Recommended Ultrasound Terminology

AcronymsFigures

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image format

A spatial arrangement or  pattern of  pixels or voxels. In two dimensional imaging, for  example, a typical 2D image  consists of M x N pixels in a rectangular pattern.

Related terms: pixel, voxel

image fusion

The process of aligning and/or combining relevant information from two or more images and/or imaging modalities into a single image. For example, ultrasound/MRI and ultrasound/CT fusion.

 
image optimization

Any technique or processing procedure that is used to obtain the best image to achieve a stated aim. The usual aim is to obtain the image that will have the greatest diagnostic value.

 
image plane

See scan plane.

imaginary number

In mathematics, the second of the two numbers comprising a complex number.

Related term: complex number

immersion coupling

A method of coupling an ultrasonic transducer to an object by placing both in a bath of a coupling medium, such as water.

impedance

See acoustic impedance.

impedance, acoustic

See acoustic impedance.

impedance (fluid)

The ratio of pressure to the flow rate in a vessel. The ratio may be expressed as a function of frequency in time- varying flow. Impedance summarizes the effect on the flow rate of resistance, compliance, and inertia when the pressure varies with time.

impedance ratio

The ratio Z2/Z1, where Z1 and Z2 are the characteristic acoustic impedances of two contiguous media, respectively.

impediography

A technique for measuring and displaying acoustic impedances, whereby the impedance magnitude or phase  is plotted as a continuous function of position or as an image.

impulse

A short excitation, much shorter than the response of the system excited.

Related terms: energizing pulse, impulse excitation (electrical), impulse response, pulse, transmitter pulse

impulse (electrical)

A type of excitation in which a very short electrical impulse is applied to the device or system for the purpose of either generating a short pulse or for characterizing the system response. Also called shock excitation.

Related terms: energizing pulse, impulse, impulse response, pulse, transmitter pulse

impulse (mechanical)

Time integral of a force over the time during which the force is applied.

impulse response

The response of a device or system following an impulse.

Related terms: energizing pulse, impulse, impulse excitation (electrical), impulse response, transmitter pulse

inclusive mode

Combined operating mode having acoustic output levels (peak negative acoustic pressure and spatial-peak temporal-average intensity) less than those corresponding to a specified discrete operating mode.

incoherence

A condition in which the component wavelets in a sound beam or waveform are not in phase. This occurs, for example, when several independent unsynchronized transducer outputs are combined to produce a sound beam.

Related term: compare with coherence

indentation test (tissue)

A mechanical test of the elastic properties of a tissue sample by which a known compressive load is applied to the sample and the resultant deformation is measured.

inertial cavitation

A short-lived cavitation event initiated by a negative pressure wave. A spherical cavity contracts such that the inward motion approximates that of a Rayleigh cavity, and the speed of collapse increases until a rapid rise in pressure within the cavity arrests the inward motion. Sometimes called collapse cavitation, it is associated with large mechanical stresses, high localized pressures and temperatures, shock waves and jet generation, and chemical reactions involving free radicals. Previously called transient cavitation.

Related term: Rayleigh cavity, cavitation, noninertial cavitation, stable cavitation, transient cavitation

infrasound

Acoustic oscillation whose frequency is below the low-frequency limit of audible sound (about 20 Hz).

inhomogeneous

Refers to a property of a medium whose value is slightly different throughout the medium.

Related term: Contrast with homogeneous, heterogeneous

inhomogeneous enhancement

Coexistence of enhanced and unenhanced areas. Patterns such as mosaic or honeycomb-like enhancement are included among inhomogeneous enhancement patterns.

initialization mode

A defined state of an ultrasound system corresponding to the mode of operation and system settings when a new patient procedure is initiated.

in phase

Having waveforms that are of the same frequency and that pass through corresponding values at the same instant.

insertion loss

The decrease in received power when an object is placed within a signal pathway relative to the power in its absence. In the context of a 1-way ultrasound transmission pathway, if A1 is the attenuation (in decibels) in the absence of an object of interest and A2 is the attenuation (in decibels) in its presence, then the insertion loss (IL) is given by IL = A2 – A1.

Usually refers to the ratio of the round trip (pulse echo) into a specified electrical load (A2) relative to the source connected to the same specified load (A1) expressed in decibels (dB) as a function of frequency.

in situ

The condition in which the structure of interest is in its natural or normal location.

insonation

See insonification.

insonification

Application of sound to an object, medium, or person.

instantaneous acoustic (or sound) pressure

The value of the pressure amplitude minus the ambient pressure at a particular instant in time and at a particular point in an acoustic field. The unit is pascal (Pa).

instantaneous particle acceleration

The time derivative of instantaneous particle velocity.

instantaneous particle displacement

In an elastic medium, a vector whose extremity is the position of the particle at a given instance and whose origin is at the equilibrium position of the particle.

instantaneous potential sound energy density

One half of the quotient of the square of the instantaneous sound pressure divided by the modulus of elasticity of the medium.

instantaneous sound pressure

At a point in a medium, the difference between sound pressure: the pressure existing at the instant considered and the static pressure.

instantaneous (value)

The value of a quantity at a given point in time. This is in contrast to quantities that represent values averaged over a time interval.

integer

A number that can be written without a fractional component. For example, 1, 2, 4, 9, 0, –2, –4, and –8 are integers. The following are not integers: ½, –¾, 3.1459, and √2.

