Ch 13 Spectral Doppler Flashcards
Hemodynamics is based on the investigation of what 2 physical principles?
Blood flow + circulation
The fundamental doppler principles are partly based on what principles?
Hydraulic principles: investigation of steady flow of a uniform fluid through a solid tube
Blood is not uniform due to what?
Containing solid matter
(it travels through “elastic tubes” which expand + contract)
Blood flow characteristics are based on a range of factors, list 5?
-Type of vessel (artery vs vein)
-Size of vessel
-Resistance to flow offered by vessel
-Phase of cardiac cycle the flow is occurring
-Disease processes which cause vessel narrowing
What is the driving force behind all fluid flow?
Pressure - differences in pressure is required for flow to occur
Does flow follow the path of least or most resistance?
Least - ex. higher pressure at 1 end of a tube than another causes fluid to move from an area of higher pressure to an area of lower pressure
Blood flows from the LA into the LV once when happens?
Once the pressure in the LA exceeds the pressure in the LV, causing the MV to open
Resistance to flow is determined by that 3 factors?
-Bloods viscosity
-Radius of vessels lumen
-Length of vessel
Rate of flow is determined by what 2 things?
-Pressure difference
-Resistance to flow
Define viscosity?
The ease in which fluid particles move past one another
Higher viscosity causes greater or lesser resistance to flow?
Greater
Define Poiseuille’s Law?
Relationship b/w flow rate, pressure difference + resistance
Define laminar flow?
Movement of fluid in “layers” or streamlines that travel parallel to one another, in the same direction + at approx the same velocity
List 4 types of laminar flow?
-Plug
-Parabolic
-Skewed
-Disturbed
Where would plug flow occur?
At entrance of a vessel where velocities of all streamlines are roughly the same, with the exception of mild disturbances caused by valves
Examples:
-RVOT + LVOT
-MV + TV inflows
Define parabolic flow? Where would this occur?
-Occurs in long, straight vessels.
-Walls cause friction + slowing of flow, while the center moves at a higher velocity
Examples:
-Peripheral vessels of cardiovascular system
-Pulmonary veins
Define curved skewed flow? Where would we see this flow?
-Asymmetric flow profile caused by vessel curvature.
-Higher velocities on the outside curve, lower velocities on the inside curve.
Example:
-Carotid artery
Define U-Shaped skewed flow? Where would we see this flow?
-Complex flow based on many variables.
-Higher velocities on inner side of ascending limb + on outer side of descending limb.
Example:
-Aortic arch
Define disturbed flow? Where would we see this flow?
-Laminar blood flow that is NOT traveling in a straight path.
-There is laminar flow at the outer walls of the vessel, then slower circular flow (Eddy flow) on the inner side of branches.
Example:
-PA Bifurcation
When would turbulent flow occur?
When blood passes through an area of obstruction or a narrowed orifice
Examples:
-Stenosis
-Regurgitation
-Septal defects
Flow obstructions increase or decrease velocities?
Increases - causing a curling whirlpool flow pattern called vortices (casts off jets at different velocities + directions)
If there is an increase in velocity at a narrowing/stenosis, what happens to the pressure?
There is a decrease + drop in pressure at the stenosis
According to the continuity principle, when there is a narrowed orifice will the blood velocity increase or decrease across it?
Must increase
The continuity principle is based on conservation of what?
Mass - “whatever mass flows in, must flow out”
Flow before a stenosis + after a stenosis must be greater, lesser or equal?
Equal
In order to maintain the same volume of flow, velocities at a stenosis will be greater or lesser than the velocity proximal + distal to the stenosis?
Greater
Volumetric flow rate relates to what 2 things?
-Average flow velocity
-Cross sectional area of particular location
When we want to doppler a structure, do we want the u/s beam parallel or perpendicular to blood flow?
Parallel
What does a cosine of 1 mean?
100% detectable doppler shift
What happens if the u/s beam is perpendicular to blood flow when we want to doppler?
No doppler shift will be recorded (cosine of 0)
Should we use angle correct for cardiac doppler applications?
