15.1 Gastrointestinal Contrast Procedures (Esophagram, UGI, Small Bowel, Barium Enema)

15.1 Gastrointestinal Contrast Procedures

Fluoroscopic examinations of the gastrointestinal (GI) tract rely on radiopaque contrast media to visualize mucosal patterns, luminal patency, sphincteric competence, motility, and anatomical anomalies. Radiologic technologists must master contrast agent properties, patient positioning mechanics, dynamic swallow maneuvers, and precise projection angles to achieve high-diagnostic-yield examinations while minimizing radiation exposure.

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Contrast Media Selection for GI Studies

Contrast agents utilized in gastrointestinal radiography fall into two primary chemical categories: insoluble barium sulfate suspensions and water-soluble iodinated compounds.

1. Barium Sulfate (${\ ext{BaSO}}_4$)

• Chemical Nature: An insoluble inorganic salt possessing a high atomic number ($Z = 56$), rendering it radiopaque to diagnostic X-ray beams.
• Suspension Viscosity:
  • Thick Barium: Formulated with a 3:1 to 4:1 ratio of barium powder to water. Creates a thick, viscous paste designed to adhere to mucosal walls. It flows slowly, making it ideal for double-contrast stomach studies and detailed esophageal coating.
  • Thin Barium: Formulated with a 1:1 ratio of barium powder to water. Flows rapidly through the GI lumen, making it suitable for outlining single-contrast contours, small bowel follow-through procedures, and lower GI colon studies.
• Toxicity & Safety: Inert and non-toxic when contained strictly within the gastrointestinal lumen. However, if barium leaks into the peritoneal or mediastinal cavities, it cannot be absorbed by tissue. Peritoneal barium leakage leads to severe granulomatous inflammation, adhesions, and potentially fatal barium peritonitis.

2. Water-Soluble Iodinated Contrast Media

• Primary Agents: Diatrizoate meglumine and diatrizoate sodium compounds (commercially known as Gastrografin or Gastroview).
• Absolute Indications: Indicated whenever there is a suspected perforation, visceral rupture, presurgical evaluation of suspected bowel wall tears, or evaluation of postoperative anastomotic leaks.
• Physiologic Considerations & Cautions: These hyperosmolar agents draw intravascular fluid into the bowel lumen via osmotic pressure, causing rapid bowel transit and potential systemic dehydration or hypovolemia in pediatric and elderly patients. Furthermore, if aspirated into the tracheobronchial tree, hyperosmolar iodinated agents can induce pulmonary edema and chemical pneumonitis. Non-ionic, low-osmolality contrast agents (such as iohexol) should be utilized if an esophagotracheal fistula or aspiration risk is suspected.

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1. Esophagram (Barium Swallow)

An esophagram (barium swallow) provides a dynamic fluoroscopic and static radiographic evaluation of the pharynx and esophagus from the hypopharynx down to the esophagogastric (EG) junction at the level of T11.

Indications & Clinical Goals

Common clinical indications include dysphagia (difficulty swallowing), odynophagia (painful swallowing), achalasia, esophageal strictures, anatomical diverticula (e.g., Zenker's diverticulum), foreign body impaction, gastroesophageal reflux disease (GERD), and esophageal varices.

Standard Radiographic Projections

1. Right Anterior Oblique (RAO 35°–40°):
   • Technical Rationale: The RAO is the single most vital projection of the esophagus. Rotating the patient 35° to 40° right anterior oblique projects the esophagus into the homogeneous tissue window located between the thoracic spine posteriorly and the heart/sternum anteriorly.
   • Central Ray (CR): Perpendicular to the Image Receptor (IR), centered to the mid-esophagus at the level of T5–T6 (2 to 3 inches inferior to the jugular notch).
2. Lateral Position:
   • Visualizes the entire esophagus in profile, demonstrating the retrocardiac space, the anterior wall, and posterior swallowing mechanics clear of the shoulder girdle.
3. AP / PA Position:
   • Outlines the esophagus from the lower neck down to the stomach, assessing mucosal symmetry, luminal caliber, and extrinsic indentations from the aortic arch and left main bronchus.

Dynamic Swallow Maneuvers

Specialized physiological maneuvers are performed during fluoroscopy to increase intra-abdominal pressure or demonstrate esophageal motility defects and reflux:

• Valsalva Maneuver: The patient takes a deep breath and bears down as if having a bowel movement against a closed glottis. This increases intrathoracic and intra-abdominal pressure, dilating the esophageal lumen and demonstrating esophageal varices or mucosal insufficiency.
• Mueller Maneuver: The patient attempts forced inspiration against a closed airway after full expiration. Used to differentiate vascular rings from mucosal lesions.
• Water Siphon Test (Water Test): Performed with the patient in a slightly head-down (Trendelenburg) or LPO position while drinking a cup of water through a straw under fluoroscopy to confirm active gastroesophageal reflux.
• Toe-Touch Maneuver: The patient bends forward at the waist to touch their toes. This posture increases intra-abdominal pressure, effectively forcing barium upward to demonstrate hiatal hernias and incompetence of the cardiac sphincter.

