GI Studies
Contrast Enema
Anatomy
Students should be able to identify the following structures on radiographic images:
Cecum, Appendix, Ascending Colon, Right Colic (Hepatic) Flexure, Transverse Colon, Left Colic (Splenic) Flexure, Descending Colon, Sigmoid Colon, Rectum, Anus, Taeniae coli, haustra.
Indications, Contraindications, and Patient Preparation
Indications
- Colitis (inflammation of colon, causes include infection, diet, stress)
- Diverticulitis/diverticula (outpouchings of mucosa)
- Neoplasms (colon cancer → “apple-core” lesions)
- Volvulus (twisting of bowel)
- Intussusception (telescoping, common in infants)
- Appendicitis (clinical suspicion; appendix demonstrated in many cases)
Contraindications
- Suspected bowel perforation (use water-soluble iodinated contrast instead of barium)
- Recent colonoscopy with biopsy (risk of perforation)
- Severe diarrhea, gross bleeding, or acute appendicitis (contraindicated for prep)
Patient Preparation
- Low-residue diet 1–2 days before exam
- Laxative afternoon before exam (irritant or saline type)
- NPO after midnight
- No laxatives for patients with: severe diarrhea, obstruction, gross bleeding, or appendicitis
- Occasional cleansing enema as alternative prep
Routine Projections (ARRT Required)
PA or AP Abdomen (Scout and Post-Filling)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine (AP) or prone (PA).
- Adjustments: Align midsagittal plane to midline of table and IR; arms at sides.
- CR: Perpendicular to IR at the level of the iliac crest.
- Patient instructions: Suspend respiration on expiration.
- Exposure: On expiration.
Evaluation Criteria
- Coverage (what anatomy must be included and how you verify it’s complete): Entire large intestine from cecum to rectum included.
- Rotation checks (how symmetry or alignment tells you if positioning is correct): Iliac wings symmetric; spine midline.
- Motion checks (how sharpness confirms patient cooperation/exposure timing): Sharp barium outlines; no peristaltic blur.
- Technique checks (what contrast, density, soft tissue visibility, and artifacts to look for): Adequate penetration to visualize haustra and mucosal pattern.
- Clinical aim (when applicable, e.g., reflux, obstruction, displacement, etc.): Demonstrate overall bowel anatomy and contrast distribution.
Anterior Obliques (RAO / LAO)
CR Location & Positioning
- SID: 40 inches
- Patient position: 35–45° anterior oblique.
- Adjustments: For RAO, rotate right side toward table; for LAO, rotate left side toward table.
- CR: Perpendicular to IR at level of iliac crest and 1 inch lateral to midsagittal plane.
- Patient instructions: Suspend respiration on expiration.
- Exposure: On expiration.
Evaluation Criteria
- Coverage: Entire colon demonstrated.
- Rotation checks: Proper flexure open for the projection—RAO opens right colic (hepatic) flexure; LAO opens left colic (splenic) flexure.
- Motion checks: Clear mucosal pattern, no motion blur.
- Technique checks: Uniform contrast coating; no overexposure.
- Clinical aim: Demonstrate unobstructed views of both colic flexures.
Rationale: Anterior = Adjacent — each anterior oblique opens the same-side (adjacent) flexure: RAO → right (hepatic) and LAO → left (splenic), because the side down moves anteriorly, placing that flexure free of superimposition.
Posterior Obliques (RPO / LPO)
CR Location & Positioning
- SID: 40 inches
- Patient position: 35–45° posterior oblique.
- Adjustments: RPO demonstrates left colic (splenic) flexure; LPO demonstrates right colic (hepatic) flexure.
- CR: Perpendicular to IR at iliac crest and 1 inch lateral to midsagittal plane.
- Patient instructions: Suspend respiration on expiration.
- Exposure: On expiration.
Evaluation Criteria
- Coverage: Entire colon included.
- Rotation checks: Correct flexure open depending on position.
- Motion checks: No motion; mucosal detail visible.
- Technique checks: Adequate contrast density across colon.
- Clinical aim: Assess flexures not well seen on AP/PA images.
Rationale: Posterior = OP-posite — each posterior oblique opens the opposite flexure: RPO → left (splenic) and LPO → right (hepatic), because the side up moves anteriorly, bringing the opposite flexure into profile.
Left Lateral Rectum
CR Location & Positioning
- SID: 40 inches
- Patient position: Left lateral recumbent.
