PET tracers are usually applied by intra-venous injection and then brought to the tissue of interest by circulation. Often, a part of the tracer may be bound to red blood cells. Another part may be processed in organs and end up as labeled metabolites circulating in blood plasma. The remaining category of tracer in plasma is the unchanged (authentic) tracer (parent) which is available for exchange with tissue and represents the input curve relevant for modeling.
In PKIN, the following four types of blood data are supported to model the contributions of the different forms of tracer in blood to the expected PET signal:
Whole Blood and Plasma Activity
The whole blood and plasma activity concentrations must be prepared in text files, and can be loaded using Load Whole Blood Activity and Load Plasma Activity from the Kinetic menu. Such text files with the blood data can be prepared for example in MS Excel and then saved as tab-delimited or csv separated text files. There are two variants of the format:
Plasma and Parent Fractions
The plasma and parent fractions need to be prepared in a similar file
and loaded using Load Plasma/WB Ratio or Load Authentic Fraction from the Kinetic menu.
1.The header line is mandatory in the format shown above with valid units in square brackets after the column headers.
2.If no whole blood data is loaded into PKIN, the plasma concentration is used for blood spillover correction.
3.If the activity of unchanged tracer in plasma is loaded instead of the total plasma activity, no correction with the parent fraction is required. No further action is required in this case, because per default it is assumed that the parent fraction equals the constant of 1.
4.There are a few models which require two input curves, and in principle models with up to 10 input curves can be handled in PKIN. For these models the loading sub-menus contain appropriately labeled entries.