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

Abstract

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. 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. 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. 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.