Positron CT of experimental orbital tumor and aseptic inflammation using 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG) as tracer

We evaluated the diagnostic value of positron CT scanning in experimentally, produced malignant tumor and aseptic finflammation in the orbit in rabbits. We used 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG) as tracer which reflects the early phase of glucose metabolism in the tissue and which, therefore, is a known excellent method for cancer detection. We used positron CT instrument ECAT-II (ortec) in the present study. Experimental malignant tumor was produced by injecting tumor strain VX-2 into the orbit in 5 rabbits. Croton oil was injected into the orbit in 3 rabbits to produce aseptic inflammation. Positorn CT examinations and autoradiography of the orbit were performed following intravenous injection of 3 to 7 mCi of 18F-FDG. High radioactivity levels appeared in the positron CT image of both malignat tumor and aseptic inflammation. Normal orbits showed relatively low radioactivity. The ECAT number, which represents the relative radioactivity for each pixel, showed a gradual increase in the orbital tumor until it reached a constant level 40 minutes afer injection. In contrast, the ECAT number for aseptic inflammation, the brain and normal orbit reached a constant level a few minutes after injection of 18F-FDG. Autoradiograms showed high radioactivity both in the tumor and inflammation. The findings suggest that positron CT using 18F-FDG as tracer promises to be of clinical value in the diagnosis of orbital malignancies. (author)