In vivo 31 P nuclear magnetic resonance studies of T 1 and T 2 relaxation times in rat brain and in rat brain tumors implanted to nude mice

31 P NMR spin‐lattice ( T 1 ) and spin‐spin ( T 2 ) relaxation times of phosphocreatine, ATP, inorganic phosphate, and phosphomonoesters have been measured in vivo at 4.7 T in rat brain and rat brain tumors implanted on nude mice. The relaxation data were acquired using a phase‐cycled saturation‐recovery spin‐echo sequence. The problems associated with the phase modulation of the ATP lines by the homonuclear coupling constants were overcome by using selective refocusing pulses for the T 2 measurements. In all the metabolites, large differences (1 to 2 orders of magnitude) are observed between the two relaxation times. T 1 values in rat brain tumors are 30 to 90% longer than their counterparts in normal rat brain. T 2 values follow the same trend with smaller variations except for phosphocreatine values which seem much less sensitive to the metabolic state of the tissues. © 1987 Academic Press, Inc.