There is heterogeneity in metabolic topography of AIE which is characterized by hypometabolism most commonly involving the parietal and occipital cortices and hypermetabolism most commonly involving the basal ganglia. Scenium analysis using regional Z-scores can complement visual evaluation for demonstration of these metabolic patterns on FDG PET.

Aim In this study, we investigated the relationship of cerebral tau deposition (18F-tau-AD-ML 104 PET/CT) with glucose metabolism (18F-FDG PET/CT) and cognitive function in patients with Alzheimer disease (AD). Patients and Methods Seventy subjects (Mini Mental State Examination [MMSE] score <18 = 37 [AD]; MMSE score, 18–24 = 16 [early AD]) and 17 controls were included in this study. All participants underwent detailed neurological and neuropsychological evaluation, followed by 18F-tau-AD-ML 104 and 18F-FDG PET/CT imaging. Region-wise SUVmax ratios at 50 to 60 minutes postinjection were calculated for 18F-tau-AD-ML 104 and 18F-FDG, using the cerebellar cortex as the reference region. Linear models were used to investigate the association of regional 18F-tau-AD-ML 104 retention with 18F-FDG uptake and cognition (MMSE scores). Results 18F-Tau-AD-ML 104 retention was observed in the parietal lobe, temporal lobe, hippocampus, parahippocampus, frontal lobe, anterior and posterior cingulate, and precuneus in advanced and early AD patient as compared with normal controls with regional hypometabolism in overlapping regions on 18F-FDG PET. Significant negative association was found between 18F-tau-AD-ML 104 regional retention and glucose metabolism in the parietal lobe, temporal lobe, hippocampus, parahippocampus, frontal lobe, anterior and posterior cingulate, and precuneus among patients with advanced and early AD. In advanced and early AD patients, a negative association was found between 18F-tau-AD-ML 104 regional retention (precuneus) and cognition (MMSE score), whereas a positive association was observed between 18F-FDG regional uptake (precuneus) and cognition (MMSE score). Conclusions Tau pathology overlapped with areas of hypometabolism on FDG PET in the brains of AD patients. Tau deposition was found to have negative association with cognitive scores in these patients.

Ga-PSMA PET/CT is the upcoming imaging modality for staging, restaging and response assessment of prostate cancer. However, due to neuroendocrine differentiation in some of patients with prostate cancer, they express somatostatin receptors instead of prostate specific membrane antigen. This can be exploited and other modalities like Ga-DOTANOC PET/CT and F-FDG PET/CT should be used in such cases for guiding management. We hereby discuss a similar case of 67-year-old man of adenocarcinoma prostate with neuroendocrine differentiation, which shows the potential pitfall of Ga-PSMA PET/CT imaging and benefit of Ga-DOTANOC PET/CT and F-FDG PET/CT in such cases.

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The prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells. Few other malignancies have shown expression of PSMA. We present a case of 35-year-old man with medullary thyroid carcinoma, post total thyroidectomy and bilateral neck dissection, now presenting with rising calcitonin levels (doubling time 9 months) and local neck recurrence with negative I-MIBG scan. We decided to perform Ga-PSMA-HBED-CC PET/CT scan to assess PSMA expression and explore the therapeutic option in view of rising serum calcitonin. It revealed intense PSMA uptake in the soft tissue mass in left thyroid bed and cervical lymph nodes.

Superscan is a well-known finding described in skeletal scintigraphy characterized by intense radiotracer uptake in axial skeleton and decreased uptake in soft tissues and kidneys. Metabolic skeletal superscan has also been described in ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) in various conditions. We describe here a case of 12-year-old boy who presented with a scalp swelling, progressive pallor, easy fatigability, poor appetite, and fever for 6 months. The initial diagnosis was inconclusive. ¹⁸F-FDG PET/CT revealed metabolic skeletal superscan and the final histopathological diagnosis was acute lymphoblastic leukemia.

Objective: Evaluation of utility of fluorine-18 fludeoxyglucose ( 18 F-FDG) positron emission tomography/CT (PET/CT) for restaging patients with primary malignant germ cell tumours (GCTs). Methods: Data of 92 patients (age, 31.94 6 10.1 years; male/ female, 86/6) with histopathologically confirmed malignant GCTs (gonadal, 88; mediastinal, 4; seminomatous, 47 and non-seminomatous, 45) who underwent 18 F-FDG PET/CT for restaging (suspected recurrence/post-therapy evaluation) were retrospectively analysed. Two experienced nuclear medicine physicians reviewed the PET/CT images in consensus, qualitatively and semi-quantitatively [maximum standardized uptake value (SUVmax)]. Histopathology (if available) and clinical/imaging/biochemical follow-up (minimum of 6 months) were employed as the reference standard. Results:18 F-FDG PET/CT was interpreted as positive in 59 and negative in 33 patients. Local disease was seen in 5, nodal disease in 50 and distant metastasis in 22 patients. PET/CT was true positive in 49, false positive in 10, true negative in 30 and false negative in 3 patients. 18F-FDG PET/CT showed sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 94.2%, 75.0%, 83.0%, 90.9% and 85.8% overall; 90.0%, 74.0%, 72.0%, 90.9% and 80.8% in seminomatous GCT; and 96.8%, 76.9%, 91.1%, 90.9% and 91.1% in non-seminomatous GCT, respectively. Difference in PET/CT accuracy for seminomatous and non-seminomatous GCTs was not significant (p 5 0.263). PET/CT demonstrated disease in 13 patients with negative/equivocal conventional imaging findings and in 9 patients with normal tumour markers. No site-or histology-based difference was seen in SUVmax. Conclusion:18 F-FDG PET/CT demonstrates high diagnostic accuracy for restaging patients with malignant GCTs. It has comparable diagnostic performance in both seminomatous and non-seminomatous malignant GCTs. Advances in knowledge:The present article demonstrates high diagnostic accuracy of 18 F-FDG PET/CT for restaging both seminomatous and non-seminomatous malignant GCTs in a large patient population.Germ cell tumour (GCT) is the commonest malignancy in males aged between 20 and 35 years.1 With cisplatin-based chemotherapy, high long-term cure rates can be achieved in patients with GCTs.2 Traditionally, the follow-up of patients with GCT is carried out with clinical examination, measurement of serum tumour markers [alpha-fetoprotein (AFP), beta-human chorionic gonadotropin (b-HCG) and lactate dehydrogenase (LDH)], and with conventional imaging investigations such as CT or MRI.3 A major issue in the management of GCTs is post-chemotherapy residual masses, which harbour viable tumour cells in about 11-37% of cases. 4 Unfortunately, CT or MRI cannot predict the histology of residual masses and has limited specificity in post-therapy setting.5

Medulloblastoma, also known as cerebellar primitive neuroectodermal tumor, is the most common brain tumor in children and arises in the posterior cranial fossa. We present the case of a patient with desmoplastic type of medulloblastoma, which showed recurrence more than once. When Ga-DOTANOC PET-CT was done, the lesions showed somatostatin receptor expression, opening another potential therapeutic option for this patient.