Diagnostic Ultrasonography - Chpt. 1

Front 1

Acoustic impedance

Back 1

measure of a material's resistance to the propagation of sound; expressed as the product of acoustic velocity of the medium and the density of the medium

Front 2

Amplitude

Back 2

strength of the ultrasound wave measured in decibels

Front 3

Angle of incidence

Back 3

angle at which the sound beam strikes the interface

Front 4

Angle of reflection

Back 4

angle at which the beam of the sound is reflected from an interface; the angle of reflection equals the angle of incidence

Front 5

Attenuation

Back 5

reduction in the amplitude and intensity of a sound wave as it propagates through a medium; attenuation of ultrasound waves in tissue is caused by absorption and by scattering and reflection

Front 6

Axial resolution

Back 6

refers to the minimum distance between two structures positioned along the axis of the beam where both structures can be visualized as separate objects

Front 7

Bulk modulus

Back 7

amount of pressure required to compress a small volume of material a small amount

Front 8

Compression

Back 8

region of increased particle density

Front 9

Crystal

Back 9

special material in the transducer that has the ability to convert electrical impulses into sound waves

Front 10

Cycle

Back 10

a sequence of events occurring at regular intervals; a wavelength cycle is that of a particle density that varies from maximum in the compression zone to a minimum in the reflection zone and back to maximum in the successive compression zone to complete

Front 11

Decibel (dB)

Back 11

unit used to quantitatively express the ratio of two amplitudes or intensities; decibels are not absolute units, but express one sound level or intensity in terms of another or in terms of a reference (e.g., the amplitude 10 cm from the transducer is 10

Front 12

Dynamic range

Back 12

ratio of the largest to smallest signals that an instrument or component of an instrument can respond to without distortion

Front 13

Focal zone

Back 13

the region over which the effective width of the sound beam is within some measure of its width at the focal distance

Front 14

Frame rate

Back 14

rate at which images are updated on the display; dependent on frequency of the transducer and depth selection

Front 15

Fraunhofer zone

Back 15

the field farthest from the transducer during the formation of the sound beam

Front 16

Frequency

Back 16

number of cycles per second that a periodic event or function undergoes; number of cycles completed per unit of time; the frequency of a sound wave is determined by the number of oscillations per second of the vibrating source

Front 17

Fresnel zone

Back 17

the field closest to the transducer during the formation of the sound beam

Front 18

Gain

Back 18

measure of the strength of the ultrasound signal; can be expressed as a simple ration or in decibels; overall gain amplifies all signals by a constant factor regardless of the depth

Front 19

Gray scale

Back 19

B-mode scanning technique that permits the brightness of the B-mode dots to be displayed in various shades of gray to represent different echo amplitudes

Front 20

Hertz (Hz)

Back 20

unit for frequency, equal to 1 cycle per second

Front 21

Intensity

Back 21

power per unit area

Front 22

Interface

Back 22

surface forming the boundary between media having different properties

Front 23

Kilohertz (kHz)

Back 23

1000 Hz

Front 24

Lateral resolution

Back 24

the minimum distance between two objects where they still can be displayed as separate objects

Front 25

Megahertz (MHz)

Back 25

1,000,000 Hz

Front 26

Period

Back 26

duration of a single cycle of a periodic wave or event

Front 27

Piezoelectric effect

Back 27

generation of electric signals as a result of an incident sound beam on a material that has piezoelectric properties; in the converse (or reverse) piezoelectric effect, the material expands or contracts when an electric signal is applied

Front 28

Power

Back 28

rate of energy flow over the entire beam of sound; in general terms it is the rate at which energy is transmitted and is often measured in watts (W) or milliwatts (mW)

Front 29

Pulse duration

Back 29

the time interval required for generating the transmitted pulse; the pulse duration is calculated by multiplying the number of cycles in the pulse times the period

Front 30

Pulse repetition frequency (PRF)

Back 30

in pulse-echo instruments, it is the number of pulses launched per second by the transducer

Front 31

Real-time

Back 31

ultrasound instrumentation that allows the image to be displayed many times per second to achieve a "real-time" image of anatomic structures and the motion patterns

Front 32

Refraction

Back 32

change in the direction of propagation of a sound wave transmitted across an interface where the speed of sound varies

Front 33

Resolution

Back 33

ability of the transducer to distinguish between two structures adjacent to one another

Front 34

Slice thickness

Back 34

thickness of the section in the patient that contributes to echo signals on any one image

Front 35

Spatial pulse length

Back 35

the product of a number of cycles in the pulse and wavelength of the pulse

Front 36

Temporal resolution

Back 36

ability of the system to accurately depict motion

Front 37

Time gain compensation (TGC)

Back 37

also referred to as depth gain compensation (DGC); ability to compensate for attenuation of the transmitted beam as the sound wave travels through tissues in the body; usually, individual POT (potentiometer) controls allow the operator to manually change the amount of compensation necessary for each patient to produce a quality image

Front 38

Transducer

Back 38

any device that converts energy from once form to another

Front 39

Velocity

Back 39

in ultrasound, the tissue density determines the speed (velocity) of the ultrasound wave

Front 40

Wave

Back 40

propagation of energy that moves back and forth or vibrates at a steady rate

Front 41

Wavelength

Back 41

distance over which a wave repeats itself during one period of oscillation

Front 42

Aliasing

Back 42

technical artifact occurring when the frequency change is so large that it exceeds the sampling view and pulse repetition frequency

Front 43

Color flow

Back 43

velocity in each direction is quantified by allocating a pixel to each area; each velocity frequency is allocated a color; flow toward the transducer may be red; flow away from the transducer may be blue

Front 44

Doppler shift

Back 44

change in frequency of a reflected wave; caused by motion between the reflector and the transducer's beam

Front 45

Continuous wave (CW) Doppler

Back 45

one transducer continuously transmits sound, and one continuously receives sound; used in higher-velocity flow patterns

Front 46

Doppler angle

Back 46

the angle that the reflector path makes with the ultrasound beam; the most accurate velocity is recorded when the beam is parallel to flow

Front 47

Frequency shift

Back 47

amount of change in the returning frequency compared with the transmitting frequency when the sound wave hits a moving target, such as blood in an artery

Front 48

Gate

Back 48

the sample site from which the signal is obtained with pulsed Doppler

Front 49

Laminar

Back 49

normal pattern of vessel flow; flow in the center of the vessel is faster than it is at the edges

Front 50

Nyquist sampling limit

Back 50

in pulsed Doppler, the Doppler signal must be sampled at least twice for each cycle in the wave if the Doppler frequencies are to be detected accurately

Front 51

Pulsed wave (PW) Doppler

Back 51

sound is transmitted and received intermittently with one transducer

Front 52

Rarefaction

Back 52

region of decreased particle density

Front 53

Resistance

Back 53

passive force in opposition to another active force; occurs when tissue exerts pressure against the flow

Front 54

Spectral analysis

Back 54

analysis of the entire frequency spectrum

Front 55

Spectral broadening

Back 55

echo fill-in of the spectral window that is proportional to the severity of the stenosis (may also be due to poor technique or gain that is too high)