Ultrasound FAST Exam Flashcards
What is frequency?
the number of cycles per second
units = hertz
What is the wavelength?
the length of one complete cycle
if frequency is high, wavelength is short
What part of the US machine does the ultrasound transmission and reception?
the transducers
use piezoelectric units for US transmission
Describe what happens in pulsed-echo mode?
the transducer makes a pulse of US, then listens for the echo
99% of the time is spent listening
Which will penetrate better, higher frequency or lower frequency?
lower frequency - the wavelenth is longer so it can penetrate better
(think of whales vs dolphins)
What will have higher resolution? Higher frequency or lower frequency?
Higher frequency will have better resolution because there’s more “listening” time
What happens to the ultrasound signal as it propagates?
weakens (reflections, scatters, absorption)
Which will have better transmission of sound: high density or low density?
higher density - so liver is better at it than lungs
lungs will look balck
Which will have better transmission of sound: flexible tissue or stuff tissue?
flexible - so liver is better than bone
bone will just look black
What are hte two scanning formats?
linear and sector
linear is straight down, sector spans out
What would you want to use when locating a blood vessel - high frequency or low frequency?
high frquency - it only needs to penetrate a couple inches and will give better resolution
Do you use high frequency or low frequency for the FAST exam? why?
low frequency because you need to be able to penetrate down further
To compensate for signal attentuation, the system will amplify the ultrasound signal through what?
gain - it’s the amount of amplification added to the signal coming from the transducer to the screen
What does hyperechoic mean and what is an example of something that would look that way?
something that blocks any further signal, so it looks like a shadow below it
a gallstone would do this because it’s calcified
What are some organs that will look medium gray-scale?
organs like the liver and spleen
What are the two image format options?
B mode and M mode
What is B mode?
brightness mode - used for images like FAST
What is M mode?
It’s motion mode - they only look at one x-ray beam over a period of time to see movement
What happens with the mirror artifact near the liver?
Above the liver i slung, so you’d expect to see black, but you don’t
instead, the diaphragm reflects back the liver so you see just darker gray above it
How can the mirror artifact be useful diagnostically?
You should see gray, so if you see black, you know there’s something wrong with the pleural cavity - potentially a hemothorax or effusion
What are three tips for US technique?
approach from the same side always
dim the lights
lots of goop
