Plain radiography and barium studies
Plain abdominal radiography has very limited diagnostic value. The main indication for its use is the initial evaluation of patients with an acute presentation when bowel obstruction or wall perforation is suspected. When searching for free gas under the right hemidiaphragm, a standing chest X-ray is more informative.
Traditional barium contrast studies remain cost-effective, but are gradually becoming obsolete. Their main advantage is high spatial resolution, providing excellent mucosal detail. There are two main methods:
- Barium follow-through — the patient drinks a large volume of barium suspension or a water-soluble contrast agent.
- Enteroclysis — administration of contrast under pressure via a nasojejunal tube for better control over bowel distension.
For maximal contouring of the mucosal folds, double contrast is used — the introduction of air following barium. However, current consensus states that the diagnostic value of the method often does not justify the radiation exposure received by the patient.
Computed tomography (CT)
CT plays a leading role in the assessment of intramural and extramural lesions, as well as the state of the mesentery. Intravenous contrast enhancement is mandatory for a complete examination. Maximum mucosal enhancement (enteric phase) is achieved approximately 50 seconds after injection (or 14 seconds after the aortic peak).
CT enterography involves the rapid oral intake of large volumes of neutral-density fluid (0–30 HU). These include water, milk, polyethylene glycol (PEG) solutions, and low-density barium (VoLumen).
- Neutral and negative agents are best suited for examining the mucosa and assessing bowel wall enhancement.
- PEG solutions provide sustained luminal distension as they are not absorbed, but they may cause cramps.
- Positive contrast agents (iodine, high-density barium) are used mainly to search for abscesses and perforations.
CT enteroclysis differs in that the contrast (up to 2 liters) is administered directly through a tube using a pump (at a rate of up to 150–200 mL/s). Anti-peristaltic drugs are administered to the patient to induce an artificial ileus. Although this method provides ideal loop distension, CT enterography is much better tolerated by patients with comparable diagnostic accuracy.
Ultrasound and Magnetic resonance imaging
Ultrasound (US) involves no ionizing radiation, making it indispensable for young patients requiring frequent monitoring (e.g., in Crohn's disease). The use of high-frequency transducers (5–17 MHz) provides excellent resolution of the bowel wall. Color Doppler and contrast-enhanced ultrasound (CEUS) allow for the assessment of vascularization, reflecting inflammation activity. The method is highly operator-dependent.
Magnetic resonance imaging (MRI) provides superior soft-tissue contrast and 3D visualization. High-quality MRI requires homogeneous luminal contrast and dynamic intravenous enhancement. Of particular value are high-temporal-resolution cine sequences (cine sequences). They allow real-time observation of peristalsis and help differentiate temporary spasm from true fibrotic stricture. To detect small tumors, T1-weighted gadolinium-enhanced images with fat suppression are the most sensitive.
Angiography and radionuclide methods
In acute gastrointestinal bleeding, angiography can visualize the source if blood loss exceeds 0.5 mL/min. Since slower bleeding is often intermittent, angiography may yield false-negative results. It is important to avoid oral positive contrast agents prior to angiography.
Radionuclide imaging is indispensable in complex diagnostic cases:
- Red blood cell scintigraphy detects minor and intermittent bleeding.
- Technetium-99m pertechnetate scintigraphy is the best method for detecting a Meckel's diverticulum with ectopic gastric mucosa.
- 111In-octreotide scintigraphy is used to search for carcinoid tumors.
- Fluorodeoxyglucose PET/CT (FDG-PET) is effective in oncology and for assessing the activity of inflammatory bowel disease.
For selecting oral contrast in CT: Neutral (water/PEG) — to examine the bowel wall and mucosa itself. Positive (iodine/barium) — to find a "hole" (perforation) or an abscess.
Class and exam questions
Which is better for detecting free gas when perforation is suspected?
Standing chest X-ray. It is significantly more informative than a standard plain abdominal radiograph.
What is the fundamental difference between enterography and enteroclysis?
In enterography, the patient drinks the contrast agent independently. In enteroclysis, the fluid is administered under pressure via a special nasojejunal tube for maximal distension of the bowel lumen.
Why is oral barium or iodine not allowed before emergency angiography?
Positive contrast in the intestinal lumen will create dense artifacts on images, which will obscure the vascular pattern and prevent visualization of contrast extravasation from the injured vessel.
What else to study on this topic
- Specifics of using polyethylene glycol (PEG)-based preparations and additives (methylcellulose, locust bean gum)
- Protocols for dynamic motility assessment on MRI (cine sequences)
- Application of contrast-enhanced ultrasound (CEUS) in Crohn's disease
- Specifics of detecting Meckel's diverticulum using pertechnetate scintigraphy
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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