- Adjustments: Flex knees slightly; align midaxillary plane to IR.
- CR: Perpendicular to midaxillary line at level of ASIS.
- Patient instructions: Suspend respiration.
- Exposure: On expiration.
Evaluation Criteria
- Coverage: Rectum and distal sigmoid colon clearly demonstrated.
- Rotation checks: Posterior margins of pelvis superimposed.
- Motion checks: No motion blur in rectal region.
- Technique checks: Adequate soft tissue detail to evaluate rectal walls.
- Clinical aim: Evaluate rectal and distal sigmoid regions for strictures, polyps, or masses.
PA Axial (Billings Method)
CR Location & Positioning
- SID: 40 inches
- Patient position: Prone.
- Adjustments: MSP aligned to midline of table.
- CR: Angled 30–40° caudad, entering at level of ASIS and exiting at level of pubic symphysis.
- Patient instructions: Suspend respiration.
- Exposure: On expiration.
Evaluation Criteria
- Coverage: Rectosigmoid region elongated.
- Rotation checks: Pelvis not rotated; symmetric obturator foramina.
- Motion checks: No motion artifact.
- Technique checks: Uniform contrast with open rectosigmoid loop.
- Clinical aim: Elongate and visualize the sigmoid region free of overlap.
AP Axial (Billings Method)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine.
- Adjustments: MSP centered to table.
- CR: Angled 30–40° cephalad, entering 2 inches below ASIS at midline.
- Patient instructions: Suspend respiration.
- Exposure: On expiration.
Evaluation Criteria
- Coverage: Rectosigmoid region elongated.
- Rotation checks: No pelvic rotation.
- Motion checks: Clear, motion-free mucosal outlines.
- Technique checks: Correct angle to avoid superimposition of rectum and sigmoid loops.
- Clinical aim: Demonstrate the rectosigmoid area with minimal overlap.
Procedure Adaptation
- Double-contrast studies use high-density barium and room air to enhance mucosal detail, improving visualization of polyps and early neoplasms.
- Water-soluble iodinated contrast is used if perforation or recent biopsy is suspected.
- Pediatric studies for intussusception may also serve as a therapeutic reduction under controlled pressure.
- Geriatric patients require slower filling and careful monitoring of balloon inflation.
- Enema bag height must not exceed 24 inches above the table to prevent overfilling or perforation.
Exposure Factors & Technical Considerations
- SID: 40 inches
- kVp: 100–125 (single contrast); 90–100 (double contrast)
- mAs: Short exposure times, use fluoroscopy to monitor filling
- Contrast:
- Single contrast → thin barium sulfate
- Double contrast → high-density barium + room air
- Water-soluble iodinated contrast → suspected perforation cases
- Collimation: Large field to include entire colon
Memory Aids
- “Anterior = Adjacent, Posterior = OP-posite”
- Anterior obliques open the adjacent (same-side) flexure:
- RAO → Right (hepatic) flexure
- LAO → Left (splenic) flexure
- Posterior obliques open the OP-posite flexure:
- RPO → Left (splenic) flexure
- LPO → Right (hepatic) flexure
- Anterior obliques open the adjacent (same-side) flexure:
- “Billings Angles Straighten the Sigmoid”
- “Keep the Bag Below Two Feet” – 24 inches maximum to prevent overpressure.
- “Air + Barium = Mucosal Clarity” – Double contrast for fine detail.
Hows & Whys of Contrast Enemas
Anatomy
- How do you differentiate the large from the small intestine on images?
The large intestine shows haustra and a larger caliber arranged peripherally; the small bowel is more central with feathery plicae circulares. - Which flexure sits higher in the body?
The right (hepatic) flexure lies lower and right under the liver; the left (splenic) flexure lies higher and left under the spleen. - How can you identify the cecum and appendix on images?
The cecum appears as a pouch in the right lower quadrant below the ileocecal valve, and the appendix projects inferomedially from it. - How can you differentiate the sigmoid colon radiographically?
It is the most mobile portion of the colon, forming an S-shaped loop in the lower pelvis; it often requires angulation or oblique positioning to project free of overlap.
Positioning
- Why is the PA (prone) projection preferred over AP for overview images?
Prone positioning gently compresses the abdomen, separates overlapping loops, and spreads contrast for a clearer mucosal survey. - Why is respiration suspended on expiration for all overhead images?
Expiration lowers the diaphragm and reduces motion, improving abdominal contrast and decreasing lung superimposition over the upper colon. - Why use the Sims position for rectal tip insertion?
