The PMOD kinetic modeling tool represents a flexible environment for the simulation and fitting of models over time. While initially aimed at the compartment models employed in Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), models for other modalities such as magnetic resonance or optical imaging can also be easily incorporated due to the general approach and the plug-in structure for the models.

PKIN incorporates the following features:

- import of time-vectors from measurements of blood and tissue activity via text files or directly from the Volume-Of-Interest (VOI) tool,
- fitting of metabolite correction curves to derive free tracer activity from total plasma activity,
- representation of the plasma and whole-blood activity by a fitable model for data smoothing and extension beyond the last measurement,
- selection of a comprehensive list of compartment models, reference models and graphical plots,
- weighted or non-weighted fitting of the selected model to the measurement whereby each parameter can be enabled or fixed, and can optionally be restricted within a physiological range,
- coupled fitting of measurements from different tissues to improve the accuracy for parameters assumed to be identical across tissues,
- calculation of goodness-of-fit criteria usable for model comparisons,
- Monte Carlo simulations to assess the identifiability of model parameters using a standard or user-defined distribution of the measurement errors,
- sensitivity analysis of compartment models to quantify the correlation between the model parameters,
- visualization of the relative contributions of the different compartments to the model curve,
- generation of synthetic studies representing compartmental kinetics for testing the performance of simplified pixel-wise models,
- batch mode operation to fit or Monte Carlo simulate a set of prepared studies,
- saving of the fitted parameters into text files for further statistical investigations.

Starting the Kinetic Modeling Tool

The kinetic modeling tool is started with the **Kinetic **button from the PMOD toolbar

or by directly dragging kinetic modeling (.km) files onto the above button.

The user interface is organized as shown below. The left part of the display visualizes the data, the model and the fit. The green squares represent the tissue measurement values (tissue time-activity curve, TAC), the red squares the input curve, the yellow squares the blood spillover curve (whole blood time-activity curve), and the blue circles the calculated model curve with the current model configuration shown to the right. The lower curve display shows the unweighted residuals between the measurement and the model curve.

The right part gives access to the different operations which are described in the following sections.

The **Menu **is located in the lower left corner and is used for data operations such as loading, saving or closing.

Loaded data sets can be added into new tabs, so multiple data sets can be available simultaneously and selected for processing using the named tabs.