Recommended Ultrasound Terminology

AcronymsFigures

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target

An object to be interrogated by an ultrasound beam. For example, (1) a device specially designed to be inserted into the ultrasonic field to serve as the object on which the radiation force is to be measured, (2) a scatterer or ensemble of scatterers giving rise to a signal within the effective ultrasonic beam, or (3) a string in a test object.

targeted microbubble

See target-specific microbubble.

target-specific microbubble

A microbubble prepared to transport ligands that are specific for a given tumor, thrombus, or other target. Used in therapeutic applications. Sometimes called targeted microbubble or therapeutic microbubble.

temporal

Pertaining to time.

temporal-average intensity

See this entry under intensity.

temporal-peak acoustic pressure

The maximum value of the modulus of the instantaneous acoustic pressure at a particular point in an acoustic field. The unit is pascal (Pa).

temporal-peak intensity

See this entry under intensity.

temporal resolution

See resolution (temporal).

tensile modulus

The ratio of tensile stress to tensile strain.

tensile strain

The fractional change in the length of an object when subjected to a tensile stress.

tensile stress

The force per unit area that when applied to an object causes the object to lengthen or stretch. The unit is pascal (Pa).

Related term: Compare with compressive stress

tensor

A generalization of the concepts of vectors and matrices. In elastography, tensors are represented by matrices containing 9 elements arranged in 3 rows and 3 columns. Each element is a vector representing the magnitude and direction of a stress or strain.

Related terms: stress tensor, strain tensor

test object

A device for the evaluation of one or more parameters of an ultrasound system. In distinction with a phantom, it does not necessarily duplicate the acoustical properties of the human body. It usually contains wires and possibly other targets giving rise to echoes in response to an ultrasonic pulse.

Related term: Compare with phantom

test object, Doppler

A device designed to create a reproducible acoustic and physical setting in which one or more aspects of a Doppler system’s performance may be tested or calibrated.

texture pattern of echoes

The sonographic pattern arising from an area of interest in the body. The pattern depends primarily on the transducer frequency and beam characteristics and secondarily on the structure of the scattering tissues.

Related term: Compare with speckle

theoretical angular beam width

The computed or predicted beamwidth based on some criteria such as the -6dB width in terms of a subtended angle. The computed quantity can be  pressure, velocity, or intensity.   Often taken to be the value in the far field of an unfocused beam or at the focal length of a focused aperture.

Related terms: beamwidth, far field, focal length, focused field

theranostics

The development of more specific, individualized therapies for various diseases, by combining diagnostic and therapeutic capabilities into a single agent.

therapeutic microbubble

See target-specific microbubble.

therapeutic ultrasound

The use of ultrasound for the treatment of disease and injury rather than for diagnosis. The practice of applying ultrasound to a region of the body to achieve soft tissue healing, functional restoration, and pain reduction.

thermal dose

The quantity of ultrasound energy absorbed by a structure that is exposed to an ultrasound beam. The unit is joule (J).

thermal dose index

A dimensionless quantity representing the likelihood of an ultrasound-induced, thermal bioeffect that takes into account both the magnitude and duration of the rise in temperature of the exposed tissue

thermal energy

Energy due to random molecular motion.

thermal index (TI)

A dimensionless number used to represent the likelihood of an ultrasound-induced bioeffect caused by a rise in temperature. It is numerically defined as the ratio of the attenuated power of an ultrasound beam to the attenuated power that would cause the exposed tissue to rise to a maximum of 1°C in a specific tissue model.

Related terms: bone thermal index (TIB), soft tissue thermal index (TIS), transcranial thermal index (TIC), output display standard (ODS), mechanical index (MI)

thermally equivalent time

The duration of exposure to an acoustic beam required to produce the same magnitude of a thermally induced bioeffect, ie, an “isoeffect,” at a specified reference temperature, usually 43°C, as is produced by an exposure of a different duration and temperature, where the temperature may vary in time. The thermal dose used most often clinically is the cumulative number of equivalent minutes at 43°C, CEM43°C, or simply CEM43.

