Improved estimation of tissue hydration and bound water fraction in rat liver tissue

Based on recent improvements in the field, biexponential data from fresh rat liver and monoexponential data from cold storage experiments allow quantification of three distinct relaxation components in liver tissue: bound water (4.2%, R1 = 12.0 +/- 1.7 s-1, R2 = 440 +/- 180 s-1); structured water (59%, R1 approximately 3.3 +/- 0.07 s-1, R2 approximately 24.9 +/- 1.1 s-1); and free water (approximately 37%, R1 = R2 approximately 0.4 s-1). However, only the relaxation rates of the structured water component change with water content: R1A (s-1) = 6.53* Ms/Mw - 0.77 (r2 = 0.911); R2A (s-1) = 71.15 * Ms/Mw - 3.09 (r2 = 0.956), respectively. This suggests a slow exchange between bound and structured water in liver cells.