What is Ultrasound?
A complete scientific explanation of the technology, operating principles, preparation and benefits of ultrasound imaging.
What is Ultrasound
Ultrasound is a non-invasive medical examination that helps physicians diagnose and treat illnesses. It is based on exposing a part of the body to high-frequency sound waves that produce images from inside the body.
Unlike X-rays or computed tomography, ultrasound examinations do not use ionising radiation — making them safe even for pregnant women and newborns.
Because images are created in real time, they can visualise both the structure and movement of internal organs, as well as blood flow through vessels.
Completely Safe
No ionising radiation. Safe for pregnant women, children and newborns.
Real-Time
Dynamic imaging that monitors organ movement and blood flow.
Non-Invasive
No needles, no radiation, no special preparation in most examinations.
Types of Ultrasound
Click each type to learn more.
2D Ultrasound
Displays thin, flat sections of the body in real time.
3D Ultrasound
Renders sound wave data into high-resolution three-dimensional images.
4D Ultrasound
3D in motion — real-time three-dimensional imaging.
Doppler / Triplex
Evaluates the direction and velocity of blood flow through vessels.
Elastography
Maps tissue stiffness — tumours deform less than surrounding healthy tissue.
Doppler / Triplex Techniques
Doppler ultrasound measures the direction and velocity of blood cells based on the Doppler effect. Click for a detailed description.
Colour Doppler
Colours represent the velocity and direction of blood flow.
Power Doppler
Extremely sensitive technique — detects even minimal flow.
Spectral Doppler
Displays blood flow as a time–velocity waveform graph.
The Ultrasound Machine
The machine consists of a console with an integrated computer and electronic components, a display screen and the probe (transducer) — a handheld device that resembles a microphone.
The probe sends high-frequency sound waves into the body and detects the reflected waves. The image appears immediately on the screen in real time.
Operating Principles
The operating principle is similar to the sonar of bats, ships and submarines. Sound waves reflect off internal organs, and by measuring these echoes, the size, shape and composition of each structure is calculated.
The image is created from the amplitude, frequency and return time of the sound signal. The computer processes the data and produces a real-time image.
How the Examination is Performed
Simple, painless, in 30–60 minutes. No special preparation in most examinations.
Positioning
You lie comfortably on an examination table — on your back or side, depending on the area being examined.
Gel application
A special water-soluble gel is applied to the skin to eliminate air pockets between the probe and the skin.
Scanning
The radiologist moves the probe gently over the skin, systematically scanning the area of interest.
Evaluation
Images appear in real time. Selected still frames are saved for analysis.
Report
The radiologist analyses the findings and issues an official signed written report with selected images.
Special techniques: Some examinations use intracorporeal probes — transoesophageal echocardiography (heart via oesophagus), transrectal (prostate) and transvaginal (uterus/ovaries).
Preparation
Comfortable clothing
Loose, easy-to-move clothing.
Wear loose, comfortable clothing that allows easy access to the examination area. You may need to remove jewellery or metal objects from the area. A dedicated examination gown is provided for some examinations.
12-hour fasting
For abdominal examinations: avoid food/drink for ~12 hours.
Fasting is essential for upper abdominal examinations (liver, gallbladder, pancreas). Food causes gallbladder contraction and gas accumulation in the intestine, which obstruct sound waves. Water and medication are usually permitted.
Full bladder
For pelvic examinations: drink 3 glasses of water 2 hours before.
A full bladder acts as an acoustic "window" — it displaces the gas-filled bowel from the examination area and allows clear imaging of the uterus, ovaries and prostate. Drink 3 glasses of water 2 hours before and avoid urinating until the examination.
Special instructions
Always follow your doctor's instructions.
Preparation varies according to the type of examination. For thyroid, breast, musculoskeletal or vascular examinations, no special preparation is usually required. Your doctor will provide personalised instructions at the time of booking.
What You Will Feel
The examination is usually completely painless and quick.
You may feel slight pressure from the probe in sensitive areas.
In Doppler examinations, characteristic pulses are heard — the sound of blood flow.
After completion, the gel is easily removed and you can immediately resume your activities.
Who Interprets the Results
A radiologist, specially trained in analysing imaging examinations, evaluates the images and issues an official signed written report together with selected images.
The report is delivered to the referring physician. The radiologist can also discuss the results with the patient immediately after the examination.
Δρ. Παπαγεωργίου Σταύρος
PhD Radiologist · 40+ years of experience
Benefits & Limitations
Benefits
- Non-invasive — no needles or injections
- Painless and quick examination
- No ionising radiation
- Clear imaging of soft tissues
- Real-time dynamic imaging
- Safe for pregnant women and foetuses
- Lower cost than other methods
- Suitable for biopsy guidance
Limitations
- Sound waves are disrupted by air — not suitable for lungs or intestine.
- In obese patients, penetration is reduced due to signal attenuation.
- Limited penetration of bones — only the external surface is visualised.
- MRI or CT is required for internal bony/joint structures.
In these cases alternative methods are used: computed tomography (CT), magnetic resonance imaging (MRI) or barium examination.