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The blood and plasma activity concentrations require interpolation procedures for kinetic modeling, as described above.
Operational Model Curve
This Gamma + 2 Exponentials model is very similar to the Compartment Model with 3 Eigenvalues. However, it includes a power term uB which allows better modeling of sharp peaks.
Parameter Fitting
The Gamma + 2 Exponentials model includes a Begin parameter, three Amplitudes (A1, A2, A3) and a Halftimes (T1, T2, T3), and a Power Exponent (B). This functional form supports a peak rising from time Begin followed by an exponentially decreasing tail. The initial default of the Power Exponent is a fixed value of 1 which corresponds to the Compartment Model with 3 Eigenvalues. Use the Fit plasma activity or Fit whole blood button to fit the operational model curve to the measurements. Then, for better fitting of the peak, enable the Power Exponent and fit again. The form of the curve reacts very sensitively to changes of the parameters. Note that all samples are considered, not only the ones after Begin.
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.