Diagnostic Imaging - Image Formation Flashcards
Ultrasound frequencies are above…
human hearing range
Velocity is
frequency x wavelength
There is an inverse relationship between
frequency and wavelength
ultrasound transducers are assembled in an
array
What is an array?
group of piezoelectric effects within transducer housing which causes currents to regenerate and produce images
Electric current causes crystal to resonate at a certain frequency emitting…
an ultrasound wave of that frequency where the amount of returning echo produces an image
Types of array determine…
the type of transducer
Linear array transducers have a …. and are great for…
straight surface
great for tendons or rectal scans
Curvilinear array transducers have a … surface, which increases…
curved, wider surface
increases surface area
Phased array transducers are… and have a smaller… making it great for viewing …
blockier
footprint
between the ribs
Why do we use gel when doing an ultrasound?
Sound cannot pass through air so gel is used as a coupling agent
What types of frequencies can be found in a transducer/probe?
- single frequency
- range of frequencies
- multiple frequencies simultaneously
What happens to the ultrasound beam inside the patient?
Reflection
Refraction
Absorption
What is axial resolution?
the higher the frequency, the greater the resolution, the poorer the depth penetration
low frequency, lower resolution, better penetration
what is the most ideal for axial resolution?
use the highest MHz with the best resolution of the image created
Higher frequency means
a thinner beam which means better lateral resolution
The focal point is …
the narrowest area of beam making for better lateral resolution
After the focal point, the beam gets
wider, leading to worse resolution
What are the various modes of scanning?
A- mode (aptitude)
B-Mode (brightness)
M-mode (Motion)
In B-mode, the brightness is proportional to…
the strength of the echo
B-mode is used to evaluate…
tissue echotexture
Define: Anechoic
Without echoes
appears black
Define: hypoechoic
some echoes present
appears dark grey
Define: hyperechoic
large number of returning echoes
appears bright grey
What is M-mode?
time against motion
When is M-mode commonly used?
to assess the contractility of the heart
What are some of the common controls found on an ultrasound machine?
depth
frequency
power
gain
TGC (time gain compensation)
focus
Depth on ultrasound allows you to
scan with the least depth of tissue between it and the transducer
When should frequency be changed on ultrasound?
based on the depth of the tissue
What does power control on ultrasound?
general brightness of an image
higher power means
a stronger beam
too high of power means there are
more artefacts w/ meaningless echoes displayed in the image
too low of power means
the returning echoes are not strong enough to create an adequate image so the image is too dark
Power does not…, it just…
change the beam itself
amplifies the signal of returning echoes.
What does TGC do?
each slider controls signal amplification within the corresponding band in the image
TGC can be adjusted to achieve
even brightness
Altering the focus on ultrasound allows you to
focus an area of interest and improve resolution
The focus is the …
narrowest point of the beam
Narrower beam means
higher resolution
What types of artefacts can be found on ultrasound?
reverberations
comet tails
acoustic shadowing
acoustic enhancement
edge shadowing
mirror image
side lobe artifact
other…
What type of artefact is demonstrated here?
Reverberations
What artefact is present here?
Comet tails
What artefact is present here?
Acoustic Shadowing
What artefact is present here?
Acoustic enhancement
What artefact is present here?
Edge shadowing
What artefact is present here?
Mirror image
What artefact is present here?
Side lobe artefact
What is doppler used for?
to measure movement, usually blood flow
What are the different types of doppler?
- color flow doppler
- continuous wave
- pulsed wave
- power doppler
What does color flow doppler show?
color-codes the direction of flow
What type of doppler uses this? What does it mean?
Color-flow doppler
Blue away, red towards
blue takes longer to move away from you, red means it is coming towards you/the probe
Tells you the direction of the flow of blood
When using color flow doppler, what can it measure?
how long it is expected for blood to move vs how long it actually takes.
when using color flow doppler, what is important to remember?
you must have the probe pointed parallel to the blood flow you are looking at.
Continuous wave doppler shows the
direction and velocity of flow
pulsed wave doppler shows
the direction and velocity of lower velocity flow in a limited ‘gate’ area
What type of doppler is demonstrated here?
Pulsed wave doppler
What should you remember when using PW and CW dopplers?
blood flow velocity cannot be overestimated, only underestimated
Power doppler shows
flow and movement
power doppler is good for viewing
vascularity in tumors
What is an exception to a power doppler?
it does not give velocity or direction, but rather that there is flow
Which doppler has an audible sound?
Power doppler
