Time-course of effects of external beam radiation on [18F]FDG uptake in healthy tissue and bone marrow

[18F]FDG-PET Evaluation of Spinal Pathology in Patients in Oncology: Pearls and Pitfalls for the Neuroradiologist

[¹⁸F]FDG-PET is a widely used technique for specific evaluation of disease and treatment response in oncology. However, the principles behind [¹⁸F]FDG-PET imaging allow a wide-ranging array of benign and malignant pathologies to be identified on both initial and routine surveillance imaging. This is important for clinicians and radiologists, alike, in that effective and accurate evaluation of malignancy and metastatic disease, specifically involving the spine and central nervous system, is crucial. In this article, we review the normal and posttherapy appearance of the spine on [¹⁸F]FDG-PET, the various types and patterns of metastatic disease that involve the spine and spinal cord, and, finally, important spinal pathologies that may mimic malignancy on [¹⁸F]FDG-PET.

Radiation-Induced Metabolic Shifts in the Hepatic Parenchyma: Findings from 18F-FDG PET Imaging and Tissue NMR Metabolomics in a Mouse Model for Hepatocellular Carcinoma

Purpose: By taking advantage of 18F-FDG PET imaging and tissue nuclear magnetic resonance (NMR) metabolomics, we examined the dynamic metabolic alterations induced by liver irradiation in a mouse model for hepatocellular carcinoma (HCC). Methods: After orthotopic implantation with the mouse liver cancer BNL cells in the right hepatic lobe, animals were divided into two experimental groups. The first received irradiation (RT) at 15 Gy, while the second (no-RT) did not. Intergroup comparisons over time were performed, in terms of 18F-FDG PET findings, NMR metabolomics results, and the expression of genes involved in inflammation and glucose metabolism. Results: As of day one post-irradiation, mice in the RT group showed an increased 18F-FDG uptake in the right liver parenchyma compared with the no-RT group. However, the difference reached statistical significance only on the third post-irradiation day. NMR metabolomics revealed that glucose concentrations peaked on day one post-irradiation both, in the right and left lobes—the latter reflecting a bystander effect. Increased pyruvate and glutamate levels were also evident in the right liver on the third post-irradiation day. The expression levels of the glucose-6-phosphatase (G6PC) and fructose-1, 6-bisphosphatase 1 (FBP1) genes were down-regulated on the first and third post-irradiation days, respectively. Therefore, liver irradiation was associated with a metabolic shift from an impaired gluconeogenesis to an enhanced glycolysis from the first to the third post-irradiation day. Conclusion: Radiation-induced metabolic alterations in the liver parenchyma occur as early as the first post-irradiation day and show dynamic changes over time.

Imaging Radiation-Induced Gastrointestinal, Bone Marrow Injury and Recovery Kinetics Using 18F-FDG PET

Positron emission tomography using 18F-Fluro-deoxy-glucose (18F-FDG) is a useful tool to detect regions of inflammation in patients. We utilized this imaging technique to investigate the kinetics of gastrointestinal recovery after radiation exposure and the role of bone marrow in the recovery process. Male Sprague-Dawley rats were either sham irradiated, irradiated with their upper half body shielded (UHBS) at a dose of 7.5 Gy, or whole body irradiated (WBI) with 4 or 7.5 Gy. Animals were imaged using 18F-FDG PET/CT at 5, 10 and 35 days post-radiation exposure. The gastrointestinal tract and bone marrow were analyzed for 18F-FDG uptake. Tissue was collected at all-time points for histological analysis. Following 7.5 Gy irradiation, there was a significant increase in inflammation in the gastrointestinal tract as indicated by the significantly higher 18F-FDG uptake compared to sham. UHBS animals had a significantly higher activity compared to 7.5 Gy WBI at 5 days post-exposure. Animals that received 4 Gy WBI did not show any significant increase in uptake compared to sham. Analysis of the bone marrow showed a significant decrease of uptake in the 7.5 Gy animals 5 days post-irradiation, albeit not observed in the 4 Gy group. Interestingly, as the metabolic activity of the gastrointestinal tract returned to sham levels in UHBS animals it was accompanied by an increase in metabolic activity in the bone marrow. At 35 days post-exposure both gastrointestinal tract and bone marrow 18F-FDG uptake returned to sham levels. 18F-FDG imaging is a tool that can be used to study the inflammatory response of the gastrointestinal tract and changes in bone marrow metabolism caused by radiation exposure. The recovery of the gastrointestinal tract coincides with an increase in bone marrow metabolism in partially shielded animals. These findings further demonstrate the relationship between the gastrointestinal syndrome and bone marrow recovery, and that this interaction can be studied using non-invasive imaging modalities.

