A decade ago this functional information provided by PET was coupled with excellent anatomical information provided by Computed Tomography (CT), introducing a new and powerful duo-modality intended to improve the diagnosis value and to fulfil the drawbacks of using two separate imaging modalities, especially in the field of Oncology. Furthermore, one of the revolutions and at the same time one of the "curses'' on PET when introducing this excellent duo-modality was, and still is, the frequent use of Fluorodeoxyglucose (FDG) when performing whole body static PET/CT. Due to short scanning time and good image quality this approach has become a golden standard tool for tumour imaging. However, when performing static imaging the fourth dimension, time, is frozen and this approach generates a "univariate'' image volume, which illustrates only the mean tracer distribution of the administered tracer during the scanning time. This deflates the key strength of the PET, the exploratory dimension, which is based on "tracing a molecule labelled with a positron emitting radionuclide''. Moreover, static imaging requires a good knowledge about the kinetic behaviour, affinity and the specificity of the administered tracer which requisites many experiments and years of experience.
On the other hand a dynamic PET imaging (where a sector is scanned sequentially during different time points called frames) generates sequential image volumes which have poorer image quality compared with images obtained when performing static imaging. However, these sequential image volumes can be regarded as multivariate image volumes from which physiological, biochemical and functional information can be "traced'' and derived by analyzing the distribution and kinetics of the administrated radiolabelled molecules. This implies that each of the image volumes displays/contains part of a kinetic information representing physiological behaviour of the administered tracer during different time points (the 4-th dimension). Due to presence of the fourth dimension, dynamic image volumes could be quantified and analysed using several approaches/methods such as graphical modelling, parametric images, pixel-wise modelling, and multivariate image analysis.
The important question still remains:
What are scientists looking for when they are utilizing an excellent imaging tool such as PET?
Ugly yet informative or fine-looking but frozen information?
Comment: The docent lecture was held in English.