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Table 1 Glossary of commonly used terms in quantitative ultrasound

From: Quantitative ultrasound imaging of soft biological tissues: a primer for radiologists and medical physicists

Term Definition
Absorption Loss in energy of the propagating compression wave due to local tissue heating
Acoustic impedance Product of the speed of sound by the density of the tissue
Attenuation Decrease in amplitude of acoustic waves propagating through soft tissues; caused by loss of mechanical energy due to wave absorption, reflection, refraction, diffraction, and scattering
Attenuation coefficient Ratio of one radiofrequency echo magnitude to another at a different depth; expressed in decibel per centimeter per megahertz (dB/cm/MHz)
Attenuation coefficient slope Linear relation between the attenuation coefficient and frequency; expressed in dB/cm
Backscatter Analysis of echoes received by the transducer due to reflection and scattering of compression waves
Backscatter coefficient (BSC) Formal definition of the backscatter intensity returned by a tissue and defining its sub-resolution structure; expressed in cm/steradian
Brightness mode (B-mode) Ultrasound mode providing two-dimensional images in grayscale for assessment of anatomy
Compression wave Type of acoustic wave in which the oscillation motion is parallel to the direction of wave propagation; also known as a longitudinal wave
Diffraction Type of interaction between a wave and a physical medium in which the sound is dispersed when travelling through a hole smaller than the wavelength
Homodyned-K (HDK) statistical models Descriptive statistical model used to fit the histogram distribution of ultrasound speckle with 3 parameters for tissue characterization
In-phase and quadrature (I/Q) demodulated data Low-frequency representation of the radiofrequency signal obtained by the quadrature demodulation process
Nakagami statistical models Descriptive statistical model used to fit the histogram distribution of ultrasound speckle with 2 parameters for tissue characterization
Point spread function (PSF) Response of an ultrasound system to a single reflector much smaller than the acoustic wavelength but with sufficient impedance to generate an echo
Quantitative ultrasound (QUS) Field of ultrasound imaging that aims to quantify the interactions between a compression acoustic wave and a biological tissue for its structural sub-resolution characterization
Radiofrequency (RF) Acoustic signals detected by the ultrasound transducer with a frequency bandwidth dictated by the ultrasound probe characteristics
Reflection Type of interaction between an acoustic wave and a physical medium in which the wave bounces back at the same angle but at a different direction; reflections generate an echo detected by the ultrasound transducer when transmitted and reflected angles are in the field of view of the probe
Refraction Type of interaction between an acoustic wave and a physical medium in which the wave is bent at an angle and travels at a different speed due to a mismatch in acoustic impedance of encountered tissue interfaces
Scattering Type of interaction between an acoustic wave and a physical medium in which the wave in bounces at angles of 360 degrees; scattering occurs when the tissue structure is much smaller than the acoustic wavelength
Shear wave Type of acoustic wave in which the oscillation motion is perpendicular to the direction of the wave propagation; also known as transverse waves
Speed of sound (SoS) Square root of the bulk elasticity modulus of the tissue divided by its density; expressed in m/s
Structure factor size estimator (SFSE) Spectral representation of the backscatter coefficient modeled with 2 fitting parameters obtained by considering wave interference phenomena with a structure factor term, from which is extracted the packing factor and the mean size of scatterers
Ultrasound tissue characterization (UTC) Historical term to describe the field of quantitative ultrasound; nowadays, the term QUS is preferred because UTC is also used to describe image processing strategies to extract image characteristics of a tissue