Critical Thinking/Difficult Cases/Optimization/Physics

Question 1

What causes FLOW BELOW THE BASELINE in triphasic (2)

Answer 1

Stored energy & elastic recoil of the artery walls

small distal vessels resistance

Question 2

What does a POSITIVE Doppler shift indicate?

Answer 2

Flow is toward the origin of the doppler pulse because the received frequency is higher than the transmitted frequency

Question 3

EASIER to determine flow at a Doppler angle of 5 degrees or 85 degrees

Answer 3

Flow direction is easiest to determine at a Doppler angle closest to zero

Question 4

What causes flow distal to a critical stenosis to appear damped? (3)

Answer 4

Drop in pressure due to kinetic energy loss
Decreased flow
Decreased volume

Question 5

What happens to the flow if the intracranial ICA is occluded? (2)

Answer 5

High resistance flow in the CCA

Normal ECA flow

Question 6

What happens to flow distal to a stenosis of the distal CCA?

Answer 6

Prox CCA - biphasic
Distal CCA stenosis - high PSV
ECA and ICA - tardus parvus waveform

Question 7

High bifurcation - use

Answer 7

Curvilinear probe

Question 8

When do you use a straight box (2)

Answer 8

Tortuous vessels

TRV image

Question 9

Extensified calcified plaque- what do you see and how do you image?

Answer 9

Obliterates colour

Assess flow distal for PST or tardus parvus

Question 10

What to do with slow / trickle flow

Answer 10

Lower PRF
Increase colour gain
Use power Doppler (only for presence of flow - NOT able to show you flow direction or aliasing)

Question 11

High bifurcation - use

Answer 11

Curvilinear probe

Question 12

When do you use a straight box (2)

Answer 12

Tortuous vessels

TRV image

Question 13

Extensified calcified plaque- what do you see and how do you image?

Answer 13

Obliterates colour

Assess flow distal for PST or tardus parvus

Question 14

What to do with slow / trickle flow

Answer 14

Lower PRF
Increase colour gain
Use power Doppler (only for presence of flow - NOT able to show you flow direction or aliasing)

Question 15

Power Doppler useful in what situations (7)

What is it not able to do? (2)

Answer 15

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

Question 16

Tachycardia (2)

Answer 16

HR >100 bpm

Decreased PSV

Question 17

Bradycardia (2)

Answer 17

HR <60 bpm

Increased PSV

Question 18

A greater depth does what to PRF? What does this result in

Answer 18

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

Question 19

Improve angle (4)

Answer 19

Heel toe
60 degrees
Change colour box angle
Change window of insonation

Question 20

Colour gain too low versus too high

Answer 20

Low = occlusion/poor fill in
High = bleeding

Question 21

If you increase the angle, what happens to velocity and Doppler shift?

Answer 21

Increase velocity (falsely)
Decrease Doppler shift

Question 22

Sample volume and vessel size

Answer 22

Small vessel = larger gate

Large vessel = smaller gate

Question 23

Spectral velocity scale should be ____ of display. What adjusts the scale?

Answer 23

2/3 of display

PRF adjusts velocity scale

Question 24

What is spectral colour/wall filter
What happens if it’s set too high
And set too low

Answer 24

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

Question 25

Aliasing:
Manifests
Caused by
How to fix

Answer 25

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,

Question 26

Qualitative vs quantitive

Answer 26

color flow/ power Doppler is qualitative

Spectral Doppler/pulse Doppler is quantitative

Question 27

A decrease in Doppler shift occurs with

Answer 27

Decrease in Fo
Decrease in flow velocity
When cos angle is smallest (close to 90)

Question 28

The dimensionless index that indicates the likelihood of turbulence to occur is

Answer 28

Reylond’s #

Question 29

Laminar flow tends to be disturbed if Reynolds # exceeds ____

Answer 29

2000

Question 30

Reynold’s # equation

What variables mostly affect it (2)

Answer 30

Re = (velocity * radius) / (viscosity * density)

Velocity and radius

Question 31

Acceleration time > ____ s indicates greater than 50% stenosis

Answer 31

> 0.1 sec

Question 32

Resistive index

Answer 32

PSV-EDV/PSV

Question 33

2 measurement tools for quantifying tardus parvus (2)

Answer 33

Pulsatility index (S-D/M)
Acceleration time

Question 34

Doppler spectrum display-what do we see?

Answer 34

The vessel
Sample volume
Doppler line of sight

Question 35

Colour flow info - what do we see?

Answer 35

Relationship between direction of flow and colours in the flow image

Question 36

PRF colour vs. Doppler

Answer 36

Colour: based on the average Doppler frequency shift/velocity

Spectral: values are shown as absolutes, without averaging

Question 37

A higher PRF is needed for the spectral Doppler to ensure (2)

Answer 37

Systolic velocities are shown accurately

No aliasing

Question 38

X, Y, Z axis on spectral display

Answer 38

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