Basic Physics Flashcards
Amplitude
Peak pressure and magnitude of sound wave
Period
Length of time to complete one cycle
Wavelength
Distance of a complete cycle
Frequency
Number of cycles per second (cycles/sec)
Hertz (Hz)
cycles per second
Ultrasound is sound greater than ________ Hz
>20,000 Hz
Diagnostic US is in _________ Hz range
2-20 megaHz
Increasing period __________ frequency
Decreases frequency
Velocity
Propagation of speed through a medium
Velocity is _____________ in a given medium
Constant
Velocity is determined by the _____________
Stiffness and density of medium
Frequency and wavelength are _________ related
Inversely
Power
Strength of sound wave
Diagnostic ultrasound uses _________ waves
Pulsed
Pulse Duration (PD)
Length of time from beginning to end of a pulse
Pulse Repetition Period (PRP)
Length of time from beginning of one pulse to the next
Pulse Repetition Frequency (PRF)
Number of pulses per second (pulse/sec)
PRP and PRF are __________ related
Inversely
Duty Factor
% of time spent producing a pulse
Duty Factor formula
PD (sec) /PRP(sec) X 100 (usually less than 0.01)
Spatial Pulse Length (SPL)
Length or distance of a pulse
Piezoelectric Effect
electrical current generates vibration of crystals to produce sound, vibration of crystals produces electrical current
Image depth
time elapsed between signal pulse and echo
Brightness
related to echo intensity along grey scale
Attenuation
Weakening of sound beam as it moves through medium
Increasing frequency __________ attenuation
Increases
Increasing distance ____________ attenuation
Increases
Absorbtion
Energy absorbed and converted to heat
Refelction
Sound reflected back to transducer
Scattering
Sound reflected in multiple directions
Scattering occurs when
Sound strikes material so small as to approach wavelength
Increasing frequency __________ scattering
Increases
Refraction
Redirection of sound beam as it crosses from one medium to another, causing bending of sound wave
Refraction occurs when
Differing propagation speed between two media
Impedence
Resistance to propagation of sound
Impedence is related to
Tissue density and propagation speed
Acoustic impedance mismatch
Difference in acoustic impedance at a boundary
The greater the acoustic impedance mismatch
The greater the amount of reflection
Angle of insonation
The angle between the incident ultrasound beam and an imaginary line that is perpendicular to the boundary of the object of interest
Resolution
The ability of the sound waves to discriminate between two different, closely spaced objects
Axial resolution
The ability to distinguish between two closely spaced objects along same beam
Axial resolution is dependent on
SPL and frequency
Axial resolution increases with ________ frequency
increasing
Lateral resolution
The ability to distinguish between two closely spaced objects at the same depth
Lateral resolution is dependent on
Width of the US beam, transducer shape, and focal zones
Temporal resolution
The ability to detect moving objects at various points in time
Synonym for temporal resolution
Frame rate
To improve temporal resolution
Narrow imaging sector, decrease scanning depth, decrease line density, decrease number of focal zones
Hyperechoic
More echo than surrounding tissue
Isoechoic
Same echo as surrounding tissue
Hypoechoic
Less echo than surrounding tissue
Anechoic
No echo
2D or B-mode
Brightness mode
In B-mode US, strong echoes are represented by _____ dots and weak or no echoes are represented by ______ dots
White dots, black dots
M-mode
Motion mode
M-mode display
B-mode image with tracing of movement over time
Color
Color imposed over B-mode image
Color scale
Information on mean velocity and direction of flow, color superiorly represents flow toward transducer, and inferiorly away from transducer
BART
Blue away, red toward
Power Doppler
Greater sensitivity for low flow states, no directional information
Spectral Doppler
Quantitative assessment of flow velocity at a single point within the gate (pulsed wave) or along the entire line of interrogation (continuous wave)
Gain
Overall displayed brightness of echo signal
Time Gain Compensation (TGC)
allows adjusting gain by depth
Depth
Adjusts the field of view to increase or decrease scanning area
Frequency dial
Adjusts the frequency of sound emitted by the probe
Tissue Harmonic imaging
The transducer listens for sound waves returning at multiples of the frequency of the pulse that was emitted from the transducer, less artifact and attenuation
Curvilinear array used for
Abdominal, pulmonary, and OB/GYN studies
Linear array used for
Vascular access, soft tissue, MSK, vascular, superficial
Phased array used for
Cardiac (and FAST)
Endocavitary used for
Endovaginal pelvic and peritonsilar abscess
Sagittal
Splits patient into right and left
To obtain sagittal images, transducer indicator pointed toward
Patient’s head
Transverse
Splits patient into top and bottom
To obtain transverse images, transducer indicator pointed toward
Patient’s right
Coronal
Splits patient into front and back
To obtain transverse images, transducer indicator pointed toward
Patient’s head
Acoustic shadowing
Due to reflection of sound with dark shadow behind reflection