Maverick Modules 11-16 Flashcards
What is sound?
Series of repeating pressure waves that propagate through a medium
sound is mechanical
How is sound measured?
pressure wave frequency (Hz) which is cycles per second
What are the Hz frequencies for US?
2MHz - 20MHz
What do high and low frequency probes image?
- High frequency probes images superfically
- Low frequency probes images deep
you can have anywhere between ____ and ____ crystals in your transducer
128-512 (the more crystals will give you a sharper image)
What are the acoustic impedance views of different materials?
Impedance is the measure of a material’s tendancy to transmit sound waves
Structures with high propagation velocity will appear ____ in the US image
white
Acoustic impedance is impacted by the ____ and ____ of the material
elasticity and density
Homogeneous mediums reflect ____ sound
No sound is reflected (homogeneous like fluid)
Loss of signal is also known as
attenuation
What attenuation principle is depicted below?
Absorption
What attenuation principle is depicted below?
Reflection
What attenuation principle is depicted below?
Scattering
What attenuation principle is depicted below?
Refraction
What three factors affect how tissues reflect ultrasound waves?
- Acoustic Impedance Mismatch
- Angle of Insonation
- Smoother or Specular Reflections
What is Anisotropy?
Objects that are 90 degrees to the US beam generate the best reflection
Which angle below will give a better image of the nerve?
Why?
A2 due to Angle of Insonation (we want 90 degree angle of the structure, not the skin)
What is “toeing in”?
this will make your probe and needle parallel to one another so the US beam is perpendicular to the needle
- you get a stronger reflection from the needle and weaker from the target
What’s the most important safety tip when utilizing ultrasound?
Always see the needle tip
Do we want a shallow or deep approach with our needle to see it with US the best?
Shallow, the more parallel the angle of insonation is, the more needle we see with the US
What type of reflection is noted below?
Specular Reflection (large smooth surfaces reflect sound like a mirror)
What type of reflection is noted in the image below?
Diffuse Reflection (bumpy surfaces change the way the sound is reflected b ack)
What types of tissue/material are typically responsible for acoustic shadowing?
- Bones
- Calcifications
- Gas
What type of material is typically responsible for posterior acoustic enhancement?
Homogenous Liquids (Cysts typically let the sound pass directly through it and have no reflection)
What is Gain Artifact?
too much signal bouncing around and the picture appears very hyperechoic
What artifact indicates that the ultrasound probe is perfectly parallel with your needle?
Needle Reverberation Artifact
- result of multiple echos or reflections from the delay of an echo before returning to the transducer
- parallel and in plane US beam
Which axis is the most commonly used for nerve blocks?
Short axis view (transverse view)
Instead of “find your needle” what should we do?
Make the needle find your beam
