of the upper thigh level as a landmark to measure muscle area for sarcopenia assessment on computed tomography (CT). METHODS: In the 116 healthy subjects who performed CT scans covering from mid-abdomen to feet, the skeletal muscle area in the upper thigh level at the inferior tip of ischial tuberosity (SMA(UT)), the mid-thigh level (SMA(MT)), and L3 inferior endplate level (SMA(L3)) were measured by two independent readers. Pearson correlation coefficients between SMA(UT), SMA(MT), and SMA(L3) were calculated. Inter-reader agreement between the two readers were evaluated using intraclass correlation coefficient (ICC) and Bland-Altman plots with 95% limit of agreement (LOA). RESULTS: In readers 1 and 2, very high positive correlations were observed between SMA(UT) and SMA(MT) (r = 0.91 and 0.92, respectively) and between SMA(UT) and SMA(L3) (r = 0.90 and 0.91, respectively), while high positive correlation were observed between SMA(MT) and SMA(L3) (r = 0.87 and 0.87, respectively). Based on ICC values, the inter-reader agreement was the best in the SMA(UT) (0.999), followed by the SMA(L3) (0.990) and SMA(MT) (0.956). The 95% LOAs in the Bland-Altman plots indicated that the inter-reader agreement of the SMA(UT) (− 0.462 to 1.513) was the best, followed by the SMA(L3) (− 9.949 to 7.636) and SMA(MT) (− 12.105 to 14.605). CONCLUSION: Muscle area measurement at the upper thigh level correlates well with those with the mid-thigh and L3 inferior endpoint level and shows the highest inter-reader agreement. Thus, the upper thigh level might be an excellent landmark enabling SMA(UT) as a reliable and robust biomarker for muscle area measurement for sarcopenia assessment. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-022-05032-2.