Dual-Tracer Imaging on a Long-Axial-Field-of-View PET: A Proof-of-Principle Study with [18F]FGln and [18F]FDG

Abstract

Current protocols necessitate imaging 2 ¹⁸F-labeled tracers in separate sessions. Herein, we report on the development and testing of a protocol that sequentially images 2 ¹⁸F-labeled tracers-¹⁸F-(2S,4R)4-fluoroglutamine, commonly known as [¹⁸F]FGln, and [¹⁸F]FDG-in a single session on a long-axial-field-of-view PET scanner to study cancer metabolism. Methods: A single [¹⁸F]FGln scan was used to estimate the minimal injected activity and scan duration to calculate an accurate volume of distribution. This was followed by a dual-tracer study in a second patient with a low-dose (41-MBq), shortened (29-min) [¹⁸F]FGln scan, followed by a full-dose (394-MBq) [¹⁸F]FDG scan for 60 min. Protocol performance was assessed using the resulting kinetic parameters. Results: [¹⁸F]FGln subsampling demonstrated stable estimates of volume of distribution with a scan duration of 30 min and a dose of 37 MBq. The dual-tracer [¹⁸F]FDG image obtained 60 min after injection was of diagnostic quality, with minimal (6%) residual [¹⁸F]FGln signal. Conclusion: This proof-of-principle dual-tracer study demonstrated the feasibility of a [¹⁸F]FGln/[¹⁸F]FDG protocol that leveraged the high sensitivity of long-axial-field-of-view PET to inject the first tracer at a low dose and the second tracer at a greater dose, overwhelming the signal from the first tracer.

Keywords: PET; cancer metabolism; dual-tracer PET; dynamic PET imaging; long–axial-field-of-view PET/CT.

Graphical abstract

FIGURE 1.

Proposed dual-tracer study schema.

FIGURE 2.

Subsampling studies of a dynamic [¹⁸F]FGln study. Full-dose [¹⁸F]FGln study (263 MBq [7.1 mCi]; scan duration of 70 min) was subsampled to estimate lowest possible dose and scan time (green arrow) while faithfully recapitulating calculation of V_T compared with full dataset.

FIGURE 3.

Representative images from dual-tracer dynamic study. Maximum-intensity-projection PET images of [¹⁸F]FGln (left) and [¹⁸F]FGln/[¹⁸F]FDG (right). [¹⁸F]FDG was injected at 29 min.

FIGURE 4.

Representative axial [¹⁸F]FGln image (A) and whole-tumor time–activity curve (red) with VOI measurements (black) (B). (C) [¹⁸F]FGln input function (red) and tumor (black) time–activity curves, projected [¹⁸F]FGln values (dotted lines), [¹⁸F]FGln/[¹⁸F]FDG values (blue), and [¹⁸F]FDG values with [¹⁸F]FGln signal correction (magenta).