Ultrasound Flashcards
(39 cards)
What frequencies does ultrasound use
Sound waves with higher frequency than we can hear
Between 1-15MHZ
What are sound waves like?
It is a longitudinal wave with compressions and rarefactions of the molecules it is travelling through.
How is an ultrasound Image obtained?
When ultrasound passes through the body it will hit boundaries and beam is split into four:
- transmitted beam
- reflected beam
- refracted beams
- scattered beam
Reflected beam back to its source gives the image
How does the ultrasound transducer produce an image?
In the ultrasound transducer, or probe, crystals emit packets of sound and then wait and “listen” for any returning echoes. The machine then constructs the image based on the loudness of the echo and the time it takes to return to the probe.
What is ultrasound machine measuring
the amount of reflection at a particular boundary.
What is acoustic impedence and how does it vary
describes how much resistance an ultrasound beam encounters as it passes through a tissue
the physical density of the tissue (d, in kg/m3) the velocity of the soundwave
How is acoustic impedence linked to reflection
Larger difference in acoustic impedence means greater amount of reflectiom
What tissue has the highest/ lowest acoustic impedence
Highest- bone
Lowest- air
What colour is fluid on an ultrasound
Black (no sound is reflected)
What colour is bone on an ultrasound and why?
White because lots of sound is reflected back
What colour are things on ultrasounds
Fluid- black
Tissue- grey (denser the tissue the whiter it’ll be)
What are the important things to consider when setting up an ultrasound?
Frequency of wave
Gain applied to returning echo (amplification of the ultrasound signals your transducer records.)
Where the ultrasound is focused
What are the pros/ cons of low frequency for ultrasound
Good penetration but poor resolution
What are the pros and cons of high frequency for ultrasound?
Poor depth of penetration but good resolution
What does gain have to compensate for/
The further the sound has to travel, the quieter the returning echo will be
When is gain turned up and why?
For deeper tissues to give a balanced image
What are the different types of transducers?
Sector transducers
Phased array
Linear array
Curved array
What are the pros, cons and uses of sector transducers?
Pros; small contact area, but divergent beam so can get a wide field of vision
Cons; they do not give good detail in the near field and also the fact that the beam diverges means the sound is more spread out in the far field, so does not have optimal resolution. You also need to warm them up by turning them on a few minutes before use due to the mechanical movement
Uses: intraabdominal regiosn, echocardiograms
What are the pros, cons and uses of phased array transducers?
Pros; diverging Beam, so good resolution
Cons: reduced near field divisions
Uses:echocardiogram
What are the pros, cons and uses of linear array transducers?
Pros: good near field resolution, and as the beam does not diverge, they give good far field resolution too but with a limited field of view
Cons: large contact area, so can only really be used for areas with easy access
Uses: abdomen or limbs
What are the pros, cons and uses of curved array transducers?
Pros; with a diverging beam to give a wider field of view in the deeper tissues.
Cons: large contact area
Uses; abdominal organs
How is frequency linked to resolution
Higher frequency means higher resolution
Why are stand off pads used?
If probe is too close to tissue then no image is shown
Increases distance between probe and superficial tissue
What is the mediolateral position?
Proximal aspect at the top
Cranial aspect at left
