Medical ultrasound, also known as sonography, is a safe and non-invasive imaging technique. Unlike X-rays or CT scans, this procedure does not use ionizing radiation, making it the preferred method for monitoring pregnancy and examining soft tissues. This procedure allows medical professionals to visualize organs, blood flow and tissues, enabling them to diagnose various conditions quickly. Because it provides immediate visual feedback with minimal health risks, ultrasound serves as a critical first-line diagnostic tool in modern medicine, enabling physicians to make informed treatment decisions with high accuracy.

What is an ultrasound?

According to Mayo Clinic, an ultrasound is a medical procedure that uses high-frequency sound waves to generate images of internal body structures. The images can provide valuable information for diagnosing and treating a variety of diseases and conditions.

The core of the equipment is the transducer. This is a handheld device that looks like a microphone. It helps to convert sound waves into electrical signals. Depending on the area being examined, the procedure can be performed either externally on the skin or internally. External ultrasounds are most common. Internal ultrasounds, like transesophageal, offer enhanced detail.

The procedure is mainly performed in a hospital’s radiology department or a private clinic. In most cases, it is painless, though you might feel slight pressure as the sonographer (a trained technician) moves the wand to get a clear view. The ability to visualize soft tissues makes the procedure particularly useful when other imaging modalities, such as X-rays, fall short. The images are displayed instantly on the computer screen, enabling immediate assessment.

How it works

Picture this: a bat flies at night and can maneuver even in the narrowest parts of darkness without crashing. Well, bats use echolocation (sonar) for navigation. The science behind ultrasound is based on the same principles of sonar. The transducer emits high-frequency sound waves into the body. These patches are far too high for your ear to hear. Your provider applies a thin layer of gel to your skin, allowing the ultrasound waves to be transmitted from the transducer through the gel and into your body.

According to the Cleveland Clinic, as these sound waves travel through your body, they hit boundaries between tissues, such as fluid and soft tissue, or soft tissue and bone. When they hit these boundaries, some of the sound waves bounce back to the transducer as echoes. The transducer picks up the reflected sound waves and relays them to a specialized computer. The computer calculates the distance and intensity of the echoes and then converts the electrical signal pattern into real-time images or videos.

What an ultrasound can detect

Ultrasound excels at visualizing soft tissues and fluid-filled organs. This procedure can detect a broad range of conditions across many organ systems.

In the abdomen, the test allows for detailed visualization of the liver, gallbladder, spleen, pancreas and kidneys. The test can determine the size, shape and consistency of these organs, helping healthcare professionals rule out enlargement or atrophy. In the pelvis, ultrasound is used to assess the uterus, ovaries and bladder. Pelvic ultrasounds can detect cysts, fibroids and structural abnormalities that may affect fertility.

Vascular structures are another major category. As explained by Mayo Clinic, Doppler ultrasound is a special technique that visualizes blood flow through arteries and veins. It can detect blockages (stenosis) in the carotid arteries, which is a risk factor for stroke. Additionally, this procedure is highly effective for superficial structures. This includes the thyroid gland in the neck, the testes and breast tissue. In breast imaging, it helps distinguish a fluid-filled cyst from a solid mass.

Limitations

Ultrasound is an essential tool, but it has its limitations. Sound waves do not travel well through air or bone, which is their primary limitation. Because bone reflects sound waves entirely, ultrasound cannot see what is inside or behind bony structures. This makes it ineffective for detailed imaging of the brain (in adults) or the spinal cord, as they are encased in the skull and vertebrae.

Air and gas also disrupt sound waves. Therefore, this procedure is generally poor at imaging the lungs (which are filled with air) or the bowel and stomach (which often contain gas). If you have a condition affecting the intestines, a CT scan is usually required for a clear view and detailed information, according to Johns Hopkins Medicine.

Another major limitation is depth penetration. In obese patients, the increased tissue attenuates sound waves as they travel deeper into the body. This can result in lower-quality images, making it challenging to visualize deep abdominal structures, such as the pancreas. Elsewhere, scientific literature published in the National Library of Medicine notes that the success of the examination depends heavily on the operator’s skill and experience.

Risks and safety considerations

In every medical procedure, safety considerations are usually the top priority. Both patients and medical experts are required to adhere to established safety guidelines to prevent any disasters. Diagnostic ultrasound is considered one of the safest medical procedures available. The most significant safety benefit is the absence of ionizing radiation.

Radiation (used in X-rays and CT scans) can damage your DNA and slightly increase your risk of getting cancer over time. But since ultrasound only uses sound waves, it is safe for repeated use, which is why it is the standard for fetal monitoring. Because it uses zero radiation, ultrasound is the only imaging method safe enough for routine use during pregnancy to monitor fetal health.

“Having repeated experience in prenatal diagnosis and fetal therapy builds knowledge. This is the only way we can approach the fetus like a patient. With sophisticated ultrasound, we now have ways to identify fetal problems and guide treatment,” says Dr. Justus Rabach, MD, Clinical Medicine and Bachelor of Surgery (MBChB).

