Computed Tomography (CT) is a non-invasive imaging diagnostic technique that uses X-rays and computer processing to generate three-dimensional cross-sectional images of human organs and tissues. Its primary purpose is to accurately diagnose the location, morphology, and extent of lesions, and it is commonly used in emergency situations, preoperative assessments, and cancer follow-up scenarios.
CT scans can quickly provide high-resolution images of anatomical structures, especially in emergency settings where they can immediately identify bleeding, fractures, or organ damage. Compared to traditional X-rays, CT can integrate data from different angles to form three-dimensional views, helping physicians to plan more precise treatments.
CT scans are mainly divided into three types: standard CT, spiral (helical) CT, and low-dose CT. Spiral CT uses continuous movement of the scanning bed and X-ray equipment to shorten examination time and reduce motion blur of dynamic organs such as the lungs. Enhanced CT with iodine contrast agents can highlight blood vessels, tumors, or inflammatory tissues.
The operating principle involves collecting X-ray data from multiple angles, which are then reconstructed by computer algorithms into thin-layer image slices, subsequently assembled into a three-dimensional model. Contrast agents absorb X-rays at different wavelengths, making specific tissues appear with different densities in the images, aiding physicians in identifying lesion characteristics.
CT scans are suitable for various clinical needs, including:
Additionally, CT plays a critical role in tumor treatment evaluation, preoperative planning, and emergency classification (such as differentiating stroke or abdominal pain causes).
Before the scan, metal objects should be removed, and some examinations require fasting or water intake to fill the stomach and intestines. When using contrast agents, allergy testing and renal function assessment are necessary beforehand. The scan duration is approximately 5 to 30 minutes, depending on the scope and equipment efficiency.
X-ray radiation dose varies by the scanned area; head scans typically involve about 2-4 mSv, while abdominal scans may reach 5-10 mSv. Low-dose CT techniques can reduce radiation exposure by 30%-50%, especially suitable for patients requiring repeated scans.
The core advantages of CT include:
Its non-invasive nature makes it a standard procedure for preoperative assessment, especially in emergency settings where it can effectively shorten decision-making time. Three-dimensional reconstruction also assists physicians in planning complex surgical pathways.
Main risks include:
Children should have dosage adjusted according to weight, pregnant women should avoid unnecessary scans, and special patients require renal function evaluation before contrast use.
Contraindications include severe renal failure, history of severe iodine contrast allergy, and uncontrolled thyroid dysfunction. Patients should inform their doctor of pregnancy possibility, cardiac or renal history, and allergies before the scan.
During the procedure, patients need to remain still; restless patients may require sedation. Diabetic patients using contrast agents should adjust their hypoglycemic medications beforehand, and increase hydration post-scan to promote contrast excretion.
CT and MRI are often used complementarily: MRI excels at soft tissue resolution but takes longer, while CT is faster for diagnosing fractures or bleeding in emergencies. Compared to ultrasound, CT is unaffected by gas or bone interference, making it suitable for lung or pelvic examinations.
In tumor treatment, CT can be combined with positron emission tomography (PET-CT) to improve lesion localization accuracy. Post-examination treatment decisions may also incorporate blood tests or biopsy results, forming a multimodal diagnostic system.
Multiple studies show that CT has a sensitivity of over 90% for detecting pulmonary nodules and an accuracy of over 95% for diagnosing cerebral hemorrhage. In emergency chest pain assessment, CT coronary angiography can accurately exclude acute conditions such as aortic dissection.
Clinical guidelines recommend low-dose CT for lung cancer screening in heavy smokers, which can reduce lung cancer mortality by 20%. In liver cancer staging, CT arterial phase scans can accurately assess tumor vascular supply, influencing treatment strategies in 70% of cases.
Alternative techniques include:
Choosing alternatives depends on the lesion type, patient condition, and available resources. MRI is advantageous for brain and spinal cord examinations, while ultrasound is often used as a first-line rapid screening tool.
What preparations are needed before a CT scan?
Before the examination, healthcare providers will give specific instructions based on the scanned area, such as fasting for 4-6 hours for abdominal or pelvic scans, or drinking a particular contrast agent to enhance image clarity. If iodine contrast is to be injected, inform your doctor of any allergies or kidney issues; they will assess the risks and adjust the plan accordingly.
How is radiation exposure risk managed in CT scans?
Although CT involves radiation, modern equipment has optimized dose control techniques, and the medical team follows the "ALARA" principle (As Low As Reasonably Achievable). For children or those requiring repeated scans, the necessity is carefully evaluated, and appropriate scan ranges are used to reduce long-term risks.
Can people with chronic kidney disease undergo contrast-enhanced scans?
Since iodine contrast agents can affect kidney function, patients with chronic kidney disease should have renal function tests before the scan. The doctor may adjust the dose or postpone the scan to ensure safety. Post-scan, increasing hydration and following medical advice can help reduce the risk of acute kidney injury.
How soon can normal activities be resumed after the scan?
Most patients can resume daily activities immediately after the scan. However, if sedatives or contrast agents cause mild discomfort such as dizziness, resting for a few hours before driving or engaging in detailed work is recommended. For complex brain or cardiac scans, the healthcare team will provide individual instructions based on the results.
What are the criteria for choosing between CT and MRI?
CT is preferred for rapid high-resolution imaging suitable for emergency trauma, lung diseases, or quick diagnosis; MRI is more sensitive for soft tissue and neurological lesions but takes longer and can be affected by metal implants. The physician will select the most appropriate modality based on symptom severity, organ location, and patient health status.
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