Intro To US Flashcards
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
What frequency would be best to penetrate tendons and small parts like the eye?
A. 10MHz
B. 5MHz
C. 2MHz
10 MHz
High frequency, small wavelength -> superficial penetration
What is power vs gain?
Power is the strength of the signal going into the tissue
Gain is the amount of signal coming back to the transducer
What is time-gain compensation?
Can selectively choose areas to suppress or enhance so you can have a homogenously gray image
Eg if you increase gain in deep tissues -> increase gray in that area so tissue doesnt appear hypoechoic
T/F: structures should be viewed at edges, away from the focal point of the US beam
False!
Investigate structures near the focal point
M-mode is for??
Motion
Doppler is for ?
Determine direction of flow
How should you prep an animal for an abdominal US?
12h fasting Free water access Avoid stress Shave fur Dorsal recumbancy US on left side with dog head in direction of machine
Acoustic coupling gel!
Each organ should be examined in how many planes?
Two
Eg sagital/dorsal/transverse
If you are taking a sagital plane, the transducer should be oriented __________
Cranially
Is you are scanning in a transverse plane, the transducer should be oriented toward ??
Left (towards the examiner)
What “echo”-signs are we looking for?
Size Shape Number Location Margination Echogenicity
What do you call an area of an US that is homogenously black?
Anechoic
An area that is lighter in intensity in an US is called?
Hypoechoic
If two structures have the same echogenicity, they are ________
Isoechoic
A structure that has high echogenicity and is bright white is called?
Hyperechoic
Put the following tissues from anechogenic to most hyperechogenic
Air Bone Fat Kidney Liver Prostate Spleen Urine
Urine < kidney < liver < spleen < prostate < fat < bone/air
T/F: you can compare echogenicities of different tissues that are at different depths
False
The earliest accumulation of free abdominal fluid occurs where?
Apex of the bladder and between liver lobes
Can you assess any tissues distal to fluid
Nope - acoustic enhancement
Transudate will appear ________ on US
Anechoic
Exudate, blood, or chyle will appear ___________ on US
More echogenic (speckled)
T/F: When doing a fine needle aspirate you should see the see the whole length of the needle with US
True
