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 |