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 to ol for the non-invasive assessment of murine body composition. DESIGN: Twenty C57/BL6 male mice with a wide range of body adiposities unde rwent both pre- and post-mortem whole-body MRS to assess body composition. MRS measures were compared to the results obtained by chemical carcass anal ysis, the current 'gold standard' for determination of body composition. MEASUREMENTS: Areas under the curve (AUC) for lipid and water peaks of whol e body MRS spectra (AUC(lipid) and AUC(H2O), respectively) were used to det ermine percentages of body fat (%FAT(MRS)) and fat free mass by MRS (%FFMMR S) Total body fat, total body water, fat free mass, and total lean mass wer e determined by chloroform/methanol extraction of lipid from dessicated who le carcass and compared to MRS measures (%FAT(MRS), %FFMMRS, AUC(lipid), an d AUC(H2O)) The variability of the MRS technique was assessed by determinin g 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 percent age (r = 0.994, P < 0.001) and total body fat (r = 0.980, P < 0.001) derive d from chemical carcass analysis over a broad range of adiposities (7-48% b ody 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 c orrelated 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 cor related 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 le an mass (r = 0.792, P < 0.001). AUC(H2O) was strongly associated with carca ss analysis determinations of total body water (r = 0.964, P < 0.001), tota l 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 measur es of body fat, body water, fat free mass, and lean mass in living mice wit h a broad range of adiposities.