Physics Module 3 Terms

Front 1

ABSORPTION

Back 1

The conversion of energy from the sound wave into heat within the medium.

Depends on properties of the medium as well as the frequency of operation.

Front 2

AMPLIFICATION

Back 2

Making something larger, greater, or stronger.

Used synonymously with the term "gain"

Front 3

ATTENUATION

Back 3

A decrease in intensity and amplitude due to wave interactions with eh medium including absorption, refraction, and reflection.

Front 4

ARTIFACT

Back 4

A broad category which includes an image feature or characteristic which is not representative to the true anatomical location or characteristic.

Front 5

ATTENUATION ARTIFACTS

Back 5

Artifacts that result from attenuation such as shadowing, enhancement or refraction.

Front 6

COMET TAIL

Back 6

A specific form of reverberation named for the appearance of a flashlight or "tail" produced when sound reverberates within a metallic structure such as surgical clips, needles, and prosthetic valve apparatus.

Front 7

COMPOUND IMAGING

Back 7

A technique to improve signal-to-noise and reduce artifacts by transmitting multiple frames at slightly varying steer angles and then averaging together to create one image.

Front 8

CONVERSION OF ENERGY

Back 8

One of the fundamental tenets of physics. This theorem states that energy cannot be created or destroyed but is only changed from one form to another form.

Front 9

CRITICAL ANGLE

Back 9

The incident angle at which total internal reflections occur.

Front 10

ECHO

Back 10

A sound wave which has been reflected off a surface and is heard after the original sound.

Often refer to a cardiac scan.

Front 11

EDGE/REFRACTIVE SHADOWING

Back 11

A drop out or decrease in intensity which results from refraction.

Generally occurs from the edges of specular reflections.

Front 12

ENHANCEMENT ARTIFACT

Back 12

A brighter than normal echo below a structure which is either a weaker reflector or less absorbing than normal.

Front 13

FREQUENCY COMPOUNDING/FUSION

Back 13

Averaging two or more images created at different transmit frequencies.

lower frequency images = better penetration,

higher frequency images = better resolution.

Front 14

FUNDAMENTAL FREQUENCY

Back 14

Transmit frequency when performing harmonic imaging.

Front 15

HUYGEN'S PRINICPLE

Back 15

States that all points on a wavefront can be treated as point sources producing spherical secondary wavelets, whose tangential surface predicts the new position of the wave front over time.

Front 16

INCIDENT ANGLE

Back 16

The angle formed between the beam direction and the normal at the point of incidence.

Can also be measured as the angle formed between he wavefront and the reflecting interface a the point of reflection.

Front 17

INSONIFICATION (DOPPLER) ANGLE

Back 17

Measured between the beam steering direction and the direction (head) of the flow.

Front 18

LOCATIONAL ARTIFACTS

Back 18

Artifacts that result in structures appearing either displaced in an image from the true location or the presence of a structure or signal which does not even exist.

Front 19

MECHANICAL INDEX

Back 19

A parameter that indicates the likelihood of mechanical bioeffects (cavitation) occurring.

Calculated by dividing the peak rarefaction pressure by the square root of the operating frequency.

Front 20

MIRROR IMAGE ARTIFACTS

Back 20

An artifact that produced when a structure is located in front of a specular reflector which results in the structure being displayed twice: once in the correct locations, and one distal to and symmetric about the specular reflecting surface.

Front 21

MULTI-PATH ARTIFACT

Back 21

An artifact that results in a structure being displayed artificially deeper than reality because the beam does not propagate in a straight line to and from the object.

Occurs generally in the presence of specular reflectors.

Front 22

NORMAL INCIDENCE

Back 22

Implies that the wave propagation direction is perpendicular to the interface ( or that the wavefront is parallel to the interface).

No refraction

Front 23

RANGE AMBIGUITY ARTIFACT

Back 23

An undesirable result of the fact that sound continues to travel and reflect back form depths deeper than the Doppler gate depth.

Not a problem unless the Doppler sample volume (gate) is shallow.

Front 24

RAYLS

Back 24

The unit for acoustic impedance

Front 25

RAYLEIGH SCATTERING

Back 25

Frequency dependent scattering.

This type of reflection occurs from structures which are small relative to the wavelength.

Front 26

REFLECTION

Back 26

The phenomenon of causing a propagating wave to change direction such that some of the wave does not continue to propagate forward.

Front 27

REFRACTION

Back 27

The bending of a beam at an interface of two media. For this to occur there must be a change in propagation speed and an incident angle other than 0 degrees (other than normal).

Front 28

REVERBERATION

Back 28

An artifact caused by sound bouncing between multiple structures.

Front 29

RING DOWN ARTIFACT

Back 29

When sound reverberates within an air sac the boundaries of the air sac are redrawn repeatedly creating a bright tail.

Also refers to the reverberation which commonly occurs at the surface of the transducer.

Front 30

SCATTER/BACKSCATTER

Back 30

A type of reflection which results in energy being redirected back toward the source.

This type of reflection occurs from surfaces which are rough with respect to the wavelength.

Relatively angle independent.

Front 31

SHADOWING

Back 31

Caused by any form of attenuation stronger than the attenuation of the surrounding area.

Front 32

SNELL'S LAW

Back 32

The rule which predicts how much refraction occurs. When the incident angle does not equal the transmitted angle, refraction has occurred. The greater the difference between eh incident angle and the transmit angle, the more refraction that has occurred.

Front 33

SPECTAL MIRRORING

Back 33

A Doppler artifact which results from one of two sources: imperfect separation between the forward and reverse flow channels and quadrature, or from and insonification angle close to 90 degrees such that the elements on one side of the center of the aperture are seeing flow at an angle less than 90 degrees while elements of the other side of the center line of the aperture are seeing flow at angles greater than 90 degrees.

Front 34

SPECULAR REFLECTION

Back 34

Strong angularly dependent reflection in which the angle of incidence equals the angle of reflection.

mirror-like reflection

Front 35

THERMAL INDEX

Back 35

A model produced parameter that indicates the calculated worst case temperature rise in degrees Celsius.

TIS=Thermal Index in Soft Tissue

TIB=Thermal Index in Bone

TIC=Thermal Index in Cranial Bone

Front 36

TOTAL INTERNAL REFLECTION

Back 36

The result of dramatic refraction at an interface between two structures such that no energy is transmitted across the interface, and all of the energy is reflected internally.

Front 37

VISCOSITY

Back 37

The ratio of the shear stress to the shear rate of a fluid, or more simply stated: a measure of the resistance of a fluid to flow due to attraction of the molecules.

Front 38

WAVEFRONT

Back 38

The front surface of the wave.