Recommended Ultrasound Terminology
E
early phase of enhancement
See arterial phase of enhancement.
echo
A sound wave that has been reflected and arrives with such a magnitude and sufficient time interval after the direct transmitted sound wave to be distinguishable.
See: pulse echo
echocardiogram
An ultrasound image of the heart.
Related terms: 2-dimensional echocardiography, 3-dimensional echocardiograph
echocardiograph
An instrument used to record an echocardiogram.
echocardiography
Examination of the heart by diagnostic ultrasound.
echo contrast agent
Related term: contrast agent
echoencephalography
Examination of the brain by diagnostic ultrasound.
echo enhancement
See acoustic enhancement.
echogenic
Describes a structure or medium (eg, tissue) that is capable of producing echoes. Contrast with the terms hypoechoic, hyperechoic, and anechoic, which refer to the paucity, abundance, and absence of echoes displayed on the image.
echogenicity
The tendency of a tissue or material to generate echoes.
echogram
A record obtained using acoustic reflection techniques with one of the various display modes.
echography
Any imaging method using reflected sound.
Related term: sonography
echo listening time
Pulse repetition period minus the pulse duration. It is the time between one pulse and the next during which the transducer is able to detect echoes.
echolucent
A misnomer for anechoic and/or transsonic.
Related terms: anechoic, transsonic
echo-ophthalmography
Examination of the eye and orbit by diagnostic ultrasound.
echo ranging
A technique for measuring distances in materials of known acoustic velocity by measuring the transit time for the sound to propagate from the transducer to the target and return. Echo-ranging techniques, in particular pulse- echo ultrasound, form the basis of most ultrasonic visualization systems.
Related term: pulse echo
echoscope
Instrument that displays a sonogram on a screen.
echo (signal) shaping
Image modification in which the echo waveform is changed using techniques such as limiting and differentiation.
echo strength
The magnitude of an echo.
echoventriculography
A method for echoencephalographic measurements of the cerebral ventricles or measurement of other ventricles as appropriate in the field of application.
edge enhancement
An image-processing technique that makes edges in an image more apparent.
effective acoustic center
For a sound-emitting transducer, in a specified direction and range of distances, position of the virtual point source from which sound pressure varies inversely with distance.
effective area of an ultrasonic transducer
The equivalent area of a perfect pistonlike ultrasonic transducer, which has a predicted axial acoustic pressure distribution that approximately corresponds to the observed axial acoustic pressure distribution over a limited axial distance. The unit is square meter (m2).
Related term: active aperture
effective frequency
A single frequency used to characterize a signal containing many frequencies. The effective frequency of an ultrasound beam is determined by the centroid of the power spectrum of the acoustic waveform at the pressure focus over the –3-dB bandwidth.
Related term: bandwidth, acoustic working frequency
effective pressure
The root mean square value of acoustic pressure. The unit is pascal (Pa).
effective radius of a hydrophone active element
The radius of a stiff disk receiver hydrophone that has a predicted directional response function with an angular width equal to the observed angular width. The angular width is determined at a specified level below the peak of the directional response function. For the specified levels of 3 and 6 dB, the radii are denoted by a3 and a6, respectively. The unit is meter (m).
Related term: effective area of an ultrasonic transducer
effective wavelength
The effective wavelength of a field is equal to the longitudinal sound velocity in the propagation medium divided by the effective frequency.
elastic compression modulus
See bulk elastic modulus.
elastic modulus
The ratio of a specified stress to the corresponding strain in the material.
elastic spring
A purely elastic element in a viscoelastic model in which the resulting force is proportional to the strain; the graphical symbol for a spring (E) is:
elastogram (tissue)
An image depicting the spatial distribution of tissue stiffness or other elastic parameters. This specialized ultrasound technique visualizes differences in tissue elasticity, which can aid in identifying abnormalities. Examples are axial strain elastogram, lateral strain elastogram, modulus elastogram, shear strain elastogram, and poro-elastogram.
elastography (tissue)
An imaging technique producing an elastogram.
Related term: elastogram
elastomicrography
An elastographic method where the resolution of the elastograms is below 1 mm.
electroacoustic effect
The occurrence of a deformation of a material after applying an electrical voltage on opposite sides.
electroacoustic force factor
Of a reciprocal electroacoustic transducer, (1) the quotient of the resulting sound pressure in the blocked acoustical system by the corresponding current in the electrical system; or (2) the quotient of the resulting open-circuit voltage in the electrical system, by the volume velocity in the acoustical system; if there is gyroscopic antireciprocal coupling, the sign is reversed.
electroacoustic reciprocity principle
For a linear, passive reversible electroacoustic transducer, the principle according to which the relationship between the voltage (or current) sensitivity of the transducer when used as a sound receiver and its corresponding current (or voltage) sensitivity when used as a sound emitter depends only on the system geometry, the frequency, and the physical properties of the medium.
electroacoustic transducer
Transducer designed to receive input signals from an electrical system and to furnish acoustic output signals or vice versa.
electromechanical force factor
Of a reciprocal electromechanical transducer, (1) the quotient of the resulting force in the blocked mechanical system by the corresponding current in the electrical system; or (2) the quotient of the open-circuit voltage in the electrical system by the corresponding velocity in the mechanical system; if there is gyroscopic antireciprocal coupling, the sign is reversed.
electromechanical transducer
Transducer designed to receive input signals from an electrical system and to furnish output signals to a mechanical system or vice versa.
electronically swept scanning (3-dimensional)
Producing 3-dimensional echo information with a 2-dimensional array using electronic sweeping.
Related term: Contrast with mechanically swept scanning
electronic focusing
Method to achieve transmit and/or receive focusing of an array transducer by means of signal time delays or phase adjustments between neighboring elements of the array.
