Sokoloff model - Revisited "Delay" fitting parameter.  Ensured that when  "Max Delay" option = 0 before model calculation,  the resulting Delay parameter remains 0 (i.e. optimization is done by K1,k2,k3 only).

Investigated "arrival time" difference issue between Data TAC and Model Curve. This seem to work well now, at least for the PET-derived IDIF.