4. Stomach upper GI series, AP supine projection

This upper GI series (UGI) was performed using a double contrast technique, i.e., two different contrast agents were administered to the patient prior to the study. First, the patient drank a small volume of dense barium sulfate, a metalic salt that is inert and not absorbed across the GI mucosa. This casts a very radiopaque shadow. Then the patient swallowed some sodium bicarbonate granules with a small sip of water, which combines with the granules to liberate CO₂. The gas distends the lumen of the stomach and provides radiolucent contrast to the thin film of barium (sulfate) coating the mucosal surface. Note how well the rugae are visualized.