GI Studies
40 Small Bowel Series (Small Bowel Follow-Through / Enteroclysis)
Anatomy and Physiology
- Stomach (empties into the small intestine)
- Duodenal bulb, duodenum, ligament of Treitz, duodenojejunal flexure
- Jejunum (upper 2/5 of remainder, feathery appearance when filled with contrast)
- Ileum (lower 3/5, smoother appearance, longest portion)
- Ileocecal valve (joins large intestine in RLQ)
- Cecum
🔑 Key Features
- Small intestine ≈ 22 feet long, ~1 inch diameter.
- Functions: digestion (mechanical/chemical), nutrient absorption, water & salt reabsorption.
- Movements: peristalsis (propels contents) and rhythmic segmentation (mixes contents).
- Transit time: 2–3 hours from stomach to ileocecal valve.
- Jejunum: LUQ and LLQ, mucosal folds = “feathery.”
- Ileum: RLQ, smoother appearance, ends at terminal ileum.
Indications, Contraindications, and Patient Preparation
Indications
- Enteritis / gastroenteritis
- Neoplasms (benign or malignant masses, strictures, obstructions)
- Malabsorption syndromes
- Ileus (mechanical or paralytic)
Contraindications
- Suspected GI perforation → do not use barium; substitute water-soluble iodinated contrast (e.g., Gastrografin).
- Suspected large bowel obstruction → rule out with barium enema or acute abdomen series before oral barium.
Patient Preparation
- NPO 8 hours prior (usually after midnight).
- No smoking or chewing gum during fasting period (stimulates secretions, interferes with mucosal coating).
- Explain that exam is lengthy (2–3 hours average). Encourage ambulation between films to speed transit.
Projections & Imaging Procedure
PA (Preferred) or AP Small Bowel
CR Location & Positioning
- SID: 40 inches
- Patient position: Prone (preferred → separates loops of bowel); supine if contraindicated.
- CR: Perpendicular to IR.
- Initial film: center higher (≈ L2) to include stomach.
- Subsequent films: center to iliac crest.
- Pt. Instructions: Drink 2 cups (16 oz) thin barium as quickly as possible. Imaging timed from completion of ingestion.
- Timing: 0 minutes (immediately), then every 15–30 minutes until contrast reaches ileocecal valve (2–3 hours typical).
- Exposure: On expiration.
Evaluation Criteria
- Entire small intestine demonstrated, including stomach on initial image.
- Time markers and patient ID visible.
- No rotation (symmetric iliac wings, spine centered).
- Terminal ileum spot film obtained fluoroscopically.
Enteroclysis (Double-Contrast Small Bowel Study)
CR Location & Positioning
- Patient position: Supine, catheter placed fluoroscopically through stomach into duodenum to ligament of Treitz.
- Contrast:
- High-density barium injected first.
- Then methylcellulose (negative contrast) instilled to distend bowel and provide double contrast.
- Images: Same as small bowel series, but enhanced mucosal detail.
Evaluation Criteria
- Optimal mucosal coating, bowel distended by methylcellulose.
- Entire small bowel visualized, with clear detection of strictures, obstructions, or mucosal disease.
Procedure Adaptation
- Prone positioning preferred → separates loops of bowel.
- Encourage ambulation or give cold water mid-study to promote peristalsis.
- Terminal ileum must always be imaged with fluoroscopy.
- Diagnostic intubation: When catheter used but only thin barium instilled (not double contrast).
- Pediatrics: Shorter transit time; may require smaller volumes.
- Crohn’s disease or suspected obstruction: Enteroclysis or Enteroview (oral prep combining barium + methylcellulose + gas crystals) may be preferred.
Exposure Factors & Technical Considerations
- SID: 40 inches
- kVp: 100–110 (single contrast), 90–100 (double contrast)
- mAs: Short exposure to limit motion blur
- Contrast: Thin barium sulfate (positive contrast); methylcellulose = negative contrast (adheres to bowel while distending it)
- Collimation: Include stomach through terminal ileum
- Shielding: Gonadal shielding when possible
Hows & Whys of Small Bowel Radiography
Anatomy & Physiology
- What do small bowel studies examine?
Both the form and function of the small bowel. - Why must time markers be included?
To confirm that bowel function and transit time are within the normal range (contrast should reach ileocecal valve in 2–3 hours). - How long does the exam usually take?
Approximately 2–3 hours for barium to reach the ileocecal valve (faster if patient ambulates).
Contrast & Technique
- How many cups of barium are used?
Two cups (16 oz) of thin barium are usually given initially. Radiologist may add cold water later to improve distension. - Why is prone positioning preferred?
It separates loops of bowel, reducing overlap and improving visibility of mucosal detail. - What is enteroclysis used for?
A double-contrast technique that improves detection of strictures, Crohn’s disease, or malabsorption syndromes. - Why is methylcellulose used in enteroclysis?
It is a negative contrast medium that distends the bowel while allowing barium to coat the mucosa, producing optimal double-contrast visualization. - Why must dehydration be monitored with iodinated contrast?
Water-soluble contrast can cause fluid shifts, so patients are advised to hydrate after the study.
Clinical Considerations
- Why can’t barium be used in suspected perforation?
It is not absorbed and must be surgically removed if it escapes into the peritoneal cavity. - What contrast is used if perforation is suspected?
Water-soluble iodinated contrast (e.g., Gastrografin). - Why is prone preferred over supine?
To separate loops of bowel for better evaluation. (Supine may be used if prone is contraindicated.)
Pathology & Indications
- What conditions are evaluated with small bowel series?
Enteritis or gastroenteritis, Neoplasms (tumors, strictures, blockages), Malabsorption syndromes, and Ileus (mechanical or paralytic) - What are radiographic signs of ileus?
“Stair-step” or ladder-like loops of dilated, air-filled bowel.