Echocardiography II - Part 1. Flashcards
What is the use Doppler?
Doppler technique allows:
(1) Detection and analysis of moving blood cells or myocardium;
AND
(2) provides hemodynamic information about the direction, velocity, character, and timing of blood flow or muscle motion.
What is an advantage of using Doppler echocardiography over more invasive procedures, such as cardiac catherization?
Doppler echocardiography permits the ability to measure blood flow within the heart by noninvasive means.
What are the four main types of Doppler echocardiography utilized during a routine echocardiogram examination?
(1) Pulsed-Wave Doppler (PWD) allows examination of flow at very specific sites. There are limitations in the maximal velocity that can be recorded.
(2) Continuous Wave Doppler is not site-specific, so blood cells are examined all along the sound beam.
(3) Color-Flow Doppler color codes the velocities and directions of flow; is a form of PWD.
(4) Tissue-Doppler imaging records myocardial velocities, not blood cells; it is a form of PWD.
Define the term, “Doppler Shift/Doppler Effect”.
The Doppler effect or Doppler shift is the change in frequency of a wave when there is a change in position between the sound source and the reflecting structures (blood cells in our case).
Think about an ambulance moving towards you (the observer). As the ambulance moving closer to the observer, the wave crests and frequency increase as the distance decreases. Vice-a-versa, as the ambulance moves away from the observer.
How is Doppler Effect/Shift applied during an echocardiogram examination?
Positive frequency shift – Cells moving toward the transducer reflect an increased number of sound waves and so the received frequency is higher than the transmitted frequency. Therefore, a POSITIVE shift and waveforms will be displayed ABOVE the baseline.
Negative frequency shift – Cells moving away from the transducer reflect a decreased number of sound waves and so the received frequency is less than the transmitted frequency. Therefore, a NEGATIVE shift and waveforms will be displayed BELOW the baseline.
How does the use of Pulsed-wave Doppler (PWD) allow for the precise measurement of flow at specific depth positions?
By recording frequency shifts during certain time intervals and ignoring other returning echoes. Flow is measured within the same depth as the position of the gate.
How does Continuous-wave Doppler (CWD) differ from Pulsed-wave Doppler in terms of detecting the depth of the reflected signal?
Unlike Pulsed-wave Doppler, Continuous-wave Doppler continuously sends out and receives sound, without detecting the depth of the reflected signal. It detects frequency shifts along the entire ultrasound beam, but lacks the ability to measure velocity at a specified depth, known as RANGE RESOLUTION.
How is the cursor utilized in the Continuous-wave Doppler (CWD) method?
In Continuous-wave Doppler, the cursor, which represents the sound beam, is manually placed over the 2D image. Frequency shifts are calculated all along this beam.
What kind of frequency shifts spectrum is detected in Continuous-wave Doppler (CWD)?
Continuous-wave Doppler detects a full spectrum of frequency shifts. This is because velocities vary all along the line of interrogation or the ultrasound beam.
In Continuous-wave Doppler (CWD), what happens to the lower velocities when the highest velocities are recorded?
The lower velocities are hidden within the higher flow profiles. This is due to the method’s inability to specify depth or range resolution.
What specific velocity is typically of interest in the application of Continuous-wave Doppler (CWD)?
The highest velocity is generally of interest in the application of Continuous-wave Doppler, such as the velocity of a regurgitant flow.
When using Doppler echocardiography, what variables may affect the accuracy of measuring velocities?
(1) Transducer frequency and (2) Intercept angle
By what direction of the interrogation angle does the transmitted wave have to be in, in order to ensure the most accurate velocity?
RULE 1 of intercept angles: The closer to parallel the transmitted wave is with the direction of blood flow being interrogated, the more accurate the velocity is
True or false, the intercept angle can be large enough that the velocity may be overestimated.
False.
RULE 2 of intercept angles. Velocity cannot be overestimated, just underestimated.
Define Pulse repetition frequency.
The time interval between pulses must be two times the sample depth.
TI = 2(Depth)
How does the depth of the target area affect the time between pulses in Doppler ultrasound
As the depth of the target area increases, the time between pulses must also increase. This is due to the increased distance that the ultrasound signal has to travel.
What is the impact of increased time between pulses on the Pulse Repetition Frequency (PRF)?
The increase in the time between pulses results in a decreased PRF. The PRF is inversely related to the time between pulses - as one goes up, the other goes down.
How does a decreased PRF influence the Doppler frequency shift that can be accurately measured?
Decreased PRF results in a decrease in the Doppler frequency shift that can be accurately measured. The lower the PRF, the lower the maximum Doppler shift that can be detected without causing aliasing.
What is the maximum Doppler shift that can be recorded accurately?
The maximum Doppler shift that can be recorded accurately is equal to one-half the PRF, also referred to as the Nyquist Limit. When this limit is exceeded signal ambiguity results, which is called aliasing.
Doppler shift= ½ PRF
The Nyquist limit is greatly exceeded and we cannot understand where the flow is going or determine its velocity. In this situation, what change would allow you to record a velocity that exceeds the Nyquist limit?
A. Moving the probe so your interrogation angle is less.
B. Switching to CWD
C. Moving the patient.
D. Switching to a higher PRF
B. Switching to CWD
In this situation switching to CW Doppler will allow to record the velocities that exceed the Nyquist limit to be recorded.
The maximum velocity that can be recorded at any given depth with no ambiguity is inversely proportional to transducer frequency. Therefore, should we use high frequency or low frequency transducers to record a high-velocity flow?