No! B/c will likely only make things worse
How can we avoid errors in calculating the velocity of blood flow?
Ensuring the intercept angle of the u/s beam + direction of blood flow is as parallel as possible
We use doppler in various forms for hemodynamic assessment of the heart, what are they?
-Velocity + pressure measurements (PW + CW)
-Assessment of myocardial tissue velocities (TDI)
-Recognition of normal + abnormal blood flow (CD, PW, CW)
How can we differentiate CW + PW tracings?
CW: no spectral window
PW: spectral window (anechoic space in waveforms)
Should we use CD before using any type of doppler?
Yes!
What does the x-axis + y-axis represent in a spectral doppler display?
X-axis: time across cardiac cycle (adjusted by sweep speed)
Y-axis: velocity scale (adjustable by scale into m/s or cm/s)
Define antegrade + retrograde flow?
Antegrade: flow above baseline, towards probe
Retrograde: flow below baseline, away from probe
Define velocity (frequency shift)?
Measurable speed of flow
Define signal amplitude?
-Brightness of pixels
-Velocities are shown in shades of grey + correspond to the amplitude (dB) of the signal
The brightness of a signal + the density of a signal relates to what?
The intensity of velocity present
A min of how many spectral waveforms should be present in our tracings?
Min 3
What is a “full envelope” in a spectral tracing?
Means there is a complete, full + clear waveform we can trace
List 2 ways PW is recognizable?
-Spectral window present in waveforms (however abnormal flow may cause spectral broadening)
-Presence of a sample volume box (=)
Does PW detect flow in 1 location or along the cursor line?
1 location - detects flow in the particular location the sample volume box is set + only that location
(useful for determining velocities in a specific location)
Do we commonly adjust the sample volume box with PW doppler?
No, usually only with pediatrics. Can cause spectral broadening if box is set too large.
(do not need to worry about FR when changing sample volume box size)
The length of the sample volume box (how big we make the box) with PW determines what?
The amount of time the pulses of u/s are being sent out for
What is PRF determining with PW?
How often PW “samples” the velocities it encounters
Does a higher PRF mean PW is taking more or less samples?
More
(higher PRF = more often it takes a sample, lower PRF = less often it takes a sample)
When is the new signal sent out with PW?
Not until the original signal is received back
PW needs how many samples per cycle to prevent aliasing?
2
(when doppler shift exceeds 1/2 PRF aliasing occurs)
What is a disadvantage to PW?
-Is subject/prone to aliasing at higher velocities (b/c sampling 1 specific spot)
-Limited amount of sample time which limits how high of a velocity it can detect
(PW can’t “see” what it can’t sample)
What describes the max doppler shift/max doppler velocity that can be displayed properly using PW?
The Nyquist limit (scale) - applies to any form of doppler
The Nyquist limit is determined by what?
The sampling rate (PRF)
List 2 ways that CW is recognizable?
-Lack of spectral window present in waveforms
-Lack of a sample volume box along cursor line
How does CW detect flow?
-Along the entire cursor line
-U/s signals are constantly sent + received along the entire length of u/s beam, which accurately measuring high velocities
What is an advantage to using CW?
Useful for determining high velocities that will be prone to aliasing
What is a disadvantage of CW?
The constant signals on the entire beams make it difficult to tell what depth the signal is exactly coming from (range ambiguity)
Do we measure what is more averaged amongst the spectral waveforms, or the waveform that is the outlier?
Always measure what is more averaged + constant throughout the tracing. Shows what is true to the pt.
What word describes why it is important that Sonographers understand the way normal, waveforms appear, as well as their timing in the cardiac cycle?
Ambiguity
In theory, the best CW signals will come from which probe?
Pedof/blind probe
Why does the pedof probe give us the best CW signals?
-Smaller footprint (easier to angle for flow alignment, can get more parallel)
-Uses lower frequency (1.9 MHz) which improves sensitivity
-Higher “signal to noise” ratio (clearer spectral envelope)
When is the pedof probe used?
Primarily in evaluating stenosis (m/c aortic)
Is CW or PW ambiguous?
