Ga-DOTA-exendin-4 PET/CT performed significantly better than In-DOTA-exendin-4 SPECT/CT and MRI in the localisation of benign insulinomas and should be considered in patients where localisation fails with CT/MRI ( ClinicalTrials.gov , NCT02127541).

PET studies with biomarkers of regional neuronal activity (cerebral glucose metabolism or blood flow [CBF]) and amyloid-b (Ab) depositions provide complementary information for the early diagnosis of dementia and follow-up of patients with dementia. We investigated the validity of relative regional CBF estimates (R 1 ) gained from pharmacokinetic analyses of 11 Clabeled Pittsburgh compound B ( 11 C-PIB) PET studies as a marker of neuronal activity and neurodegeneration. Methods: Twenty-two patients with cognitive impairment (16 patients with early Alzheimer disease) underwent 18 F-FDG and 11 C-PIB PET studies for the assessment of regional glucose metabolism and Ab load. Parametric images of R 1 (relative CBF) and binding potential (BP ND ; Ab load) were generated by 2-step simplified reference tissue model (SRTM2) analyses of dynamic 11 C-PIB data. Volume-of-interest and voxel-based statistical analyses were performed to investigate the association between normalized 18 F-FDG uptake and 11 C-PIB R 1 and the correlation of these measures with symptom severity (Mini-Mental State Examination [MMSE] scores) in patients with Alzheimer disease. Results: SRTM2 analyses provided high-quality 11 C-PIB R 1 images that were comparable to 18 F-FDG PET images. Regional 11 C-PIB R 1 values strongly correlated with normalized regional 18 F-FDG uptake when correlations were calculated separately for each patient (R 2 [mean 6 SD], 0.73 6 0.11) or across all regions of all patients (R 2 , 0.62). A regression model including 18 F-FDG uptake, subject identification, and region grouping (into cortical, subcortical, and limbic regions to allow for possible differences in flow/metabolism coupling) accounted for 86% of total 11 C-PIB R 1 variability. Voxel-based correlation analyses of 18 F-FDG uptake and 11 C-PIB R 1 with MMSE scores revealed similar core findings of positive correlations in the posterior cingulate gyrus/precuneus and negative correlations (preserved activity) in the bilateral sensorimotor cortex. There was no correlation between Ab load (BP ND ) and MMSE scores. Conclusion: These results strongly suggest that 11 C-PIB R 1 can serve as a complementary biomarker of neuronal activity and, thus, neurodegeneration in addition to Ab load given by 11 C-PIB BP ND . Further studies are needed to validate the diagnostic value of dual-biomarker 11 C-PIB PET studies in comparison with combined 18 F-FDG and 11 C-PIB PET studies. Compared with the latter, dual-biomarker 11 C-PIB PET greatly reduces costs and burden for patients.

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111 In-DOTA-exendin-4 SPECT/CT has been shown to be highly efficient in the detection of insulinomas. We aimed at determining whether novel PET/CT imaging with [Nle 14 ,Lys 40 (Ahx-DOTA-68 Ga) NH 2 ]exendin-4 ( 68 Ga-DOTA-exendin-4) is feasible and sensitive in detecting benign insulinomas. Methods: 68 Ga-DOTA-exendin-4 PET/CT and 111 In-DOTA-exendin-4 SPECT/CT were performed in a randomized cross-over order on 5 patients with endogenous hyperinsulinemic hypoglycemia. The gold standard for comparison was the histologic diagnosis after surgery. Results: In 4 patients histologic diagnosis confirmed a benign insulinoma, whereas one patient refused surgery despite a positive 68 Ga-DOTA-exendin-4 PET/CT scan. In 4 of 5 patients, previously performed conventional imaging (CT or MR imaging) was not able to localize the insulinoma. 68 Ga-DOTA-exendin-4 PET/CT correctly identified the insulinoma in 4 of 4 patients, whereas 111 In-DOTA-exendin-4 SPECT/CT correctly identified the insulinoma in only 2 of 4 patients. Conclusion: These preliminary data suggest that the use of 68 Ga-DOTA-exendin-4 PET/CT in detecting hidden insulinomas is feasible.