Abdominal ultrasound is a non-invasive imaging diagnostic technique that uses high-frequency sound waves to generate real-time images of internal organs. Its primary purpose is to evaluate structural abnormalities or lesions in the liver, gallbladder, pancreas, kidneys, and other abdominal organs. Because it does not involve ionizing radiation and allows dynamic observation of organ function, it has become the preferred initial screening method for abdominal diseases.
The procedure must be performed by trained healthcare professionals. Patients usually do not require special preparation; however, fasting may be necessary for some examinations to reduce intestinal gas interference. The results can be compared immediately with clinical symptoms to assist physicians in developing treatment strategies.
Abdominal ultrasound is divided into general diagnostic and special contrast-enhanced types. The diagnostic type uses sound waves with a frequency of 2-5 MHz, transmitted through the skin, and reflected signals are received to form two-dimensional or three-dimensional images of organs. The contrast-enhanced type involves injecting a contrast agent containing microbubbles to enhance vascular imaging.
The biological mechanisms include mechanical effects and thermal effects of sound waves: mechanical effects cause slight vibrations in tissue cells to promote substance exchange, while thermal effects can regulate local blood flow. These properties make it useful as an adjunct in treatments such as cyst ablation or botulinum toxin injection localization.
Mainly used for solid organ lesions such as hepatic masses, gallstones, renal edema, and ascites. It has unique advantages in dynamic observation of pancreatic inflammatory changes and portal blood flow abnormalities, effectively assessing renal blood flow dynamics or portal hypertension in liver cirrhosis.
During the examination, the patient lies supine while the medical staff applies gel to the skin and moves the probe to scan. Diagnostic examinations typically take about 15-30 minutes, with contrast-enhanced types requiring an additional 10-15 minutes for contrast injection. The energy output is usually controlled below 1 W/cm² to ensure safety.
Therapeutic ultrasound parameters are adjusted based on the lesion. For example, in focused ultrasound ablation of liver tumors, sound wave intensity needs to reach 50-100 W/cm² with precise targeting. Physicians adjust frequency and scanning angles according to organ size and lesion depth.
The main advantages include real-time imaging feedback and immediate diagnostic capability, allowing dynamic observation of organ contraction and blood flow changes. Its lack of ionizing radiation makes it suitable for repeated examinations in pregnant women and children. Additionally, it is more cost-effective than CT or MRI, making it a routine outpatient screening tool.
The vast majority of patients experience only a cold or pressure sensation from contact with the probe, with severe complications being extremely rare. Contrast agents may cause allergic reactions, with an incidence of less than 0.01%. Long-term high-intensity therapeutic ultrasound may lead to tissue temperature rise, but modern equipment is equipped with temperature monitoring systems.
Key Precautions: Obese patients may experience degraded image quality due to sound wave attenuation. Metal implants should be disclosed before the examination to avoid potential magnetic interference.
Fasting before the examination is recommended to reduce intestinal gas interference. Pregnant women should undergo the procedure after medical evaluation. Contraindications include patients with pacemakers, open wounds at the examination site, and severe coagulation disorders.
There is no direct interaction with radiological examinations, but diagnostic results may influence subsequent treatment choices. For example, liver tumor localization can directly assist in surgery or radiofrequency ablation. Compared to MRI, ultrasound has advantages in evaluating fluid accumulation.
Patients on anticoagulant therapy should inform the medical staff before the examination to avoid bleeding that could affect imaging interpretation. The choice of imaging modality should be based on lesion characteristics; for example, endoscopic ultrasound is recommended for posterior pancreatic lesions.
The diagnostic accuracy exceeds 90% for hepatic solid lesions and is highly sensitive (up to 98%) for gallstones. Doppler ultrasound can accurately measure blood flow velocity and resistance index, aiding in the assessment of the severity of liver cirrhosis.
Clinical studies show that ultrasound-guided biopsy has an accuracy rate of 95% with complication rates below 1%. Its accuracy in locating kidney stones is comparable to CT scans, with no radiation exposure risk.
Alternatives include computed tomography (CT) and magnetic resonance imaging (MRI). CT provides more precise assessment of bony structures but involves radiation exposure. MRI offers higher soft tissue resolution but takes longer and is more expensive. Nuclear medicine scans (e.g., PET-CT) are used for metabolic activity assessment but have longer examination cycles.
In emergencies, X-ray films may be used for preliminary screening, but they do not provide as detailed anatomical information as ultrasound. In special cases, such as suspected pancreatitis, endoscopic ultrasound can provide more accurate deep tissue imaging.
Is special preparation required before the examination? Do I need to fast or be empty stomach?
Fasting for 6 to 8 hours before an abdominal ultrasound is usually recommended to reduce gastrointestinal gas interference and improve image clarity. If examining the liver, gallbladder, or pancreas, fasting may be necessary; for kidney or fetal examinations, fasting requirements may be more flexible. Specific instructions should be followed according to the examination site and physician’s guidance.
Will there be discomfort during the examination? Will it cause pain or fever?
The ultrasound procedure is painless and non-invasive. The probe contact may cause a gentle pressure sensation but does not cause pain or fever. If the area has chronic inflammation or a tumor, pressure from the probe may cause temporary discomfort, which is normal.
Is anesthesia needed? Can children cooperate?
Generally, adults do not require anesthesia. However, children may have difficulty remaining still for a long time, so parental reassurance or mild behavioral restraint may be necessary. In uncooperative young children, physicians may consider mild sedation, but this is uncommon.
How will the report describe the nature of lesions if abnormalities are found?
The report will describe the size, shape, margin clarity, and internal echo features of the lesion, combined with blood flow signal analysis. For example, a "hypoechoic mass with irregular vascular distribution" may suggest malignancy, but final diagnosis requires clinical correlation and additional tests.
How long after abnormal findings are detected should follow-up be conducted?
The follow-up interval depends on the lesion’s risk level: benign cysts may be monitored every 6-12 months; suspected malignant lesions are recommended for CT or tumor marker evaluation within 3-6 months. The physician will develop an individualized plan based on lesion growth rate and patient condition.
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