Measurement of Spin-Lattice Relaxation Times in Systems Undergoing Chemical Exchange

A new method is presented for measuring spin-lattice relaxation times in systems with chemical exchange. The method is based on an analysis of the effect of exchange on saturation factors. Unlike the inversion-recovery method with saturation, our experiment does not require selective excitation; it also does not require a fit of data to a multiple-exponential model, in contrast to inversion recovery without saturation. A number of variations of the experiment are presented, which are applicable to different regimes of T₁ and exchange-rate values. The methods are demonstrated for the creatine kinase reaction in an in vitro sample.