<unk> s 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<unk> . 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. Consumption of the<unk>  begins 90 minutes to two hours prior to the CT/Fluoroscopic scan, as instructed in the patient education provided. For a<unk>  Swallow or Dysphagiagram the<unk>  is consumed after the study begins to discern if the patient has difficulties swallowing or masticating. Consumption is paced, beginning two hours before the scan is to occur, with levels marked on the provided container indicating how much is to be consumed between each of the two hours prior to the test. A small portion of the<unk>  is reserved for the minutes just before the test, to ensure that as much of the gastrointestinal tract as possible is coated. After the scan is complete, the patient is encouraged to eat and drink normally, with special attention to plenty of fluids. The<unk><unk>  is excreted through defecation, so extra fluid intake helps prevent constipation, which is a possible side effect (see Johns Hopkins Medicine Health Library for an example of a possible patient education instruction sheet).
Barium sulfate suspension
Sodium hydroxide
Amylmetacresol
Sodium hypochlorite
Podophyllum resin
Hydrochloric acid
Silver diammine fluoride
Iron sucrose