GI Studies
41 Small Bowel Series (Small Bowel Follow-Through / Enteroclysis)
Anatomy & Pathology
Anatomy
- Stomach – Empties its contents into the duodenum through the pyloric sphincter.
- Duodenum – First portion of the small intestine; includes the duodenal bulb, descending and horizontal portions, and the ligament of Treitz at the duodenojejunal flexure.
- Jejunum – Comprises the upper two-fifths of the remaining small bowel; demonstrates a feathery mucosal pattern when filled with contrast.
- Ileum – The lower three-fifths of the small bowel; smoother in appearance and the longest segment, ending at the terminal ileum in the right lower quadrant (RLQ).
- Ileocecal valve – The junction between the terminal ileum and cecum of the large intestine; regulates passage into the colon.
- Cecum – The first portion of the large intestine, located in the RLQ, receiving contents from the ileum.
Key functional features:
- Average length ≈ 22 feet and diameter ≈ 1 inch.
- Functions include digestion, nutrient absorption, and water and salt reabsorption.
- Transit time from stomach to ileocecal valve is approximately 2–3 hours.
- Movements include peristalsis (propelling) and rhythmic segmentation (mixing).
Common Pathologies
- Enteritis / Gastroenteritis – Inflammation of the small bowel, often producing thickened mucosal folds or poor barium coating.
Technique note: Use lower kVp (≈ 90) to enhance mucosal detail. - Neoplasms / Strictures / Obstructions – Tumors or narrowing that delay or prevent passage of contrast.
Technique note: Spot fluoroscopy at delayed intervals; compression may assist detection. - Malabsorption Syndromes – Inability to properly absorb nutrients; may show rapid barium transit or dilution of contrast.
Technique note: Adjust timing intervals to document early contrast clearance. - Ileus (Mechanical or Paralytic) – Loss of normal peristalsis; gas-filled, dilated loops with little movement of contrast.
Technique note: Use upright or decubitus views to differentiate obstruction from paralysis. - Crohn’s Disease (Regional Enteritis) – Chronic inflammatory disease with “string sign” and fistulas.
Technique note: Enteroclysis or double-contrast study provides superior mucosal detail. - Celiac Disease / Sprue – Malabsorption disorder producing flocculated contrast and dilated folds.
Technique note: Perform routine follow-through; document early and late distribution patterns.
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 Series
CR Location & Positioning
- SID: 40 inches
- Patient position: Prone (preferred) to separate bowel loops; supine if contraindicated.
- Adjustments: Align midsagittal plane to IR; arms at sides; legs extended.
- CR: Perpendicular to IR.
- Initial image: Center high (≈ L2) to include stomach.
- Subsequent images: Center to iliac crest.
- Patient instructions: Drink two cups (≈ 16 oz) of thin barium rapidly; imaging begins when ingestion is complete.
- Exposure: Suspend respiration on expiration.
- Timing: First image at 0 minutes, then every 15–30 minutes until barium reaches the ileocecal valve (typically 2–3 hours).
Evaluation Criteria
- Coverage: Entire small bowel demonstrated, including stomach on the first image and terminal ileum on the final.
- Rotation checks: Symmetric iliac wings; spine centered; no patient rotation.
- Motion checks: Sharp mucosal pattern; minimal motion blur.
- Technique checks: Adequate penetration without overexposure; visible time markers.
- Clinical aim: Assess bowel transit, contour, and mucosal integrity from stomach to ileocecal junction.
Enteroclysis (Double-Contrast Small Bowel Study)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine.
- Adjustments: Under fluoroscopy, catheter advanced through stomach and duodenum to the ligament of Treitz.
- CR: Perpendicular to IR, centered to mid-abdomen.
- Contrast: Instill high-density barium (positive contrast), followed by methylcellulose (negative contrast) to distend bowel.
- Patient instructions: Remain still; procedure performed under fluoroscopy.
- Exposure: Suspend respiration on expiration.
Evaluation Criteria
- Coverage: Entire small bowel visualized from duodenum to terminal ileum.
