Ultrasound Flashcards
What is the frequency of medical US?
2-20 milllion Hz
What is the transducer?
Contains piezo-electric crystal
Converts energy from electrical to acoustic
What frequencies do transducers come in + what are they good for?
High (7-18) - high resolution but low depth, good for superficial vessels
Low (2-6) - penetrate deeper but lower resolution eg abdo + obstetric
What is acoustic impedence?
Property of each tissue - depends on density + speed of sound waves passing through it
What is shadowing?
Calcium is a strong reflector so causes shadowing posteriorly (eg in gallstones)
What do vessels, bones, soft tissue, nerves + muscle look like + what terminology do we use to describe it?
Vessels - black - anechoic
Bones - white - hyperechoic
Soft tissue - grey - isoechoic
Nerves - honeycomb - hypo/hyperechoic
Muscle - gray - isoechoic with white strands
How to alter depth + why
Start with high depth then decrease to put area of interest around 3/4 of screen depth
What is gain compensation?
Selectively amplifying echoes from deep tissues
What are calipers used for?
Allows measures to be made
What are the commonly seen artefacts?
Shadowing
Acoustic enhancement
Reverberation
Comet tail
What is shadowing?
Strong reflective region of calcium that reduce energy remaining in beam distal to it
What is acoustic enhancement?
Occurs when sound waves pass through low acoustic impedance to normal acoustic impedance
Occurs in vessels, bladder, cysts
What is reverberation?
Large echo created by strong reflector - bounces back after hitting probe
Continues to bounce back and forth giving impression of multiple lines - equally spaces + gradually losing brightness
What is a comet tail artefact?
multiple reflections occur within small strongly reflecting object
What is a FAST scan?
Focussed assessment with sonography for trauma
Checks for fluid/ air in pericardial, peritoneal + pleural cavity
Where are the probes placed in a FAST scan?
Subcostal cardiac
RUQ
LUQ
Pelvis
What is static vs dynamic US access?
Static = mapping
Dynamic = views needle in real time
How to US aorta
Put probe transverse across body
Push down to move bowel, aorta will appear cross sectionally, verterbra posteriorly
Measure using calipers the diameter
Turn probe longitudinally to measure diameter again
Transverse, measure down to the bifurcation