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2. Upper Gastrointestinal (UGI) Series

The Upper GI series evaluates the distal esophagus, stomach, and duodenal loop.

Patient Preparation

Strict NPO (nothing by mouth) for at least 8 hours prior to the procedure. Smoking and chewing gum are prohibited on the morning of the exam to prevent excess gastric juice secretion, which thins the barium coating.

Single-Contrast vs. Double-Contrast UGI

• Single-Contrast UGI: The stomach is filled completely with thin barium suspension to evaluate gross stomach contours, organ motility, gastric wall flexibility, filling defects, and major mass lesions.
• Double-Contrast UGI: Employs a dense thick barium suspension combined with gas-producing effervescent granules (containing sodium bicarbonate and citric acid). As the granules dissolve in gastric secretions, they release carbon dioxide (${\ ext{CO}}_2$) gas. The gas distends the gastric walls while thick barium paints the mucosal surface, providing high-resolution visualization of fine rugal folds, early mucosal erosions, and gastric polyps.

Gastrointestinal Positioning & Barium Distribution Rules

Understanding how gravity dictates contrast displacement in the stomach is mandatory for board examinations. Because barium sulfate has a high specific gravity, it always settles into the dependent (lowest) anatomical structures, while air or gas rises to non-dependent (highest) structures.

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3. Small Bowel Follow-Through (SBFT)

The Small Bowel Follow-Through investigates the functional motility and anatomical mucosal structure of the small intestine (duodenum, jejunum, and ileum).

Procedure Protocols

• Combined UGI / SBFT: Initiated immediately after an Upper GI series by giving the patient an additional 16 oz of thin barium suspension.
• Standalone SBFT: The patient drinks two glassfuls of thin barium after a preliminary scout abdominal radiograph (KUB).

Timing & Radiographic Intervals

1. Initial Radiograph (15 Minutes): Center the Central Ray higher (at the level of L1-L2, about 2 inches above the iliac crest) to include the stomach and proximal jejunum.
2. Intermediate Radiographs (30 and 60 Minutes): Center the CR at the iliac crest (L4-L5). Subsequent exposures are taken at 15- to 30-minute intervals during the first hour.
3. Delayed Radiographs (Every 30–60 Minutes): Continued until the barium column reaches the ileocecal valve and enters the cecum, which typically occurs within 2 to 3 hours in healthy patients.
4. Terminal Ileum Fluoroscopy: Once barium enters the cecum, fluoroscopic spot images are acquired using a compression paddle. Applying localized compression separates overlapping loops of the terminal ileum to visualize early signs of Crohn's disease or regional enteritis.

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4. Barium Enema (BE / Lower GI Series)

The Barium Enema evaluates the large intestine (colon and rectum).

Patient Preparation

The colon must be entirely cleansed of fecal material. Preparation involves a low-residue diet for 2 to 3 days, increased clear fluid intake, administration of saline cathartics (magnesium citrate or bisacodyl), and cleansing enemas on the morning of the exam.

Contrast Methodologies

• Single-Contrast BE: Uses a thin barium suspension ($15% - 25% \ ext{ w/v}$) inserted via an enema bag suspended no higher than 18 to 24 inches (45–60 cm) above the table top. Used to evaluate obstruction, volvulus, intussusception, or diverticulitis.
• Double-Contrast BE: Uses a high-density thick barium ($75% - 95% \ ext{ w/v}$) followed by controlled room air or ${\ ext{CO}}_2$ insufflation. Essential for identifying small mucosal polyps, early carcinomas, and inflammatory colitis.

Radiographic Projections & Angle Corrections

• AP / PA Projections: General survey of colon filling and overall anatomy centered to the iliac crests.
• RAO & LAO Obliques (35°–45°):
  • RAO: Opens the right colic (hepatic) flexure, ascending colon, and sigmoid colon clear of superimposition.
  • LAO: Opens the left colic (splenic) flexure and descending colon.
• LPO & RPO Obliques (35°–45°):
  • LPO: Opens the right colic (hepatic) flexure.
  • RPO: Opens the left colic (splenic) flexure.
• Chassard-Lapine Method (AP Axial):
  • Patient Posture: Patient sits on the edge of the table, leaning fully forward at the waist so the abdominal wall touches the thighs.
  • Alternative AP Axial Tube Angle: Angle CR 30° to 40° cephalad entering 2 inches inferior to the ASIS at the pubic symphysis (or 30° to 40° caudad for PA axial) to uncoil and elongate overlapping loops of the rectosigmoid junction.
• Right & Left Lateral Decubitus (Double-Contrast):
  • Right Lateral Decubitus: Demonstrates the medial wall of the ascending colon and the lateral wall of the descending colon filled with air.
  • Left Lateral Decubitus: Demonstrates the lateral wall of the ascending colon and the medial wall of the descending colon filled with air.