Temperature- and pH-dependence of proton relaxation rates in rat liver tissue

In this study proton NMR relaxation rates R1 and R2 and pH of untreated fresh rat liver tissue as well as changes up to 4 h after tissue excision was investigated. Measurements were performed in the temperature range from 7 to 45°C. Dynamic changes in all parameters were observed at higher temperatures (≥30°C). A qualitatively different time course after tissue excision of all three parameters was obtained for 45°C. The relative alterations like the change of relaxation rates referred to a reference value can predict tissue viability. A good correlation between R2 and pH in the range of 7–37°C was detected and is described by an improved analytical model for R2 as a function of temperature and pH. The observed data lead to an empirical model given by R2(pH, T) = 39.8 + (10.2∗ΔpH) + (0.1∗ΔT) + (0.2∗ΔpHΔT), were the reference pH value was chosen 7.4 and the reference temperature value 37°C (310.15 K), respectively.