25 January 2007
With the increasing interest in personal health, nutritional status and fitness, several methods of estimating body fat have been developed and used in clinical settings. Hormonal effects and changes in metabolic pathways during the development of diseases (e.g. type 2 diabetes mellitus) lead to specific changes in the volume fractions and distribution of fat-containing compartments in the body. Magnetic resonance (MR) has been proven to be a reliable and non-invasive tool for the assessment of fatty and lean tissue, with a high spatial resolution of approximately 1 mm. Modern MR systems with large receiver coil arrays and automatic positioning tables allow whole-body imaging in examination times of about 20 min. Special highly specific fat-selective imaging techniques provide total suppression of water signals and allow a sensitive visualization of fatty infiltration in ‘lean’ organs, such as liver or skeletal musculature. Whereas fat-selective imaging requires at least 1–2% of lipids in parenchymal tissue to provide signal intensity in the images above the noise level, volume-selective [<sup>1</sup>H]MR spectroscopy is even more sensitive. Volume fractions of lipids down to 0.1% can be quantitatively assessed using [<sup>1</sup>H]MR spectroscopy, and several portions of lipids (fatty septa vs. intramyocellular fat) can be distinguished in skeletal musculature.