Abstract
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.
Highlights
In the event of a nuclear disaster or accident, healthcare facilities would need to triage patients with varying degree of radiation exposure and dose
Fig 1. 18F-FDG uptake of the gastrointestinal tract is greater in 7.5 Gy whole body irradiated and upper half body shielded animals when compared to sham
At a lower dose of 4 Gy whole body irradiated (WBI), which does not cause the gastrointestinal syndrome, 18F-FDG Positron emission tomography (PET)/CT imaging was not able to detect any significant increase in uptake compared to sham (SUV = 1.88±0.37, n = 4) at 5 days after radiation (Fig 2)
Summary
In the event of a nuclear disaster or accident, healthcare facilities would need to triage patients with varying degree of radiation exposure and dose. Severity of the exposure is characterized on a spectrum which includes the hematopoietic and gastrointestinal syndrome. At a higher dose (!6 Gy in humans) patients are diagnosed with the gastrointestinal syndrome which is characterized by severe diarrhea, loss of blood and electrolytes and can lead to death 10–14 days post exposure [1]. Differentiating between survival groups across these syndromes becomes more difficult when partial body shielding occurs [5,6,7]. Nuclear accidents, such as Chernobyl and Fukushima-Daiichi, highlight the urgency for developing radiomitigators against acute radiation exposure (DREARE). There has been intense efforts by the scientific community, spurred by several federal government initiatives, to investigate the mechanisms underlying DREARE and for developing medical counter measures to mitigate its deadly effects [8]
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