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

OBJECTIVE: To evaluate proton magnetic resonance spectroscopy (MRS) as a tool for the non-invasive assessment of murine body composition. DESIGN: 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. MEASUREMENTS: Areas under the curve (AUC) for lipid and water peaks of whole body MRS spectra (AUC(lipid) and AUC(H2O), respectively) were used to determine percentages of body fat (%FAT(MRS)) 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 (%FAT(MRS), %FFMMRS, AUC(lipid), and AUC(H2O)) The variability of the MRS technique was assessed by determining the coefficients of variation (COV) associated with %FAT(MRS), AUC(lipid), and AUC(H2O) for mice of three different adiposities. RESULTS: %FAT(MRS) 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 %FAT(MRS) measured pre- vs post-mortem (r = 1.00, P < 0.001). AUC(lipid) 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). AUC(H2O) 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 %FAT(MRS) and AUC(lipid) were less than 10%. The COVs for AUC(H2O) were less than 2%. CONCLUSIONS: 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.