Intro To US Flashcards
(46 cards)
How does an ultrasound produce an image?
High-freq sound waves 1-30MHz
Sound in to tissues and return as echo
What is the propagation velocity of US wave?
1540m/sec
For US purposes, a constant velocity of sound is assumed within soft tissues even though differences do exist
What is acoustic impedance?
Property of tissue on how much resistance there is to ultrasound waves
=velocity x tissue density
What is wavelength ?
Distance between one peak or trough and the next
What is the frequency of an US?
Cycles per second (hertz)
If you have small wavelength and high frequency US, how does this impact your resolution and penetration?
Better resolution.
Poor penetration
If you have a low frequency, long wavelength US, how does this impact resolution and penetration
Poor resolution
Better penetration
What are the types of attenuation that can occur when US waves interact with tissue?
Reflection (acoustic impedance)
Refraction
Absorption
T/F: attenuation increases with increased distance from the transducer and lower frequency transducer
False
Attenuation increases with increased distances from the transducer and HIGHER frequency
What is acoustic impedance?
Characteristic of propagation medium
A rejected sound wave is generated at the interface of an impedance mismatch (eg air and bone)
T/F: there is no acoustic impedance in a homogenous medium
True
There is no propagation mismatch —> no reflections occur
The more difference between two mediums, the more wave is reflected back, this will appear how on the US?
Reflection will appear bright white
The amount of sound reflected in US depends on ______________
Acoustic impedance
What assumptions does a US make when generating an image?
Speed of sound in all body tissues is 1540m/s
Beam only travels in a straight long with constant rate of attenuation
The beam is infinitely think with all echos originating form its central axis
The depth of a reflector is accurately determined by the time taken for sound to travel from transducer to reflector and back
What is acoustic shadowing?
Distal to highly reflective objects
Eg -air and bone
Interface absorbs or reflects entire sounds resulting in anechoic area
Clean acoustic shadowing occurs at the __________________ interface
Tissue-bone
Complete absence of reverberation artifacts
Dirty acoustic shadowing occurs at the ______________ interface
Tissue-gas
99% of the soundwave gets reflected
What is acoustic enhancemt?
Fluid of homogenous acoustic impedance attenuated less sound than the surrounding tissue
-> machine overcompensates and results in a HYPERechoic area distal to the structure
What is edge shadowing?
Reflection and refraction around the edges of a round structure
No sound returned -> HYPOechoic area
**useful to identify small round structures
What is slice thickness artifact?
On round surfaces, US assumes flat and averages acoustic impedance between the round edge and area within that edge—> grey average
-can mimic sediment
What type of US artifact produces a false image on the other side of a reflector?
Mirror image artifact
At highly reflective interface (air/fluid) beam is reflected onto a structure, but US assumes image is in straight line —> appears on other side of reflector
How can you determine a mirror image artifact vs a true image?
The false image is more grey and less defined because it is a reflection
What frequency would be best to penetrate a small dog/cat
A. 10MHz
B. 5MHz
C. 2MHz
A 10 MHz
-> higher frequency, smaller wavelength has less penetration
What frequency would be best to penetrate large animals?
A. 10MHz
B. 5MHz
C. 2MHz
C. 2 MHz
Lower frequency, larger wavelength -> deeper penetration
