Ultrasound Flashcards
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
What are the pros of using ultrasound
Good for soft tissue
Good for small scale/ details
Real time motion can help see how organs function
What are cons of using ultrasound?
Requires good practice and skill to obtain good image
Difficult to interpret images unless in real time
Difficult to assess how structures are related spatially to each other due to narrow field of vision
What is anechoic structures?
Produce no echo
All sound passes through the tissue and none is reflected back
Appears black on ultrasound image
Usually blood, fluid
What are hypoechoic structures
Produce little echo
Most of the sound passes through the tissue but some is reflected back
Appears dark grey
Tissues with high water content (cartilage, muscle, renal medulla)
What are medium echogenicity structures?
A medium amount of sound is passed through
A medium amount of sound is reflected back
Appear lighter grey
Liver. Spleen, Prostate, testes
What is hyperechoic structures?
Produces much echo
Little sound passes through the echo
Large amount reflects back
Appears white on ultrasound
Gas, bones dense connective tissue
What are homogenous tossues
They have the same/ similar appearance throughout
What are heterogenous tissues?
Have a mixed or regular pattern
What effects does increasing the ultrasound frequency have on the properties of the beam
Decreased tissue penetration
Increased image resolution
What environment is it best to perform an ultrasound in?
Quiet, calm, Dark/lights off, comfortable seat for scanner and restrained. Bed for the patient to lie on
What patient preparation would you need to do
Clip over the site to be scanned
Clean the skin with alcohol/surgical spirit to remove grease and dirt.
Apply a generous amount of coupling gel to the skin and rub in.
Why do you need to add a gel to the patient and the transducer for ultrasound work
The acoustic impedance of transducer head, air and tissue is very different and so unless the gel is put on the transducer to allow free passage of ultrasound across the air gap between transducer and tissue, all the ultrasound is reflected back before it has even entered the body. Therefore, no image would be possible.
Why do you need to adjust the contrast and brightness on the ultrasound machines?
These settings optimize the screen settings for viewing NOT CREATING the image, taking into account the environment you are viewing the screen in
What Frequencies are commonly used in Veterinary Ultrasound?
Most small animal ultrasound is done at a range of 4-10 MHz
Large animal ultrasound may use a range between 2-18MHz
What is echogenicity?
the brightness of an image caused by the reflection of soundwaves
