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Pixelwise Kinetic Modeling Tool (PXMOD)
The PMOD pixelwise modeling tool (PXMOD) is aimed at the quantitative analysis of functional studies, mainly with Positron Emission Tomography (PET) or Single Photon Emission Tomography (SPECT). Such studies typically result in a sequence of images which monitor the uptake and distribution of an injected tracer over time. The image pixel values represent the average tracer activity concentration in tissue (TAC) during the acquisition period.
The PXMOD tool provides a range of models which can be applied to each pixelwise TAC. When a suitable model is chosen, the resulting model parameters quantify a physiologic process such as perfusion or glucose consumption, or a quantity such as the receptor binding potential. Functional (or parametric) maps are created by assembling images from the result parameter values in the individual pixels.
Comparison of PXMOD and PKIN
PXMOD is a counter-part of the general kinetic modeling tool PKIN which mostly deals with regionally averaged TACs. PKIN supports a more interactively oriented workflow and offers more models than PXMOD. Please refer to the PKIN Users Guide for an introduction into kinetic modeling. The characteristics of the two modeling tools are summarized below.
•Support for more models, particularly more complex ones. This is possible, because due to better noise characteristics of the TACs, it is justified to fit more complex models.
•Interactive working style with a history of tested models and various facilities to compare results.
•Methods to impose physiologic constraints for improving fitting robustness like coupled fitting.
•Mechanisms to improve robustness of fitting like randomized fitting and initial parameter calculation by linearized solutions.
•Parametric mapping mapping support for the pixels in VOIs of limited size.
•Support for less models because simplified, robust methods are required for analyzing the noisy pixel-wise TACs.
•Processing in workflows which are adjusted according to the selected model.
•Interface to PKIN for transferring TACs and interactive fitting. This allows for quality control mechanisms and the collection of prior information for tailoring PXMOD processing.
•Internal use of PKIN models where possible.
•Allows to calculate images of the spatial distribution of a tissue property.