LONGITUDINAL RELAXATION AND DIFFUSION MEASUREMENTS USING MAGNETIC-RESONANCE SIGNALS FROM LASER-HYPERPOLARIZED XE-129 NUCLEI

Methods for T-1 relaxation and diffusion measurements based on magneti c resonance signals from laser-hyperpolarized Xe-129 nuclei are introd uced. The methods involve optimum use of the perishable hyperpolarized magnetization of Xe-129. The necessary theoretical framework for the methods is developed, and then the methods are applied to measure the longitudinal relaxation constant, T-1, and the self-diffusion constant , D, of hyperpolarized Xe-129. In a cell containing natural abundance Xe-129 at 790 Torr, the T-1 value was determined to be 155 +/- 5 min a t 20 degrees C and at 2.0 T field. For a second cell at 896 Torr, at t he same field and temperature, the T-1 value was determined to be 66 /- 2 min. At a higher field of 7.05 T, the T-1 values for the two cell s were found to be 185 +/- 10 and 88 +/- 5 min, respectively. The Xe-1 29 self-diffusion constant for the first cell was measured to be 0.057 cm(2)/s and for the second cell it was 0.044 cm(2)/s. The methods wer e applied to Xe-129 in the gas phase, in vitro; however, they are, in principle, applicable for in vivo or ex vivo studies. The potential ro le of these methods in the development of newly emerging hyperpolarize d Xe-129 MRI applications is discussed. (C) 1997 Academic Press.