Abdominal computed tomography (Abdominal CT scan) is a non-invasive imaging technique that uses X-ray and computer synthesis principles to produce three-dimensional cross-sectional images of abdominal organs. This examination is mainly used to assess structural abnormalities within the abdominal cavity, such as tumors, inflammation, bleeding, or organ injuries, and is commonly employed in emergency and outpatient diagnostic processes. Compared to traditional X-rays, CT scans provide higher-resolution anatomical information, assisting physicians in accurately locating lesions and determining their extent.
The procedure typically takes 30 minutes to an hour, during which the patient must lie flat and remove metal objects. In some cases, contrast agents are injected to enhance the visibility of blood vessels or specific organs. This technique, combining high resolution and rapid imaging, has become the preferred diagnostic tool for diseases of the liver, pancreas, kidneys, and other organs.
Abdominal CT scans are divided into "non-contrast" and "contrast-enhanced" types. Non-contrast scans utilize differences in X-ray absorption by various tissues in the abdomen to generate basic images; contrast-enhanced scans are performed after intravenous injection of contrast agents to make blood vessels and abnormal tissues more clearly visible. The scanner rotates in a spiral manner, capturing multiple layers of images per second, which are then integrated by a computer into a three-dimensional model.
The diagnostic mechanism relies on differences in tissue X-ray absorption coefficients: fat tissue absorbs less and appears black, bones absorb more and appear white, while organs and lesions show varying shades of gray, revealing tumors, edema, or hemorrhage. Dynamic scanning capabilities further allow observation of organ function changes, such as hepatic blood perfusion.
Mainly used for suspected abdominal emergencies, such as acute abdominal pain, internal bleeding, or trauma assessment. Common applications include:
It is also used for cancer staging, such as determining the extent of liver or peritoneal metastasis from colorectal cancer. In emergency settings, CT scans can quickly screen for life-threatening conditions like bowel strangulation, acute pancreatitis, or liver and spleen rupture, making it a critical examination in emergency departments.
Fasting for 4-6 hours before the scan is required, and oral contrast agents may be administered to enhance intestinal outline. The contrast dose is calculated based on body weight, with adults typically receiving 100-150ml of iodine-based contrast intravenously. During the scan, the patient must remain in a fixed position, with the scan covering from the diaphragm to the pelvis.
Contrast-enhanced scans are performed in three phases: arterial, portal venous, and delayed phases, with intervals of several minutes to track the dynamic distribution of contrast agents. The radiation dose is approximately 2-5 mSv, equivalent to the total natural background radiation exposure over 1-2 years, but the diagnostic value in suspected emergency cases far outweighs the radiation risk.
The key advantages of CT scans include:
Compared to ultrasound, which is limited by gas or bone interference, CT can clearly visualize retroperitoneal tissues and vascular structures. In diagnosing liver or kidney cancers, CT sensitivity exceeds 90%, effectively distinguishing benign from malignant lesions.
Main risks include:
Severe contraindications include: Pregnant women (embryonic development is more sensitive to radiation), and patients with severe renal failure (contrast agents may cause nephrogenic systemic fibrosis). A few patients may experience issues due to claustrophobia or obesity affecting scan quality.
Before the scan, inform medical staff of:
Contraindications include:
CT scans do not directly interact with medications, but contrast agents may affect subsequent blood tests (e.g., renal function tests). It is recommended to delay blood electrolyte tests for 24 hours after contrast injection. In diagnostic workflows, CT is often complemented by ultrasound, MRI, or PET-CT: ultrasound for initial screening, CT for precise localization, and MRI for soft tissue analysis. Combining these modalities can improve diagnostic accuracy.
Radiation medicine studies show that CT has a diagnostic accuracy of 85-95% for abdominal emergencies. For hepatocellular carcinoma, the combined arterial and delayed phase scans have a specificity of up to 92%. Multicenter studies indicate that CT detects lesions in acute abdominal pain patients 3-5 times more frequently than traditional X-rays.
For kidney stones, CT sensitivity reaches 98%, accurately distinguishing urinary calculi from other calcified lesions. Clinical guidelines recommend CT as the first-line examination for suspected abdominal aortic aneurysm, accurately determining tumor size and vascular invasion.
Ultrasound without contrast agents is suitable for initial screening but limited by bowel gas or body habitus. Magnetic resonance imaging (MRI) offers better soft tissue resolution than CT but requires longer examination times and is not suitable for patients with metal implants. Abdominal X-ray can quickly screen for bowel obstruction or free air but has lower resolution. PET-CT combines metabolic activity analysis but is costly and cannot replace CT for structural diagnosis. The choice depends on specific clinical scenarios.
Before the examination, medical staff usually require fasting for 4-6 hours and avoiding caffeinated drinks. If contrast agents are to be injected, inform the doctor of any allergies, kidney function issues, or diabetes to assess risks. Remove metal objects and wear metal-free clothing, and inform if pregnant or possibly pregnant.
What side effects may occur after using contrast agents in an abdominal CT scan? How to handle them?Some patients may experience skin flushing, dizziness, or allergic reactions after contrast injection; severe cases may cause breathing difficulties, requiring immediate notification of medical staff for antihistamines. If contrast is administered rectally, some may feel bloated or urge to defecate; walking around after the scan can help relieve discomfort. Drinking plenty of water post-examination aids in metabolizing the contrast.
How soon can normal activities resume after the examination? Are there any special precautions?If no sedatives are used, most patients can resume normal activities immediately. If contrast agents were used, it is recommended to rest for 2-4 hours afterward and avoid driving or operating machinery. Patients with kidney issues should follow medical advice to increase fluid intake and have regular follow-up tests for renal function.
Why are some abdominal CT scans performed in stages?Staged scans (such as before and after contrast injection) allow observation of vascular perfusion and dynamic changes in lesions, aiding in distinguishing benign from malignant tumors or assessing vascular abnormalities. For example, initial baseline scans followed by immediate post-contrast scans provide more precise visualization of blood flow and lesion extent.
How are treatment plans determined when abnormal results are found in abdominal CT?Results should be evaluated in conjunction with clinical symptoms and other tests by radiologists and specialists. If tumors or abnormal tissues are detected, further procedures like biopsy or functional imaging (e.g., PET-CT) may be arranged. Treatment strategies are formulated based on lesion nature, overall health, and cancer staging, including surgery, chemotherapy, or radiotherapy.
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