See dynamic focusing.
electronic sector scan
Sector scanner using a phased array transducer without mechanically moving parts.
electronic tissue model
Electronic apparatus that produces signals that mimic acoustic echoes received from tissue.
electrostatic actuator
Device comprising an auxiliary electrode that permits the application of an electrostatic force to the metallic or metallicized diaphragm of a microphone to obtain a calibration.
electrostatic loudspeaker
Loudspeaker that operates by electrostatic forces.
electrostatic microphone/capacitor microphone/condenser microphone
Microphone that operates by variation of electrical capacitance.
elevation axis
An axis in the elevation plane perpendicular to the beam axis.
elevational focus
Focal depth of the ultrasound beam in the elevational plane.
Related term: slice thickness
elevation plane
Usually the plane that contains the beam axis and is perpendicular to the principal longitudinal (azimuth or scan) plane. It can also refer to any plane perpendicular to the principal longitudinal (azimuth or scan) plane offset from the azimuth beam axis. (see Figures 27, 33, and 36).
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Related term: azimuthal plane, slice thickness
elevational resolution
The resolution at right angles to the scan plane. This is sometimes referred to as orthogonal resolution, vertical resolution, or slice thickness resolution.
encapsulated bubble
A gas bubble that is covered with a layer of a material to retard the dissolving of the gas into the surrounding liquid. Microbubbles used in ultrasonic applications are encapsulated to permit them to last long enough to be useful.
Related terms: contrast agent, microbubble
endocavitary
Term describing sonographic examinations that use a transducer that is placed within a body cavity, including endoesophageal, endorectal, endovaginal, and endovascular.
Related terms: transesophageal, transrectal, transvaginal imaging
end-of-cable loaded sensitivity of a hydrophone
The ratio of the voltage at the end of any integral cable or connector of a hydrophone, when connected to a specified electrical input impedance, to the instantaneous acoustic pressure in the undisturbed free field of a plane wave in the position of the acoustic center of the hydrophone if the hydrophone were removed. The unit is volt per pascal (V/Pa).
end-of-cable open-circuit sensitivity factor
A modified expression for the free-field pressure sensitivity to account for the impedance of the cable connected to a hydrophone to an oscilloscope.
Related term: free-field pressure sensitivity
end-of-cable open-circuit sensitivity of a hydrophone
The ratio of the open-circuit voltage at the end of any integral cable or connector of a hydrophone to the instantaneous acoustic pressure in the undisturbed free field of a plane wave in the position of the acoustic center of the hydrophone if the hydrophone were removed. The unit is volt per pascal (V/Pa). Note: This definition differs from that given in Subclause 8.8 of IEC Publication 866, as the latter refers to a hydrophone excluding any integral cable.
endovaginal imaging
Imaging of the female pelvis while the transducer is placed in the vagina.
Related term: transvaginal imaging
energy per pulse
The ratio of the average acoustic power to the pulse repetition frequency, measured in joules (J).
energy, kinetic
Energy associated with the motion of a mass. It is equal to ½ mv2, where m is mass, and v is velocity.
energy, potential
Energy associated with the ability to do work. Examples are the gravitational (or hydrostatic energy of an object (or volume of fluid) raised to a height in a gravitational field and pressure in a fluid.
energy, total fluid
The sum of the kinetic energy (related to velocity), inertial energy (related to acceleration), potential energy (related to pressure or gravity), and viscous energy (related to fluid friction) in a volume of fluid. The unit of energy is joule (J).
energy, viscous
Energy used to overcome the internal cohesion of a liquid to, for example, maintain laminar flow. Energy expended in this way is converted to heat.
enhanced subharmonic imaging
Related term: subharmonic contrast-enhanced sonography
ensemble (of scatterers)
A collection of inhomogeneities that scatter acoustic energy.
ensemble length (color flow Doppler)
The number of pulses emitted by a color flow Doppler imaging system to create Doppler data in the image. Also known as packet length.
entrance beam dimensions
The dimensions of the beam cross-sectional area where the beam enters the patient. For contact transducers, these dimensions can be taken as the dimensions of the radiating element. Also called the footprint of the transducer on the patient.
entrance dimensions of the scan (for auto-scanning)
The dimensions of the scan cross-sectional area over the surface through which the scan beams enter the patient.
Related term: footprint
entrance effect (fluid)
The change in the velocity profile experienced by flow when there is a sudden change in the diameter of a vessel. Laminar flow will tend to stabilize some distance downstream: the distance over which this occurs is known as the entrance length.
Related term: laminar flow
envelope
A smooth curve connecting the maximum peaks of the absolute values of a signal (see Figure 26).
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Related term: analytic signal envelope
error detection
The ability to detect errors that are made because of noise or other impairments during reception or transmission of signals.
estimator (statistical)
A measure that approximates the actual quantity that is to be measured.
evanescent wave
For an incident wave past the critical angle at the boundary of a second medium, the exponentially decaying nonpropagating wave in the second medium.
Related terms: angle of incidence, angle of reflection, critical angle, refraction
exit effects
The change in the velocity profile experienced by flow when there is a sudden increase in the lumen area, for example, downstream from a stenotic orifice. Flow disturbance can result, with accompanying energy loss.
expansion amplifier
Amplifier that yields more amplification the stronger the input signal (reciprocal of compression).
exposimetry
Measurement methods for quantifying and estimating acoustic output reaching a region of interest.
exposure time
The total amount of time the transducer assembly is delivering ultrasonic energy to the subject. For a pulsed waveform, this includes the time between pulses.
ex vivo
The condition of being outside the living body. An ex vivo study refers to one carried out on tissue after it has been extracted from a living body. It is used to denote the removal of an organ, such as the kidney, for study or reparative surgery, after which it is returned to its original site.
