Ultrasound Scan: How It Works, What It Detects & Why It’s Safe

An ultrasound scan is a non-invasive diagnostic imaging test that uses high-frequency sound waves to create real-time images of organs, tissues, blood vessels and, during pregnancy, the developing baby. It does not use ionizing radiation, making it a widely used imaging method for evaluating many health conditions when performed by trained professionals for an appropriate medical reason.

At City Imaging & Clinical Labs, ultrasound imaging can help doctors investigate symptoms such as abdominal pain, swelling, urinary problems, menstrual irregularities and suspected abnormalities in different organs. Depending on the symptoms and clinical findings, a doctor may recommend an ultrasound scan alone or combine it with blood tests, urine tests or other imaging investigations to reach an accurate diagnosis.

Understanding how an ultrasound works, what it can detect, how to prepare and when additional tests may be needed can help patients feel more confident before their appointment.

What Is an Ultrasound Scan?

An ultrasound scan, also known as sonography, is a diagnostic procedure that uses high-frequency sound waves to produce images of structures inside the body.

Unlike X-rays and CT scans, which use ionizing radiation, ultrasound uses sound waves to generate images. A healthcare professional moves a small device called a transducer over the skin or uses a specialised probe for certain internal examinations.

Ultrasound is commonly used to examine the liver, gallbladder, kidneys, urinary bladder, uterus, ovaries, thyroid gland, breasts, muscles, tendons and blood vessels. It is also widely used during pregnancy to assess fetal development.

The type of ultrasound recommended depends on the patient's symptoms, medical history and the area that needs to be examined.

How Does an Ultrasound Scan Work?

Ultrasound imaging works through the transmission and reflection of high-frequency sound waves. The procedure generally involves the following steps:

1. Preparation Before the Scan

The preparation depends on the type of examination. For an ultrasound of the abdomen or pelvis, the patient may need to fast or drink water to fill the urinary bladder. Other ultrasound examinations, such as a thyroid or breast ultrasound, usually require little or no special preparation.

2. Application of Ultrasound Gel

A clear, water-based gel is applied to the skin over the area being examined. This gel helps sound waves travel between the transducer and the body by reducing the air gap between them.

3. Transmission of Sound Waves

The sonographer or other appropriately trained professional moves the transducer over the skin. The device sends high-frequency sound waves into the body.

4. Formation of Images

As sound waves encounter different tissues and organs, some waves return to the transducer as echoes. The ultrasound system processes these echoes and converts them into images displayed on a monitor.

5. Image Assessment and Reporting

The images are reviewed by a qualified doctor, such as a radiologist, when required by the examination and clinical setting. The findings are documented in a report that helps the treating doctor decide whether further investigations or treatment are necessary.

Most external ultrasound examinations are painless. Patients may experience mild pressure from the transducer, particularly when the area being examined is tender.

What Can an Ultrasound Scan Detect?

Ultrasound can help identify structural abnormalities, fluid collections, certain masses, organ enlargement and changes in blood flow. However, its ability to detect a condition depends on the body part, the type of ultrasound, the patient's anatomy and the nature of the suspected disease.

Common applications include:

1. Liver and Gallbladder Conditions

An abdominal ultrasound can help assess liver size and structure, fatty liver changes, gallstones, gallbladder inflammation and enlargement of the bile ducts. Doctors may recommend this examination for symptoms such as upper abdominal pain, persistent discomfort, jaundice or abnormal liver function test results.

Related tests may include:

• Liver Function Test (LFT)
• Complete Blood Count (CBC)
• Ultrasound Whole Abdomen
• MRI Abdomen or CT Scan, when clinically indicated

2. Kidney and Urinary Tract Problems

Ultrasound can assess kidney size, certain kidney stones, swelling caused by urinary obstruction, cysts and abnormalities of the urinary bladder. It may be recommended for patients experiencing flank pain, difficulty passing urine, recurrent urinary tract infections or blood in the urine.

Related tests may include:

• Kidney Function Test (KFT)
• Urine Routine and Microscopy
• Urine Culture
• Ultrasound KUB (Kidneys, Ureters and Bladder)
• CT KUB, when a more detailed assessment is needed

Not every urinary stone is visible on ultrasound, so a doctor may recommend additional imaging if symptoms persist despite a normal or inconclusive scan.

3. Uterus, Ovaries and Pelvic Conditions

Pelvic ultrasound is used to examine the uterus, ovaries and other pelvic structures. It can help identify uterine fibroids, ovarian cysts, certain pelvic masses and abnormalities of the endometrium. Depending on the indication, the examination may be performed through the lower abdomen or transvaginally.

