Model selection

The first step of a pixelwise processing is to select an adequate model from the model list. As a consequence, the user-interface elements are configured according to the model requirements.

Image data loading

As a next step the image data is defined and then loaded. During loading, image transformations such as smoothing may be applied.

Image masking

Optionally, a mask can be created interactively to restrict pixelwise processing to the area of interest. Masking mainly serves for removing background pixels which might result in disturbing outliers. The created mask needs to be saved and is automatically added to the protocol definition. If a mask is applied, threshold-based masking within the model is disregarded.

VOI definition

Often, dedicated time-activity curves (TACs) are required for the preprocessing and/or the pixelwise processing. In this case, there is an optional step for outlining appropriate tissue VOIs interactively. The resulting VOI definitions or the related TACs need to be saved and are automatically added to the protocol definition.

Blood preprocessing
(blood-based models only)

As a next step the tracer activity in arterial plasma (the input curve) is selected and loaded. It may require some corrections, for example to compensate for a delayed arrival and a dispersed shape at the site of data analysis. For some models the whole-blood activity can also be supplied for blood spillover correction.

The result of blood preprocessing is shown on a separate pane. For all subsequent processing steps the corrected blood curve is used.

Note: Blood data is not required for reference models and some other models. In this case the blood-related panels are not hidden.

Model preprocessing

Depending on the model, some preliminary calculations may be required, for example  look-up tables or the specification of initial parameters for the pixelwise fits. These calculations are typically based on the TACs obtained in the VOI definition step. It is recommended to inspect the preprocessing results in order to ensure that the model works properly with the prepared configuration. Therefore the results are shown on a separate panel.

Pixelwise processing

Once preprocessing competed successfully, the user can specify which of the parametric maps are to be calculated, and whether they should be restricted to a certain (physiological) value range. If results are outside the restriction, a NaN ("not a number") value is entered into the parametric map.

For the rapid processing during a prototyping phase, e.g. for determining the adequate table look-up range, the pixelwise calculations can be limited to the current slice.

Result explorations

The results may be explored in many different ways such as:

▪Comparison of the different maps in the included fusion tool.

▪Pixelwise arithmetic among the maps in the included fusion tool.

▪Comparison of the pixelwise outcome with results when analyzing the TACs interactively in the kinetic modeling tool (PKIN, optional tool).

Saving of the parametric maps

Each fitted model parameter results in a separate functional map. These quantitative images can be saved in any of the supported formats.

Saving of the protocol

PXMOD only uses explicit information for the calculation. Therefore, at the end of a processing, a protocol file can be saved which will allow to exactly reproduce the processing.