Multi-center trial with an in vitro NMR protocol. EEC Concerted Research Project

The EEC Protocol for in vitro measurement of T1 and T2 presented in paper II of this series was tested in 15 centers on a variety of instruments. This article discusses the results of this protocol trial using biological samples (rat liver and thigh muscle) and two reference gel samples. Each reference gel was prepared as a single batch, dispensed into appropriate sample tubes and sent to all participants. Details of instrument types and operating conditions are given, along with measurement frequencies and temperatures and the results of precision testing. The relaxation time measurements from the gels for the trial are compared with temperature and frequency effects examined in independent centers under similar conditions. The relaxation time values for biological tissues are examined in the light of the scatter of such values in the general literature. To check the effects of data analysis methods on relaxation times, full relaxation data for one reference sample was provided by each group. This was re-analyzed in three centers using different methods; these results are compared with the values calculated by each group using its own method. In general, the results from different groups show good consistency with the reference values. The use of this Protocol has helped reduce scatter in results from biological samples and has provided information for improvement of individual operating conditions and improvement of the protocol to its final form.