- Rotation checks: Vertebral column centered; no pelvic or shoulder rotation.
- Motion checks: Fine mucosal detail visible; no peristaltic blur.
- Technique checks: High contrast between barium and methylcellulose; no pooling or leakage.
- Clinical aim: Demonstrate mucosal pattern, strictures, or early Crohn’s changes using optimal double-contrast visualization.
Procedure Adaptation
- Prone positioning preferred – Separates bowel loops and enhances visualization of mucosa.
- Ambulation between exposures – Promotes peristalsis and shortens transit time.
- Cold water or methylcellulose may be administered mid-study – Stimulates peristaltic activity.
- Terminal ileum – Always evaluated under fluoroscopy for competence and pathology.
- Diagnostic intubation – Thin barium instilled via catheter for partial contrast study.
- Pediatric patients – Shorter transit; use smaller barium volume.
- Suspected obstruction or Crohn’s disease – Enteroclysis preferred for mucosal detail.
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
- Special consideration: Hydrate patients after iodinated contrast use to prevent dehydration
Memory Aids
- “Prone to Show the Loops” – Prone position separates bowel loops for better mucosal detail.
- “Feathery = Jejunum; Smooth = Ileum” – Quick pattern recognition guide.
- “Two Cups, Two Hours” – Typical barium volume and transit time.
- “Enteroclysis = Enhanced” – Double-contrast for detailed mucosal assessment.
Hows & Whys of Small Bowel Radiography
Anatomy
- What do small bowel studies examine?
Both the form and function of the small intestine—from stomach emptying through the ileocecal valve. - How can the jejunum and ileum be differentiated radiographically?
The jejunum appears feathery due to prominent mucosal folds; the ileum appears smoother with fewer folds. - How can the location of the ileocecal valve be confirmed?
By fluoroscopic observation in the RLQ where the terminal ileum joins the cecum. - How can normal peristalsis be identified?
By sequential movement of barium through the loops at each timed interval.
Positioning
- Why is prone positioning preferred for small bowel images?
It spreads the loops of bowel, reducing overlap and improving visualization of mucosal detail. - Why is supine positioning used for some patients?
For those unable to lie prone due to trauma, pain, or surgical conditions. - Why are timed interval images obtained?
To evaluate the rate of peristalsis and document normal or delayed transit time (average 2–3 hours to ileocecal valve). - Why should the patient ambulate between images?
Walking stimulates peristalsis and helps move barium through the small bowel more efficiently.
Technique & Image Evaluation
- How is a complete small bowel series confirmed?
Contrast must reach the ileocecal valve, documented by fluoroscopy and spot imaging of the terminal ileum. - How can proper exposure be evaluated?
Soft tissue detail and mucosal patterns are visible throughout the bowel without overexposure. - How can peristaltic motion blur be minimized?
Use short exposure times and time images between contractions when possible. - How can optimal mucosal coating be achieved in enteroclysis?
By sequentially instilling barium followed by methylcellulose to distend and coat the bowel uniformly. - How can rotation be identified?
Asymmetry of iliac wings or off-center vertebral column indicates patient rotation. - How can delayed transit or obstruction be recognized?
Persistent loops of opacified bowel with little progression between intervals suggest ileus or blockage.
Clinical Applications
- Why must time markers be included on all images?
They provide essential data for assessing bowel function and transit rate. - Why can’t barium be used if perforation is suspected?
It is not absorbed by the body and can cause peritonitis if it leaks into the abdominal cavity. - Why is iodinated contrast used for suspected perforation or obstruction?
Water-soluble agents (e.g., Gastrografin) can be absorbed if leakage occurs, reducing risk. - Why is enteroclysis sometimes preferred over standard small bowel follow-through?
It provides controlled double-contrast imaging with enhanced visualization of early mucosal disease. - Why must hydration be encouraged after using iodinated contrast?
To prevent dehydration due to osmotic fluid shifts into the bowel lumen. - How can findings assist diagnosis of specific pathologies?
Transit delay indicates ileus; “string sign” suggests Crohn’s disease; separation of loops may signal obstruction.