Related term: thermally equivalent time index

thermally equivalent time index

See thermal dose index.

thermoelastic expansion

The enlargement of a material due to the absorption of energy. The absorption of energy causes the local temperature to rise, the temperature elevation results in a rapid volumetric expansion of the material initiating the onset of an acoustic wave.

thresholding

Elimination of weak echoes and noise with amplitudes that are below a selected threshold level to increase the signal-to-noise ratio in a sonogram.

through-transmission imaging

The process of imaging by transmitting a sound beam through the specimen and receiving the transmitted energy on a far surface by a receiving transducer or array.

Related terms: holography, transsonogram

time-compensated gain

See time-gain compensation.

time constant

Time required for the amplitude of an exponentially decaying field quantity to decrease to 1/e = 0.368 times an initial amplitude.

time delay estimation (TDE)

The estimation of the delay between two similar waveforms. This estimation is usually made by techniques such as cross-correlation lag and signal phase measurements.

time-gain compensation (TGC)

A means of altering receiver gain with time introduced to compensate for loss in echo amplitude, usually due to attenuation and diffraction, with depth. Sometimes called depth gain compensation, ramp, attenuation compensation, and swept gain.

Related terms: automatic gain control, lateral gain control

time-intensity curve

See wash-in–wash-out curve.

time interval histogram

A kind of frequency spectral display in which the signal is displayed as a histogram representing the frequency of occurrence of a spectrum of bands of zero crossing frequencies.

time-motion display

See M-mode.

time reversal

A fundamental symmetry found in physics that states that the reversal of the final conditions (waveforms) of a process in time will elicit the initial conditions.

time sidelobes

The humps of the envelope of a pulse that trail behind the main peak of a pulse echo.

time to peak (contrast sonography)

The time intervening between contrast medium injection and the moment of maximum contrast enhancement.

tissue Doppler imaging

Ultrasonic imaging modality that measures and displays the velocity of tissue motion toward and away from the transducer.

tissue harmonic imaging

Harmonic imaging of tissue without the use of contrast microbubbles.

See harmonic imaging.

tissue-mimicking material

A material possessing acoustic propagation properties, such as the speed of sound, scatter, and attenuation, similar to that of tissue. This type of material is often used in the construction of phantoms.

tissue-mimicking phantom

A test object composed of materials possessing one or more acoustic properties that are the same as in tissue.

tissue-specific contrast medium

Sonographic contrast medium capable of being retained within a specified tissue (mainly, liver and spleen).

T-M echography

See M-mode.

T-M mode

See M-mode.

tomography

A method of imaging that uses projections from multiple angles to reconstruct an ultrasound image. A coplanar ring of transducers is most often used to transmit and receive projected sound beams, although two linear arrays may also be used. 3D tomographic images can be formed by translating the array in the elevational plane or by making a 2D array of transducers.

Related Term: ultrasound computed tomography

tone burst signal

A tone burst signal is one that has a constant amplitude for a certain length of time before decreasing essentially to zero. This pattern of excitation may occur once or be repeated many times. The product of the duration of the tone burst and the carrier frequency (ie, the effective frequency) must be 2 or more.

torsion modulus

See shear modulus.

total pressure

The sum of the ambient pressure and the acoustic pressure.

total reflection

A phenomenon in which no transmission across a boundary occurs if the angle of incidence is equal to or larger than the “critical angle.”

See critical angle.

transceiver

A transducer used for both transmission and reception of acoustic energy. This is the customary configuration in diagnostic ultrasound.

See pulse-echo and pulse-echo imaging.

transceiver voltage response

The ratio of the voltage amplitude of the energizing pulse to the resulting voltage amplitude corresponding to the echo from a perfect planar reflector at a specified distance at normal incidence. Usually measured in decibels (dB).

