Comprehensive assessment of distinct abdominal fat compartments beyond liver content in overweight/obese patients using MRI and ultrasound imaging.

Background: Ectopic fat deposition, involving lipid infiltration within organs and fat accumulating surrounding organs, plays a crucial role in the development of metabolic abnormalities in obesity. Current imaging measurements of obesity primarily focus on lipid infiltration within liver, neglecting fat deposition in other areas. This study aims to explore the methods of measuring and correlating different types of abdominal ectopic fat deposition in obese patients using magnetic resonance imaging (MRI) and ultrasound techniques, and to investigate the relationship between these fat parameters and obesity-related metabolic markers.

Methods: Abdominal ectopic fat deposition including liver fat content, mesenteric fat thickness (MFT), perirenal fat thickness (PrFT) and preperitoneal fat thickness (PFT) were measured in 220 overweight/obese patients using both MRI and ultrasound techniques. Correlation analysis validated the concordance of fat parameters at specific sites between the two imaging methods and identified the cutoff values of hepatic attenuation coefficient (AC) for diagnosis of liver steatosis. Additionally, we investigated the correlation between fat parameters by both methods and obesity-related metabolic markers.

Results: Ultrasonic measurement of PrFT and hepatic AC both had high correlation with PrFT (r = 0.829, p < 0.001) and hepatic Proton-density fat fraction (PDFF, r = 0.822, p < 0.001) measured via MR. Hepatic AC cutoff values for diagnosing mild, moderate, and severe fatty liver were 0.705 dB/cm/MHz (AUC = 0.922), 0.755 dB/cm/MHz (AUC = 0.923), and 0.875 dB/cm/MHz (AUC = 0.890) respectively. Hepatic AC correlated significantly with AST and ALT (r = 0.477 ~ 0.533, p < 0.001). MFT measured by ultrasound were positively associated with glycated hemoglobin (r = 0.324 ~ 0.371, p < 0.001) and serum triglyceride levels (r = 0.303 ~ 0.353, p < 0.001). PrFT measured by both methods showed significant positive correlations with serum creatinine levels (r = 0.305 ~ 0.308, p < 0.001).

Conclusions: Both MRI and ultrasound demonstrate metabolic correlations in quantifying mesenteric, hepatic, and perirenal fat. In addition to assessment of liver fat content, the measurements of ectopic fat deposition by MRI or ultrasound are a simple and crucial way for comprehensive fat evaluation in individuals with overweight/obesity.