A Dual Tracer (18)F-FCH/(18)F-FDG PET Imaging of an Orthotopic Brain Tumor Xenograft Model

Early diagnosis of low grade glioma has been a challenge to clinicians. Positron Emission Tomography (PET) using (18)F-FDG as a radio-tracer has limited utility in this area because of the high background in normal brain tissue. Other radiotracers such as (18)F-Fluorocholine ((18)F-FCH) could provide better contrast between tumor and normal brain tissue but with high incidence of false positives. In this study, the potential application of a dual tracer (18)F-FCH/(18)F-FDG-PET is investigated in order to improve the sensitivity of PET imaging for low grade glioma diagnosis based on a mouse orthotopic xenograft model. BALB/c nude mice with and without orthotopic glioma xenografts from U87 MG-luc2 glioma cell line are used for the study. The animals are subjected to (18)F-FCH and (18)F-FDG PET imaging, and images acquired from two separate scans are superimposed for analysis. The (18)F-FCH counts are subtracted from the merged images to identify the tumor. Micro-CT, bioluminescence imaging (BLI), histology and measurement of the tumor diameter are also conducted for comparison. Results show that there is a significant contrast in (18)F-FCH uptake between tumor and normal brain tissue (2.65 ± 0.98), but with a high false positive rate of 28.6%. The difficulty of identifying the tumor by (18)F-FDG only is also proved in this study. All the tumors can be detected based on the dual tracer technique of (18)F-FCH/ (18)F-FDG-PET imaging in this study, while the false-positive caused by (18)F-FCH can be eliminated. Dual tracer (18)F-FCH/(18)F-FDG PET imaging has the potential to improve the visualization of low grade glioma. (18)F-FCH delineates tumor areas and the tumor can be identified by subtracting the (18)F-FCH counts. The sensitivity was over 95%. Further studies are required to evaluate the possibility of applying this technique in clinical trials.