31P spin-lattice relaxation times and resonance linewidths of rat tissue in vivo: dependence upon the static magnetic field strength.

Phosphorus-31 NMR spin-lattice relaxation times and resonance linewidths of rat leg muscle, brain, and liver metabolites in vivo have been examined at 1.9-, 4.7-, and 8.5-T static magnetic field strengths. The resonance linewidths expressed in ppm that have been measured are independent of field strength. The spin-lattice relaxation times of muscle and brain phosphorus metabolites decrease linearly with increasing field strength while those of liver are constant over the range of static fields examined.