What is the preferred imaging modality, Magnetic Resonance Enterography (MRE) or Computed Tomography Enterography (CTE), for small bowel imaging?

MRE vs CTE for Small Bowel Imaging

MR enterography (MRE) is the preferred imaging modality over CT enterography (CTE) for small bowel imaging, especially in young patients and for monitoring disease activity, as it provides comparable diagnostic accuracy while avoiding radiation exposure. 1

Diagnostic Accuracy Comparison

Both MRE and CTE demonstrate similar high accuracy for evaluating small bowel pathology:

• Similar sensitivity and specificity: MRE (sensitivity 80%, specificity 82%) and CTE (sensitivity 81%, specificity 88%) for detecting small bowel inflammation 1, 2
• Comparable detection of complications: Both modalities have moderately high accuracy for penetrating Crohn's disease (fistulas, inflammatory masses, abscesses) 3
• Meta-analysis confirmation: A systematic review of 290 patients from six studies found no statistically significant incremental yield between MRE and CTE 2

Advantages of MRE

1. No ionizing radiation exposure: Critical for young patients requiring repeated imaging over their lifetime 1, 4
2. Superior tissue characterization:
   • Multiparametric capabilities allow better differentiation between active inflammation and fibrosis 1
   • T2-weighted imaging can detect bowel wall edema, a marker of active inflammation 3
   • Diffusion-weighted imaging correlates with moderate to severe endoscopic inflammation 3
3. Dynamic assessment: Cine imaging allows evaluation of bowel motility and functional strictures 1, 4
4. Alternative when contrast cannot be administered: Non-contrast MRE with T2-weighted and diffusion-weighted imaging remains diagnostic 3, 1

Advantages of CTE

1. Shorter acquisition time: Image acquisition in <2 seconds, reducing motion artifacts 3
2. Higher spatial resolution: Often leads to more consistent image quality in pediatric patients 3
3. Better for initial diagnosis: Helpful to exclude other etiologies such as Meckel diverticulum, celiac disease, and abdominal malignancy 3

Clinical Decision Algorithm for Choosing Between MRE and CTE

Choose MRE when:

• Patient is young (<35 years old) 3, 1
• Monitoring disease activity in stable patients 1
• Assessing treatment response 1
• Evaluating perianal disease 3, 1
• Patient has had multiple prior CT scans 1
• Pregnancy (using non-contrast protocol) 3, 1
• Iodinated contrast allergy 3, 1

Choose CTE when:

• Patient is acutely ill or septic requiring rapid assessment 3
• First cross-sectional enterography in acutely symptomatic patient 3, 1
• Older patient (>35 years old) 3, 1
• MRI contraindicated (pacemaker, claustrophobia, etc.) 3, 1
• Local expertise and access favor CTE 3

Important Considerations

• Radiation exposure: Cumulative radiation exposure from repeated CTE can be substantial, especially in young patients who need lifelong monitoring 1, 4
• Low-dose techniques: Should be utilized when CTE is necessary 3, 1
• Expertise matters: Both modalities require experienced readers for optimal results 1
• Standardized reporting: Improves communication with referring clinicians 3

Pitfalls and Caveats

• MRE typically costs more and takes longer than CTE 1
• MRE may be limited by patient factors such as claustrophobia or inability to hold breath 3
• CTE with oral contrast but without enterography technique may be needed in patients who cannot tolerate large volumes of neutral oral contrast 3
• Both techniques require proper bowel distension with oral contrast for optimal assessment 3