Abbreviated scan protocols to capture 18F-FDG kinetics for long axial FOV PET scanners

Abstract

Purpose: Kinetic parameters from dynamic ¹⁸F-fluorodeoxyglucose (FDG) imaging offer complementary insights to the study of disease compared to static clinical imaging. However, dynamic imaging protocols are cumbersome due to the long acquisition time. Long axial field-of-view (LAFOV) PET scanners (> 70 cm) have two advantages for dynamic imaging over clinical PET scanners with a standard axial field-of-view (SAFOV; 16-30 cm). The large axial coverage enables multi-organ dynamic imaging in a single bed position, and the high sensitivity may enable clinically routine abbreviated dynamic imaging protocols.

Methods: In this work, we studied two abbreviated protocols using data from a 65-min dynamic ¹⁸F-FDG scan: (A) dynamic imaging immediately post-injection (p.i.) for variable durations, and (B) dynamic imaging immediately p.i. for variable durations plus a 1-h p.i. (5-min-long) datapoint. Nine cancer patients were imaged on the Biograph Vision Quadra (Siemens Healthineers). Time-activity curves over the lesions (N = 39) were fitted using the Patlak graphical analysis and a 2-tissue-compartment (2C, k₄ = 0) model for variable scan durations (5-60 min). Kinetic parameters from the complete dataset served as the reference. Lesions from all cancers were grouped into low, medium, and high flux groups, and bias and precision of K_i (Patlak) and K_i, K₁, k₂, and k₃ (2C) were calculated for each group.

Results: Using only early dynamic data with the 2C (or Patlak) model, accurate quantification of K_i required at least 50 (or 55) min of dynamic data for low flux lesions, at least 30 (or 40) min for medium flux lesions, and at least 15 (or 20) min for high flux lesions to achieve both 10% bias and precision. The addition of the final (5-min) datapoint allowed for accurate quantification of K_i with a bias and precision of 10% using only 10-15 min of early dynamic data for either model.

Conclusion: Dynamic imaging for 10-15 min immediately p.i. followed by a 5-min scan at 1-h p.i can accurately and precisely quantify ¹⁸F-FDG on a long axial FOV scanner, potentially allowing for more widespread use of dynamic ¹⁸F-FDG imaging.

Keywords: 18F-FDG flux; Dynamic imaging; FDG.

Fig. 1

Schematic of the current dynamic imaging protocol for ¹⁸F-FDG (top), along with the two proposed abbreviated scan protocols: Protocol A: early dynamic imaging only (middle); and Protocol B: early dynamic imaging plus a static scan

Fig. 2

A Example maximum intensity projection SUV images of 5-min duration (60–65 min p.i.) for two representative patients with lymphoma (left) and breast cancer (right). Color scale is SUV 0–5. B shows TAC from all lesions from the representative patients. Note that the mass of lesions indicated in the lymphoma patient was separated for analysis into many smaller individual lesions, whose TAC are shown in B

Fig. 3

Bias of flux estimated using Patlak graphical analysis as a function of dynamic scan duration for both abbreviated scan protocols

Fig. 4

Bias of flux estimated using an irreversible two-tissue-compartment model as a function of dynamic scan duration for both abbreviated scan protocols

Fig. 5

Bias of delivery (K₁) estimated using an irreversible two-tissue-compartment model as a function of dynamic scan duration for both abbreviated scan protocols

Fig. 6

Bias and precision of microparameters k₂ (top) and k₃ (bottom), estimated using a 2-tissue-compartment model using both protocol A (left) and protocol B (right)

Fig. 7

Recommended scan protocol