Liver tissue characterization by in vitro NMR: tissue handling and biological variation.

The extraction of reliable and useful relaxation time data for tissue characterization by NMR requires strict protocols, optimized for each type of biological tissue, which include parameters like storage duration and temperature as well as measurement parameters. Spin-lattice relaxation times in liver tissue vary not only with NMR frequency but also with their "time-after-excision characteristics," while spin-spin relaxation times are almost independent of most parameters which influence T1 at 20 MHz in normal liver tissue (e.g., species, sex, circadian rythm, starvation). T2, however, being more sensitive to water content and pH changes, is well suited for detecting nonspecific tissue alterations (e.g., due to ischemia, chemical toxins). Following the suggestions outlined herein, investigation of at least 120 min of time-after-excision (storage) effects allows the significant distinguishing of various physiological differences in normal liver tissue as well as improvement of early detection of liver pathologies.