CW
Spectral doppler is used to calculate what?
Pressure gradients b/w chambers
Does spectral doppler allow quantification or qualification of the pressure gradient for areas of narrowing (ex. calcified AoV)?
Quantification
What is the Bernoulli equation?
P = 4V^2
(P = pressure gradient, V = velocity)
Solving for the Bernoulli equation gives us what information?
The pressure difference b/w 2 chambers at a specific point in time
As velocity increases, does pressure increase or decrease?
Decreases
Determine the max pressure gradient across the TV based on the max velocity (4.15 m/s) of the TV regurgitation?
P = 4V^2
P = 4(4.15)^2
P = 69.0 mmHg
What does TDI + DTI stand for?
TDI: tissue doppler imaging
DTI: doppler tissue imaging
What does TDI record?
Records velocities within the myocardium itself + at the corners of the MV + TV annuli
List 3 variations/uses for TDI?
-Colors are overlaid on the 2D image to enhance definition (like a chroma map)
-Pseudo “color m-mode” of sorts by placing cursor through area of interest
-Sample volume box along cursor line to obtain a spectral waveform (our primary focus!!!)
The red/blue colors with TDI indicates what?
Movement of tissue - tells us when the annulus is moving antegrade/retrograde
Is myocardial velocity with higher or slower than blood?
Slower
Is the TDI scale set much higher or lower when compared to PW + CW?
Lower - scale should be much lower than PW + CW
(don’t change the scale with tissue doppler)
Does BART apply to tissue like it does for blood?
Yes!
What is TDI primarily used for?
Assessing diastolic function/dysfunction of the LV + systolic function of RV
List 4 other TDI applications we will learn more about in cardiac 2?
-Estimation of LV filling pressures
-Differentiating b/w restrictive + constrictive physiology
-Early diagnosis of genetic disease of the heart
-Differentiating athletic hearts from hypertrophic cardiomyopathy
When should we adjust our spectral doppler scale?
-Adjust it to avoid cutting any waveform peaks off (increase scale to fix aliasing)
-Should show the signal of interest
Waveforms of interest should take up how much of the spectral doppler screen?
Approx 2/3
If we see stenosis, how can we optimize + adjust our spectral doppler scale to prepare for acquisition?
Increase our scale to make room for the waveforms b/c stenosis has high velocity
The baseline is used along with the doppler scale to eliminate what?
Aliasing, the baseline should be optimized for the entire doppler signal
Areas of antegrade flow will appear above or below the baseline? Where should we move the baseline?
Above - move the baseline down to make room in advance
Areas of retrograde flow will appear above or below the baseline? Where should we move the baseline?
Below - move the baseline up to make room in advance
How many beats should be displayed on a spectral tracing?
At least 3 beats
A min sweep speed of what is recommended?
100 mm/s
When would we adjust our sweep speed?
Fast HR: increase it (spreads out waveforms)
Slow HR: decrease it (shows more waveforms)
What is the sample volume length m/c set at?
3mm (typically not necessary to adjust it)
What can happen if we increase our sample volume length?
Possible to create more noise in our doppler signal + create spectral broadening
What do wall filters do?
Allows for removal of high intensity, low velocity signals called clutter from our display
What causes clutter in our tracings?
Can be due to movement of chamber walls or valve leaflets
When might we turn our wall filter down very low?
When trying to detect very low velocities, so we can detect a doppler signal
Why would we adjust our doppler gain in our spectral tracings?
For clear visibility of waveforms, while preventing artifact + clutter
(1dB is optimal gain level)
What is spectral broadening?
It is the filling in of the PW doppler spectral windows, due to a wide range of velocities present in the sample volume box
Do some pathologies occur during normal flow?
Yes, know cardiac cycle timing to help decipher what we are seeing
What are 2 helpful tips to keep in mind when dopplering?
-Have cursor line as parallel to flow as possible
-May have to intentionally alter image + be off axis to align flow to cursor line
Are velocities + pressure gradients under or overestimated the more perpendicular the jet is to our cursor?
Underestimated
