The blood and plasma activity concentrations require interpolation procedures for kinetic modeling, as described above.

Operational Model Curve

The **Compart, 2 EV **model is an alternative model to the **Compart, 3 EV**** **model for the plasma activity curve of FDG [1]. It assumes repeated eigenvalues (EV) and has the following functional form:

Parameter Fitting

Similar to the **3 Exponentials**** **model it includes a **Begin **parameter and two **Amplitude**s (A_{1}, A_{2})** **and a **Halftime**s (T_{1}, T_{2}). However, the functional form supports a peak rising from time **Begin** followed by an exponentially decreasing tail. Use the **Fit plasma activity** or **Fit whole blood** button to fit the operational model curve to the measurements. Note that all samples are considered, not only the ones after **Begin**.

The form of the curve reacts very sensitively to changes of the parameters. The example above illustrates a result is model may be more suited for simulations rather than actual data processing.

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.

Reference

1. Feng D, Huang SC, Wang X: Models for computer simulation studies of input functions for tracer kinetic modeling with positron emission tomography. International journal of bio-medical computing 1993, 32(2):95-110.