See transceiver.

transcranial

Passing or performed through the skull.

transcranial thermal index (TIC)

See cranial thermal index (TIC).

transcranial ultrasound

A procedure in which an ultrasound beam is transmitted through the skull bone to treat or examine the brain, cerebral blood vessels, and other intracranial structures.

transducer

A device capable of converting energy from one form to another. Specifically in ultrasonics, it is a device capable of converting electrical energy to mechanical energy within the ultrasonic frequency range and conversely of converting mechanical energy to electrical energy. If the device is used only to transmit or to receive, the device should be referred to as the “transmitting” or “receiving” transducer. If, in the application, the device performs both functions, the term may be left unqualified or called a transceiver.

transducer aperture

The totality of the radiating surfaces of the transducer elements or transducer(s) (see Figures 2, 5, 7, and 9).

Related term: source aperture

transducer aperture plane

The plane that is orthogonal to the beam axis of the unsteered beam and is adjacent physically to the ultrasonic transducer totality of the radiating surfaces of the transducer elements or transducer(s) (see Figures 5, 7, and 9).

Related terms: source aperture, source aperture plane, transducer aperture

transducer array

A group of transducers working together to form a functional unit. Arrays may be of several types, depending on the transducer configuration: linear, annular, rectangular, etc.

Related terms: 1 dimensional array, 1.25-dimensional array, 1.5-dimensional array, 1.75-dimensional array, 2-dimensional array, convex array, curved array, linear array, matrix array, phased array, row column array

transducer assembly

Those parts of medical ultrasonic equipment comprising the ultrasonic transducer and/or ultrasonic transducer element group together with any integral components, such as an acoustic lens, integral standoff, etc. The transducer assembly is usually separable from the ultrasound instrument console.

See standoff, transducer element, ultrasonic transducer element group.

transducer dynamic response

See dynamic response.

transducer efficiency

The ratio of ultrasonic output power from a transmitting transducer to the electrical input power. Also, the ratio of electrical output power from a receiving transducer to the ultrasonic input power. These ratios need not be equal.

Related term: transducer loss

transducer element

An individually electrically addressable transducer with a radiating surface. It is a single part of a contiguous arrangement of other transducers (see Figures 18 and 19).

transducer element group

See ultrasonic element group.

transducer loss

The ratio of ultrasonic output power from a transmitting transducer connected to an electrical source of a known impedance to the electrical power of the source connected to a load matching its impedance. Also, the ratio of electrical output power from a receiving transducer connected to a known electrical load to the ultrasonic input power as connected to a known medium such as water or tissue. Usually these ratios are expressed in decibels (dB).

Related term: transducer efficiency

transducer output face

External surface of a transducer assembly that is either directly in contact with the patient or is in contact with a water or liquid path to the target. Also called probe face.

Related term: transducer assembly

transducer ring-down

The duration of decay of oscillation following the generation of a pulse. When an ultrasonic transducer is used in the pulsed mode, it is shock excited by a voltage spike, which puts energy into the resonant mechanical system of the transducer. This energy is dissipated by the combination of the viscous damping in the transducer, the acoustic load at the front and back of the transducer, and the dynamic damping provided by the trailing edge of the excitation. The resulting damped oscillation has been referred to by some authors as “ring-down.” The total damping provides for improved axial resolution by shortening the pulse duration.

transducer standoff distance

Shortest distance between the transducer output face and the patient entry plane. The term “contact” is used to connote direct contact between the transducer output face and the patient, with the transducer standoff distance equal to zero. The unit is millimeter (mm).

Related term: standoff

transducer self-heating

The temperature elevation occurring within a transducer probe caused by circuits overcoming electrical resistance and by absorbed ultrasound. When a heated transducer is placed in contact with tissue, temperature elevation can be caused by heat conduction. This mechanism is different from the temperature elevation occurring in tissue caused by the absorption of propagating ultrasonic energy.

transducer voltage response

See transceiver voltage response.

transesophageal echocardiogram (TEE) 

A sonographic examination performed with a special transducer that is inserted into the esophagus to examining the heart.

transfer function

A mathematical formula used to characterize a system. It is the ratio of the output frequency spectrum to the input frequency spectrum and therefore permits the prediction of the output of any linear system for any given input.

transient

A pulsed, damped oscillation or other temporary phenomenon occurring in a system before reaching a steady- state condition.

transient elastography

A method similar to sonoelasticity imaging but where the applied shear wave is a transient pulse, and the detection involves estimating the velocity of the shear wave from rapid B-mode imaging sequences. The speed of propagation of the shear wave is related to the density and shear elasticity of the medium.

transition distance

For a given longitudinal plane, the equivalent area of the ultrasonic transducer aperture width divided by π times the effective wavelength. For example, for a circular transducer or spherical transducer of radius a, it is zt = a2/λ. For a square transducer with a side L, zt = L2/λ (see Figure 3).

