Validation of whole-body magnetic resonance spectroscopy as a tool to assess murine body composition

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Abstract
To evaluate proton magnetic resonance spectroscopy (MRS) as a tool for the non-invasive assessment of murine body composition. Twenty C57/BL6 male mice with a wide range of body adiposities underwent both pre- and post-mortem whole-body MRS to assess body composition. MRS measures were compared to the results obtained by chemical carcass analysis, the current 'gold standard' for determination of body composition. Areas under the curve (AUC) for lipid and water peaks of whole body MRS spectra (AUClipid and AUCH2O, respectively) were used to determine percentages of body fat (%FATMRS) and fat free mass by MRS (%FFMMRS). Total body fat, total body water, fat free mass, and total lean mass were determined by chloroform/methanol extraction of lipid from dessicated whole carcass and compared to MRS measures (%FATMRS, %FFMMRS, AUClipid, and AUCH2O). The variability of the MRS technique was assessed by determining the coefficients of variation (COV) associated with %FATMRS, AUClipid, and AUCH2O for mice of three different adiposities. %FATMRS in live mice was highly correlated with body fat percentage (r=0.994, P<0.001) and total body fat (r=0.980, P<0.001) derived from chemical carcass analysis over a broad range of adiposities (7-48% body fat content by carcass analysis). There was no difference in %FATMRS measured pre- vs post-mortem (r=1.00, P<0.001). AUClipid was highly correlated with chemically derived total fat mass (r=0.996, P<0.001) and body fat percentage (r=0.981, P<0.001), while %FFMMRS was strongly correlated to chemical determinations of percentage body water (r=0.994, P<0. 001), percentage fat free mass (r=0.993, P<0.001), and percentage lean mass (r=0.792, P<0.001). AUCH2O was strongly associated with carcass analysis determinations of total body water (r=0.964, P<0. 001), total fat free mass (r=0.953, P<0.001), and total lean mass (r=0.89, P<0.001). In mice of 6%, 12%, and 43% body fat, COVs determined for %FATMRS and AUClipid were less than 10%. The COVs for AUCH2O were less than 2%. MRS provides precise, accurate, rapid, and non-invasive measures of body fat, body water, fat free mass, and lean mass in living mice with a broad range of adiposities.