Doppler Ultrasound Flashcards
Why do you need the spectral doppler aligned as much as you can with the cursor?
The probe only measured direct RBC that coming toward or away at a direct angle
What is the cosine of 0?
Cosine or 0 = 1
(Beam is directly in line)
What is the cosine of 90?
Cosine of 90 = 0
(Why perpendicular structures are not measured)
What is the doppler equation?
(Change in) Delta F (Doppler shift) = V (Cos Ø) 2FT/C
FT = Transmitted frequency
Cos Ø = Angle between velocity of probe and RBC flow
C = Speed of ultrasound in Soft tissue (1540 m/s)
What angle will you start to have errors in velocities when using spectral doppler cursors?
20-30 degrees off true alignment start to have Doppler shift errors
What is your Pulse Repetition Frequency with continuous wave doppler?
infiniti (Always sending signals)
Theoretically, what is your nyquist limit with continous wave doppler?
Super high (does not limit)
What is the aliasing veloicty of Continous wave doppler?
Doesnt have one
What is the benefit of continous wave doppler?
You are able to measure very high peak velocities
What can continous wave doppler not do?
i.e. What are the limitations of Continous wave doppler
Range ambiguity (Cannot tell if peak velocities coming from any point)
How many crystals does continous wave doppler have?
Two
- One continously sending signals
- One continuously listening to signals
What are the advantages of continous wave doppler?
- Velocity will not alias
- No nyquist limit
- Infinite pulses per minute
- High velocities measured
What is the pulse wave doppler needed to measure diastolic function through the mitral valve?
- PWD ont he mitral tips (Inflow velocities) (E wave and A wave)
- Tissue doppler (Lower velocity but higher amplitude) (E’ and A’)
What E’ is considered normal diastolic function?
E’ > 10 cm/sec
What are the advantage of PWD?
- Range resolution (measure velocities at a specific location)
What are the limitations of PWD?
- Nyquist limit (AKA max doppler shift) before aliasing velocity occurs
Aliasing = Limited Max Velocity
Nyquist limit = Nyquist frequency
Nyquist limit = Max Delta F = 1/2 Pulse Range Frequency (PRF)
How do high velocities on PWD appear?
Negative (Due to aliasing)
What are the ways you could decrease aliasing?
- Use a low transmitted frequency
- Decrease the depth (increase Pulse Range Frequency PRF)
- Optimize the baseline
- Use Continous Wave Doppler
How can you remember color flow doppler what is blue and red?
BART (to the probe)
Blue = Away
Red = Toward
How does turbulent blood flow appear when it goes towards and away from the probe?
Away = Green
Toward = Yellow
BART
GAYT
What are the limitations of Color Flow Doppler?
- Aliasing (Form of PWD)
- Decreased Temporal Resolution (Frame rate)
- Velocity measurements are estimates (Mean Velocity)
- Not as exact as PWD and CWD
What are the cosine values of:
Cosine 0 degrees
Cosine 30 degrees
Cosine 45 degrees
Cosine 60 degrees
Cosine 90 degrees
Cosine 0 degrees = 1
Cosine 30 degrees = [Square root of 3] / 2
Cosine 45 degrees = [Square root of 2] / 2
Cosine 60 degrees = [Square root of 1] / 2 = 1/2
Cosine 90 degrees = 0
What is the optimal incidence angle for pulse wave doppler?
Parallel (Zero degrees) to blood flow
An U/S probe interrogates a blood vessel with an incident angle of zero degrees. The probe emits a frequency of 10 MHz and the returning echos have a vessel frequency of 10.5 MHz. What is the velocity of the blood vessel
- Use Doppler Equation
Velocity = Delta F / [Cos angle * 2 FT / C]
Velocity = [10.5 - 10 MHz] / [Cos 0 degrees * 2 (10 MHz) / (1540 m/s)]
Answer = D (38.5 m/s)
An U/S probe interrogates a blood vessel with an incident angle of 60 degrees. The probe emits a frequency of 10 MHz and the returning echos have a vessel frequency of 10.5 MHz. What is the velocity of the blood vessel?
77 m/s
A 12 MHz transducer interrogates blood flow using PWD in a vessel with a blood flow velocity of 100 cm/sec and a pulse repetition frequency of 6000 Hz. Which of the following is the highest Doppler shift that can be measured?
C = 3000 Hz
Highest doppler shift = Nyquist limit = Half of the PRF (Pulse wave frequency, which in this vignette is 6000 Hz)
What do wall filters function to do?
Filter out part of Doppler signals
What do low pass wall filters do?
Filter out high velocities (Allows low velocities to PASS)
What do high pass wall filters do?
Filters out low velocities (Allows high velocities to pass)
What are low pass wall filters used for?
Tissue Doppler Imaging (TDI)
TIssue movement = Low velocities, High amplitude signals
What are high pass wall filters used for?
Used for blood flow velocities
(HIgh velocity, Low amplitude signals with high pass filter on and low pass filter off)
What are the 5 functions of an ultrasound receiver?
- Amplification
- Compensation
- Compression
- Demodulation
- Rejection
What does rejection do on echo?
Rejects low amplitude 2D, 3D and M-mode signals
Is does NOT reject doppler
Very low level signals are ignored
What are the two other names for rejection in echo?
- Threshold
- Suppression
What frequency range is high pass wall filtering set at?
200 - 800 Hz
For tissue doppler
- What filter is on?
- What filter is off?
- What amplitude signal is on?
- What velocity?
For Tissue Doppler (TDI)
Low Pass filter on
High pass filter off
High amplitude
Low velocity
For blood flow velocities doppler
- What filter is on?
- What filter is off?
- What amplitude signal is on?
- What velocity?
For blood flow velocities doppler
Low Pass filter OFF
High pass filter ON
Low amplitude
High velocity
What is the difference from rejection vs. Wall Filters?
Rejection involves amplitude of the 2D signals
- Low amplitude signals are ignored
Wall Filters* acceptance/rejection of different *doppler shifts
Again, what is the doppler equation?
Change in Frequency (Ft - Fr) = Blood flow velocity (cosine angle) * 2Ft / C(speed of sound)
Why is “2” adjacent to the Frequency transmitted in the Doppler equation?
2 Doppler shifts
- 1st Doppler shift occurs when sound wave strikes RBC (Reception of sound wave by the red cell by itself creates a doppler shift)
- 2nd Doppler shift - Reception of the reflected sound wave by the transducer moving from the RBC
What is a power doppler?
What does it NOT have? (2 things)
Only signifies presence of a doppler shift (Only tells you have a +/- Delta F
NO Direction
No Speed
What is power doppler known as? (2 synonymous terms)
- Energy Mode
- Color Angio