In vitro proton T1 and T2 studies on rat liver: analysis of multiexponential relaxation processes.

At 37 degrees C and 20 MHz, the T1 and T2 proton relaxation processes in intact rat liver tissue are multiexponential functions which in the majority of cases were decomposed into a major (alpha* approximately 90%, T1* = 374 ms, T2* = 58 ms) and a minor (alpha** approximately 10%, T1** = 130 ms, T2* = 181 ms) component. Both, T1 and T2, are temperature-dependent with a temperature shift of delta T1 = 1.5 ms/degrees C and delta T2 = 0.5 ms/degrees C, respectively. Storage of liver tissue at 4 degrees C and 37 degrees C led to remarkable changes of the T1 and T2 values. For T2 these changes occurred after a shorter storage time than for T1, but they are more pronounced for T1. To avoid such influences the relaxation measurements were performed within one hour after excision of the tissue. Even at 4 degrees C, long-term storage (greater than 3 h) must be avoided. A method for the quantitative determination of the fat content in liver based on multiexponential analysis of the T1 relaxation process was evaluated employing mixtures of triolein with liver homogenate. Triolein is a two-component system with T1* = 144 ms (alpha* = 62%) and T1** = 355 ms (alpha** = 38%). Finally, liver-specific protocol conditions were defined for in vitro relaxation studies.