Technical note: how to determine the FDG activity for tumour PET imaging that satisfies European guidelines

Abstract

Background: For tumour imaging with PET, the literature proposes to administer a patient-specific FDG activity that depends quadratically on a patient's body weight. However, a practical approach on how to implement such a protocol in clinical practice is currently lacking. We aimed to provide a practical method to determine a FDG activity formula for whole-body PET examinations that satisfies both the EANM guidelines and this quadratic relation.

Results: We have developed a methodology that results in a formula describing the patient-specific FDG activity to administer. A PET study using the NEMA NU-2001 image quality phantom forms the basis of our method. This phantom needs to be filled with 2.0 and 20.0 kBq FDG/mL in the background and spheres, respectively. After a PET acquisition of 10 min, a reconstruction has to be performed that results in sphere recovery coefficients (RCs) that are within the specifications as defined by the EANM Research Ltd (EARL). By performing reconstructions based on shorter scan durations, the minimal scan time per bed position (T min) needs to be extracted using an image coefficient of variation (COV) of 15 %. At T min, the RCs should be within EARL specifications as well. Finally, the FDG activity (in MBq) to administer can be described by [Formula: see text] with c a constant that is typically 0.0533 (MBq/kg(2)), w the patient's body weight (in kg), and t the scan time per bed position that is chosen in a clinical setting (in seconds). We successfully demonstrated this methodology using a state-of-the-art PET/CT scanner.

Conclusions: We provide a practical method that results in a formula describing the FDG activity to administer to individual patients for whole-body PET examinations, taking into account both the EANM guidelines and a quadratic relation between FDG activity and patient's body weight. This formula is generally applicable to any PET system, using a specified image reconstruction and scan time per bed position.

Keywords: EANM guidelines; FDG-PET; Scan time protocol; Tumour imaging.

Figures

Fig. 1

Flowchart demonstrating the eight steps to obtain a patient-specific FDG activity formula

Fig. 2

Phantom PET/CT images. Axial PET (a) and attenuation CT (b) images from the IQ phantom on the scanner bed. The phantom spheres and background were filled with FDG activity (ratio 10:1), and the scan duration was 10 min. The squares illustrate three ROIs in one axial plane that are used to determine the COV

Fig. 3

Comparing COV in the phantom background compartment measured at several scan durations, in graphs with standard scale (a) and log-log scale (b). A power-law fit resulted in COV = 1.26 T−0.51. The coefficient of determination r2 was 0.98, which indicates a good fit of the trend line to the data. Using the fit result, [Btrue] = 1.84 kBq/mL and COVmax = 0.15, formula 1 resulted in Tmin = 62 s. The log-log scale graph can be described by log (COV) = log (a) − b · log (T) in which the steepness of the curve is described by (b)