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Excerpt
In clinical routine, body composition can noninvasively be assessed with several anthropometric methods 8. A measure of obesity grade and body fat content is the body mass index (BMI), defined as the ratio of weight and squared height according to the National Institutes of Health/World Health Organization (NIH/WHO) BMI guidelines 8. Other measures, such as skin‐fold thickness, waist circumference, or waist‐to‐hip ratio (WHR) estimate abdominal fat mass, whereas body impedance analysis (BIA) provides an estimate of the total amount of adipose and muscle tissue in the body 9. However, the accuracy of anthropometric methods and their capability to differentiate subcompartments, such as visceral versus subcutaneous fat, is limited 12. Accordingly, imaging methods that directly depict body fat and muscle volumes are being used increasingly. Among these, dual‐energy x‐ray absorptiometry (DXA) and CT are limited by radiation exposure and a nonspecific classification of fat and muscle tissue based on Hounsfield units 14. In comparison, MRI allows for direct accurate quantification of fat and water‐bound protons, preferentially based on proton density contrast weighting 16 and Dixon‐related fat–water‐separation methods 21.
Recent literature has shown that fat‐referenced two‐point Dixon imaging provides highly accurate and precise compartmental quantification of adipose tissue and lean tissue volumes 23. Moreover, fat‐referenced (ie, fat signal normalized to the signal from pure fat voxels) lipid quantification effectively eliminates bias in fat concentration estimates as a result of T1 weighting of the fat and water signal 28. These body composition analyses are of interest, especially in specific populations like patients with metabolic syndrome or myopathy.
A first step in this direction would be represented by a semi‐automatic identification of “all fat” and “all water” MR signal voxels and their corresponding volumes.
However, age and gender‐dependent normative values of MR‐derived adipose tissue and muscle volumes (normalized for body height) are needed that can serve as reference standards for further investigations of pathological changes in diseased patients.
Thus, the purpose of this study is to prospectively evaluate whole‐body adipose tissue and muscle volumes in a healthy Swiss population (BMI 17.5 to 26.2 kg/m2) using fat–water‐separated MRI‐based acquisition and segmentation methods at 3 Tesla (T), and compare them with anthropometric and BIA measurements.
