硫酸钡
Barium sulfate suspensions are provided by a radiologist or radiographer in advance of, or during a CT scan or fluoroscopic study to allow for better visualization of the gastrointestinal tract, such as in upper or lower gastrointestinal series. In upper gastrointestinal series, the patient is instructed to take nothing by mouth, which means to abstain from eating and drinking (fasting), with the exception of drinking the barium sulfate suspension. The amount of time for this fast may vary, depending on the instructions given by the imaging facility and the area of the body to be scanned, but generally lasts for several hours prior to the scan. The patient generally skips one meal, along with abstaining from all liquids, clear or otherwise, during this time.