Data and image processing
a) Quantification of three-dimensional PET data sets using compartment and non-compartment models
Dynamic PET data sets are evaluated and evaluated with regard to the diagnostic and prognostic value with different compartment and non-compartment models developed and implemented in the department. Compartment models are derived from pharmacology and have been used for the first time for PET studies in the brain to assess the pharmacokinetic behavior of fluorodeoxyglucose (FDG). We have used a modified two-compartment model with an additional blood compartment for oncologic patients for the first time. The model allows the calculation of so-called transport rates (k1, k2, k3, k4) and the exchange surface, the so-called distribution volume VB. In the example of FDG, k1 refers to the influx rate of FDG, k2 to the efflux rate, k3 to the phosphorylation, and k4 to the dephosphorylation.
b) Parametric imaging
Fig. 10a
© dkfz.de
Nuclear medicine images are functional images that reflect the mean activity distribution at a defined time. With the help of mathematical models it is possible to visualize an isolated parameter.
The following figure shows an FDG-PET cross-sectional view in a small pelvis in a patient with ovarian carcinoma and a suspected recurrence. Circumscribed FDG accumulation dorsal of the bladder, which indicates a tumor recurrence.
Fig. 10b
© dkfz.de
Such images are called parametric images. It is for example possible by means of a regression model, to represent only the perfusion-dependent part of a dynamic measurement with FDG in a tumorous lesion.
A parametric image showing the phosphorylated part of FDG. Due to the higher contrast the delineation of the lesion is better. This was an operative confirmed tumor recurrence.
c) Software fusion
In addition to the combined PET-CT or SPECT-CT devices, the so-called hybrid devices, it is possible to fuse arbitrary tomographic modalities by means of suitable evaluation programs. For this purpose, certain algorithms are used. We use the mutual information technology for the fusion of PET with CT or MRT recordings.
© dkfz.de
Fig. 11: Central tumor in the left lung with subsequent partial collapse of the lung. The mutual information technology allows the fusion of arbitrary modalities.
Above: Fusion of parametric PET images of the metabolism of FDG (color) and the blood volume (gray)
Center: Fusion of the parametric PET metabolism (color) with a corresponding CT image (gray)
Below: Fusion of the parametric PET metabolism (color) with a corresponding MRI image (gray)
d) GenePET
Tracer kinetics in PET are closely associated with molecular biology. If tissue samples from the PET-evaluated areas exist, PET and gene expression data can be evaluated correlatively. In this way it is possible to detect dependencies of the tracer kinetics on genes as well as to determine which genes modulate the kinetics (e.g., hypoxia and FDG kinetics). Furthermore, the gene expression data allow the search for new targets for potential radiopharmaceuticals.
© dkfz.de
Fig. 12: Correlative analysis of gene array data of a tissue sample of a tumor (left) and the corresponding PET results (right). The gene expression data are color coded as an image and thus allow a fast detection of genes, which are expressed significantly increased.