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 detection -of brain tumor tissue by PET using 18F-fluorodeoxyglucose (FDG). -The aim of this study was to evaluate whether the examination of -amino acid transport with the SPECT tracer ¹²³I-alpha-methyl-L- -tyrosine (IMT) allows better identification of tumor tissue than FDG-PET. Methods: Nineteen patients (16 with gliomas, 3 with nontu-morous lesions) were included in the study. Two independent -observers classified PET and SPECT images as positive or negative -for tumor tissue and defined the extent of tumor with regions of -interest. Tracer uptake of FDG and IMT was quantified by calculating -the tumor uptake relative to contralateral gray and white matter. Results: SPECT studies were interpreted concordantly in 18 pa-tients (kappa = 0.77) and all tumors were identified by both -observers. PET studies were interpreted discordantly in 4 patients -(kappa = 0.52) and only 10 tumors were identified by both observ-ers. Interobserver variability in definition of tumor extent was signif-icantly lower in the IMT-SPECT than in the FDG-PET studies (p = 0.03). Mean tumor uptake relative to gray and white matter was 1.93 ±0.42 and 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 than FDG, even when only glioblastomas were -analyzed. No significant correlation was observed between the -various uptake ratios of FDG and IMT. Conclusion: Despite the -lower resolution and lower sensitivity of SPECT compared with PET, IMT-SPECT was clearly superior to FDG-PET in the detection and -delineation of tumor tissue.