Related term: Contrast with Rayleigh distance

transition zone

That portion of the acoustic field around the transition distance that includes neighboring parts of the near field (Fresnel zone) and the far field (Fraunhofer zone). The transition zone has no distinct boundaries but frequently is taken to be centered at the position of the transition distance.

transit time broadening

The spectral broadening that occurs as a consequence of the movement of scatterers through a Doppler sample volume of finite size. The smaller the sample volume, the more pronounced the transit time broadening. Also known as geometric or intrinsic spectral broadening.

transluminal echography

A sonographic technique in which an ultrasound transducer is brought into a body cavity or blood vessel and the ultrasound is transmitted through the wall. Endovascular, transesophageal, and endovaginal echography are examples.

transmission

A general term implying passage of energy through a material.

transmission coefficient

Ratio between pressure amplitude of incident and transmitted waves at an interface between two media:

t = 2Z2/(Z2 + Z1), where t is the transmission coefficient, and Z1 and Z2 are acoustic impedances of the media.

transmission imaging

The production of an image by analysis of sound that completely traverses the body and is detected by a second transducer located on the opposite side.

transmission loss

See attenuation loss.

transmit beam pattern

See beam pattern.

transmit beamformer

A transmit beamformer organizes the excitation pulses going to array elements to control the ultrasound beam propagating from the transducer elements.

See beamformer, delay and sum beamformer, and receive beamformer.

transmit focus

The focal point of an emitted ultrasound beam.

Related term: Contrast with receive focus

transmit power

See output power.

transmitted acoustic pulse

The acoustic pulse transmitted from the transducer into the medium following the application of an energizing pulse.

transmitter pulse

An electrical pulse of any shape used to excite an ultrasonic transducer.

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

transmitting transducer

A transducer dedicated to transmitting sound.

transpulmonary contrast medium

All modern commercially available contrast media consist of microbubbles able to pass through the pulmonary vascular bed and reach the left cardiac chambers and the peripheral circulation. It is no longer necessary to specify this characteristic.

transrectal imaging

Imaging of the anatomic structures within the pelvic region while the transducer is inserted in the rectum.

transsonic

Describes a region of a relatively unattenuating medium. A distinction should be made between a transsonic region and a shadowing region; generally, this is done by observing the back boundary and underlying structures.

Related term: Compare with anechoic

trans-sonogram

See through-transmission imaging.

transvaginal imaging

Imaging of the anatomic structures within the female pelvis while the transducer is placed in the vagina.

Related term: endovaginal imaging

transverse image plane

A plane perpendicular to the long axis of the body or structure of interest. With respect to the body, a transverse plane extends from left to right and divides the body into cephalic and caudal regions (see Figure 1).

transverse oscillation method

A way of implementing vector Doppler on conventional imaging systems and transducers. It uses two parallel receive beams with a 90° phase shift to calculate longitudinal and lateral Doppler components to create a 2-dimensional velocity vector field.

transverse plane (ultrasound beam)

A plane that is perpendicular to the beam axis.

transverse wave

Wave in which the direction of particle displacement at each point of the medium is parallel to the wavefront.

triplex imaging

Presentation of 3 modes: usually 2-dimensional, color flow, and pulsed Doppler.

tumor stain

Dense (homogeneous or inhomogeneous) enhancement of a (hypervascular) lesion during the arterial phase. An angiographic term that should be avoided in contrast-enhanced sonographic imaging.

turbulence

Disorganized flow, chaotically oriented in many directions simultaneously. Occurs in disturbed flow when a critical value of the Reynolds number is exceeded.

type testing values

For acoustical output parameters, the maximum probable acoustical output levels for a specified system.