Imaging Studies III: Gastrointestinal Motility Studies and Virtual Colonoscopy

Gastric emptying studies assess how quickly food moves from the stomach into the small intestine. Patients ingest a meal containing a radioactive tracer, typically technetium-99m sulfur colloid mixed with scrambled eggs. A scintiscanner tracks the tracer's movement to measure emptying rate and diagnose gastroparesis, a condition where stomach motility is impaired.

Colonic transit studies track the movement of radionuclide markers through the colon using abdominal X-rays taken every 24 hours over 4 to 5 days. Patients swallow a capsule containing approximately 20 markers and maintain normal activities. The time markers take to traverse the colon reveals colonic motility patterns, helping diagnose obstructive defecation syndromes and other motility disorders.

Bowel preparation ensures the colon is free of stool and gas, which can obstruct imaging and reduce accuracy. Patients follow a diet regimen and take laxatives similar to traditional colonoscopy preparation. This allows the CT scanner to obtain clear, detailed cross-sectional images of the colon's interior surface for detecting polyps, tumors, and other abnormalities.

During virtual colonoscopy, a thin flexible tube is inserted into the rectum to insufflate air or carbon dioxide, expanding the colon for better visualization. The patient lies on a specialized table and is moved into a CT scanner, which takes multiple X-ray images at various angles around the abdomen. These cross-sectional images provide detailed views of the colon's structure and interior surface.

Virtual colonoscopy, or CT colonography, is noninvasive and does not require advancing a colonoscope through the entire colon. Instead, it uses CT imaging after insufflating air or carbon dioxide into the colon. This less intrusive approach makes it a preferred option for many patients while still effectively detecting polyps, tumors, and other abnormalities.

Technetium-99m sulfur colloid is a radioactive tracer that readily binds to scrambled eggs, the solid component of the test meal. This allows the scintiscanner to detect and track the tracer's movement through the gastrointestinal tract. The radioactive marker provides clear imaging data to measure gastric emptying rate and diagnose motility disorders.

Gastrointestinal motility studies diagnose disorders including diabetic gastroparesis, where stomach motility is impaired causing delayed emptying, and dumping syndrome, where food passes too quickly from the stomach to the small intestine. Colonic transit studies detect obstructive defecation syndromes and chronic constipation. Virtual colonoscopy identifies polyps, tumors, and structural abnormalities of the colon and rectum.