I103] The case for quantitative imaging in nuclear medicine

Abstract

Nuclear medicine provides the opportunity to image molecular processes in the human body. Positron emission tomography (PET) is quantitatively the most accurate nuclear medicine modality. It was developed in the 1970s as an in vivo method to measure regional pathophysiological processes. In the 1990s the focus moved to the detection of local increases in uptake, first in the brain (activation studies) and later in oncology (finding metastases), where [18F]FDG emerged as a highly sensitive staging technique. This focus on sensitivity has overshadowed the other main characteristic of PET, its quantitative nature. In recent years there has been a new shift. PET is now seen as a promising tool for precision medicine, i.e. a method to monitor or even predict response to therapy. For precision medicine quantification is essential, which can be achieved by tracer kinetic modelling in combination with a dynamic scanning protocol. In routine nuclear medicine practice, however, usually static scans are performed at some time after tracer injection. Unfortunately, based on this practice, nowadays many studies use simplified semi-quantitative methods without first validating those methods. In this presentation several examples are provided to illustrate that simplified methods may lead to less accurate or even misleading results. This is due to the fact that a static scan contains multiple signals, such as free, non-specifically bound and specifically bound tracer, and uptake may be affected by confounding physiological processes, such as changes in perfusion. Simplification is important for routine clinical practice, but it requires careful studies to find the optimal balance between accuracy and simplicity. It is argued that the use of simplified approaches without proper validation is indeed unethical.