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88 Objectives To determine if 18F-FDG (FDG) could replace 67Ga (Ga) for differentiating acute interstitial nephritis (AIN) from acute tubular necrosis (ATN). Methods 50 rats were divided into 3 groups: Controls (10), AIN (20) & ATN (20). Half of the animals in each group were studied with FDG & half with Ga. AIN animals were imaged 14 days after a single injection of 150 mg/kg puromycin aminonucleoside. ATN animals were imaged 8 days after intraperitoneal injection of 6 mg/kg cisplatin. FDG imaging was performed on a micro-PET system 45 min after tail vein injection of 7.4 MBq FDG. Kidney SUV’s were determined. After imaging, organs were removed & kidney/spine tissue counting ratios generated. Renal tissue samples were evaluated by a pathologist for evidence of cellular infiltration. Ga imaging was performed 48 hr after tail vein injection of 3.7 MBq Ga. Static images were acquired at maximum magnification (zoom = 2.19, 5.9 mm/pixel) with a pinhole collimator for 10 min. Regions of interest were drawn around kidneys & adjacent lumbar spine; kidney:spine image count ratios were generated. An experienced Nuclear physician interpreted all images visually. Results For FDG, AIN & ATN SUV’s were significantly higher than Control SUVs, but similar to each other (Table). Tissue analysis results were similar. The reader could distinguish FDG AIN & ATN from Controls, but not from each other. For Ga, kidney:spine ratios were significantly higher for AIN than ATN & Controls, which were similar to each other. Tissue analysis results were similar. The reader could differentiate AIN from ATN & Controls, but not ATN from Controls. Cellular infiltration was predominantly mononuclear, & was significantly higher in AIN than in ATN & Controls (2.3±0.5 versus 0.6±0.5 cells, p=0.002). Conclusions The results indicate that FDG-PET cannot replace Ga for differentiating acute interstitial nephritis from acute tubular necrosis.

Background Despite an increasing number of O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET) PET studies in supratentorial gliomas, studies regarding the usefulness of 18F-FET PET in brainstem and spinal cord gliomas to date remain scarce. Methods Thirty-six 18F-FET PET scans were performed in 29 patients with brainstem (n = 29 scans) or spinal cord glioma (n = 7 scans). In 32 of 36 PET scans, a dynamic acquisition was performed. Fifteen scans in 15 patients were performed to assess newly diagnosed lesions, and 21 scans were obtained during follow-up: for diagnosing tumor progression (n = 15 scans in 14 patients) as well as for treatment monitoring (n = 6 scans in 3 patients). Four patients underwent additional serial scans (range, 1-2), and 3 of these 4 patients were examined for more than one indication. Maximum and mean tumor/brain ratios (TBRmax/mean) of 18F-FET uptake (20-40 min post injection) as well as kinetic 18F-FET uptake parameters were determined. Final diagnoses were confirmed histologically (54%) or by clinical follow-up (46%). Results In all newly diagnosed high-grade (n = 3 patients) and in 5 of 11 patients with low-grade gliomas, 18F-FET uptake was increased (TBRmax ≥2.5 and/or TBRmean ≥1.9). In 2 patients with newly diagnosed gliomas without MR contrast enhancement, 18F-FET PET nevertheless showed increased metabolism. At suspected progression, the combination of TBRs with kinetic 18F-FET parameters correctly identified presence or absence of progressive disease in 9 of 11 patients (82%). Conclusions This preliminary study suggests that 18F-FET PET adds valuable diagnostic information in brainstem and spinal cord glioma, particularly when the diagnostic information derived from MRI is equivocal.

BACKGROUND: The aim of this study was to investigate the potential of dynamic O-(2-[(18)F]fluoroethyl)-L-tyrosine ((18)F-FET) PET for differentiating local recurrent brain metastasis from radiation injury after radiotherapy since contrast-enhanced MRI often remains inconclusive.METHODS: Sixty-two patients (mean age, 55 ± 11 y) with single or multiple contrast-enhancing brain lesions (n = 76) on MRI after radiotherapy of brain metastases (predominantly stereotactic radiosurgery) were investigated with dynamic (18)F-FET PET. Maximum and mean tumor-to-brain ratios (TBRmax, TBRmean) of (18)F-FET uptake were determined (20-40 min postinjection) as well as tracer uptake kinetics (ie, time-to-peak and slope of time-activity curves). Diagnoses were confirmed histologically (34%; 26 lesions in 25 patients) or by clinical follow-up (66%; 50 lesions in 37 patients). Diagnostic accuracies of PET parameters for the correct identification of recurrent brain metastasis were evaluated by receiver-operating-characteristic analyses or the chi-square test.RESULTS: TBRs were significantly higher in recurrent metastases (n = 36) than in radiation injuries (n = 40) (TBRmax 3.3 ± 1.0 vs 2.2 ± 0.4, P < .001; TBRmean 2.2 ± 0.4 vs 1.7 ± 0.3, P < .001). The highest accuracy (88%) for diagnosing local recurrent metastasis could be obtained with TBRs in combination with the slope of time-activity curves (P < .001).CONCLUSIONS: The results of this study confirm previous preliminary observations that the combined evaluation of the TBRs of (18)F-FET uptake and the slope of time-activity curves can differentiate local brain metastasis recurrence from radiation-induced changes with high accuracy. (18)F-FET PET may thus contribute significantly to the management of patients with brain metastases.