A. High Frequency
B. Low Frequency
B. Low Frequency. The best recordings of high velocity flows are obtained from a low frequency transducer.
Please note that this is opposite of what produces the best 2D images where high frequency transducers will produce the best quality. This means we might have to use different probes for our 2D and M-mode images and our Doppler studies.
What are the usages of High Pulse Repetition Frequency?
High Pulse Repetition Frequency (HPRF) pulsed Doppler can help with the limitations of depth ambiguity. One or more pulses are sent out before the echo from the desired depth of the first is received. This will increase the PRF and thus increases the Nyquist limit. However, it will be impossible to determine which pulse is the origin of the echo and will result in partial depth ambiguity. This HPRF can be used to get higher velocities, but differentiating between the different velocity curves will be dependent on prior knowledge.
**What can we do to avoid aliasing? **
Move the baseline (up or down).
Find an imaging plane where less depth is necessary.
Switch to CW Doppler.
Use a lower transducer frequency.
When using PW Doppler, what causes little spectral broadening of the recorded waveform?
Flow is laminar;
Intercept angle is close to zero (parallel);
The Nyquist limit is not exceeded.
How does increased spectral broadening of a waveform occur?
Improper gain setting (high gain)
Large intercept angle
Non laminar (turbulent) flow
True or false, CW Doppler always depicts spectral broadening.
True. CW Doppler always shows spectral broadening even when flow is laminar because the velocities detected all along the beam vary.
True or false, Color flow Doppler is a form a CW Doppler.
False. Color-flow is a form of PW Doppler
Describe the concept of color flow mapping.
Color-flow mapping involves the analysis of information all along hundreds of interrogation lines, each with hundreds of gates until a wedge is filled with color. Each gate sends frequency shift information back to the transducer. This information is sent to a processor which calculates the mean velocity, direction and location of blood cells at each gate. Information from each gate is assigned a color and position on the image.
What two factors is Color Flow Doppler quality dependent upon?
Pulse repetition frequency (PRF) measured in Hz.
Transducer frequency
How is aliasing depicted when using Color Flow Doppler?
Aliasing in color Doppler involves a reversal of color and the result is a mosaic of color
True or false, Aliasing can occur when analyzing normal blood flow.
True. Aliasing can occur when there is normal blood flow if we are using a high frequency transducer. This is due to the transducer frequency and would be eliminated if a lower frequency transducer were used.
Aliasing can also occur at lower velocities due to sampling time requirements.
What is Frame Rate?
Frame rate: Refers to the number of times a B-mode or color flow image is generated per minute.
What is the minimum frame rate to achieve in order to acquire smooth transitions and the appearance of a continuously moving image?
15 times/second.
What is the frame rate in color Doppler equal to?
Frame Rate (Color Doppler) = PRF / scan lines per color sector.
Can you identify what is happening here? How is the gain set?
A. Normal.
B. Low.
C. High.
A. Normal.
Can you identify what is happening here? How is the gain set?
A. Normal.
B. Low.
C. High.
B. Low.
Can you identify what is happening here? How is the gain set?
A. Normal.
B. Low.
C. High.
C. High.
What do all myocardial velocity profiles include?
- After a short isovolumetric contraction, one positive systolic wave (S),
- After a short isovolumic relaxation phase, two diastolic negative waves (E and A), respectively, in early and late diastole, with E/A ratio >1)
Define myocardial strain (St)
Myocardial St represents the deformation of a myocardial segment over a period of time and is expressed as the percent change from its original dimension (see figure below).
What is Two-Dimensional Speckle Tracking echocardiography (2D STE) and how does it work.
2D STE allows assessment of regional myocardial function.
This imaging technique is based on the tracking of speckle patterns created by interference between the ultrasound beam and the myocardium on grey- scale 2D echocardiographic images.
2D STE allows a non-Doppler assessment of regional myocardial motion by filtering out random speckles, and then performing autocorrelations to evaluate the motion of stable structures.
Describe the flow appearance using spectral Doppler of pulmonary vein flow?
Pulmonary venous flow is pulsatile and continuous. Most left atrial filling occurs during ventricular systole when the mitral valve is closed. This creates a positive deflection on the spectral image, the “S” wave. Systolic pulmonary venous flow can be biphasic. If it is the early phase, it is labelled SE while the second later phase is called SL.
During early diastole while blood is flowing into the left ventricular chamber, there is a drop in left atrial pressure and blood is passively pulled into the left atrium as blood moves through the mitral valve into the left ventricular chamber. This phase of left atrial filling is the “D” wave and is also positive on the spectral image.
Atrial contraction during the latter part of diastole causes flow to move backward into the veins because there are no valves to prevent this. This wave is referred to as the Ar wave and is negative on the spectral display.
Describe the flow appearance using spectral Doppler for IVRT?
The time interval from cessation of aortic flow to the beginning of mitral inflow corresponds to the isovolumic relaxation period. Left ventricular inflow cannot begin until left ventricular pressure drops below left atrial pressure and the mitral valve can open.
With the spectral baseline in the middle of the spectral image, downward aortic flow and upward transmitral flow should be seen. Ideally the end of systolic downward flow should show the line (click) that corresponds to aortic valve closure. Upward mitral flow should have a clear starting point or can also have a click representing mitral valve opening. The time period between these two points represents IVRT.
Describe the flow appearance using spectral Doppler for left auricular flow?
The baseline is placed in the middle of the spectral image. Filling of the left atrium and auricle during ventricular systole is seen above the baseline and coincides with the QRS complex of the electrocardiogram. Negative flow is displayed during atrial emptying late in diastole coinciding with the P wave of the electrocardiogram.
Sometimes there are other positive and negative flows on this spectral image so an ECG identifies the correct flow profiles to use.
