The blood and plasma activity concentrations require interpolation procedures for kinetic modeling, as described above.
Operational Model Curve
The Lin. Interpolation model interpolates linearly between the measured activity values. Outside the measured values the following interpolation rules apply:
▪If the first measurements occurs at t<0, the activity is assumed to be zero for all earlier times.
▪If the first measurements occurs at t>0, the activity is assumed to be zero for t<=0. Activity values from t=0 up to the first measurement are calculated by linear interpolation from activity 0 at t=0.
▪The activity is assumed to remain constant after the last measurement. For short blood curves it is therefore recommended to replace the tail of the measurements by a fitted tri-exponential model.
Parameter Fitting
The Lin. Interpolation model has no fitting parameter.
The Delay parameter serves for correcting a timing offset between tissue and blood data. Positive delays correspond to delayed blood information and hence shift the blood curve to earlier times (to the left). The Delay is only relevant during the fitting of the tissue model where it can be fitted as an additional parameter to the parameters of the kinetic model.