Kinetic analysis for PET amyloid data PYTHON

I need to fit a simplified reference tissue model (srtm) to time-activity curves to different regions of the brain. The equation for this function is given below in the file. I need to fit the srtm to the measured data time-activity curves. I need to estimate the paramters R1, K2A AND K2' and then use an optimization algorithm (Levenberg-Marquardt optimization) to find the best fit of the model to the actual data. The parameters for the best fit then need to be generated.