Relationship Between [18F]FDOPA PET Uptake, Apparent Diffusion Coefficient (ADC), and Proliferation Rate in Recurrent Malignant Gliomas

Purpose: Diffusion magnetic resonance imaging (MRI) and 6-[18F]fluoro-l-dopa ([18F]FDOPA) positron emission tomography (PET) are used to interrogate malignant tumor microenvironment. It remains unclear whether there is a relationship between [18F]FDOPA uptake, diffusion MRI estimates of apparent diffusion coefficient (ADC), and mitotic activity in the context of recurrent malignant gliomas, where the tumor may be confounded by the effects of therapy. The purpose of the current study is to determine whether there is a correlation between these imaging techniques and mitotic activity in malignant gliomas.Procedures: We retrospectively examined 29 patients with recurrent malignant gliomas who underwent structural MRI, diffusion MRI, and [18F]FDOPA PET prior to surgical resection. Qualitative associations were noted, and quantitative voxel-wise and median measurement correlations between [18F]FDOPA PET, ADC, and mitotic index were performed.Results: Areas of high [18F]FDOPA uptake exhibited low ADC and areas of hyperintensity T2/fluid-attenuated inversion recovery (FLAIR) with low [18F]FDOPA uptake exhibited high ADC. There was a significant inverse voxel-wise correlation between [18F]FDOPA and ADC for all patients. Median [18F]FDOPA uptake and median ADC also showed a significant inverse correlation. Median [18F]FDOPA uptake was positively correlated, and median ADC was inversely correlated with mitotic index from resected tumor tissue.Conclusions: A significant association may exist between [18F]FDOPA uptake, diffusion MRI, and mitotic activity in recurrent malignant gliomas

MR imaging and single-photon emission CT findings after gene therapy for human glioblastoma

BACKGROUND AND PURPOSE: Our goal was to evaluate MR imaging findings after local intracerebral gene therapy in patients with glioblastoma and differentiate postoperative contrast enhancement phenomena.METHODS: In all, 26 patients with supratentorial single lesion glioblastoma underwent tumor resection and intracerebral injection of murine retroviral vector-producer cells for gene therapy with the herpes simplex virus type I thymidine kinase gene/ganciclovir system. Serial contrast-enhanced MR studies were obtained before treatment and postoperatively on day I or 2; weeks 2, 4, 9, 13, 17, 25, and 33; and every 8 weeks thereafter. Iodomethyltyrosine single-photon emission CT (IMT-SPECT) investigations also were performed in selected cases.RESULTS: Twelve patients showed nontumorous enhancement of various intensities after treatment, arising within 18 to 72 hours and persisting at 3 to 10 months. It was characterized by a strong local enhancement up to 20 mm thick, which was initially nodular and later linear along the resection cavity wall and surrounded by massive perifocal edema. This "flare" enhancement had features that clearly differed from those of residual tumor enhancements and benign postsurgical enhancements. The IMT-SPECT investigations showed increased amino acid uptake in patients with enhancement from residual or relapsing tumor, but not in patients with flare.CONCLUSION: After local gene therapy, a unique dynamic, transient perifocal flare enhancement can occur on MR images. IMT-SPECT may help to differentiate between tumorous and nontumorous flare enhancements in patients with enhancing tissue on MR images after gene therapy for glioblastoma

18F-FET PET differentiation of ring-enhancing brain lesions

The aim of this study was to explore the differential diagnostic value of PET using the amino acid O-(2-F-18-fluoroethyl)-L-tyrosine (F-18-FET) in patients with newly diagnosed solitary intracerebral lesions showing ring enhancement on contrast-enhanced MRI.Methods: F-18-FET PET analyses were performed on 14 consecutive patients with intracerebral ring-enhancing lesions. Eleven of the patients were additionally studied with F-18-FDG PET. In all patients, the main differential diagnosis after MRI was a malignant lesion, in particular glioblastoma multiforme, versus a benign lesion, in particular brain abscess, A malignant tumor was suspected for lesions showing increased F-18-FET uptake on PET images with a mean lesion-to-brain ratio of at least 1.6 (F-18-FET PET positive). A nonneoplastic lesion was suspected in cases of minimal or absent F-18-FET uptake, with a mean lesion-to-brain ratio of less than 1.6 (F-18-FET PET negative) Histologic diagnosis was obtained by serial biopsies in 13 of the 14 patients. One patient refused the biopsy, but follow-up indicated an abscess because his lesion regressed under antibiotic therapy.Results: Histology and clinical follow-up showed high-grade malignant gliomas in 5 patients and nonneoplastic lesions in 9 patients. The findings of F-18-FET PET were positive in all 5 glioma patients and in 3 of 9 patients with nonneoplastic lesions, including 2 patients with brain abscesses and 1 patient with a demyelinating lesion. The findings of F-18-FDG PET were positive (mean lesion-to-gray matter ratio >= 0.7) in 4 of 4 glioma patients and 3 of 7 patients with nonneoplastic lesions.Conclusion: Although F-18-FET PET has been shown to be valuable for the diagnostic evaluation of brain tumors, our data indicate that, like 1(8F)-FDG PET, F-18-FET PET has limited specificity in distinguishing between neoplastic and nonneoplastic ring-enhancing intracerebral lesions. Thus, histologic investigation of biopsy specimens remains mandatory to make this important differential diagnosis