### Linear Activity Interpolation

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.