Related investigations may include:

• Ultrasound Pelvis
• Transvaginal Ultrasound (TVS)
• Complete Blood Count (CBC), particularly when bleeding or anaemia is suspected
• Beta-hCG blood test or urine pregnancy test, when pregnancy needs to be assessed

The choice of additional testing depends on the symptoms and the doctor's assessment.

4. Pregnancy and Fetal Development

Obstetric ultrasound is commonly used during pregnancy to assess fetal growth, pregnancy location, fetal heartbeat at appropriate stages, placental position, amniotic fluid and certain structural abnormalities.

Different examinations may be recommended at different stages of pregnancy. These can include an early pregnancy scan, a first-trimester screening ultrasound, a detailed fetal anomaly scan and growth scans when indicated. Ultrasound is also used for selected procedures during pregnancy under medical supervision.

Related investigations may include:

• Pregnancy Test (Urine or Beta-hCG)
• First-Trimester Screening
• Double Marker Test, when indicated
• Anomaly Scan
• Fetal Growth Ultrasound

The exact combination of tests depends on gestational age, medical history and antenatal care recommendations.

5. Thyroid Gland and Neck Abnormalities

A thyroid ultrasound provides images of the thyroid gland and can help detect thyroid nodules, cysts, enlargement and certain structural changes. It can also help doctors evaluate suspicious nodules and determine whether further assessment is needed. Ultrasound findings alone cannot reliably establish whether a thyroid nodule is cancerous.

Related tests may include:

• Thyroid Function Test (TFT)
• TSH Test
• Free T3 and Free T4
• Ultrasound-Guided Fine Needle Aspiration (FNAC), when recommended

Blood tests assess thyroid function, while ultrasound examines the gland's structure. These tests provide different types of information.

6. Breast Lumps and Soft-Tissue Abnormalities

Breast ultrasound can help evaluate a palpable breast lump, distinguish many fluid-filled cysts from solid lesions and investigate selected breast abnormalities. It may be used alongside mammography, depending on age, symptoms, breast density and clinical findings.

Related investigations may include:

• Mammography
• Ultrasound-Guided FNAC or Biopsy, when indicated

A new breast lump should be evaluated by a qualified healthcare professional even if an ultrasound result appears reassuring.

7. Blood Vessel and Blood Flow Problems

Doppler ultrasound evaluates the movement of blood through vessels. It can help identify certain blood clots, narrowed blood vessels, abnormal blood flow and venous insufficiency. A doctor may recommend Doppler imaging for limb swelling, suspected vascular obstruction or selected circulatory problems.

Related tests and examinations may include:

• Venous Doppler Ultrasound
• Arterial Doppler Ultrasound
• Carotid Doppler
• Echocardiography, for selected heart-related indications

The appropriate examination depends on which blood vessels or organs need to be assessed.

Why Is an Ultrasound Scan Considered Safe?

Ultrasound is generally considered a safe diagnostic imaging technique because it does not use ionizing radiation. It has been used extensively in medical practice, including during pregnancy. Its safety advantages include the following:

• No ionizing radiation: Ultrasound uses sound waves rather than X-rays, which makes it useful for many clinical situations where radiation-free imaging is preferred.
• Non-invasive examination: Most scans are performed externally using a transducer placed on the skin. No needles or surgical incisions are required for a routine external scan.
• Real-time imaging: Ultrasound can display movement, including fetal movement and blood flow, while the examination is being performed.
• Generally painless: Most examinations cause little discomfort, although pressure from the transducer may be uncomfortable over a tender area.
• Repeat examinations when medically indicated: A clinician may recommend repeat ultrasound examinations to monitor a condition or assess changes over time.

Are There Any Risks or Limitations?

Diagnostic ultrasound has no known harmful effects when used appropriately for standard medical imaging. However, ultrasound energy can produce heating and mechanical effects in tissues, so examinations should be performed by trained professionals using appropriate equipment and exposure settings.

Medical ultrasound should be used for a clinical purpose. Pregnancy scans should not be performed solely to obtain keepsake images or videos without a medical indication.

Ultrasound also has limitations. Sound waves do not travel well through air or bone, so the examination may not adequately assess certain structures. Image quality can be affected by bowel gas, body habitus, the location of an organ and the type of condition being investigated.

For some conditions, a doctor may recommend an MRI scan, CT scan, mammography, endoscopy or laboratory testing to obtain additional information.

Types of Ultrasound Scans

Different types of ultrasound examinations are designed for different organs and clinical needs.

