The selection of the Arterial Input Function (AIF) curve for calculating the mean AIF curve involves several criteria:

1. Peak Characteristics: The AIF should have a prominent peak from the first-pass bolus passage, followed by a smaller recirculation peak. Deviations from this pattern may indicate artifacts.

2. Concentration-Time Curve Parameters: Common parameters used to evaluate the AIF include arrival time, time to peak (TTP), first moment, full-width-at-half-maximum (FWHM), and the area under the curve. These can be determined directly from the data points or a fit to a gamma-variate function, which often provides more accurate results.

3. Artifacts Consideration: Artifacts such as dual peaks or concentrations below zero can affect the AIF readings and should be avoided.

4. Automatic vs. Manual Selection: While manual AIF selection requires a trained operator and can vary between operators, automatic selection provides quick and reproducible results without needing specialized training.

The mean AIF curve is typically represented in the control area by summarizing these features, ensuring the selected curves exhibit the desired characteristics without introducing distortions or artifacts.

For further information, you can refer to resources such as the EntoKey article on AIF or related scientific literature on the topic.