Ch. 1 Foundations of Sonography Flashcards
Change in the direction of propagation of a sound wave transmitted across an interface where the speed of sound varies
Refraction
Angle at which a sound beam strikes the interface between two types of tissue
Angle of incidence
Power per unit area
Intensity
Special material in the transducer that has the ability to convert electric impulses into sound waves
Crystal
Propagation of energy that moves back and forth or vibrates at a steady rate
Wave
Any device that converts energy from one form to another
Transducer
Number of cycles per second that a periodic event or function undergoes
Frequency
Measure of material’s resistance to the propagation of sound; expressed as the product of acoustic velocity of the medium and density of the medium
Acoustic Impedance
Generation of electric signals as the result of an incident sound beam on a material that has piezoelectric properties
Piezoelectric Effect
Region over which the effective width of the sound beam is within some measure of its width at the focal distance
Focal Zone
Reduction in amplitude and intensity of a sound wave as it propagates through a medium
Attenuation
Passive force in opposition to another, active force; occurs when tissue exerts pressure against the flow
Resistance
Surface forming the boundry between media having different properties
Interface
Region of increased particle density
Compression
Distance over which a wave repeats itself during one period of oscillation
Wavelength
Refers to the minimum distance between two structures positioned along the axis of the beam where both structures can be visualized as separate objects
Axial Resolution
Rate of energy flow over the entire beam of sound
Power
Unit used to quantitatively express the ratio of two amplitudes or intensities
Decible (db)
1,000,000 Hz
Megahertz (MHz)
Ability of the transducer to distinguish between two structures adjacent to one another
Resolution
TIme interval required for generating the transmitted pulse
Pulse duration
Sequence of events occurring at regular intervals
Cycle
Speed of ultrasound wave; determined by tissue density
Velocity
Minimum distance between two objects at which they still can be displayed as separate objects
Lateral resolution
Unit for frequency; equal to 1 cycle per second
Hertz (Hz)
Field closest to the transducer during formation of the sound beam
Fresnel zone
Angle of incidence at which the sound beams strike the interface
Angle of reflection
1000 Hz
Kilohertz (KHz)
Field farthest from the transducer during formation of the sound beam
Fraunhofer zone
Thickness of the secretion in a patient that contributes to echo signals on any one image
Slice thickness
Sound transmitted and received intermittently with one transducer
Pulse wave (PW) Doppler
Ability to compensate for attenuation of the transmittal beam as the sound wave travels through tissue in the body
Time gain compensation (TGC)
Change in frequency of a reflected wave; caused by motion between the reflector and the transducer’s beam
Doppler shift
One transducer continuously transmits sound, and one continuously receives sound; used in high- velocity flow patterns
Continuous wave (CW) Doppler
Normal pattern of vessel flow; flow in the center of the vessel is faster that it is at the edges
Laminar
Rate at which images are updated on the display; dependent on transducer frequency and depth selection
Frame rate
Analysis of the entire frequency spectrum
Spectral analysis
Technical artifact that occurs when the frequency change is so great that it exceeds the sampling view and pulse repetition frequency
Aliasing
In pulse-echo instruments, it is the number of pulses launched per second by the transducer
Pulse repetition frequency (PRF)
Ability of the system to accurately depict motion
Temporal resolution
Ratio of the largest to smallest signals that an instrument of a component of an instrument can respond to without distortion
Dynamic range
In pulse Doppler, the Doppler signal must be sampled at least twice for each cycle in the wave if Doppler frequencies are to be detected accurately
Nyquist sampling limit
Strength of ultrasound wave measured in decibels
Amplitude
Measure of strength of the ultrasound signal
Gain
Echo fil-in of the spectral window that is proportional to the severity of stenosis
Spectral broadening
Ultrasound instrumentation that allows the image to be displayed many time per second to achieve a “real time” image of anatomic structures and ther motion pattern
Real time
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
Gray scale
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
Frequency shift
Sample site from which the signal is obtained with pulsed Doppler
Gate
Angle that the reflector path makes with the ultrasound beam; the most accurate velocity is recorded when the beam is parallel to flow
Doppler Angle
