Chapter 3- Physician Principles of Doppler Flashcards
What is the 13 second rule?
important
The amount of time it takes for US to travel 1 centimeter into tissue and 1 cm back to transducer.
What is the average speed of US through soft tissue?
1540 m/sec
What is the Doppler shift?
- Remember that when an ultrasound wave this a moving target like blood, the reflected sound waves are changed.**
the difference between the wave frequency directed into tissues and what returns?
What is the idea Doppler angle for vascular:
45-60 degrees ** NO MORE THAN 60**
What is the angle of insonation?
The angle that the US beam strikes the blood cells ( where we put the sample volume/gate and how we angle the Doppler angle)
Two piezo-electric crystals are sent out.
CW Doppler **like ABI’s*
What is the main negative about CW Doppler?
No depth resolutation. If there is a stenosis its hard to know EXACTLY where it comes from. Its an estimation.
Analog CW Doppler is more of an average- it is more of an estimation
TRUE FALSE
True
Fast Fourier Transfer displays what?
ALL frequencies moving through sample area.
Fast Fourier Transfer (FFT) is an example of what kind of continuous wave?
analog or digit
Digital
*Think digital has more detail.
Pulsed wave is a primary technique we use often. How many crystals are activated to create the US wave?
1
*Think pulse wave is the #1 technique we use
Using the 13 second rule, how long would it take to obtain a signal from 3 cm deep in the tissue?
39 ( 13 x 3)
PRF stands for AND what is it?
Pulse repetition frequency, number of pulses per unit time that are sent into tissue
What is the nyquist limit and what might occur if this is exceeded?
Nyquist limit is a Doppler shift frequency is greater than 1/2 the PRF
What can we do to fix aliasing?
decrease the PRF ( due to nyquist limit)
Power Doppler uses FFT that analyzes ALL the frequencies moving through the sample area
True or False
True
We don’t know exact what direction the blood cells are moving through the vessel therefore we must angle (Parallel/perpendicular) the vessel.
Parallel.
Why does smaller sample volumes yield a weaker signal?
because its sampling less and there is like RBC to sample.
What is the negatives of a larger sample volume?
may include small vessels and spectral broadening may occur.
What is the appropriate sample volume?
** Important**
1.5-2.5 mm
When the sample volume is narrower, is it likely spectral broadening will occur?
not likely. The narrower the sample volume the less likely for spectral broadening.
In areas of stenosis , spectral broadening will occur indicating disorganized flow.
True / False
True
There is always disease associated with spectral broadening
yes or no?
NO. Usually spectral broadening can indicate disturbed flow, but sometimes the spectral broadening can happen when there’s a large sample volume .
Why does Continuous wave Doppler always have a full spectral window?
the sample volume is large
The deeper the vessel were trying to listen to is, the ( Longer/shorter) the pulse.
Longer
further away means longer pulse.
The further deeper the vessel is to listen to the more _____ the frame rate will be. Decreased/increased
Decreased
Are frame rate and depth of vessel inversely related or directly?
Inversely
Increased depth=lower frame rate
Decreased depth=higher frame rate.
What is the definition of pulsed repetition frequency (PRF)
the number of pulse listen cycles per unit time
When does the mirroring artifact occur?
With high gain settings.
What is helical flow patterns caused by and where is it often seen?
this is caused by blow flow spiraling up in the artery. Seen at carotid bulb.
