Neutral Contrast Agents for CT Enterography
For CT enterography, use water, polyethylene glycol (PEG), or methylcellulose suspensions as neutral contrast agents, with water being the most widely recommended by the American College of Radiology. 1
Standard Neutral Contrast Options
The ACR explicitly identifies the following as acceptable neutral contrast agents for CT enterography 2, 1:
- Water - Most commonly recommended by ACR guidelines 1
- Polyethylene glycol (PEG) - Provides superior bowel distension compared to water 3
- Methylcellulose suspensions - ACR-approved alternative 1
- Low w/v barium solutions - Listed as neutral option 2
Volume and Administration Protocol
Administer 1,000-2,000 mL of neutral contrast over 45-60 minutes before scanning, with imaging performed at 60 minutes. 1, 2
- The Society of Abdominal Radiology recommends 900 mL in divided doses over 45-60 minutes 2
- ACR guidelines specify 1,300-1,800 mL over 30-60 minutes for optimal distension 2
- Pediatric patients require 900-1,500 mL based on weight 1
Critical Technical Requirements
Positive oral contrast agents must be avoided in CT enterography because they obscure mucosal hyperenhancement and active inflammation. 1
- Neutral contrast allows visualization of enhancing bowel wall against hypointense luminal contents 2, 1
- Intravenous contrast is mandatory to detect mucosal hyperenhancement and inflammatory changes 1, 2
- The contrast-enhanced phase should be acquired 50-70 seconds after IV injection (between enteric and portal venous phases) 2
Patient Preparation
Patients must fast from solids for 4-6 hours before CT enterography. 1
- Liquids should be restricted during this fasting period, though water is permissible 4
- This preparation optimizes bowel visualization and contrast distribution 5
Important Contraindications and Caveats
Avoid oral phosphate-containing preparations in patients with GFR <60 mL/min/1.73 m² due to risk of phosphate nephropathy. 1, 4
Comparative Performance of Neutral Agents
While all ACR-approved neutral agents are acceptable, research evidence suggests performance differences 6, 7, 3:
- PEG demonstrates superior bowel distension compared to water and other agents, with statistically significant improvements in luminal diameter (21.88 mm vs 17.50 mm for water in the left upper quadrant) 3
- Lactulose achieved better distension than water, Metamucil, and PEG in one comparative study, with odds ratios of 9.19,3.51, and 2.68 respectively for achieving "useful" quadrants 7
- 3.8% milk showed superiority over water and dilute gastrografin for jejunal and ileal distension, though 10% of patients experienced immediate post-test diarrhea 6
Common Pitfall to Avoid
Never use standard positive oral contrast (barium or concentrated iodinated contrast) for CT enterography - this is the most critical error, as it completely obscures the mucosal enhancement patterns essential for detecting active inflammation in Crohn's disease and other small bowel pathology. 1, 2