Critical Thinking/Difficult Cases/Optimization/Physics Flashcards
What causes FLOW BELOW THE BASELINE in triphasic (2)
Stored energy & elastic recoil of the artery walls
small distal vessels resistance
What does a POSITIVE Doppler shift indicate?
Flow is toward the origin of the doppler pulse because the received frequency is higher than the transmitted frequency
EASIER to determine flow at a Doppler angle of 5 degrees or 85 degrees
Flow direction is easiest to determine at a Doppler angle closest to zero
What causes flow distal to a critical stenosis to appear damped? (3)
Drop in pressure due to kinetic energy loss
Decreased flow
Decreased volume
What happens to the flow if the intracranial ICA is occluded? (2)
High resistance flow in the CCA
Normal ECA flow
What happens to flow distal to a stenosis of the distal CCA?
Prox CCA - biphasic
Distal CCA stenosis - high PSV
ECA and ICA - tardus parvus waveform
High bifurcation - use
Curvilinear probe
When do you use a straight box (2)
Tortuous vessels
TRV image
Extensified calcified plaque- what do you see and how do you image?
Obliterates colour
Assess flow distal for PST or tardus parvus
What to do with slow / trickle flow
Lower PRF
Increase colour gain
Use power Doppler (only for presence of flow - NOT able to show you flow direction or aliasing)
High bifurcation - use
Curvilinear probe
When do you use a straight box (2)
Tortuous vessels
TRV image
Extensified calcified plaque- what do you see and how do you image?
Obliterates colour
Assess flow distal for PST or tardus parvus
What to do with slow / trickle flow
Lower PRF
Increase colour gain
Use power Doppler (only for presence of flow - NOT able to show you flow direction or aliasing)
Power Doppler useful in what situations (7)
What is it not able to do? (2)
Small vertebral A Trickle flow Overall low HR High bifurcation - carotid Renal Doppler Ovarian and testicular assessment Nodal flow
NOT possible is flow direction / detection of colour aliasing
Tachycardia (2)
HR >100 bpm
Decreased PSV
Bradycardia (2)
HR <60 bpm
Increased PSV
A greater depth does what to PRF? What does this result in
Decreases PRF (the number of pulses per square cm tissue - decreases signal processing time) diminished ability to display flow well
IMAGE AS SUPERFICIAL AS POSSIBLE
Improve angle (4)
Heel toe
60 degrees
Change colour box angle
Change window of insonation
Colour gain too low versus too high
Low = occlusion/poor fill in High = bleeding
If you increase the angle, what happens to velocity and Doppler shift?
Increase velocity (falsely) Decrease Doppler shift
Sample volume and vessel size
Small vessel = larger gate
Large vessel = smaller gate
Spectral velocity scale should be ____ of display. What adjusts the scale?
2/3 of display
PRF adjusts velocity scale
What is spectral colour/wall filter
What happens if it’s set too high
And set too low
Cut off point to filter out low frequency signals generated by low velocity (not a problem in high velocity flow states)
Too low = wall thump from arteriole systole
Too high = low velocity flow close to walls wont appear. False impression wall thickening
Aliasing:
Manifests
Caused by
How to fix
Incorrect flow direction, wrap around, misrepresentation of info sampled
Under sampling Doppler shift OR Doppler shift exceeding 1/2 PRF (nyquist limit)
Increase PRF, Doppler angle
Decrease baseline, frequency, depth sample volume,
Qualitative vs quantitive
color flow/ power Doppler is qualitative
Spectral Doppler/pulse Doppler is quantitative
A decrease in Doppler shift occurs with
Decrease in Fo
Decrease in flow velocity
When cos angle is smallest (close to 90)
The dimensionless index that indicates the likelihood of turbulence to occur is
Reylond’s #
Laminar flow tends to be disturbed if Reynolds # exceeds ____
2000
Reynold’s # equation
What variables mostly affect it (2)
Re = (velocity * radius) / (viscosity * density)
Velocity and radius
Acceleration time > ____ s indicates greater than 50% stenosis
> 0.1 sec
Resistive index
PSV-EDV/PSV
2 measurement tools for quantifying tardus parvus (2)
Pulsatility index (S-D/M) Acceleration time
Doppler spectrum display-what do we see?
The vessel
Sample volume
Doppler line of sight
Colour flow info - what do we see?
Relationship between direction of flow and colours in the flow image
PRF colour vs. Doppler
Colour: based on the average Doppler frequency shift/velocity
Spectral: values are shown as absolutes, without averaging
A higher PRF is needed for the spectral Doppler to ensure (2)
Systolic velocities are shown accurately
No aliasing
X, Y, Z axis on spectral display
X: time
Y: velocity depicted in cm/s , direction of flow shown in relation to spectrum BL, velocities with minus sign are negative Doppler shift, positive vice versa, relationship between flow direction and Doppler BL may be reversed by operator
Z: pixel brightness - proportionate to the relative number of blood cells with a specific velocity at a specific moment of time, the brightness of the pixels show the distribution of the flow energy/power at each moment of time
