Hi Troels, Are you still interested in implementing the optimisation of the R1 relaxation rate for the R1rho dispersion models? If so, we should probably discuss and plan how this would be best implemented here on the mailing list. For example what new user functions should be added (a user should explicitly turn on such a feature as it is much more preferable to measure R1), how the data and parameters should be handled, what types of checks should be added, how the target function code should be modified, and how to keep the idea compatible with off-resonance effects in the CPMG-type dispersion models. The whole concept needs to be carefully designed before any code is written. If the optimisation of R1 is no longer a goal, then don't worry about this message. Regards, Edward