While there are theoretical risks associated with ultrasound, such as thermal effects and cavitation, the U.S. Food and Drug Administration (FDA) and other health organizations have deemed diagnostic ultrasound safe when used by trained professionals. The benefits of an accurate diagnosis vastly outweigh these theoretical risks.

Alternatives or additional tests

When ultrasound cannot provide a clear answer, your healthcare provider will turn to alternative imaging techniques. One of the most common alternatives is the CT scan (Computed Tomography).

According to the Cleveland Clinic, CT scans are excellent for imaging bone, the lungs and the brain, which are areas that ultrasound cannot visualize. This procedure provides a comprehensive view of the body and is less affected by a patient’s body size. However, they are more expensive and involve radiation.

MRI (magnetic resonance imaging) is another powerful alternative. As per Healthline, MRI is superior for detailed imaging of soft tissues such as the brain, tendons and ligaments. This procedure does not use radiation but is significantly more expensive and time-consuming than ultrasound.

X-rays are typically the first step for assessing bone fractures or lung infections. They are quick and inexpensive but provide poorer detail of soft tissues and organs than ultrasound.

What cancers can ultrasound detect?

Ultrasound plays a crucial role in the early detection and characterization of various types of cancer. While a biopsy is usually needed to confirm cancer, an ultrasound helps determine if a mass is suspicious. It is widely used to evaluate thyroid cancer. If your doctor detects a lump in your neck, an ultrasound can help determine if the nodule exhibits characteristics of cancer, such as irregular borders or microcalcifications.

In breast cancer, ultrasound is a critical adjunct to mammography. It is beneficial for women with dense breast tissue. It helps differentiate between benign fluid-filled cysts and solid masses that could be malignant tumors. Liver cancer is often screened for using ultrasound in high-risk patients, such as those with cirrhosis or hepatitis B. It can detect new liver masses that require further investigation.

Ovarian cancer and uterine cancer are also evaluated using transvaginal ultrasound. This can show visual tumors on the ovaries or thickening of the uterine lining, which can be an early sign of cancer.

What cannot be seen in an ultrasound?

To manage expectations, it is essential to know what ultrasound frequently misses. As mentioned, bones act as a barrier. You cannot use ultrasound to diagnose a skull fracture or a complex break in the skull; X-rays are needed for that.

The internal structure of joints, such as the meniscus inside the knee, is often better seen with MRI, although ultrasound can visualize the tendons around the joint. The lungs are essentially invisible on ultrasound due to their air content. While it can detect fluid around the lungs, it cannot see inside the lung tissue to diagnose conditions like emphysema or small lung nodules.

Bottom line

Ultrasound is a cornerstone of modern diagnostics, offering a safe, radiation-free window into the body’s soft tissues. It is the go-to choice for obstetrics, vascular health and organ examinations, such as the gallbladder and liver. While it has limitations in bone and gas-filled areas, its ability to provide real-time, dynamic imaging makes it indispensable.

Frequently Asked Questions

Which is more accurate, a CT scan or an ultrasound?

CT scans are generally more accurate for imaging bone, the lungs, and complex abdominal issues, while ultrasound is often superior for monitoring pregnancy and visualizing soft-tissue fluid dynamics.

How long does an ultrasound procedure take?

Most ultrasound exams are quick, typically taking between 20 and 45 minutes to complete, depending on the area being examined.

What should you not do before an ultrasound?

Depending on the specific exam, you may need to avoid eating (fasting) for several hours or avoid urinating to keep a full bladder. Always follow your doctor’s specific instructions.

Citations

Mayo Clinic. Ultrasound. Mayoclinic. Published April 30, 2022. https://www.mayoclinic.org/tests-procedures/ultrasound/about/pac-20395177

Cleveland Clinic. Ultrasound: What It Is, Purpose, Procedure & Results. Cleveland Clinic. Published April 12, 2022. https://my.clevelandclinic.org/health/diagnostics/4995-ultrasound

Johns Hopkins Medicine. Computed Tomography (CT or CAT) Scan of the Abdomen. John Hopkins Medicine. Published 2019. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/computed-tomography-ct-or-cat-scan-of-the-abdomen

Edwards C, Chamunyonga C, Searle B, Reddan T. The application of artificial intelligence in the sonography profession: Professional and educational considerations. Ultrasound. 2022;30(4):1742271X2110724. doi:https://doi.org/10.1177/1742271×211072473

FDA. Ultrasound Imaging. U.S. Food and Drug Administration. Published January 12, 2024. https://www.fda.gov/radiation-emitting-products/medical-imaging/ultrasound-imaging

Cleveland Clinic. CT Scan (Computed Tomography): What is It, Preparation & Test Details. Cleveland Clinic. Published June 13, 2023. https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan

Sawyers T. CT Scan vs. MRI. Healthline. Published August 23, 2018. https://www.healthline.com/health/ct-scan-vs-mr