Methodological considerations in quantification of oncological FDG PET studies

Abstract

Purpose: This review aims to provide insight into the factors that influence quantification of glucose metabolism by FDG PET images in oncology as well as their influence on repeated measures studies (i.e. treatment response assessment), offering improved understanding both for clinical practice and research.

Methods: Structural PubMed searches have been performed for the many factors affecting quantification of glucose metabolism by FDG PET. Review articles and references lists have been used to supplement the search findings.

Results: Biological factors such as fasting blood glucose level, FDG uptake period, FDG distribution and clearance, patient motion (breathing) and patient discomfort (stress) all influence quantification. Acquisition parameters should be adjusted to maximize the signal to noise ratio without exposing the patient to a higher than strictly necessary radiation dose. This is especially challenging in pharmacokinetic analysis, where the temporal resolution is of significant importance. The literature is reviewed on the influence of attenuation correction on parameters for glucose metabolism, the effect of motion, metal artefacts and contrast agents on quantification of CT attenuation-corrected images. Reconstruction settings (analytical versus iterative reconstruction, post-reconstruction filtering and image matrix size) all potentially influence quantification due to artefacts, noise levels and lesion size dependency. Many region of interest definitions are available, but increased complexity does not necessarily result in improved performance. Different methods for the quantification of the tissue of interest can introduce systematic and random inaccuracy.

Conclusions: This review provides an up-to-date overview of the many factors that influence quantification of glucose metabolism by FDG PET.

Fig. 1

Dynamic framing duration in three groups [–50] performing dynamic oncological FDG PET for pharmacokinetic two-compartment modelling. Abbreviations are explained in Table 2. *Duration of a bolus is a few seconds

Fig. 2

The two-compartment model for FDG catabolism. C _plasma (t) the activity concentration of FDG in the blood plasma, C _free (t) the intracellular activity concentration of free FDG, C _bound (t) the intracellular activity concentration of FDG-6-PO₄, K ₁, k ₂, k ₃ and k ₄ rate constants (see Table 1), C _PET(t) the measured PET signal which is a combination of C _free(t), C _bound(t) and a fraction (shaded area, V _b) of C _plasma(t). The dotted line symbolizes the cell membrane

Fig. 3

Quantitative analysis of a T₂ adenocarcinoma of the right superior lung lobe (left top). Right top, time-activity concentration curves. Left bottom, analysis of two-compartment models by both Sokoloff 3K and Phelps 4K model. Right bottom, Patlak graphical analysis