Forward to the Past: the Case for Quantitative PET Imaging

Abstract

Positron emission tomography (PET) was developed in the 1970’s as an in vivo method to measure regional pathophysiological processes. In the 1990’s 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 drug development and precision medicine, i.e. a method to monitor or even predict response to therapy. For precision medicine quantification is essential, but nowadays many studies use simplified semi-quantitative methods without proper validation of those methods. In this review several examples are provided to illustrate that simplified methods may lead to less accurate or even misleading results. 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 not only may give rise to a waste of time and resources, but that it also may raise ethical questions, especially when used in drug development studies.