POCUS Flashcards
how are ultrasound waves produced
via the piezoelectric effect: crystal in the transducer is subjected to a voltage, which distorts the crystals and produces the US wave; the wave interacts with tissues and returns to the transducer; the distance is charted as arrival time and brightness is charted as amplitude
what two mediums reflect US
bone and air
what is the range of diagnostic US
2-17 MHz
if you needed to image deeper into a tissue (i.e. you need the waves to penetrate deeper) would you increase or decrease the US frequency
decrease
what are the trade-offs with resolution and penetration of tissues
if you have a lower frequency (deeper penetration) the resolution is worse; vs a higher frequency (only imaging superficially) will have a higher resolution
what does FAST stand for and what are the 2 types
focused assessment with sonography for trauma:
TFAST: thoracic
AFAST: abdominal
what does POCUS stand for
point of care ultrasound
what is the goal of FAST
answering a focused question/series of questions that are binary (yes/no -> usually free fluid or no free fluid)
what can POCUS be used for (4)
to gather key info in real time to narrow down/diagnose, streamline patient care, guide treatment/intervention and reduce cognitive errors
what 3 factors determine the image generated by ultrasound
- strength
- timing
- position
what can happen to sound waves at the boundary of 2 tissue types (4)
which of these generates a useable image?
- reflection
- absorption
- scattering
- refraction
reflection generates a useable image
what 2 types of tissues are strong reflectors
bone and air
what tissue has the highest acoustic impedance in the body
bone
does a linear or curvilinear probe have a higher frequency and what does this mean in terms of the tissues you might look for with them
linear has higher frequency; can be used to generate a high resolution image for superficial structures
curvilinear has a lower frequency; can be used to generate poorer resolution images of deeper structures
to do a centesis what angle should your needle be relative to the probe
45-55 degrees
what does gain change vs depth
gain: amplifies the signal
depth: how deep into the tissues you are going
what is acoustic shadowing and give an example of when it can be useful
mineralized structures or air reflect the ultrasound beam back, resulting in shadowing below the mineralization or air
what causes dirty vs clean shadowing in the GI tract? which is caused by sound reflecting materials and which is caused by sound absorbing materials
dirty: normal ingesta and gas in the GI tract; sound-reflecting materials
clean: foreign objects; sound absorbing materials
what causes acoustic enhancement
increased echogenicity deep to a structure that TRANSMITS sound well (ex. fluid filled cyst) -> fluid attenuates sound less than adjacent structures, so there is a time gain compensation resulting in deeper tissues being hyperechoic
what causes a mirror image artifact
beam encounters a highly reflective surface (ex. diaphragm), reflects to another structure (gallbladder) and reflects back to the highly reflective surface (diaphragm) before reflecting BACK to the transducer
what causes an edge artifact
when a curve surface refracts the ultrasound beam, making the tissues in this region fan-shaped hypoechoic areas
what is an artifact that happens in most patients
side lobe artifact
what is a twinkle artifact and why can it be useful
when colour flow Doppler is used; focus of alternating colours (tornado) below a highly reflective object (ex. a calculus in the urinary bladder)
useful because it is more sensitive at detecting urinary stones than acoustic shadowing - can also be used to differentiate kidney fat from mineralization
