THE RESPONSE OF THE STRONGLY COUPLED AB SYSTEM OF CITRATE TO TYPICAL H-1 MRS LOCALIZATION SEQUENCES

The response of the strongly coupled AB system of citrate to the STEAM and PRESS spatial localization sequences is developed analytically an d then verified experimentally at 2.35 T. At this field strength, the response predicted by the complete Strong-coupling calculation is show n to differ greatly from that of the simpler weak-coupling approximati on. It is shown that the strong-coupling effects induce a significant field-strength dependence in the time-dependent modulations of the res ponse to either sequence. These effects are illustrated for the STEAM and PRESS responses at field strengths of 1.5, 2.35, and 4.7 T. Indepe ndent of the chosen sequence, the increase in the signal-to-noise (SIN ) of the frequency response with increasing field strength is shown to be significantly less for the citrate system than for uncoupled spins . The factors which weaken the SIN dependence of the citrate AB signal with increasing field strength are quantified and discussed. (C) 1995 Academic Press, Inc.