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What major types of enteric contrast agent are available?
Enteric contrast agents are substances used in imaging studies (especially CT, fluoroscopy, and radiography) to opacify the gastrointestinal (GI) tract for better visualization. These agents enhance the contrast between the bowel lumen and surrounding structures.
Major Types of Enteric Contrast Agents
1. Positive Contrast Agents
These appear white (radiopaque) on imaging due to their high density.
- Barium sulfate
- Most commonly used for fluoroscopy (e.g., barium swallow, enema)
- Not absorbed—remains in GI tract
- Contraindicated if perforation is suspected (risk of peritonitis)
- Water-soluble iodinated contrast agents (e.g., Gastrografin, Omnipaque)
- Used when bowel perforation or leak is suspected
- Absorbable if extravasated into peritoneum
- May cause diarrhea (osmotic effect, especially Gastrografin)
2. Negative Contrast Agents
These appear black (radiolucent) due to low density.
- Air or gas (e.g., room air, carbon dioxide)
- Common in double-contrast studies (e.g., with barium)
- Improves mucosal detail
- Used in procedures like virtual colonoscopy, pneumocolon, or pneumogastrography
3. Neutral Contrast Agents
These have density similar to water and are used to distend the bowel without obscuring mucosal enhancement.
- Water
- Often used in CT enterography or MR enterography
- Allows better assessment of the bowel wall
- Polyethylene glycol (PEG)
- Common in bowel prep and CT enterography
- Methylcellulose or mannitol
- Non-absorbable, used as oral contrast for bowel distension
| Type | Examples | Imaging Appearance | Uses |
|---|---|---|---|
| Positive | Barium, iodinated agents | Radiopaque (white) | Fluoroscopy, CT, GI studies |
| Negative | Air, carbon dioxide | Radiolucent (black) | Double-contrast, virtual colonoscopy |
| Neutral | Water, PEG, mannitol, methylcellulose | Isoattenuating (gray) | CT/MR enterography |
Summary
- Barium sulfate enteric contrast agents (predominantly used in gastrointestinal fluoroscopic and CT studies) are utilized for distention and opacification of the gastrointestinal tract and may be administered by mouth, per rectum, via an ostomy, or via an indwelling bowel catheter.
- Iodinated enteric contrast agents can alternatively be utilized to distend and opacify the bowel.