Your doctor will recommend the type of scan according to the symptoms and the clinical question that needs to be answered.

How to Prepare for an Ultrasound Scan

Preparation varies according to the examination. Following the instructions provided by your diagnostic centre can help improve image quality.

• Abdominal ultrasound: Fasting for a specified period may be required, depending on the organs being examined.
• Pelvic ultrasound: You may be asked to arrive with a full urinary bladder.
• Transvaginal ultrasound: The bladder is usually emptied before the examination, unless instructed otherwise.
• Pregnancy ultrasound: Preparation depends on the stage of pregnancy and the type of scan.
• Thyroid, breast and musculoskeletal ultrasound: Special preparation is generally not required.

Wear comfortable clothing that allows easy access to the area being examined. Inform the healthcare team about relevant medical conditions, previous imaging reports and any specific concerns before the procedure.

Do not stop prescribed medication or change your normal treatment unless your doctor advises you to do so.

When Should You Get an Ultrasound Scan?

A doctor may recommend an ultrasound scan when symptoms, examination findings or previous test results suggest that imaging is necessary. Common reasons include:

• Persistent or unexplained abdominal pain
• Suspected gallstones or kidney stones
• Abdominal swelling or a palpable lump
• Urinary symptoms or suspected urinary obstruction
• Menstrual irregularities or pelvic pain
• Evaluation of pregnancy
• A new breast lump or thyroid swelling
• Swelling in an arm or leg when a vascular problem is suspected
• Follow-up of a previously identified cyst, nodule or other abnormality

An ultrasound is not necessary for every symptom. The decision should be based on clinical evaluation, and urgent symptoms should not be ignored while waiting for a routine scan.

Ultrasound Scan vs CT Scan vs MRI Scan

Although all three imaging methods help doctors diagnose medical conditions, they work differently.

These tests are not interchangeable in every situation. The most suitable examination depends on the suspected condition, urgency, medical history and the information the doctor needs.

Frequently Asked Questions About Ultrasound Scans

Is an ultrasound scan completely safe?

Diagnostic ultrasound is generally considered safe when performed appropriately for a medical indication. It does not use ionizing radiation, but trained professionals should still use suitable equipment and exposure settings.

Does an ultrasound scan hurt?

Most external ultrasound examinations are painless. Mild pressure may be felt when the transducer is moved over the skin, especially over a tender area.

How long does an ultrasound scan take?

Many routine ultrasound examinations take approximately 15–30 minutes. Some examinations may take longer depending on the area being examined and the complexity of the findings.

Can an ultrasound detect cancer?

Ultrasound can identify certain masses and suspicious structural changes, but it cannot confirm or exclude every cancer. Further investigations, such as biopsy, FNAC, MRI or CT, may be needed depending on the findings.

Do I need to fast before an ultrasound scan?

Not always. Fasting is commonly required for some abdominal examinations, while many other scans do not require it. Follow the preparation instructions provided for your specific examination.

Can an ultrasound detect kidney stones?

Ultrasound can detect many kidney stones and signs of urinary obstruction, but some stones may not be visible. A doctor may recommend a CT KUB if further assessment is necessary.

Which tests may be required along with an ultrasound?

Additional tests depend on the symptoms and suspected diagnosis. Examples include LFT for liver-related concerns, KFT for kidney function, urine tests for urinary symptoms, thyroid function tests for thyroid disorders and beta-hCG for pregnancy assessment. Not every patient needs these additional investigations.

Is ultrasound safe during pregnancy?

Ultrasound is widely used during pregnancy and is generally considered safe when medically indicated and performed by trained professionals. The number and timing of scans should follow appropriate antenatal care recommendations.

Book an Ultrasound Scan at City Imaging & Clinical Labs

Ultrasound imaging is an important part of modern diagnostic care because it helps doctors examine internal organs, investigate symptoms and monitor selected medical conditions without using ionizing radiation.

At City Imaging & Clinical Labs, patients can enquire about the availability of relevant ultrasound examinations and receive information about preparation requirements and appointments. The choice of scan should be guided by a qualified healthcare professional according to the patient's symptoms and medical needs.

If your doctor has recommended an ultrasound scan, follow the preparation instructions and bring previous reports when available. If the results indicate a need for further evaluation, your doctor can advise whether related pathology tests, Doppler studies, CT scans or MRI scans would be appropriate.

Disclaimer: This article is for general educational purposes and does not replace medical advice, diagnosis or treatment. The need for an ultrasound or any additional investigation should be determined by a qualified healthcare professional.