Brain: normal variations and benign findings in fluorodeoxyglucose-PET/computed tomography imaging

Brain 18F-fluorodeoxyglucose (18F-FDG) PET allows the in vivo study of cerebral glucose metabolism, reflecting neuronal and synaptic activity. 18F-FDG-PET has been extensively used to detect metabolic alterations in several neurologic diseases compared with normal aging. However, healthy subjects have variants of 18F-FDG distribution, especially as associated with aging. This article focuses on 18F-FDG-PET findings in so-called normal brain aging, and in particular on metabolic differences occurring with aging and as a function of people’s gender. The effect of different substances, medications, and therapy procedures are discussed, as well as common artifacts.

Combination of radiation and burn injury alters [¹⁸F] 2-fluoro-2-deoxy-D-glucose uptake in mice

Radiation exposure and burn injury have both been shown to alter glucose utilization in vivo. The present study was designed to study the effect of burn injury combined with radiation exposure on glucose metabolism in mice using [¹⁸F] 2-fluoro-2-deoxy-D-glucose (¹⁸FDG). Groups of male mice weighing approximately 30 g were studied. Group 1 was irradiated with a ¹³⁷Cs source (9 Gy). Group 2 received full thickness burn injury on 25% TBSA followed by resuscitation with saline (2 ml, IP). Group 3 received radiation followed 10 minutes later by burn injury. Group 4 were sham-treated controls. After treatment, the mice were fasted for 23 hours and then injected (IV) with 50 μCi of ¹⁸FDG. One hour postinjection, the mice were sacrificed, and biodistribution was measured. Positive blood cultures were observed in all groups of animals compared to the shams. Increased mortality was observed after 6 days in the burn plus radiated group as compared to the other groups. Radiation and burn treatments separately or in combination produced major changes in ¹⁸FDG uptake by many tissues. In the heart, brown adipose tissue, and spleen, radiation plus burn produced a much greater increase (P < .0001) in ¹⁸FDG accumulation than either treatment separately. All three treatments produced moderate decreases in ¹⁸FDG accumulation (P < .01) in the brain and gonads. Burn injury, but not irradiation, increased ¹⁸FDG accumulation in skeletal muscle; however, the combination of burn plus radiation decreased ¹⁸FDG accumulation in skeletal muscle. This model may be useful for understanding the effects of burns plus irradiation injury on glucose metabolism and in developing treatments for victims of injuries produced by the combination of burn plus irradiation.

The diagnostic value of 18F-FDG-PET/CT in hematopoietic radiation toxicity: a Tibet minipig model

This study was undertaken to assess the diagnostic value of 2-[(18)F]-fluoro-2-deoxy-D-glucose positron emission tomography with computed tomography ([(18)F]-FDG-PET/CT) in the detection of radiation toxicity in normal bone marrow using Tibet minipigs as a model. Eighteen Tibet minipigs were caged in aseptic rooms and randomly divided into six groups. Five groups (n = 3/group) were irradiated with single doses of 2, 5, 8, 11 and 14 Gy of total body irradiation (TBI) using an 8-MV X-ray linear accelerator. These pigs were evaluated with [(18)F]-FDG-PET/CT, and their marrow nucleated cells were counted. The data were initially collected at 6, 24 and 72 h after treatment and were then collected on Days 5-60 post-TBI at 5-day intervals. At 24 and 72 h post-TBI, marrow standardized uptake value (SUV) data showed a dose-dependent decrease in the radiation dose range from 2-8 Gy. Upon long-term observation, SUV and marrow nucleated cell number in the 11-Gy and 14-Gy groups showed a continuous and marked reduction throughout the entire time course, while Kaplan-Meier curves of survival showed low survival. In contrast, the SUVs in the 2-, 5- and 8-Gy groups showed early transient increases followed by a decline from approximately 72 h through Days 5-15 and then normalized or maintained low levels through the endpoint; marrow nucleated cell number and survival curves showed approximately the same trend and higher survival, respectively. Our findings suggest that [(18)F]-FDG-PET/CT may be helpful in quickly assessing the absorbed doses and predicting the prognosis in patients.