The sequential steps for converting blood measurements to an input curve are explained in a dedicated section. The current plasma fraction model serves for converting a whole-blood activity curve into a plasma-activity curve.

It is assumed that a curve representing the measured fractions of plasma/whole-blood activity has been loaded with **Load Plasma/WB Fraction**.

Operational Model Curve

The **Watabe **model allows replacing the tail of the fraction curve by an analytical function. The **Begin **parameter defines at what time the models switches from linear interpolation to the Hill function.

The illustration below shows an example with the Hill function fitted following 2 minutes (**Begin** = 120sec). The the weighting has been changed for putting more emphasis on the tail. Note that the linear interpolation assumes a fraction of 1 at t=0.

Parameter Fitting

The model supports the fitting of the parameters **Begin**, **scale**, **A**, **B**, **C.** Fitting is started with the **Fit plasma fraction** button, which only takes the samples after the **Begin **time into consideration.

Use without Measured Fraction

If no measured plasma/whole-blood fraction data is available, the **Watabe **model can still be applied. In this case the **Begin **time is disregarded, and the functional defined by the entered parameters applied.

References

1. Watabe H, Channing MA, Der MG, Adams HR, Jagoda E, Herscovitch P, Eckelman WC, Carson RE: Kinetic analysis of the 5-HT2A ligand [11C]MDL 100,907. J Cereb Blood Flow Metab 2000, 20(6):899-909. DOI