Synonym: whole number

integrated backscatter

An estimate of the backscattered ultrasonic energy from a volume of tissue. It is computed from the mean value of the backscattered energy over a finite bandwidth or time period.

integration

A mathematical operation applied to a function over an interval giving the area under the function between the upper and lower limits of the interval. Integration is the inverse of differentiation.

Compare to differentiation

intensity

The rate of energy flow (power) through a unit area perpendicular to the direction of propagation. The unit of intensity is watts per square meter (W/m2) or, more commonly, watts per square centimeter (W/cm2). The particular intensity intended should be specified as defined below:

intensity calibration factor (hydrophone)

The received hydrophone voltage squared per unit of intensity in a plane wave of specified frequency, ƒ, in water at a specified temperature.

intensity modulation

Regulation of the luminance of a display to represent information, such as echo amplitude, as variations of the luminance.

interference

The phenomenon in which two or more waves add together (constructively or destructively, depending on their relative amplitudes and phases).

interference, constructive

The phenomenon of interference in which the resultant wave has an amplitude greater than that of either of the two interfering waves alone.

interference, destructive

The phenomenon of interference in which the resultant wave has an amplitude less than that of either of the two interfering waves alone.

interferometry

Method of measuring a property of a material or wave that uses interference between two or more waves.

intermediate scattering

Scattering from an intermediate-sized scatterer which is approximately the same size as the incident acoustic wavelength

See intermediate-sized scatterer.

intermediate-sized scatterer

Scatterer whose dimensions are on the order of the ultrasonic wavelength, which produces diffractive scattering.

Related terms: diffractive scatterer, diffuse reflector, Rayleigh scatterer, specular reflector

intermittent imaging

Low–frame rate imaging (usually <5 Hz). Often used in contrast imaging to limit interaction between the acoustic field and the microbubbles.

intermittent mode

Very low–frame rate acquisition, generally used during and immediately after the destruction mode. The high-power pulses of the destruction mode may be emitted automatically under software control or manually by the operator. Some protocols include continuous acquisition during the arterial phase and intermittent imaging thereafter.

Related term: destruction-replenishment (or destruction-reperfusion) technique

interpulse interval

See pulse repetition period.

interpulse phase inversion

See pulse inversion mode imaging.

interval delay imaging (archaic)

See intermittent imaging.

interval delay imaging

When microbubbles are disrupted by a high-pressure beam (see intermittent mode), and intense enhancement is detected, it is necessary to wait a minimum interval to have replenishment of the insonated area by new incoming microbubbles. Hence, the intermittent mode is also known as the interval delay scanning technique.

See intermittent mode.

Related term: destruction-replenishment (or destruction-reperfusion) technique.

intracardiac imaging

Ultrasonic imaging from within the heart. Also commonly referred to as ICE: intracardiac echocardiography

intraoperative imaging

In vivo imaging performed during a surgical procedure.

intravascular ultrasound (IVUS)

The application of ultrasound for imaging or therapy from inside blood vessels using a miniaturized ultrasound probe(s) attached to a catheter.

inverse discrete Fourier transform (IDFT)

Digital version of inverse Fourier transform. A computational technique used in ultrasound signal processing to analyze frequency components of echoes, aiding in image formation and Doppler analysis.

Related term: inverse Fourier transform, Fourier transform, discrete Fourier transform

inverse Fourier transform

A mathematical integral or algorithm that converts a spectrum into a waveform.

See: Fourier transform, discrete Fourier transform.

inverse problem (elastography)

The mathematical problem of deriving the distribution of elastic moduli in a target from the knowledge of the distribution of the strains therein, the boundary conditions, and knowledge of applied stress, under some restrictions.

in vitro

Experimental condition in which a specimen of interest is removed from an organism and studied in an artificial environment, usually a test tube or a Petri dish.

in vivo

Tissue in its natural condition within the living subject.

ionizing radiation

Radiation sufficiently energetic to be able to eject one or more electrons from atoms to produce ions. Ultrasound is a nonionizing kind of radiation.

isochronous

An adjective meaning “at the same time”; a synonym for synchronous or simultaneous.

isochronous volume

Region where acoustic waves or wavefronts arrive at the same time.

isoenhanced lesion

Lesion with the same echogenicity (enhancement) as that of the surrounding normal parenchyma.

isotropic

Having nondirectional properties (ie, physical properties that are independent of direction). For example, the speed of sound is not a function of the direction of propagation through an isotropic material. In contrast, the velocity of sound in muscle differs when propagating parallel to the fibers than when propagating at a right angle to the fibers; thus, muscle is anisotropic.

Compare to anisotropic