Fig. 1.

Challenges for ⁸⁹Zr-immuno-PET tumor delineation and quantification. Example of ¹⁸F-FDG-PET (a) for a patient with a non-Hodgkin lymphoma showing intense tumor uptake (black arrow) and excellent contrast, while ⁸⁹Zr-immuno-PET (b) with ⁸⁹Zr-labelled-rituximab shows limited contrast for this tumor. Red arrows indicate uptake in blood vessels. Example of tumor delineation by two observers (observer 1 = blue line, observer 2 = black line) for ¹⁸F-FDG-PET (c) and ⁸⁹Zr-immuno-PET (d). This example illustrates that excellent interobserver reproducibility (SUV_max = 10 for both observers) can be expected for ¹⁸F-FDG-PET, despite variability in tumor delineation. The limited tumor contrast for ⁸⁹Zr-immuno-PET may result in substantial interobserver variability, even for SUV_max (a value of 2 and 3 for observers 1 and 2, respectively)