On the correlation between tissue hydration state and proton NMR relaxation rates in experimental liver transplantation.

As the tissue hydration state is one of the most important parameters to predict viability cold stored livers before transplantation, we investigated the correlation between the tissue inverse total water fraction, reflecting the hydration state, and proton relaxation times in cold stored rat liver and orthotopic liver transplantation in a pig model. In cold stored rat liver excellent linear correlations between relaxation rates R1 (= 1/T1) and R2 (= 1/T2) and inverse total water fraction 1/Pw were obtained. In pig liver transplants, the slope and intercept obtained from a linear regression model are twice as high for R1 and almost identical for R2; however, correlation coefficients are lower due to increased biological variation and a smaller range in storage conditions, reflected by the range of water content. Proton nuclear magnetic resonance relaxation times measured during the cold storage on the whole organ non-invasively show also linear correlation with the inverse total water fraction, but the method is presently not accurate enough to estimate the hydration state of the liver tissue with sufficient precision. NMR relaxation times obtained from liver biopsies have the potential to predict tissue viability in experimental liver transplantation independent of species, strain and gender, and thus may be useful in estimating the viability of human donor livers (or at least add a new complementary information to the information gained by standard liver selection and function test before and after transplantation).