It relaxes abdominal musculature and aligns the rectal canal for easier, safer insertion with less patient discomfort. - Why must the enema bag height not exceed 24 inches above the table?
Limiting hydrostatic pressure prevents painful overdistension, reflux, and reduces the risk of perforation. - Why are 35–45° obliques used for RAO/LAO and RPO/LPO?
This rotation swings a target flexure away from the spine and overlapping colon, opening the jointed bend for unobstructed visualization. - Which does flexures are opened by anterior oblique projections?
Anterior obliques open the same-side (adjacent) flexure (RAO → right/hepatic; LAO → left/splenic) - Which does flexures are opened by posterior oblique projections?
Posterior obliques open the opposite flexure (RPO → left/splenic; LPO → right/hepatic). - Why center at the level of the iliac crest for most overheads?
The iliac crest approximates mid-colon height, balancing inclusion of the transverse colon above and sigmoid/rectum below on a single film. - Why perform a left lateral rectum projection?
A true lateral removes pelvic overlap, depicting rectal walls and distal sigmoid for strictures, masses, and ulceration. - Why use a 30–40° caudad angle for the PA axial (Billings)?
Caudad angulation elongates the rectosigmoid loop and prevents self-superimposition, revealing mucosal detail without overlap. - Why use a 30–40° cephalad angle for the AP axial (Billings)?
Cephalad angulation achieves the same rectosigmoid elongation from the supine approach when PA positioning isn’t feasible. - Why roll the patient during a double-contrast exam?
Systematic rolling coats the mucosa with high-density barium while air distends the lumen, maximizing surface contrast and lesion conspicuity. - Why might you choose PA decubitus views in a double-contrast exam (if performed)?
Decubitus with horizontal beam highlights air–barium levels and demonstrates dependent vs nondependent wall coating for subtle polyps.
Technique & Image Evaluation
- How do you confirm correct obliquity on oblique images?
The target flexure is open and free of overlapping transverse/descending/ascending colon; On anterior obliques excessive overlap means under-rotation, separation beyond expected means over-rotation. On posterior obliques, if the flexure remains overlapped by the transverse colon, increase rotation slightly. - How can you tell the PA axial (Billings) angle is appropriate?
The rectosigmoid is elongated with minimal self-overlap; too little angle leaves stacked loops, too much angle foreshortens and pushes anatomy off field. - How can you tell the AP axial (Billings) angle is appropriate?
The rectosigmoid appears straightened and centered; under-angulation shows persistent overlap, over-angulation projects the segment too cephalad. - How do you verify a true left lateral rectum?
Posterior margins of the ischia/ilia are superimposed and rectal walls are crisp; posterior cortical separation signals rotation. - How do you confirm adequate mucosal coating in a double-contrast exam?
A thin, even barium layer outlines haustra and mucosal relief while air distends the lumen; pooling or heavy clumps indicate suboptimal coating. - How do you judge adequate distension without overinsufflation?
Haustra are visible and walls are taut but not smoothened flat; excessive air effaces haustra and can cause patient discomfort. - How do you confirm full coverage on overview images?
Cecum (with appendix region), both colic flexures, transverse colon, descending colon, sigmoid, and rectum are included; if not, add focused spot or additional overheads. - How do you detect motion or peristaltic blur?
Indistinct mucosal edges or smeared barium menisci suggest motion; repeat with shorter exposure and reinforced breath-hold. - How do you confirm appropriate exposure?
Trabecular pattern of pelvis and clear barium–air interfaces are visible without burn-out; adjust kVp (lower for double contrast) to emphasize mucosa.
Clinical Applications
- Why is double contrast often preferred for screening?
High-density barium plus air reveals fine mucosal changes, improving detection of small polyps and early neoplasia. - Why use water-soluble iodinated contrast with suspected perforation or recent biopsy?
Iodinated contrast can be absorbed if it leaks; barium leakage requires surgical management. - Why can pediatric intussusception sometimes be reduced during BE?
The controlled hydrostatic or pneumatic pressure can unfold the telescoped bowel under real-time fluoroscopic monitoring. - Why communicate continuously during filling and positioning?
Patient feedback helps prevent overdistension, reduces spasm, and decreases motion—improving safety and image quality simultaneously. - Why document time, bag height, and contrast type for quality/safety?
These parameters directly affect pressure, coating, and diagnostic yield, and are essential for reproducibility and post-procedure review.
