Use of proton MR spectroscopy and MR imaging to assess obesity.

We used 1H MR spectroscopy and MR imaging at 9.4-T to quantify and localize fat and water in the abdominal regions of 12 lean, normal, and obese mice. The D2O dilution method which measures also the equilibrium plasma D2O concentration by 2H MR spectroscopy was used to quantify body water and fat. In obese mice, the intensity of the fat 1H resonance was about 120% that of the water 1H resonance, about threefold higher than its value (about 45%) in normal mice. In lean mice, the fat/water intensity ratio was about 1:4, about half that in normal mice. Total body water was similar in obese and normal mice (19.9 +/- 1.5 and 18.7 +/- 1.3 mL) despite their very different body weights (50.1 +/- 3.1 g and 30.2 +/- 3.1 g, respectively), but slightly lower in lean mice (14.8 +/- 1.2 mL water; 22.1 g +/- 2.0 g weight). Selective methylene-proton images showed marked accumulation of fat in the abdomen and the retroperitoneal and subcutaneous spaces of obese mice. Selective water-proton images allowed clear resolution of the renal cortex, medulla, papilla, and urinary pelvis. The readily measurable resonance intensity ratio of abdominal fat to water is a sensitive index by which to characterize obesity.