What Is an Ultrasound Scan?

What Is an Ultrasound Scan?

An ultrasound scan — also called sonography or diagnostic medical sonography — is a medical imaging technique that uses high-frequency sound waves to create real-time images of the inside of the body. Unlike X-rays or CT scans, ultrasound uses no ionising radiation whatsoever, making it one of the safest diagnostic tools available in modern medicine.

The technique was first developed for clinical use in the 1950s and has since become one of the most widely used diagnostic methods globally. It is the first-line imaging choice for assessing soft tissues, organs, blood vessels, and developing pregnancies — precisely because it is safe, painless, and provides immediate results.

At Sonoworld, every scan is performed by a consultant-level practitioner using high-resolution equipment. You receive verbal results during your appointment and a written report within 24 hours. For a full overview of what we scan, see our appointments page.

How Does Ultrasound Work?

The physics behind ultrasound is straightforward. A small handheld device called a transducer — or probe — emits pulses of high-frequency sound waves into the body. These sound waves travel through soft tissues and fluids, and when they encounter a boundary between different tissue types (for example, between the liver and a cyst), they reflect back to the transducer as echoes.

A computer processes the timing and intensity of these returning echoes and converts them into a real-time image on the screen. Because different tissues reflect sound differently, the resulting image distinguishes between solid structures, fluid-filled cavities, and blood flow — all without any radiation.

1. Gel is applied to the skin. A water-based gel eliminates air pockets between the probe and your skin, which would otherwise block the sound waves.
2. The transducer emits sound waves. The probe is moved gently over the skin. It emits pulses of sound at frequencies between 2 and 18 MHz — far above the range of human hearing.
3. Echoes return to the probe. Sound waves bounce back from tissue boundaries. The probe detects these returning echoes and sends the data to the ultrasound machine.
4. Real-time images are generated. The machine converts the echo data into a live image. Your practitioner interprets this in real time and explains what they are seeing during the scan.
5. You receive your results. Your practitioner provides verbal findings immediately. A detailed written report follows within 24 hours.

Types of Ultrasound Used at Sonoworld

Different scan types use the same underlying technology but vary in how the probe is positioned and what it measures.

• B-mode (2D): The standard greyscale image most people recognise — used for abdominal, pelvic, and musculoskeletal assessments.
• Doppler: Measures blood flow direction and velocity — essential for vascular assessments such as DVT scans and carotid artery scans.
• Transvaginal (TV): An internal probe provides higher-resolution images of the uterus and ovaries — used for pelvic scans and fertility assessments.
• Echocardiography: Specialist cardiac ultrasound that assesses heart structure and function — see our echocardiogram page.
• Musculoskeletal (MSK): High-frequency probes assess tendons, ligaments, and muscles — used for MSK scans and ultrasound-guided injections.

Is Ultrasound Safe?

Yes — diagnostic ultrasound has an excellent safety record spanning more than 60 years of clinical use. The British Medical Ultrasound Society (BMUS) states that there is no confirmed evidence that diagnostic ultrasound has caused harm to any patient, including during pregnancy. This conclusion is supported by extensive laboratory and epidemiological research. [Verified: BMUS Guidelines for the Safe Use of Diagnostic Ultrasound Equipment, accessed July 2026]

Why Ultrasound Is Safe

• No ionising radiation: Sound waves carry no ionising energy and cannot damage DNA or cells.
• Safe in pregnancy: Ultrasound is the standard imaging modality throughout pregnancy and is used routinely by the NHS from the first trimester.
• Safe for all ages: From newborns to elderly patients, there are no age-based contraindications to diagnostic ultrasound.
• Repeatable: Scans can be performed as many times as clinically indicated without any cumulative risk.
• Non-invasive: External ultrasound requires no needles, no contrast agents, and no anaesthetic.

Ultrasound vs Other Imaging

MRI also uses no radiation but is significantly more expensive and less accessible for same-day appointments.

What Can an Ultrasound Scan Detect?

Ultrasound is the first-line imaging investigation for a wide range of conditions across multiple organ systems. It excels at assessing soft tissues, fluid-filled structures, and blood flow — areas where X-rays provide limited information.

Private Ultrasound vs NHS Ultrasound

The clinical quality of the scan itself is the same whether performed privately or on the NHS — both use the same technology and the same clinical standards. The difference lies in access, speed, and the appointment experience.

When a Private Scan Makes Sense

A private scan is worth considering when you cannot wait for an NHS appointment, when you want to understand a symptom before your GP appointment, when you need a scan not covered by your NHS referral, or when you simply want the reassurance of a same-day result. See our transparent pricing page for all-inclusive fees with no hidden costs.

What to Expect at Your Appointment

Most patients are surprised by how straightforward and comfortable a private ultrasound appointment is. Here is what typically happens from the moment you arrive to when you leave.

1. Arrival and check-in. You arrive at our central London clinic. There is no long wait — your appointment is scheduled to start on time.
2. Brief clinical history. Your practitioner takes a brief history — why you are having the scan, any relevant symptoms, and any previous imaging. This takes 3–5 minutes and ensures the scan is targeted correctly.
3. The scan itself. You lie on the examination couch. Gel is applied to the area being scanned. The probe is moved gently over the skin. Most scans take 20–30 minutes. You can see the screen throughout.
4. Verbal results. Your practitioner explains what they found during the scan — in plain language, with time for your questions. You leave the clinic knowing what was seen.
5. Written report within 24 hours. A detailed written report is sent to you within 24 hours. This can be shared with your GP, specialist, or insurance provider.

Preparation Varies by Scan Type

Some scans require specific preparation — for example, a full bladder for pelvic scans, or fasting for abdominal scans. Others require no preparation at all. See our full ultrasound preparation guide for scan-specific instructions.

Frequently Asked Questions

Answers to the questions we are most commonly asked about ultrasound scans.