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55 Cards in this Set

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Acoustic impedance
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
Amplitude
strength of the ultrasound wave measured in decibels
Angle of incidence
angle at which the sound beam strikes the interface
Angle of reflection
angle at which the beam of the sound is reflected from an interface; the angle of reflection equals the angle of incidence
Attenuation
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
Axial resolution
refers to the minimum distance between two structures positioned along the axis of the beam where both structures can be visualized as separate objects
Bulk modulus
amount of pressure required to compress a small volume of material a small amount
Compression
region of increased particle density
Crystal
special material in the transducer that has the ability to convert electrical impulses into sound waves
Cycle
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
Decibel (dB)
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
Dynamic range
ratio of the largest to smallest signals that an instrument or component of an instrument can respond to without distortion
Focal zone
the region over which the effective width of the sound beam is within some measure of its width at the focal distance
Frame rate
rate at which images are updated on the display; dependent on frequency of the transducer and depth selection
Fraunhofer zone
the field farthest from the transducer during the formation of the sound beam
Frequency
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
Fresnel zone
the field closest to the transducer during the formation of the sound beam
Gain
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
Gray scale
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
Hertz (Hz)
unit for frequency, equal to 1 cycle per second
Intensity
power per unit area
Interface
surface forming the boundary between media having different properties
Kilohertz (kHz)
1000 Hz
Lateral resolution
the minimum distance between two objects where they still can be displayed as separate objects
Megahertz (MHz)
1,000,000 Hz
Period
duration of a single cycle of a periodic wave or event
Piezoelectric effect
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
Power
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)
Pulse duration
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
Pulse repetition frequency (PRF)
in pulse-echo instruments, it is the number of pulses launched per second by the transducer
Real-time
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
Refraction
change in the direction of propagation of a sound wave transmitted across an interface where the speed of sound varies
Resolution
ability of the transducer to distinguish between two structures adjacent to one another
Slice thickness
thickness of the section in the patient that contributes to echo signals on any one image
Spatial pulse length
the product of a number of cycles in the pulse and wavelength of the pulse
Temporal resolution
ability of the system to accurately depict motion
Time gain compensation (TGC)
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
Transducer
any device that converts energy from once form to another
Velocity
in ultrasound, the tissue density determines the speed (velocity) of the ultrasound wave
Wave
propagation of energy that moves back and forth or vibrates at a steady rate
Wavelength
distance over which a wave repeats itself during one period of oscillation
Aliasing
technical artifact occurring when the frequency change is so large that it exceeds the sampling view and pulse repetition frequency
Color flow
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
Doppler shift
change in frequency of a reflected wave; caused by motion between the reflector and the transducer's beam
Continuous wave (CW) Doppler
one transducer continuously transmits sound, and one continuously receives sound; used in higher-velocity flow patterns
Doppler angle
the angle that the reflector path makes with the ultrasound beam; the most accurate velocity is recorded when the beam is parallel to flow
Frequency shift
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
Gate
the sample site from which the signal is obtained with pulsed Doppler
Laminar
normal pattern of vessel flow; flow in the center of the vessel is faster than it is at the edges
Nyquist sampling limit
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
Pulsed wave (PW) Doppler
sound is transmitted and received intermittently with one transducer
Rarefaction
region of decreased particle density
Resistance
passive force in opposition to another active force; occurs when tissue exerts pressure against the flow
Spectral analysis
analysis of the entire frequency spectrum
Spectral broadening
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)