Magnetic Resonance Imaging-Based Assessment of Bone Marrow Fat and T2 Relaxation in Adolescents with Obesity and Liver Steatosis: A Feasibility Pilot Study

<b>Background:</b> Adolescents suffering from obesity are at higher risk of bone fragility due to hepatic steatosis, which may lead to an inflammatory microenvironment in the bone marrow. We therefore aimed to assess the reliability of measuring the bone marrow fat fraction (BMFF) and T2* of the lumbar vertebral marrow using the proton density fat fraction (PDFF) sequence for adolescents with obesity and liver steatosis. <b>Method:</b> This was an observational feasibility pilot study on adolescents living with obesity and liver steatosis. Anthropometric measurements were obtained. Participants underwent abdominal MRI, MR elastography and dual-energy X-ray absorptiometry (DXA). Regions of interest were drawn using the radiology interface from the central L1 to L4 vertebrae on fat and T2* maps from the PDFF sequence. ImageJ was used to measure abdominal compartment fat areas. Descriptive analyses, the intraclass correlation coefficient, and correlation results were obtained from anthropometric, adiposity, BMFF, and T2* measurements. <b>Results:</b> We recruited 23 adolescents with a body mass index > 85th percentile and mean age = 14.7 years (interval 12-17 years), and <i>n</i> = 18 (78%) were boys. BMFF and T2* measurements were successful in 100% of cases. The intra-operator reproducibility of the BMFF and T2* measurements was excellent: ICC = 0.99 (95% confidence interval (CI) [0.986; 0.999]) and ICC = 0.99 (95% CI [0.992; 0.999]), respectively. The inter-operator ICC was good for BMFF (ICC = 0.89; 95% CI [0.705; 0.963]) and moderate for T2* (ICC = 0.66; 95% CI [0.239; 0.873]). Only BMFF was inversely correlated with vertebral-bone mineral density (<i>r</i> = -0.67; <i>p</i> = 0.0009). However, T2* measurements showed a positive linear relationship with the total body fat tissue percentage measured by DXA (<i>r</i> = 0.48; <i>p</i> = 0.03) and the total abdominal fat area (<i>r</i> = 0.45; <i>p</i> = 0.04). <b>Conclusions:</b> PDFF could be a reliable imaging biomarker for bone health assessment in adolescents living with obesity.