Common Parameters across Regional TACs of a Single Study
For a simultaneous fit of TACs from a single study the user specifies the coupling on the Coupled pane:
In the upper section the kinetic model parameters are listed. Check those parameters which are to be coupled among regions. The lower section lists all selectable regional TACs (having the same model). Check all regions which are to be included in coupled fitting.
Fit coupled starts the fitting process as follows:
- A global target curve is created by stacking the TACs of the checked regions (valid points only).
- The corresponding weights are calculated according to the weighting configuration for each TAC.
- A table of fitted parameters is formed by entering the common parameters once and adding all the other fit enabled parameters in the coupled regions. The initial values of common parameters are taken from the first checked region, for the other parameters from the individual regional models. If Fit blood parameters is enabled on the Fitting pane, the fit-enabled parameters of the blood curves are also taken into account. As a convenience there is a button Fit coupled and delay
to estimate a blood delay which considers the information from all coupled regions.
- The optimizer calculates the model curve in all checked regions, creates the global result curve corresponding to the target curve, weighs all the residuals and forms the global sum of squares as the figure of merit. The parameters are adjusted until the cost function has been minimized, and the resulting parameters are copied back to the individual models.
Note: Coupled fitting may take significant processing time. Thus the Batch mode facility may be a helpful option to run such jobs at less busy times.