Ultrasound Terminology

Acoustic Shadow – The loss of sound wave echoes from structures that lie behind a strongly reflective structure such as bone due to the failure of the sound beam to pass through an object.

Anechoic – Tissues that do not generate an echo such as fluid in the bladder appear black on ultrasound imaging.

Artifact – Product of an US image such as gas in the bowel or an acoustic shadow that does not represent an actual anatomical structure.

Attenuation – The reduction in the intensity or amplitude of a sound wave caused by absorption, scattering or reflection of the sound wave as it travels through the tissue.  Higher attenuation results in loss of penetration and echo. Attenuation is due to sound wave scatter, reflection and absorption.

B-mode – (Brightness) A two-dimensional cross-sectional image displayed on a screen in which the brightness of echoes and their position on the screen are determined by the time it takes the echoes to return to the transducer.  

Central Processing Unit (CPU) – The computer that translates the electrical pulses that result from the returning sound waves (echo) into an image to be displayed on a screen

Cineloop – The US system memory stores a recent sequence of images in a series of frames allowing a continuous loop of images to be reviewed.

Coupling Agent – The gel or gel pad that is used between the transducer and the skin to eliminate air (US Manual)

Echogenicity – is the capability of producing an echo.   Echogenicity is higher when the surface bouncing the sound echo reflects increased sound waves.  Correlate with the terms hyperechoic, hypoechoic and anechoic which refer to the number of echoes produced and the brightness of the on-screen display.

Enhancement –  As sound travels through a fluid-filled structure, attenuation is minimal and the structures distal to the fluid appear to have more echoes than neighboring areas.

Far-field – The area in the acoustic window that is furthest from the ultrasound transducer.

Focal Zone –  The depth of the sound beam where resolution is the highest.

Footprint –The shape of the transducer that is in contact with the patient creating the size and shape of the acoustic window.

Frame Rate – The rate at which the image is refreshed in a real-time system, displayed in frames/second.

Gain – The amplification (brightness) of a returning echo to compensate for the loss of transmission caused by absorption and reflection due to distance.

Hertz – Unit for wave frequency displayed in cycles/second; Ultrasound is measured in megahertz (MHz) = 1,000,000 hertz

Hyperechoic – A relative term that refers to the echoes returning from a structure.  Hyperechoic tissues generate a greater echo usually displaying as lighter colors during ultrasound imaging.

Hypoechoic  – Refers to structures that create weaker echoes such as a fluid.  Tissues with lower echogenicity are usually represented as darker colors on ultrasound.

Impedance – A product of tissue density affecting the velocity of sound as it passes through. The impedance of the tissue determines the reflection of a sound beam.

Interface –  Surface forming the boundary between media having different properties

Isoechoic – Tissue or structures which produces an echo of the same strength as that of the surrounding structures or tissues, making it difficult to isolate.

M-mode – Motion mode is used to evaluate moving structures such as heart valves.

Morphology – Study of how the tissue appears, noting the echogenicity and shape of the structure

Morphometry – Measurements of structure size at rest or displacement following movement.

Near-field – The area in the acoustic window that is closest to the transducer.

Penetration –  Dependent on frequency; higher frequencies give less penetration and lower frequencies penetrate deeper into the tissues

Piezoelectric Effect – Electric current created by pressure forces. Certain types of ceramic materials can convert pressure into electricity and vice versa. Transducer elements utilize this phenomenon.

Refractile Shadow –Because sound waves will bend as they pass from one medium to another, a shadow will form at the edge of a fluid-filled structure, this is a form of artifact.  

Resolution – The ability to distinguish between two adjacent structures at tissue interfaces.  

Transducer –  A device that converts energy from one form to another.  In ultrasound, electricity is converted to sound waves which are emitted into the tissue, the sound waves bounce back (echo) to the transducer where they are converted back to an electrical signal.

Ultrasound:  Sound that has a frequency greater than 20,000 Hertz (Hz), which is beyond the normal range of human hearing.

Wavelength –  The distance a wave travels in a single cycle, as the frequency becomes higher the wavelength becomes smaller.  A smaller wavelength yields a lower depth of penetration.