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Absorption
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Loss in energy of the propagating compression wave due to local tissue heating
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Acoustic impedance
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Product of the speed of sound by the density of the tissue
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Attenuation
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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
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Attenuation coefficient
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Ratio of one radiofrequency echo magnitude to another at a different depth; expressed in decibel per centimeter per megahertz (dB/cm/MHz)
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Attenuation coefficient slope
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Linear relation between the attenuation coefficient and frequency; expressed in dB/cm
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Backscatter
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Analysis of echoes received by the transducer due to reflection and scattering of compression waves
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Backscatter coefficient (BSC)
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Formal definition of the backscatter intensity returned by a tissue and defining its sub-resolution structure; expressed in cm/steradian
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Brightness mode (B-mode)
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Ultrasound mode providing two-dimensional images in grayscale for assessment of anatomy
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Compression wave
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Type of acoustic wave in which the oscillation motion is parallel to the direction of wave propagation; also known as a longitudinal wave
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Diffraction
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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
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Homodyned-K (HDK) statistical models
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Descriptive statistical model used to fit the histogram distribution of ultrasound speckle with 3 parameters for tissue characterization
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In-phase and quadrature (I/Q) demodulated data
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Low-frequency representation of the radiofrequency signal obtained by the quadrature demodulation process
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Nakagami statistical models
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Descriptive statistical model used to fit the histogram distribution of ultrasound speckle with 2 parameters for tissue characterization
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Point spread function (PSF)
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Response of an ultrasound system to a single reflector much smaller than the acoustic wavelength but with sufficient impedance to generate an echo
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Quantitative ultrasound (QUS)
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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
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Radiofrequency (RF)
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Acoustic signals detected by the ultrasound transducer with a frequency bandwidth dictated by the ultrasound probe characteristics
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Reflection
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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
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Refraction
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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
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Scattering
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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
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Shear wave
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Type of acoustic wave in which the oscillation motion is perpendicular to the direction of the wave propagation; also known as transverse waves
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Speed of sound (SoS)
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Square root of the bulk elasticity modulus of the tissue divided by its density; expressed in m/s
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Structure factor size estimator (SFSE)
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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
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Ultrasound tissue characterization (UTC)
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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
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