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

<div><p>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.</p></div

Villus Length at 5 Days Post irradiation.

<p>Villus Length at 5 Days Post irradiation.</p

Recovery in the metabolic activity of the gastrointestinal tract coincides with that of the bone marrow activity.

<p>Graph of mean standard uptake value of ¹⁸F-FDG in the gastrointestinal tract and bone marrow of upper half body shielded at 5, 10 and 35 days post radiation exposure, showing full recovery of both tissues by day 35. Data shown as mean ± SD; *P<0.05, ‡P<0.001 compared to sham animals.</p

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.

<p>Reconstructed PET/CT images showing ¹⁸F-FDG uptake (top) and corresponding hematoxylin and eosin-stained intestine sections (bottom) of sham (A), 7.5 Gy whole body irradiated (B), and upper half body shielded (C) animals 5 days post radiation exposure.</p

Direct radiation exposure to gastrointestinal tract can be detected with PET/CT imaging.

<p>Graph of mean standard uptake value of ¹⁸F-FDG in the gastrointestinal tract 5 days post irradiation. A significant increase is observed in 7.5 whole body irradiated and upper half shielded groups compared to sham group. Data shown mean ± standard deviation; *P<0.05, †P<0.01, ‡P<0.001.</p

Metabolic activity in bone marrow is lower at the higher radiation dose.

<p>Reconstructed PET/CT images showing ¹⁸F-FDG uptake of (A) sham, (B) 4 Gy and (C) 7.5 Gy whole body irradiated animals 5 days post radiation exposure.</p