Body composition analysis of obesity and hepatic steatosis in mice by relaxation compensated fat fraction (RCFF) MRI

Purpose: To develop and validate a quantitative magnetic resonance imaging (MRI) methodology for phenotyping animal models of obesity and fatty liver disease on 7T small animal MRI scanners. Materials and Methods: A new MRI acquisition and image analysis technique, relaxation-compensated fat fraction (RCFF), was developed and validated by both magnetic resonance spectroscopy and histology. This new RCFF technique was then used to assess lipid biodistribution in two groups of mice on either a high-fat (HFD) or low-fat (LFD) diet. Results: RCFF demonstrated excellent correlation in phantom studies (R-2 = 0.99) and in vivo compared to histological evaluation of hepatic triglycerides (R-2 = 0.90). RCFF images provided robust fat fraction maps with consistent adipose tissue values (82% +/- 3%). HFD mice exhibited significant increases in peritoneal and subcutaneous adipose tissue volumes in comparison to LFD controls (peritoneal: 6.4 +/- 0.4 cm(3) vs. 0.7 +/- 0.2, P < 0.001; subcutaneous: 14.7 +/- 2.0 cm(3) vs. 1.2 +/- 0.3 cm(3), P < 0.001). Hepatic fat fractions were also significantly different between HFD and LFD mice (3.1% +/- 1.7% LFD vs. 27.2% +/- 5.4% HFD, P = 0.002). Conclusion: RCFF can be used to quantitatively assess adipose tissue volumes and hepatic fat fractions in rodent models at 7T.