Brown fat uptake of 18F-FDG on dual time point PET/CT imaging.

The aim of this report was to assess the changes in the 18F-fluorodeoxyglucose (18F-FDG) uptake of brown fats on integrated positron emission tomography/computed tomography (PET/CT) imaging. The patient presented with an enlargement of the neck lymph nodes, and was suspicious for tuberculous lymphadenitis. A whole body PET/CT imaging was performed, followed by a delayed imaging of the neck and thoracic regions. A visually increased 18F-FDG uptake was taken as a positive finding. A semi-quantitative evaluation was performed using a maximum standardised uptake value (SUVmax), with a cut-off value above 2.5. There were a number of 18F-FDG avid activity areas seen at the supraclavicular, mediastinal, paravertebral and perirenal regions. These are in keeping with the physiological 18F-FDG uptake in brown fat. The differences in SUVmax between the two images ranged from -20 percent to +20 percent. Based on our observations, dual time point imaging may not be a reliable method for assessing the 18F-FDG uptake of brown fat.

PET-CT as an effective imaging modality in the staging and follow-up of post-transplant lymphoproliferative disorder following solid organ transplantation.

INTRODUCTION: To establish the role of positron-emission tomography (PET)-computed tomography (CT) in post-transplant lymphoproliferative disorder (PTLD) patients, compared to conventional imaging (ultrasonography/CT/magnetic resonance imaging) in relation to its accuracy, sensitivity and specificity. METHODS: 30 patients (26 males and 4 females), with a median age of 49.5 (range 18-74) years, were retrospectively evaluated. In 29 cases, the diagnosis was confirmed by histopathology. Malignant lymphoma was detected in 20 cases, polymorphic lymphoproliferative disorder in six cases, multiple myeloma in two cases and Hodgkin's disease in one case. A total of 49 PET-CTs (13 studies for staging at diagnosis and 36 studies at follow-up as assessment post-therapy) were compared to conventional imaging. Imaging results in accordance with disease status were assessed at a median follow-up of 17.8 (range 1.5-42.2) months post-PET-CT. RESULTS: In 41 of 49 examinations performed for staging and on follow-up, PET-CT and conventional imaging findings were concordant. Compared to conventional imaging, PET-CT showed comparable sensitivity (75 percent vs. 83 percent), similar specificity (100 percent in both modalities) and comparable accuracy (77 percent vs. 85 percent) during staging at diagnosis. PET-CT was found to be superior to conventional imaging modalities at follow-up, with greater sensitivity (100 percent vs. 81 percent), specificity (80 percent vs. 100 percent) and accuracy (97 percent vs. 83 percent). CONCLUSION: PET-CT is an accurate diagnostic tool for staging and for the follow-up of PTLD patients. It represents a good alternative imaging method to avoid contrast-related nephrotoxicity in patients who often develop impaired renal function secondary to chronic immunosuppressive therapy. However, further studies are recommended before considering PET-CT as a routine diagnostic tool in PTLD.