Tofts model (but general issue important to all models, incl. Eric's IVIM), this problem originated in Henry's report of very high Ve (>18000) in particular ROI fit.

During the parameter fitting, there might be numerous solutions (both voxelwise and Single ROI), whose Minimization Cost differ by the miniscule amount (<0.01 in relative terms of Absolute Minimum Cost).

We "Balance" the solution by considering all such solutions equally valid candidates.  Then several logics could apply.

Below is the result of one such "Balanced" solution, on the same AATH dataset.  Note, the balancing is done on the level of the single voxel without taking neighboring voxels into account.

New Option is added to the Parmetric Model processing:  "Balance Solution" - ON\OFF.

K-trans (regular)

K-trans (Balanced)

Ve (regular)

Ve (Balanced)

Residual (regular)

Residual (Balanced)