Neutral Contrast Agents for CT Enterography
For CT enterography, the recommended neutral contrast agents include low-concentration barium sulfate suspensions, water, polyethylene glycol (PEG), or methylcellulose suspensions, with patients ingesting 1,000 to 2,000 mL over 45-60 minutes prior to the examination. 1
Standard Neutral Contrast Options
The ACR Appropriateness Criteria explicitly identify the following neutral contrast agents as acceptable for CT enterography 1:
- Low-concentration (0.1% w/v) barium sulfate suspensions
- Water
- Polyethylene glycol (PEG) solutions
- Methylcellulose suspensions
These agents are classified as "neutral" because their attenuation values approximate water, allowing optimal visualization of mucosal hyperenhancement against the hypointense luminal contrast 1.
Volume and Timing Requirements
Patients should ingest 1,000-2,000 mL of neutral contrast over 45-60 minutes before scanning, with imaging typically performed at 60 minutes 1. The ACR guidelines for pediatric patients specify 900-1,500 mL based on patient weight 1. Volumes exceeding 1,000 mL provide superior bowel distension, though diagnostically acceptable images can be obtained with as little as 450 mL 2.
Comparative Performance Data
Research comparing these agents demonstrates important differences 3:
- PEG and low-concentration barium provide superior small bowel distension compared to water and methylcellulose (P < 0.0001)
- Optimal distension of the terminal ileum occurs 51-72 minutes after ingestion 3
- Water and methylcellulose have fewer side effects but inferior distension 3
A more recent study found diluted PEG solution showed comparable bowel distension to low-density barium suspension with no immediate side effects 4.
Critical Technical Considerations
Positive oral contrast agents (traditional high-density barium or iodinated contrast) must be avoided in CT enterography because they obscure mucosal hyperenhancement and active hemorrhage 1. The neutral agents allow detection of subtle inflammation that would otherwise be masked 1.
Intravenous contrast administration is mandatory to visualize enhancing lesions and inflammatory changes against the neutral intraluminal contrast 1.
Patient Preparation Requirements
Patients should fast from solids for 4-6 hours before CT enterography 1, 2. Water is permissible during the fasting period 2.
Important Contraindications
Avoid oral phosphate-containing preparations in patients with GFR <60 mL/min/1.73 m² due to risk of phosphate nephropathy 2.