Head computed tomography (CT) is a non-invasive imaging diagnostic technique that combines X-ray and computer analysis to produce three-dimensional images of the brain. It is primarily used to evaluate intracranial structural abnormalities, including hemorrhage, tumors, trauma, or vascular anomalies. This examination can quickly provide high-resolution anatomical information and is commonly used for initial assessment of emergency trauma patients or for follow-up in suspected neurological diseases.
The advantages of head CT include short operation time, high image resolution, and the ability to immediately display the relative positions of bones and soft tissues. However, its radiation exposure is higher than that of plain X-ray imaging, so benefits and risks should be weighed based on clinical needs. Patients are required to remove metal objects before the scan, and whether contrast agents are needed depends on the type of examination.
Head CT is divided into two main types: "non-contrast" and "contrast-enhanced." Non-contrast scans use direct X-ray imaging to evaluate fractures, hemorrhages, or extensive tissue damage. Contrast-enhanced scans involve intravenous injection of iodine-based contrast agents to enhance visualization of blood vessels, tumors, or infectious lesions. Mechanistically, X-rays penetrate the head and are received by detectors, with the data converted into cross-sectional images by a computer.
Newer equipment such as 64-slice or dual-source CT can shorten scan times and improve accuracy of dynamic lesions. 3D reconstruction techniques can further rebuild vascular pathways or skull structures, aiding surgical planning. During the procedure, patients need to remain still; in some cases, sedation may be used to assist children or anxious patients.
Common indications for head CT include:
Other applications include:
The examination takes approximately 5-15 minutes. Patients need to lie flat in the scanner and remain still. The type of contrast agent used requires allergy testing beforehand; typically, iodine-based contrast agents (such as iodixanol or iohexol) are used, with doses calculated based on body weight—about 70-100ml for adults per single administration. Special cases, such as pediatric patients, may require dose adjustments or sedation.
Scan parameters are adjusted according to the purpose of the examination:
The key advantages of head CT include:
In emergency medical situations, CT can diagnose intracranial hemorrhage immediately, directly influencing treatment decisions. Its images can quantify lesion size and the extent of surrounding tissue invasion, assisting physicians in determining the necessity of surgery or response to medication. Multi-phase scanning techniques can also track blood flow dynamics, improving the accuracy of lesion characterization.
Main risks include:
Serious complications include: Rare contrast allergy shock (occurrence rate <0.1%), long-term carcinogenic risk (especially with repeated scans), and psychological anxiety in claustrophobic patients. Special populations such as pregnant women should weigh the necessity of the examination against fetal risks.
Absolute contraindications: Known severe allergy to contrast agents or patients with acute renal failure requiring contrast injection. Relative contraindications include:
Before the examination, inform the doctor of:
Contrast agents may interact with certain medications:
Regarding interactions with radiotherapy, repeated CT scans can accumulate radiation dose; unnecessary repeats should be avoided. Follow-up scans after radiotherapy should consider tissue repair phases to avoid misinterpretation of images.
Head CT has a diagnostic accuracy of over 95% for acute intracranial hemorrhage, with sensitivity for subarachnoid hemorrhage reaching 85-90%. The accuracy for diagnosing cerebral aneurysms is approximately 70-80%, often serving as a preliminary screening tool for vascular imaging.
Compared to MRI, CT has clear advantages in emergency settings, capable of completing scans within 15 minutes, whereas MRI takes 30-60 minutes. It is superior in displaying calcified lesions or bone abnormalities. Large studies have confirmed that head CT can shorten decision times for thrombolytic therapy in acute stroke patients, significantly improving prognosis.
Alternative examinations include:
Ultrasound is suitable for infants with open fontanelles but has limited diagnostic value for adult brain lesions. PET-CT is used for tumor staging but is more costly. The choice of alternatives should consider lesion type, patient physiological status, and available medical equipment.
Before a head CT scan, fasting for 4-6 hours is usually required, and metal objects on the head (such as hairpins or accessories) should be removed. Patients should inform medical staff if they have a history of allergy to contrast agents or pregnancy. If sedation is needed due to anxiety, accompanying personnel should be arranged as per medical advice.
Will the procedure cause discomfort?The scan itself is painless, but patients need to keep their head still for about 10-15 minutes. Some may feel discomfort due to claustrophobia or noise from the machine. If unable to cooperate, discuss with the doctor about using mild sedatives or adjusting scan parameters to ease anxiety.
Is dizziness after the scan normal?The scan itself does not cause dizziness. If dizziness occurs afterward, it may be due to prolonged lying during the scan or a temporary reaction to contrast agents. Resting for 10-15 minutes before activity is recommended. If symptoms persist, seek immediate medical evaluation.
Does abnormal scan result require immediate treatment?Abnormal findings should be interpreted in conjunction with clinical symptoms and medical history. For example, cerebellar atrophy may be age-related, while sudden intracranial hemorrhage requires urgent intervention. The doctor will decide on follow-up or referral based on imaging features and patient condition.
How often should head CT be repeated?The frequency depends on diagnostic needs. For example, monitoring brain tumor size may be every 3-6 months, while post-trauma scans are adjusted based on symptom changes. Physicians will balance diagnostic necessity with radiation exposure risk, aiming to use lower-dose alternatives like MRI whenever possible.
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