A Dual Tracer .sup.18F-FCH/.sup.18F-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 .sup.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 .sup.18 F-Fluorocholine (.sup.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 .sup.18 F-FCH/.sup.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 .sup.18 F-FCH and .sup.18 F-FDG PET imaging, and images acquired from two separate scans are superimposed for analysis. The .sup.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 .sup.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 .sup.18 F-FDG only is also proved in this study. All the tumors can be detected based on the dual tracer technique of .sup.18 F-FCH/ .sup.18 F-FDG-PET imaging in this study, while the false-positive caused by .sup.18 F-FCH can be eliminated. Dual tracer .sup.18 F-FCH/.sup.18 F-FDG PET imaging has the potential to improve the visualization of low grade glioma. .sup.18 F-FCH delineates tumor areas and the tumor can be identified by subtracting the .sup.18 F-FCH counts. The sensitivity was over 95%. Further studies are required to evaluate the possibility of applying this technique in clinical trials.