## Time-Activity Curve Calculation and Statistics

At the end of segment assignment and VOI editing the **VOIs** list contains all defined structures of interest. It is recommended saving them separately using the button illustrated below.

There are different variants for calculating statistics.

- The regular statistics buttons above the
**VOIs **list will operate on the selected image. In the example above, statistics would be calculated from the SEGMENTS image and be useless. However, the user might select the first image tab and the averaged PET as the reference image. In this case, statistics will result in the average PET uptake. - The button in the lower right calculates the TACs of all segments decomposing the body mask at the level defined by the
**Segment** number. The example result with 13 **Segments** is illustrated below. It provides a convenient overview of the kinetics in the data.

- Normally the
**Calculate TACs** action button will be used for producing the end result: The average PET uptake curves in all defined VOIs are calculated and presented on the **Statistics** page.

Partial-Volume Correction (PVC)

Optionally, the **PVC** can be enabled.

The **LMA GTM** method uses information from the segmentation process. Assuming that the inner-most part of the segments is least affected by the partial-volume effect, it uses only a fraction of the segment data for the segment average calculation. The percentage can be set by the **Voxels to be kept** parameter. The algorithm uses the Geometric Transfer Matrix (GTM) approach for spillover compensation at a fine segmentation level which is not shown to the user. The corrected signal for all user-assigned segments is then constructed from the corrected signals contained in the segments.

The resolution of the imaging system is crucial for the GTM method. There is a list-selection for pre-defined scanners in the lower part of the PVC area, and new scanners can easily be added. Default is the generic **Rodent **scanner with isotropic resolution of 1.5mm FWHM.

With PVC enabled, PSEG will provide both the corrected and uncorrected uptake curves on the **Statistics** page.