Objectives: To determine the effectiveness of water as a negative contrast agent in PET/CT.
To determine the amount and timing of water to be administered in order to evaluate specific regions of the gastro-intestinal tract (GIT).
To evaluate whether the use of a 'bolus' of a large amount of water is effective in distinguishing physiological from pathological 18F-FDG uptake in the GIT.

Method: Over the past seven months, patients who were scanned and on review had FDG-avidity in the stomach, or had FDG-avidity of an uncertain aetiology further along the GIT, were selected for further scanning. Depending on the site of FDG uptake, patients were either given 1) 2 glasses of water on the bed immediately before scanning or 2)given 6-8 glasses of water in the space of an hour and a delay preceded before scanning over the GIT.

Results: To date, 11 patients who have had 13 FDG PET/CT scans have had further water-enhanced delayed imaging. 8(61.5%) scans proved water to be a useful contrast agent. In 11(84.6%) cases, an appropriate amount and timing of water ingested assisted in further evaluating a specific region. In 7(53.9%) cases a large bolus of water allowed the reporting doctor to effectively distinguish between physiological and pathological uptake in the GIT.

Conclusions: Patients with gastric/gastro-oesophageal/pancreatic cancers benefit from imaging with water in the stomach or small bowel. Scanning patients with discrete, FDG uptake in the large bowel following a large 'bolus' of water can help to distinguish physiological from pathological FDG uptake.