FLUORINE-18-FDG PET AND IODINE-123-IMT SPECT IN THE EVALUATION OF BRAIN-TUMORS

The high glucose utilization of normal gray matter limits the detectio n of brain tumor tissue by PET using F-18-fluorodeoxyglucose (FDG). Th e aim of this study was to evaluate whether the examination of amino a cid transport with the SPECT tracer I-123-alpha-methyl-L-tyrosine (IMT ) allows better identification of tumor tissue than FDG-PET, Methods: Nineteen patients (16 with gliomas, 3 with nontumorous lesions) were i ncluded in the study. Two independent observers classified PET and SPE CT images as positive or negative for tumor tissue and defined the ext ent of tumor with regions of interest. Tracer uptake of FDG and IMT wa s quantified by calculating the tumor uptake relative to contralateral gray and white matter. Results: SPECT studies were interpreted concor dantly in 18 patients (kappa = 0.77) and all tumors were identified by both observers. PET studies were interpreted discordantly in 4 patien ts (kappa = 0.52) and only 10 tumors were identified by both observers . Interobserver variability in definition of tumor extent was signific antly lower in the IMT-SPECT than in the FDG-PET studies (p = 0.03). M ean tumor uptake relative to gray and while matter was 1.93 +/- 0.42 a nd 2.25 +/- 0.46 for IMT and 0.93 +/- 0.32 and 1.61 +/- 0.52 for FDG. All tumor uptake ratios were significantly (p < 0.01) higher for IMT t han FDG, even when only glioblastomas were analyzed. No significant co rrelation was observed between the various uptake ratios of FDG and IM T. Conclusion: Despite the lower resolution and lower sensitivity of S PECT compared with PET, IMT-SPECT was clearly superior to FDG-PET in t he detection and delineation of tumor tissue.