US Flashcards
(31 cards)
List 5 characteristics of sound waves
-Amplitude
-Frequency
-Wavelength
-Compression
-Speed (1540m/s in tissue)
-Rarefaction
Define the Piezoelectric Effect
When an electrical current is applied across the crystal, it resonates sending out a sound wave
What frequency is the human hearing range?
20Hz - 20kHz
What does a long wavelength mean for the frequency?
It shortens
True or False?
Ultrasound waves are transverse electromagnetic waves.
False.
It is X-rays that have transverse EM waves. US waves are longitudinal and mechanical.
What frequency is above 20kHz?
Ultrasound
What is Attenuation?
The reduction in intensity with distance and is due to Reflection, Refraction, Scatter and Absorption
True or False?
The Medical US frequency is 2-17MHz
True
In the Piezoelectric Effect, what is produced when a perpendicular force is applied?
An electrical charge/signal
How are Ultrasound waves generated?
By stressing the elastic medium
Name the different types of ultrasound
-A Mode (Amplitude)
-B Mode (Brightness)
-M Mode (Movement)
-3D/4D’
-Doppler (Colour and Spectral)
What is the Doppler Effect equation?
f(d) = f(r) - f(t) = 2f(t) v (cos)u/c
If frequency is determined by the source of the sound wave, what does a shorter wavelength mean for the frequency?
It becomes higher
List 3 causes of artefacts
-The operator
-Equipment malfunction
-Tissue type
What does the safe practice ALARA acronym stand for?
As
Low
As
Reasonably
Achievable
Name and explain the two types of Acoustic Shadowing
- Calculi-beam (reflected shadowing underneath
- Polyp-soft (tissue with no shadowing)
If “high frequency = good resolution and poor penetration” then “low frequency = …”
“…poor resolution and high penetration”
Define Absorption
The transfer of energy into heat
How is Echo produced?
When the beam hits the interface between 2 tissue types and strengthens it with difference
What do the white and bright image interpretations represent?
The signal from dense tissue, like bone or a strong interface, between 2 different tissues (i.e. Diaphragm)
True or False?
Black image interpretations represent no signal from fat-filled areas such as blood and ionic fluids
False.
They represent fluid-filled areas such as blood and ionic fluids
What can machine assumptions cause?
-The beam to become effortless
-Propagation becomes straight-lined
-Brightness of the echo to directly relate to the reflectivity of the target
What does the Doppler colour setting show?
Whether the bloodflow is present and it’s direction (red flows towards and blue flows away)
Where is ultrasound energy lost?
At every interface the beam encounters
