Flexible radioluminescence imaging for FDG‐guided surgery

Purpose Flexible radioluminescence imaging (Flex‐RLI) is an optical method for imaging 18 F‐fluorodeoxyglucose (FDG)‐avid tumors. The authors hypothesize that a gadolinium oxysulfide: terbium (GOS:Tb) flexible scintillator, which loosely conforms to the body contour, can enhance tumor signal‐to‐background ratio (SBR) compared with RLI, which utilizes a flat scintillator. The purpose of this paper is to characterize flex‐RLI with respect to alternative modalities including RLI, beta‐RLI (RLI with gamma rejection), and Cerenkov luminescence imaging (CLI). Methods The photon sensitivity, spatial resolution, and signal linearity of flex‐RLI were characterized with in vitro phantoms. In vivo experiments utilizing 13 nude mice inoculated with the head and neck (UMSCC1‐Luc) cell line were then conducted in accordance with the institutional Administrative Panel on Laboratory Animal Care. After intravenous injection of 18 F‐FDG, the tumor SBR values for flex‐RLI were compared to those for RLI, beta‐RLI, and CLI using the Wilcoxon signed rank test. Results With respect to photon sensitivity, RLI, beta‐RLI, and flex‐RLI produced 1216.2, 407.0, and 98.6 times more radiance per second than CLI. Respective full‐width half maximum values across a 0.5 mm capillary tube were 6.9, 6.4, 2.2, and 1.5 mm, respectively. Flex‐RLI demonstrated a near perfect correlation with 18 F activity ( r = 0.99). Signal uniformity for flex‐RLI improved after more aggressive homogenization of the GOS powder with the silicone elastomer during formulation. In vivo , the SBR value for flex‐RLI (median 1.29; interquartile range 1.18–1.36) was statistically greater than that for RLI (1.08; 1.02–1.14; p < 0.01) by 26%. However, there was no statistically significant difference in SBR values between flex‐RLI and beta‐RLI ( p = 0.92). Furthermore, there was no statistically significant difference in SBR values between flex‐RLI and CLI ( p = 0.11) in a more limited dataset. Conclusions Flex‐RLI provides high quality images with SBRs comparable to those from CLI and beta‐RLI in a single 10 s acquisition.