Evolution of methods: from X-ray to tomography
Plain abdominal radiography has limited utility today. It is primarily used in the initial evaluation of patients with acute symptoms when perforation or intestinal obstruction is suspected. Notably, an erect chest x-ray is often more informative for detecting free air under the diaphragm.
Barium-based X-ray studies provide high spatial resolution and good mucosal detail. There are two main methods:
- Follow-through study — oral administration of a large volume of barium or a water-soluble agent.
- Enteroclysis (enteroclysis) — nasointestinal intubation and contrast administration under pressure. Double-contrast enteroclysis with air provides excellent detail.
However, these methods involve radiation exposure, and their diagnostic yield often does not justify the risks. Therefore, in non-emergency situations, they have been almost entirely replaced by CT and MR enterography. Barium studies remain cost-effective only when modern tomographs are unavailable.
Principles of CT enterography
Computed tomography plays a key role in evaluating intramural and extramural lesions, as well as mesenteric involvement. Intravenous contrast enhancement is mandatory. The enteral phase, characterized by peak mucosal enhancement, occurs approximately 50 seconds after injection (or 14 seconds after the aortic peak).
Large volumes of neutral oral contrast agents (density 0–30 HU) are used for detailed study of the bowel wall:
- Polyethylene glycol (PEG)-based preparations — less absorbed, but more frequently cause cramps.
- 0.1% low-density barium sulfate solution (VoLumen).
- Simple liquids (water, milk).
Neutral contrast is optimal for evaluating the pattern of bowel wall enhancement. Positive contrast (iodinated or high-density barium) is primarily used when perforation, abscess, or extramural pathology is suspected.
Diagnosis of vascular diseases
Multislice computed tomography (MSCT) is the primary method for diagnosing acute mesenteric ischemia. For a high-quality study, water is used as an oral agent, combined with rapid intravenous bolus injection and dual-phase scanning.
CT semiotics in acute mesenteric ischemia depend on its type:
- Acute transmural infarction: wall thinning, bowel dilation, absence of contrast enhancement. Pneumatosis intestinalis and portal venous gas serve as reliable signs of infarction.
- Non-occlusive ischemia: wall thickening and mucosal hyperenhancement.
- Mesenteric venous thrombosis: marked wall thickening, mesenteric stranding, vascular engorgement, and ascites.
Cardioembolic etiology of ischemia should be suspected in cases of parenchymal organ infarctions and a history of atrial fibrillation. Systemic vasculitis should be considered in young patients with ischemia, atypical lesion locations, and the presence of aneurysms (e.g., in polyarteritis nodosa).
In addition, multiphase MSCT angiography plays an undeniable role in diagnosing obscure gastrointestinal bleeding, providing navigation for interventional radiology (selective catheterization and embolization).
MRI capabilities in special clinical situations
Magnetic resonance imaging has significant advantages due to the absence of ionizing radiation. For example, MRI is a safe and informative method for diagnosing small bowel obstruction in pregnant patients. Using specific sequences (such as true fast imaging with steady-state precession) on coronal slices, small bowel loop dilation, the transition zone, and the direct cause of obstruction — intra-abdominal adhesions — are clearly visualized.
Class and exam questions
Why are CT and MRI replacing barium X-rays?
Tomography makes it possible to evaluate not only the lumen, but also the bowel wall itself, the mesentery, and adjacent organs. Traditional X-ray provides less information about extramural changes, and its radiation dose is often unjustified by its diagnostic yield.
Why do patients drink water or a special liquid before tomography?
This is a neutral contrast agent (e.g., PEG or water). It adequately distends the bowel loops without causing high signal ("brightening") on the scan, allowing the physician to examine wall thickness in detail and assess mucosal disorders.
Can an intestinal MRI be performed during pregnancy?
Yes. In acute clinical settings (such as intestinal obstruction), MRI safely identifies adhesions, loop dilation, and the transition zone without radiation exposure to the fetus.
What is the enteral phase in CT?
This is the time point (approximately 50 seconds after intravenous contrast injection) when the small bowel mucosa reaches peak enhancement.
What else to study on this topic
- Technique of nasointestinal intubation and double-contrast enteroclysis
- Differential diagnosis of the causes of pneumatosis intestinalis (ischemic and non-ischemic conditions)
- Features of PEG preparation use and their impact on visualization quality
- The role of interventional radiology in bowel vessel embolization
- Manifestations of systemic lupus erythematosus in the intestine: serositis, ascites, and lymphadenopathy
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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